hey everybody welcome back to the channel today I want to go through the entire biology section for the MCAT I used these Milestone review sheets and they were really really helpful for me to be able to study for the MCAT um I got 100 percentile on the MCAT and I genuinely believe that everything that I needed to know for the exam were in these review sheets and then um all the practice exams help me solidify the information and so kind of want to help you speeed run through these sheets and be able to go through them in an efficient way um and clarify any things that might not make sense and so that's what I'm going to do in this video so the first thing is parts of the cell um the nucleoid is the DNA region in a pro karot and it's really important to know that you proc carots don't have a nucleus they have nucleoids right and uh nucleoids are kind of this uh region where most of their DNA can be found okay um the next thing is nucleis and these are in UK carots and these are within the nucleus but they don't have a membrane and these are responsible for making ribosomes and if you remember um let's go to nucleis you remember a so this is kind of the way that uh let's look at it better so this is kind of the Nu the nucleus and within it is a nucleoid which is kind of this really dense material within the nucleus right this is the nucleoid over here um yeah and uh it's important to remember that they make ribosomes and ribosomes if you remember are those those things that are really important for connecting the amino acids so you can form the primary chain of amino acids that makes the eventual protein um it's important to know also that both procaryotes and ukar have ribosomes because it's really important to be able to make proteins to do all the cellular functions that they need to do peroxisomes are uh things that break down materials maybe like waste products or dangerous materials ruff r is responsible for accepting mRNA to make proteins like we just mentioned um they're rough because they're studed with these ribosomes smooth R are responsible for detoxing and making bits the Gogi apparatus is responsible for modifying and distributing proteins and they're only on UK carots and they're kind of like the packaging system of the cell uh when I was uh studying this this didn't make too much sense to me the vesicular transport and snal maturation until I finished my first year in med school um but I think I think looking at a picture would help so cop to there uh if you kind of look here right or maybe let's try to find a better picture this is a better picture so here you can kind of clearly see that you know the side of the G that faces the nucleus is called the cyst side and the side that faces the plasma membrane is called the trans side and um vesicles that go from the GGI back to the ER are studded with these cop one right on their on their vesicle and vesicles that go from the ER to the Gogi infused with the go on the Cy side are studed with Cop 2 okay and then anything that goes from the plasma membrane back to the Gogi or vice versa is studed with Cline okay so cop two goes forward cop one goes revers that's anterograde is forward and retrograde is reversed and Cline is responsible for going from plasma membrane to Gogi and Gogi to plasma membrane okay um let's look peroxisomes are responsible for collecting and breaking down materials then gets repeated twice and centrioles are nine groups of microtubules which are as we'll see part of the cytoskeleton and uh there are nine groups of these microtubules and two centrioles at right angles and I can show you a picture of this cental centrom uh so you can see that let's see what is this okay so you can see that uh sorry okay so you can see that there's two centrioles in right angles that form a croome and this is a croome this these two centrioles and they com they uh pull apart these chromosomes uh during anaphase the centrosomes okay um now we have lomes lomes are the recycling center they made by the G and single membrane and plasmids are within procaryotes and the carry DNA that is not necessary for survival uh if you kind of remember plasmas are those circular pieces of DNA that can replicate really quickly and a lot of biochemists really like the plasmid because they can insert genes of interest um to kind of um to kind of farm genes of interest that they want uh okay bacteria you should know can be in three shapes that are important to us one is basili which are rods one is coai or coxy which is a sphere and one is Spira which is spiral um I kind of think that they look like pasta which is how I remember it obligate anoes are requiring O2 obligate anob will die in O2 they need to be in a non oxygen environment facultative Anor robes can go between the two and aerot tolerant Anor robes don't use oxygen but they won't die in oxygen um it's very important to know that when you Gram stain a bacteria it can either be purple or pink if it's purple it's a thick peptidoglycan cell wall and if it's uh Pink then it's thin pepd uh peptidoglycan cell wall but it also has an outer membrane which is outside that cell okay now we have UK carot and procaryotes is also very very high yield uh UK carots are have a Etc in the mitochondria right they are that Etc is called electron transport chain they have uh large ribosomes um which uh these only have small ribosomes and they reproduce via mitosis um Pro carots on the other hand uh have an electron transport chain in the cell membrane they have small ribosomes they reproduce during via binary Vision which is a very very similar process to mitosis and plasmids carry DNA material and they can have varil Lance factors and plasmids can integrate into genomes and when they're integrated they're called episomes okay um some miscellaneous things that are not very high yield prons are infectious proteins if you've ever heard of mad cows disease or some really really bad um brain diseases those are caused by prons they trigger misfolding and um yeah they're pretty bad viroids are plant pathogens okay I kind of hinted at the cytoskeleton but it's kind of important to know that microfilaments again pretty high yield microfilaments actin is a very important one microtubules tubulin is a very important one and intermediate filaments carotin and Desmond those are important keratin and Desmond is really prominent in your nails and hair um microfilaments are the smallest microtubules are the largest and intermediate is in between those two um okay um so intermediate filaments are very important for structural support microtubules are kind of what I mentioned uh very important in the cental and croome and um moving things within the cell and microfilaments are very important just in uh General and cell motility and things like that let's see function on micro microfilaments help generate forces using cellular contraction and basic cell movements yeah so they're very important in cell motility okay tissue I was also very confused about until I finished my first year at med school this is also um kind of important epithelium is any um any uh let's say any uh type of cell that covers the uh surface of some sort of body organ right uh let's see if there's a better definition for that epithelia epithelia is a tin thin tissue forming the outer layer of a body surface um or Hollow structure so anything that's covering the outer surface that's or the body surface um or some organ or anything that's an epithelium epithelium there's several types there's the parena which is the functional part of the organ and then you can look at simple epithelium that's one layer of cells stratified is when you have multiple layers of cells pseudo stratifi is really difficult to differentiate with stratified when you're just looking at it um like at a pathology slide but pseudo stratified they're actually all um one layer but they kind of are different sizes so they look like multiple different layers cuboidal is Cube shaped columnar is you know column shaped andus is um very flat um connective tissue is you know anything usually we think of that in the extracellular Matrix but there's something that supports protects and gives structure to other tissues and organs right and if I looked at an image you can kind of see that they're like you can kind of think of them as providing structure and providing support to organs um connective tissue can be stroma which provides support and extracellular Matrix and they're very important in bone cartilage tendon blood if you think of anything that supports and give structure to something those are bone and cartilage tendon blood those are things that are involved in connective tissue okay um next we have genetic recombination this is how uh bacteria get new uh DNA uh so there's transformation which means that you're getting genetic information from the environment there's conjugation which means that um that there's a transfer of genetic information via this bridge called the conjugation bridge I kind of think of this like bacteria sex even though I should probably not but conjugation is kind of like how bacteria exchange DNA with one another so if one um if one bacteria is resistant to some sort of uh antibiotic for example it can pass that on through conjugation to another bacteria that is not uh transduction is when you transfer DNA using this virus called a bacterio which are bacteria virus and transposons are genetic information that can insert and remove themselves and transposons are kind of these like sequences of DNA that can like Jump Around um viruses so I really enjoyed studying about viruses in my undergrad just because these things look really cool um casid is a protein coat envelope is just something that some back some V viruses have verons are individual virus particles so if you're talking about several verons that's um several virus particles right back bacterial phages are viruses that are specific to bacteria and if you remember uh transduction is how you transfer DNA between bacteria using these bacterial phasers um viral DNA so um viruses can have DNA or RNA uh it could be single stranded or double stranded um if they're single stranded they can be either positive strength or negative sense right positive sense is when you can take that DNA um or RNA and you can directly sorry take that RNA and you can directly translate it into in the host cell but if you have negative scense then you have to use an RNA replicas and you have to convert it to the complimentary Strand and then you can translate it so it's one extra step within negative sense retroviruses are single stranded RNA um and then a reverse transcriptus is first needed to make it into a DNA and then you can make it again into RNA and then proteins bacteria phages can either be liic or lysogenic itic is when the virion are made until the cell just explodes but lysogenic um the virus is basically dormant and uh when stress activates that virus then it um it goes into its litic phase all right that's everything you need to know for the first page of biology okay this is the second part of biology which is uh reproduction we're going to start with cell cycle um so the cell cycle is uh pretty easy to understand uh first thing thing you need to understand is almost everything in the cell cycles interfase except for this little bit which is mitosis and mitosis is the process of cell division where one parent cell makes two daughter cells um G1 is when the cell is making mRNA and proteins to prep for mitosis right G1 is this part S phase is when the DNA is being replicated right here and the G2 phase is when the cell growth is happening and so this is where there's organel that being are being form formed and just overall preparation for mitosis and mitosis the m is mitosis and cyesis which is where the DNA is dividing and uh into two daughter cells and all the organells are dividing into two daughter cells okay so it's also important to know that during G1 the cell cycle can leave this uh sorry the cell can leave the cell cycle into g0 which is that if it doesn't need to divide then there's no need to keep staying within the cell cycle and keep producing these two daughter cells so it'll be in g0 which is kind of this dormant pH uh there are growth signals and I think this was very confusing to me I pulled up a picture when I was studying which helped me a lot and so the thing to understand here is that um let's use the color okay uh when when you're having cell division some very important steps to just remember is that cdk and cyclin bind together to create a complex that complex cdk cycl phosphates RB to RBP and then this changes shape and releases E2 2f and when e2f is released that causes a whole bunch of things that causes cell division to continue and if if this doesn't happen if cdk and cyclin don't create a complex then that's going to block the phosphorilation that means e2f is attached and that means that there's not that whole positive um growth signal to cause the cell cycle to continue right and so if you look at maybe over here you can see that uh cdk and cycl can form a complex that causes is my marker that causes uh this RB to be plus for related you have this e2f that's released and that e2f causes the cell cycle to progress right and if this doesn't happen then we're going to go this way which means this e2f is bound and there's cell cycle arrest okay so next thing is sex chromosomes and this is pretty easy sex chromosomes you should know that XX is females and XY males and human beings there are 23 pairs of chromosomes which means that there's 46 total chromosomes out of those 46 one should be from your father and one should be from your mother right uh for each pair of those chromosomes so 23 are from your mom 23 are from your dad xlink disorders are when males Express them and females can be carriers and that's because if you have an x-l disorder since a male only has one X and that X is from the mom right and the Y is from the dad so if you if the male has an xlink disorder they're going to have the disease because they only have one X whereas females they have two x's one from their dad and one for their mom so hopefully one of them is normal and the other one will contain the xlink disorder so they're just going to be a carrier but they might not actually Express the disease a y chromosome the Y chromosome has very little genetic information there's very few genes that um that you know result in some sort of phenotype so there's very few and funny way you can remember this is sorry Gene which is sorry you're a male okay um the next thing I want to cover is mitosis and meiosis I've kind of talked about mitosis a little bit but um I think it's helpful to just go through it really quickly okay so the first thing to know is that in mitosis uh I guess the first thing to know is that there's this thing called pmat which can help you remember it which is that the phases are prophase metaphase anaphase telophase you might have heard you might have learned about phases in between these um these are kind of the important ones for the MCAT uh and that the ployd is to and throughout and I'm going to talk about that a little bit more because that's important but during prophase the DNA is condensing and centrioles are migrating to opposite poles and when these centrioles migrate to opposite poles these microtubules are forming and if you remember microtubules form these centrioles and two of these centrioles form a croome and we have the nuclear envelope disappearing and basically what that's allowing is the DNA to be exposed so that we can um we can bind the DNA with these microtubules and eventually split apart that DNA because the DNA is in a condensed form called chromatin heterochromatin okay next we have metaphase and metaphase is when all the chromosomes are in the middle right chromosomes meet in the middle and that allows them to be now taken apart by um by these by these uh by these microtubules okay the next phase is anaphase and this is when we're pulling them apart and it's important to know that now we're pulling each chromosome in half right because first we duplicated these chromosomes um then we attached these chromosomes and now we're pulling them apart the next thing is telophase and telophase is when these chromosomes are cond are decondensing nuclear membranes are reforming and cyto cyesis occur so this is basically the phase in which we're actually finalizing the process of making them into do cells and I'm just going to show you a diagram so that this is all solidified in your head so this is the diagram that I pulled up and you can see that in um we have the spindle fiber right we have these centrosomes we have these sister chromatids that are bound together right and we have um yeah so this is interphase where everything is normal um now these chromosomes start to condense they've duplicated they've attached at the center point the spindle fber has formed and these centrioles are forming and they have the spindle fiber now during metaphase these all line up in the middle you can see that the nuclear envelope has disappeared here it is disappearing but here it's fully disappeared and we've attached each of these spinal fibers to these sister chromatids now we're going to pull apart these sister chromatids right okay then the last thing is we're going to form telophase telophase is where this nuclear envelope is reforming we can see that um that you know that it's still still one cell technically cytokinesis has not fully occurred but now cyesis is going to occur and we can see that there's two daughter cells and this looks just like how it was in interphase right so we can say that the ployd is 2N throughout 2 N means that the number of chromosomes is always um is always four throughout all of this right even when uh even when we're in profase right and even when we're in the uh uh even when we're divided into daughter cells we have the same amount of chromosomes now here the chromosomes have doubled the DNA count but it's attached these sister chromatids are attached so we're still calling it one chromosome even though there's two sister chromatids on this even and even though here it's half the amount of DNA material but this is just duplicated sister chromatids that are attached and so we still call that one chromosome that took me a long time to understand so just make sure you understand that before moving on the next thing is meiosis so meiosis uh I'm going to talk about this afterwards non-disjunction but that's pretty important concept so meiosis is pretty similar we have prophase one which is where the chromosomes are again condensing we have homologous chromosomes um and homologous chromosomes are basically one chromosome from your mom and one chromosome from your dad so let's say we have we're talking about chromosome 2 right you have two chromosome twos one from your mom one from your dad and here instead of a single chromosome which has uh sister chromatids by like lining up in the middle at metaphase we have the two homologous chromosomes are lining up in the middle right and we have a little thing called crossing over so let me try to see if I can find a diagram for you prophase one meiosis crossing over so here you can see that yeah I think this is a good diagram here you can see that you know normally when you have mitosis you just have one of these that lines up in the middle so let me use my marker so normally in mitosis in metaphase and mitosis you have this thing that's lining up in the middle and we're going to pull apart this chromosome using the spindle fibers from the centrosome right but here in meiosis in m in metaphase one of meiosis we have these two homologous chromosomes which look very similar because one is from your dad and one is from your mom and these two cross over they exchange a little bit of genetic material here and that basically contributes to genetic diversity and what the the purpose of meiosis one is to split apart these two chromosomes right we're not going to split apart this chromosome like we do in mitosis right we're going to split apart these two chromosomes okay and that's basically the purpose of meiosis one so if you understand that then you're ahead of the curve because that's a very difficult concept to understand um the next thing is anaphase one which is where we're splitting those apart and then finally we have telophase one which is exactly what Tas is was here where the chromosomes are decondensing nuclear membrane is reforming sometimes it doesn't cells are dividing cyto canis and you have two haid daughter cells of unequal sizes the haid daughter cells means that there's half the number of chromosomes that there used to be and the reason for that is because we're literally taking two chromosomes and we're putting one in one cell and another in another cell so obviously the two daughter cells of meiosis one is going to be haid right okay now we got to the easy part which is meiosis 2 and meiosis 2 is so similar to mitosis uh some people say it's like almost identical which is very very good for us because it's very easy to understand now so now that we have these chromosomes in um let's see myosis one and two okay so now that we have so we've we've split apart these chromosomes right and meosis one and now we're here and so now we have to go through prophase 2 which is where we have these haid cells and we're going to go through the whole same process of mitosis which is we're going to line these chromosomes in the middle and now we're going to split these chromosomes in half right by splitting apart the sister chromatids okay and then because of that we're going to have uh telophase two chromosomes are decondensing nuclear membrane is reforming cells are dividing and you have four hloy daughter cells so we went from one cell one parent cell to four hloy daughter cells the parent cell was deployed the daughter cell is hloy mitosis the parent cell was deployed and the daughter cells are deploy right mitosis is essentially we're making the exact same daughter cells as the parent cell meiosis is we creating some um genetic diversity we're trying to create daughter cells that look different and are actually genetically different because they're appid and um there's a couple of things that could go wrong here right first thing is non-disjunction and so if you have non-disjunction this can happen during anaphase and if this happens then um basically uh what you have during non-disjunction is these uh cells over here sorry these chromosomes over here are not splitting in half right and instead one of these takes both so let's just say that this uh centrosome here takes this whole chromosome and it doesn't split in half and so what we're going to result with is a um daughter cell that has an extra chromosome and a daughter cell that has one fewer chromosome so that's pretty dangerous and that's how we get things like um Down syndrome like triom 21 because there's an there's non-disjunction that happens and one chromosome doesn't divide in half or that um the homologous pair doesn't divide in half and so we get anupy anupy is when we have um the a chromosome count that is not expected right okay and law of segregation is when we're having disjunction so normal um normal segregation okay we made it through a huge topic so just make sure you reread this and make sure you understand it um I should mention that p-53 is a very important uh part of the cell cycle that's kind of responsible for a cell checkpoint um but yeah we made it through a very important topic so make sure you understand mitosis and meiosis really well and you stare at those diagrams until it makes sense because next we're going to go on to the male and female reproductive system all right so the next thing to consider is the semen the semen contains sperm as well as seminal fluid and um it it seminol fluid is basically I pulled up a a slide but seminal fluid is essentially anything that helps the sperm move um so the fluid from the prostate and other sex glands would help transport the sperm out of the body so they're responsible for transportation now the bulbo ureal glands are something that helps uh make the liquid a little bit more viscous and helps clean out the urethra before the sperm get there so if you want to see a picture I hope YouTube doesn't take me down for this but essentially the bulbo Ral gland is this gland that uh helps see that helps produce a pre-ejaculate that cleanses and lubricates the urethra before the semen arrives um the next thing is the seminol vesicles and the prostate gland so the seminal vesicles in the prostate glands if it makes so the female reproductive tract is very acidic and so the prostate gland basically produces a um a fluid that's very alkaline and helps the sperm survive in that environment now it's it's a little bit easier if you remember this Pathway to understand the sperms so it's seven up but the N is silent so it's just seeve up and uh the S is for seminiferous tubules this is where spermatogenesis or the formation of sperm cells first happens CI is very is responsible for spermatogenesis um CI cells are somatic cells so they're diploid and they're essential for testes formation as well as spog Genesis um epid denam is something that stores sperm and sperm uh are formed in the seminiferous tubules and they stored in the epidemis and they gain motility um here the next thing is the Vans Defence and the van Defence is the V here and it raises and lowers the test so if you look here it's kind of the thing that carries the sperm out of the testes um the next thing is the ejaculatory duct uh and the ejaculatory duct is essentially just anything that the duct that delivers the sperm to the urethra and the the urethra is the part the duct in which the urine or the spur or the semen sorry the urine or this semen is conducted outside the body the penis is the main uh sexual organ that makes this all possible um which is used for insemination of a female or as well as um just the the conduit for urine expulsion um so that is that is the male reproductive system just make sure you understand this it's not super high yield for the MCAT fortunately neither is the female reproductive system um but it's still important to understand all of this all right so the next thing we have to talk about is female productive system um the first thing we want to talk about is ovaries ovaries are um see ovaries are have follicles that produce OVA and they're controlled by FSH and LH and we'll talk about FSH and LH here which are going tropin releasing hormones but um yeah so I want to show you an image real quick which is um so this is the ovary and this is where U Genesis happens right and we're producing eggs in the in the female reproductive tract okay um so so we produce the female gametes using ug Genesis and um the ovaries is where we're producing the OVA estrogen is responsible for developing the reproductive Tech and it thickens the uterine wall and progesterone responds to LH and it maintains and protects the endometrium so how you can think of this is um so the endometrium is kind of this mucus lining that um so it's the mucus membrane that lines the uterus and so when we have um sexual reproduction the male penis enters the vagina and we have um the seminal fluid that's entering here right the sperm cells and we want this uterus to be protected and so what's happening is that the endometrium kind of thickens and it's it's protecting um the female uh reproductive tract and the uterus specifically and um essentially the sperm is going to travel and it's going to meet in the fallopian tube with OA um okay and so uh how I remember this is estrogen establishes and progesterone prot TS and that's kind of how you can think of the endometrium and what estrogen and progesterone do this is the pathway um so the egg and then the peronal stack sac and then we go to the fallopian tube so um the next thing is the gonadotropin releasing hormones and we have FSH and LH FSH is the follicle stimulating hormone and you can kind of think of you know the follicle so it triggers spermatogenesis in males and remember ctoi cells are kind of the thing that's responsible for spermatogenesis so it's stimulating C ctoi cells and the next thing is in females it's stimulating the development of the ovarian follicles right which are uh contained in the ovaries the next thing is the LH which is lutenizing hormone and in males that causes interstitial cells to make testosterone which is kind of like the primary uh sex hormone for males and in females it induces ovulation so it induces that um that um the gamet for the female to start moving around um the the egg right in the female to start leaving the ovary and go through the fallopian tube so um if you want to look at this diagram real quick the F follicular phase starts with the first day of the period and the luteal phase ends um with the first day of the period right and this is kind of this 28 day cycle and FSH is about 13 to 14 days and same thing with the Lial phase and the FSH is kind of responsible for um remember here it's triggering spermatogenesis but in females it's stimulating the development of the ovarian follicles and the ltil phase marks the beginning of this ovulation period where the the egg is moving through a parental stack in the fallopian tube and we can see that estrogen is increasing throughout the follicular phase and progesterone is increasing throughout the uh luteal phase primarily but you can see that it spikes at the end of the folicular phase and in the uh first few days of the Lial phase respectively and so uh this can kind of tell you what the ovarian cycle looks like uh how the FSH and LH um respond at the end of the follicular phase and the Lal phase and you should just know that you know the Lal phase is basically preparing the female for pregnancy because you know it's it's you're you have increased levels of FSH and LH and you have increased levels of estrogen and progesterone and remember estrogen and progesterone are responsible for maintaining and protecting the endometrium right so in case that the the sperm uh does enter we want to protect the endometrium so that's what estrogen and progesterone are doing in the Lal phase okay um next section okay the next thing we want to talk about is embryogenesis and development and I'll be honest with you I took an anatomy and development class in which the first uh unit we took was embryology in my undergrad years and then we also studied this in med school and I still found it very confusing to understand fertilization morula blastula gastrulation Etc fortunately you don't need to know it in a lot of depth for the C it is a pretty important topic but you don't need to know it in too much depth so knowing the basics really puts you ahead for this exam the first thing is fertilization so remember the fertilization happens in the ampula of the fallopian tube right the sperm has these acrosomal enzymes and that's responsible for kind of penetrating the corona Radia the corona radiate and the Zona paluca and it's very important that it has these acrosomal enzymes so that the sperm is able to um enter right the female gamine then the acral enzymes inject into the pronucleus and we have cortical reaction that releases calcium which depolarizes the OV membrane and makes it impenetrable right we don't want more sperm to be entering in after the first sperm has already entered so that's kind of the process is release of calcium which depolarizes membrane and makes it impen after that the next thing is morula and so this is when we have a single cell right and we have a single cell uh uh which is the embryo uh and we we want the morula and so morula is kind of the solid ball of cells um and you can see that it's just a couple of cells right uh like I've always yeah so it's just a solid mass of couple of cells and it's very very early on next we have the blastula and the blastula I'll show you that too blastula is when we have a hollow we have we start to get this blasto seal in the blastula right and so the cells you can see that there's this Inner Cell Mass right which is right here um this there's this Inner Cell mass and then there's this blasto which is this hollow space and then we have the trool blast which is the outer um cell membrane not sorry not cell membrane but just outer um I guess you could call it an outer membrane right and that's called the blastula so we're starting to get a little bit more of polarity established in this right we see that there's a fluid filled blastos seal we have implants in the it's implanted into the end endometrial lining so if you remember from the past couple of minutes the endometrial lining is where uh we're finally implanted the blastula and then we have the trop blast which eventually will become the coron or the placenta the trop blast is that outer um thing I was showing you I'll show you again so remember that this thing is the trop blast over here right this outer uh lining cells and that's eventually going to become the placenta and the uh Chon and then the next thing is the Inner Cell Mass which is going to become the organism so that's what you know this this thing over here is the Inner Cell Mass that's going to become the embryo the organism okay um so gastrulation is this process in which we're forming the ectoderm mism and endoderm and this is very important and high yield for the MCAT they're often going to ask you like oh um I don't know the mouth what is what layer did that originate from and you want to know that that's from the active term um fortunately uh this this took me a long time to understand um but fortunately there's just this really easy um pneumonic that you can just or not pneumonic but just way to remember it ectoderm is kind of like the attract ofm it's um you know your brains your nervous system your skin your hair your nails your mouth your anus everything that people are attracted to you know your nervous system so like your smarts your skin your hair your nails your mouth your anus everything that people are attracted to that's your that's a very easy way to remember it mism is your musculoskeletal your circulatory system gonads adrenal cortex things that I how I remember this is kind of like the things that are responsible for movement like the muscular skeletal system the circulatory system so like all your blood and everything your gonads um your adrenal cortex which makes those steroids right those are all kind of mm things that's how I remember it endoderm are things that are inside so the endocrine glands the GI tract the respiratory tra tra the broni the bladder stomach all these things are endoderm right if um these ways of remembering it don't Mark just make sure that you know you remember these things because it's very important that you remember it okay the next thing is neurulation neurulation is when you developed a noord the mism forms that noord and the noord induces the ectoderm the ectoderm forms neural fs and neural tubes and the neural folds form the peror nervous system right the neural FS will become neural crest cells which form the peripheral nervous system and the neural tube forms the central nervous system and I really encourage you to watch a video an animation video that uh shows neurulation in an embryo it'll help you kind of understand uh three-dimensionally what's going on I will say that this is a very very confusing topic the more that you study it and um I know like Physicians that are extremely brilliant that have taught us and just say like I don't fully understand what's going on because it's just very complicated but you should know that neurulation is this really important process that's establishing what's the peripheral and what's the central nervous system and you should remember that the nervous system is part of the ectoderm okay the next thing is stem cells stem cells can be toip potent PL potent and multi poent toip potent it can any stem cell can become any type of cell PL potent is that it can become any type of cell except for the placental structures and multipotent is that it can become multiple different types of cells but not any type of cell right so you should know that adult stem cells within the adult body are multipotent right and usually you have to uh put in transcription factors for it to become uh the type of cell that you want but if you take for example cells from um I'm guessing like the morula for example right then that might be a toy potent cell which means that it can become any type of cell because it hasn't differentiated yet um PL potent probably from the uh from the Inner Cell Mass but again I'm not entirely sure but you should just know that these are the degrees of stem cell you know stem cells are cells that can become multiple different types of cell types okay fetal circulation this is a pretty interesting topic so you should know that you know the embryo doesn't really take oxygen from the air it's kind of taking it from uh the mother right and so it takes it from this placenta and we have an umbilical vein that goes to the embryo an umbilical artery that goes away from the embryo right um so just remember that the vein goes to the embryo the artery goes away from the embryo and these are called the umbilical artery and umbilical vein and the fetal hemoglobin has to has to has to have greater oxygen Affinity than the adult hemoglobin and the reason for this is because the fetal hemoglobin they need to like really really want that oxygen in order to get it and so that's why the oxygen diffuses sorry diffuses from the placenta from the mother to the uh to the embryo and so this oxygen and carbon dioxide exchange happen happens through diffusion because the fetal hemoglobin wants that oxygen more than the adult hemoglobin okay um I'd say that these are kind of all things that you should just look at and kind of be familiar with it's not too important that you have memorized every single thing but it should just spend like a couple minutes and make sure you kind of understand this stuff all right twins can be either diotic or fraternal or identical I'm sure you know a twin and you're like either they're identical twins or they're frat twins if they're identical twins that means that they came from the same zygote and fraternal means they're different zygotes right um cell specialization determination is when a cell becomes a determines to become a specific cyle of a cell in differentiation is after determination where you're actually um selectively transcribing the genes that result in the cell specific function so the reason why a um uh a cell from the lung is different from a cell from the stomach for example is because it's not because the the genes are different it's because we've selectively transcribed different genes and different um cells so that it only expresses those specific types of genes and as a result we have a different type of cell and so that process is called differentiation induction is when a group of cells influence the fate of nearby cells this is mediated by inducers which are also commonly called growth factors I'm sure you've heard of them we have signaling signaling can be autocrine which is a cell signals to itself Parr which means a cell signals to a nearby cell juine which means um it goes to a nearby cell again through this Junction and endocrine which means it goes through the bloodstream and you can think of endocrine glands and that means they're releasing hormones through the bloodstream finally we have fetal shuns and Fetal shuns are very important because the embryo hasn't fully developed and so you can't expect the embryo's lungs to be uh like are the embryo's heart to be pumping completely or the embryo's lungs to be providing oxygen right so it has to the blood supply has to skip certain parts and this took me a long time to understand but if you just understand that then you're good so how it skips the lungs because the lungs are essentially um full of fluid it's not actually containing oxygen it's not breathing in or anything so it has to skip the lungs and that's through the forino valley it has to skip the lungs which is also through the ductus arteriosis and the forino valley goes from the right atrium to the left atrium and so it basically completely skips the lungs and the ductus arteriosis goes from the pulmonary artery to the yorta which again is skipping the lungs so it's a left to right sorry it's a right to left shunt the liver it skips the liver by because the umbilical vein goes to the inferior vne so it just completely skips the liver and the umbilical vein which is supplying oxygen from the placenta goes to the inferior vnea which will go to the right atrium okay very good next we have the nervous system which is pretty exciting stuff okay so you should know that there are three different types of neurons one is afren one is ephren and one is inter neuron afren goes up the spinal cord to send the signal ephren exits the spinal cord to again send the signal to perhaps your muscular skeletal system and Inter neurons are between those neurons you can summ you can uh sum up these uh signals from neurons uh so you can imagine that you know these nerve terminals are going to these dendroides uh going to other axon sorry let me show this real quick so you can imagine that you know there's um these nerve terminals of another uh neuron and there's another one that's here and there's another one that's here and all of these are sending signals right some of them might be sending signals that is like oh go go excitement some of these might be sending signals that are uh inhibitory right but all all of these neurons that are surrounding this one neuron might be sending it signals right and so you can send signals temporally or spatially you can sum up those signals temporally means that there's same space but different timing and spatially means that different space at the same time Action potentials basically you have a stimulus and if the stimulus if uh if it exceeds the threshold then we have this whole um depolarization repolarization refractory period and back to the resting state but if it doesn't go to the threshold then it's a failed initiation and so we won't have any um action potential right so the stimulus from other neurons for example has to exceed the threshold to cause de ization depolarization is when the sodium channels are opening and you should know definitely definitely know that if you have a neuron right the sodium is very high on the outside and very very low on the inside and the potassium is very high on the inside and very low on the outside and so if you remember that that's a really easy way to remember that when the um sodium channels is opening the sodium is going into the neuron right and that causes it we have a lot of positive ions that are going going into the neuron so this voltage goes up and then we have repolarization which means that once it gets to a certain positive um positive voltage these potassium channels start to open right and pottassium is leaving the neuron and so we have repolarization it's going down because a lot of positive ions are leaving the neuron and it goes a little bit more down than the resting state right and this is a refractory period the refractory period is this period where it can't really receive another stimulus uh and if it does receive another stimulus has to go really far way up to meet the threshold so these are there's like an absolute and effective refractory period which basically means that the neuron is probably not going to be um is not going to be excitable during that state and then it goes back to the resting state and it's ready to be stimulated again for another action potential okay should know that there's also a sodium potassium pump and the sodium potassium pump essentially responsible because we've had this whole process of the sodium coming in and the potassium coming out we need to make it go back to sodium being outside and potassium being inside and so we use this atps we use ATP to restore the sodium outside and the potassium inside and so that's what this atpa does sends sodium outside and sends pottassium inside next we have um this diagram over here and this is a synapse this is what I was trying to show you which is that the um the dendrites of one neuron are receiving signals from the nerve temp terminals from the axon of another neuron right so this is the axon this is the nerve terminal and this is the dendroid and this is the receptor and this is a chemical signal that's being sent from um the axon of one neuron to the dendroid of another neuron and this chemical signal is called neurotransmitters and the neurotransmitters are within these synaptic vesicles and synaptic vesicles will be released into the uh receptors of the dendrite of the next neuron and how that happens is that there's this action potential which is sending this electrical signal down down down releases and once this electrical signal goes down the calcium channels open calcium is also high on the outside so the calcium goes inside this causes the synaptic vesicles to go and go to this doing protein and basically exocytosis happens and these neurotransmitters which were inside the synaptic vesicles go to the receptor of the dendrite of the next neuron and this is called a post synaptic cell right um this is called a post synaptic cell this is called the Press synaptic cell and this space over here this CFT is called the synapse okay so we can remove the neurotransmitter and this is pretty high yield actually we can remove these neurotransmitters um in this synaptic CFT by breakdown of enzymes reuptake and diffusion of Clift diffusion out of cleft right and so the reason why this is kind of important is because um if we want to sort of uh manipulate different things then we can manipulate these things and we can cause neurotransmitters to be removed and so if you think about things like ssris which are made to for people who have depression to uh to have you know for serotonin to have more impact then that's kind of one of the ways that we we manipulate um we manipulate this this process for ssris to work and so sometimes in the MCAT they'll give you a passage and they'll ask you about a drug and they'll ask you does that cause um the neurotransmitter to have greater few lesser impact on the post synaptic cell so that's kind of a way that you can think about it okay um so I kind of already mentioned this but this is the dendrites this is the cell body it's also called the Soma um this is the axon right this is the nucleus over here so the nucleus is contained within the cell body and these are the nerve terminals uh the nerve terminal is what sends the um the neurotransmitters across the synapse right um you should know that this thing is called a myin sheath right and myin sheath um basically helps this conduction electrical conduction go faster that's called saltatory conduction and these little spots in which there's no milin are called nodes of ronier and this is called saltatory conduction and you should know that there's Schwan cells in the peripheral nervous system and oligodendrocytes in the central nervous system next we have gal cells um G cells are kind of what I was just talking about about Schwan cells in oligodendrocytes and I want to give you a definition of G cell so G cells are things that provide physical and chemical support to your neurons so we have asites asites are responsible for that blood brain barrier it's very important that you have this so that um you know if you're giving a drug to somebody um and maybe it has some cytotoxic effects you don't want it to go to the brain so that kind of creates that if there's these chemicals in your blood you don't want it to go directly to your brain and so there's these asdes that are helping controlling solutes go from the bloodstream to the nervous tisue something that people ask is like oh does that mean the brain doesn't get blood and no no brain definitely gets blood it's just that there's this Blood brain barrier that makes sure that these solutes are not cytotoxic the next thing is Epal cells um I don't actually know how to pronounce it but this creates a barrier between the cerebral spinal fluid and the interstitial fluid of the CNS next thing is microa which digests waste in the CNS and then like I just said the Schwan cells and the oligodendrocytes make myelin Schwan cells in the pns and alod dendrites in the CNS I will say that it's not super high yield for the gleo cells is not a very high yield topic but action potential synapse these summations neurons and this this process is a very high yield thing okay next thing is why white gr matter and gray matter um white matter is melinated cheets and gray matter is the cell bodies and dendrocytes which are dendrites which are UNM unmated it's important to know that in the brain the white is deep and the gray is outer and in the spinal cord it's reverse where the gray is deep and the white is outer so I always kind of make this diagram for myself which is this is the brain and I just want to remember that outside is gray and inside is white right and in the spinal cord I just make the same diagram for myself and I just remember that the inside is gray and the outside is white right so just remember that they're reverse um the next thing is a reflex arc reflex arcs are kind of like when the doctor Taps your knee and you want it to kind of uh jerk without you doing anything and that can be monosynaptic or poly synaptic um it can have a sensory neuron and then a motor neuron so the sensory neuron can receive their signal and the motor neuron immediately responds without any inter neuron and poly synaptic is when you have an inter neuron in between central nervous system is the brain and spinal cord and the peripheral nervous system is everything else that's a neuron in the body the peripheral nervous system and this is very high yield for you in to know can be somatic or autonomic somatic it can be somatic means voluntary autonomic means that um it happens without you thinking about it and some things in your body you just want it to be autonomic right examples are um when you're digesting food you're not thinking about the acid that's being released in your stomach and you know um the intrinsic factor that's being released by your parietal cells and all those things right um same thing like when you're breathing in you you're not thinking about all the broni and everything so you want something to be autonomic you also want something to be sematic and so uh somatic uh sensory means afferent and motor means eeper so if you sense something that's a that's a AFR neuron that's feeling it sending it to your brain and spinal cord and the motor is the E which is um the response right autonomic it can be either sympathetic or parasympathetic sympathetic means it's a fight ORF flight response and parasympathetic means it's a rest and digest process um so how I think about it is if you're in a campfire and you're seeing a bear that's fight ORF flight right but if you're just eating food by the campfire that's rest and digest and so um it's pretty easy to remember what happens in the sympathetic um if you kind of just understand that concept which is that in fight or flight we have um your broni are relaxing uh your blood is moving to Locomotion so like for example if you you need to run so you're blood is moving toward that peristalsis is decreasing peristalsis is the movement of your food through your digestive tract um the neurotransmitters are acetyl choline for preganglionic and epinephrine and norepinephrine for postganglionic um rest and digest you have reduced broni right because um you have conservative energy increase paralysis because remember you're digesting and your pre ganglionic is aetl choline and your PO ganglionic is also cetto Coline so it's only in and you can remember this because epinephrine and norepinephrine is just adrenaline basically so if you if you hear somebody like oh my adrenal spiked during that exam or uh like when I was running from that bear that my adrenaline spiked that's because you know your epinephrine and norepinephrine are the postganglionic things so after the ganglion the post ganglion uh that's what that's what the neurotrend is okay great I hope that makes sense just make sure you review this because this is all very high yield information the next concept is the endocrine system uh which is also very very high yield all right so this is the endocrine system and I want to say that out of everything that we've looked at so far this is probably the most high yield um information that I'm going to tell you and especially this this part if you kind of know um these endocrine organs and hormones then uh you know you're probably going to get a good number of questions right just because this is um this is a lot of the things that are tested in the biology section of the MCAT so the first thing you want to know is that there's a difference between peptide hormones and steroid hormones and this the main thing is that peptide hormones because they're made of amino acids are soluble and steroid hormones which are made of um cholesterol usually are not uh soluble so peptide hormones are cleed from larger polypeptide GGI modifies and activates these hormones they put they're put into vesicles and released by exocytosis right they leave um the cell and they can be pull they are p which means they cannot pass through the membrane so they use an extracellular receptor like gbcr which is what we're going to talk about right here um and so because they're polar and remember that the cell membrane is a full of lipids right they cannot pass through that membrane so they have to use um receptors on the cell membrane and then cause a variety of effects inside um that's in in that's um and so there's a lot of secondary Messengers that are very common that you'll see in the MCAT which is like Camp C2 2 plus ip3 right and uh Camp being probably one of the most common secondary messenger steroid hormones are non-polar and that means they can pass through the membrane they're usually made in the gads in the adrenal cortex right and they're made from cholesterol and they can dissolve they do not dissolve so they have to be carried by proteins so just remember that this can dissolve in water but can't move through the cell membrane and this can't dissolve so must be carried by proteins but can pass through the cell membrane and they activate nuclear receptors so instead of a receptor on the cell membrane they activate receptors inside the nucleus and that has direct action on the DNA so examples are things that we've looked at already estrogen and testosterone as well as cortisol okay um amino acid derivative hormones there's not too much to say about this they share traits from both peptides and ser hormones so catacol amines for example they use gpcr thyroxine binds intracellularly not too high yield um GPC CRS are pretty high yield and so should know that usually what happens is that epinephrine is a first Lian messenger it binds to the G protein coupled receptor which then activates the G protein right which then causes a dental cyclace to convert ATP to camp and remember I said Camp is one of the most common um secondary Messengers and then Camp causes protein kyes a to promote glycogen breakdown right so this is going to happen the glycogen breakdown and it's going to inhibit the synthesis of glycogen right so that means that we're going to have um breakdown of glycogen right that's that's an example of what gpcrs do and um you should know that at the end of this process phosphodiesterase deactivates the camp and GTP is hydrolized back to GTP this makes sure that the next time that an epinephrine molecule binds the gpcr this whole process can happen again okay we can have direct hormones and Tropic hormones direct hormones act directly on the target tissue or organ an example is insulin entropic hormones require an intermediary so as we're going to see GnRH and LH are both Tropic hormones okay you probably know that diabetes is when there's too much sugar in the blood there's two types two ways that this could happen essentially one is that we don't produce enough insulin and so glucose is not able to enter the cells another one is that the insulin receptors are desensitized so they work less uh less efficiently and so glucose is still on able to enter the cell even if we have enough insulin just because the receptors aren't working okay so I want to say that I can help you through all of this but I think most of it is going to come down to your memorization of it I can walk you through some of the ways that you can memorize all this and I will say that it does look really complicated in the beginning but the good thing is that you probably already know a lot of this from your biology classes um even if you don't know it um or just general information for example um the adrenal cortex you might know makes cortisol aldosterone androgens you might know that the pineal gland makes the Melatonin which is responsible for the Sleep Cycle uh you might know well we already know that the goads produce the testosterone estrogen and progesterone we we might know that pancreas produces insulin and glucon as well as somatostatin which I'll talk about um but essentially I want you to know that you know you shouldn't worry too much about this it shouldn't take too long to memorize the important thing is that you look at it every so often um and you focus on Space repetition to make sure that you understand all of this um it is very very high yield that you know this and so that's a good thing is that you're going to differentiate yourself if you know all this information so really quickly I'll run you through this the hypothalamus has GNR ghr TR CR dopamine ADH and oxytocin right so basically um I'll talk about ADH and oxytocin this is produced in the hypothalamus but it's released from the posterior pituitary right so if you look um so this is ADH and oxytocin are produced in the hypothalamus but they're released as you can see in the posterior pituitary dopamine dopamine decreases prolactin which we'll also talk about um CR increases AC right an act is something that we'll talk about when we get to the um to the adrenal cortex TR increases TSH right uh and TSH is something that we'll talk about in thyroid glands G HR and GNR are pretty so G&R is responsible uh for increasing FSH and LH which you can remember um are things that are very important in the male and female reproductive cycle especially in the female reproductive cycle ghrh is uh something responsible for increasing the growth hormone okay so make sure you understand all this the good thing that is that General of the hypothalamus is that it produces a lot of these hormones that are responsible for increasing the production of something else so um yeah the one thing I misspoke about that I want to correct is that the TR increases TSH which is responsible in the anterior pituitary I think I said irram that's actually something that's impos important in the anterior pituitary okay the next thing is the pancreas and as I mentioned there's insulin and glucagon soato Statin so insulin is in the beta eyelid cells and they decrease the blood sugar right so diabetes is when you have too much blood sugar your insulin is either not sufficient or The receptors are not working glucagon is in the alpha eyelets of the pancreas and it's a responsible for increasing blood glucose somatostatin is in the Delta isets and it's responsible for decreasing insulin and decreasing glucon gonads are responsible for testosterone in teses and estrogen and progesterone in ovaries remember estrogen establishes progesterone protects testosterone is responsible for just the general male sexual characteristics pineal gland is responsible for producing melatonin and if you ever heard of like melatonin sleep supplements that's something that helps you sleep because you can kind of use that to remember that melatonin controls the Sleep Cycle next we have the anterior pituitary and this is kind of the most important uh one because it has so many important hormones uh so the way that I remember this is flat Peg flat Peg is f l a t p e g right F is for FSH which again remember FSH is responsible for spermatogenesis and growth of these ovarian follicles which U which are responsible for the gitto Genesis in males and females LH is responsible for the production of testosterone as well as inducing ovulation during the Lal phase of females and you can scroll back if you want to to remember that the ACT is responsible for synthesizing and releasing glucocorticoids from the adrenal cortex so the ACT we'll see is responsible for causing these things in the adrenal cortex TSH remember trh over here promotes the production of TSH in the anterior pituitary which then uh synthesizes and release these things Tri triiodo thyro I've never known how to say these things and thyroxine from the thyroid so you can see from here it's going to cause these things prolactin increases milk production endorphins decrease pain and growth hormone increases growth of bone and muscle and increases growth in yeah increases growth in bone muscle I don't know why it said twice thyroid gland is responsible for T4 and T3 and that's made by follicle cells and it causes the basil metabolic rate to increase and calcitonin is responsible is made by par of folicular cells and they increase the calcium in bone they decrease the calcium in blood they decrease the calcium absorption in gut and they increase the calcium excretion for kidneys so calcitonin is a very important hormone when you have too much calcium in your body in your bloodstream okay the very good thing about parathyroid gland is that pth basically does the opposite of calcitonin it's a very easy way to remember it it decreases calcium in blood increases calcium in sorry decreases calcium in B bone increases calcium in blood increases calcium absorption in gut decreases calcium excretion in kidneys and then because of the bone breakdown that's happening here we have more calcium in the blood and it also activates vitamin d and vitamin D is another way of saying calcium triol okay remember I said that um the the hormones of the posterior pituitary are produced in the hypothalamus and released in the posterior pituitary ADH is a very important hormone that comes up quite a bit in the MCAT and it's responsible for decreasing the urine output in sorry decreasing the water output in your urine and also causing Vaso constriction and um when your p is really really yellow and very concentrated you can think that that's happening because you know these ADH are decreasing the H2O output and so you have a lot of solutes that's in your urine oxytocin is responsible for a lot of this bonding Behavior increased production of milk uterine contractions has a positive feedback cycle okay adrenal cortex remember that the ACT is synthesizing and releasing gluc glucocorticoids from the adrenal cortex and the adrenal cortex is releasing glucocorticoids like cortisol um you should know that cortisol is one of our stress hormones it increases glucose decreases protein synthesis decreases our immune system right it's kind of when you have a lot of stress you increase your cortisol production um mineral corticoids like aldosterone decrease the potassium in the blood increase the sodium in the blood increases the water in the blood due to osmosis and increases the blood pressure so basically when you have less blood pressure your renal artery is sensing that and telling the adrenal cortex to release aldosterone and that aldosterone will activate these channels in your collecting ducts which tells those channels to to release more potassium in your urine and reabsorb more sodium from your urine back into the bloodstream so that's what's Happening Here and the water follows the sodium and this is essentially a way to prevent your blood pressure from going low and so it increases your blood pressure finally we have androgens which are um converted to testosterone and estrogen in the goads okay lastly we have the adrenal medula and this is kind of responsible for the catacol amines remember like the adrenaline type of things epinephrine and norepinephrine and they do very similar things they epinephrine is an antihistamine and they both increase blood pressure and heart rate let's go we finished the very high yield um part so now we're going into the respiratory system okay next we're talking about the air pathway and uh the air pathway is consisting of um you know the nostril then we have the ferx FX is where food and air travel through um and then we have the larynx which is where only air is passing through right you don't want the fairings to go you don't want the food to go through the Lings because then you're going to have some sort of obstruction in your larynx right and this contains your vocal cords next we have the trachea and this is consisted of ciliated epithelium and it's collecting all the debris and then we have the broni and the broni is also collecting the debris but it's important that this is the pathway through which air is passing through right now we get to the bronchial which is the smallest branches of the AL of the broni and finally we get to these little things called alvioli and there these little sacks in the lung right so if you imagine we have have these branches all over and um and we keep getting tinier and tinier until we just have these little branches that are connecting off the bronchial and these little sacks are called alvioli and these Sachs is where diffusion occurs so you have all your blood that contains carbon dioxide coming from your pulmonary vein sorry your pulmonary artery contains all your deoxygenated blood and that's conducting diffusion with your alveoli and because of that diffusion the alveoli is giving oxygen and your pulmonary artery is giving carbon dioxide surfactant is something that's responsible for reducing surface tension and so surfactant is really important in um preventing your um saxs your alvioli from collapsing and in med school you'll learn about some things called some diseases like NE natal respiratory distress syndrome where there's not enough surfactant and so these babies are born um with you know too much surface tension and so there's collapse of their alol there okay um you should know that um pulmonary arteries are going away from the heart and pulmonary veins are going toward the heart how I remember that is arteries start with a and they always go away from the heart right um the next thing is spirometry uh spirometry is something that's really common in the allergy clinic if you ever go to one and that's kind of a way to measure your lung capacity and measure you know when you're inspiring and expiring how much air is going in and out and it's this really cool machine where you just basically breathe as hard as you can into this machine and it'll calculate how much air is going in and so you can calculate all these different metrics it doesn't calculate how much total volume is in your lung but it does give you a lot of important metrics so this is uh not a super clear diagram so I want to give you a little bit better of um diagram volume diagram chart um yeah this is good it might be too complicated let's say let's use this one okay so this is a diagram of your lung so the title volume is how much air you're breathing in and out whenever you're like how I am right now where I'm not like like trying to breathe really really in or really out it's just my normal breathing volume that's the title volume these this is usually like 500 milliliters or so then we have the inspiratory reserve volume which is what I just did when you try to inspire as much as possible how much do you go up to right that's your inspiratory reserve volume this um let me use my marker so this is the inspiratory reserve volume this is the residual volume this is the expiratory reserve volume which is that if you breathe out as much as you can right how much of that air can you breathe out that's your expiratory reserve volume and then finally you should know that when you try to breathe out as much as much as much as possible there's still this little bit of air within your lungs that you're not able to expel and that's called the residual volume okay now we have capacity so inspiratory capacity is the inspiratory reserve Volume Plus your title volume your functional Reserve capacity is your expiratory reserve Volume Plus your residual volume your vital capacity is your expiratory reserve Volume Plus your title volume plus your inspiratory reserve volume and then your total long capacity is everything right um and I wish I had a better way for you to memorize the capacities um but you know you just kind of have to memorize it I forget it all the time in med school so it's it's important to just uh it's it's not that hard to remember the the volumes but the capacities just kind of have to memorize um and that's what those terms are so now we have the medula obligant and the medula obligant is kind of responsible for sensing uh when you have too much carbon dioxide or too little oxygen and tells yourself to respirate more or less and so it's really important to know that whenever you have too much carbon dioxide whenever you have too much carbon dioxide build up in your body um you your um body is going to tell yourself that you need to breathe faster and so you'll have more respiration you might breathe like 26 breaths a minute for example instead of like your normal 18 to 20 and so what you're trying to do is breathe out that carbon dioxide um and so when you have too little carbon dioxide you're going to actually decrease the number of breaths you're taking because you don't want to do a lot of rats and get rid of that carbon dioxide so that's basically what the medula obligant is helping you do and when you have twoo little oxygen you're going to increase ventilation again okay it's uh it's good to know what the plura is the plura is basically this connective tissue that's surrounding your uh lungs and the Very out outer layer of the of the outer plura called the parietal plura that's that's composed of one layer of epithelium right so the plura are this this thing that surrounds the lungs and there's two layers of that plur there's the parietal plura which is the outside one this red thing over here and there's the visceral plur which is this blue thing over here right okay then you have a space in between which is called the plural space and when you start med school you learn about a couple of different diseases uh where there's like fluid buildup or different types of pressure that's in this plural space that's causing your lungs to kind of collapse um and then you have your lungs which are these huge huge huge sacks that surround your heart and you can see that it's very uh easy for your heart to send Blood Out uh to these lungs and then there'll be a passive diffusion between the alvioli and these arteries the pulmonary artery from the heart okay next we have in inhalation inhalation is negative pressure breathing it's an active process the diaphragm and the external intercostal muscles are Contracting you have increased intop plural space increased thoracic cavity and decrease pressure this is kind of difficult to understand so how I think of it is when I'm inspiring right when I'm inspiring basically what's happening is I'm taking air inside right but how does that air want to come inside basically because of a pressure difference right how do I create that pressure difference in the first place for the air to want to come inside basically I'm causing my um diaphragm to kind of go down right and because the diaphragm is kind of going down what's happening is that there's more volume in my thoracic cavity right and so what's happening is because there's more um space in my thoracic cavity there's more space in my intral plural space there's less pressure there's more space right less pressure and so the air from outside is slightly higher pressure and so it comes in so that's basically how I'm doing it I'm Contracting my diaphragm in my external intercostal muscles I'm creating more space in the int plural space in thoracic cavity and so I'm decreasing the pressure next we have the lung volume and the lung pressure so the lung volume increases like I just said and the lung pressure decreases and so air is rushing in exhalation is the exact opposite process the only thing is that this is inhalation is active process where I'm Contracting and exhalation is kind of a passive process where all I'm doing is just relaxing my muscles there's less volume in the lungs and so there's greater pressure and so the air is rushing out um and sometimes I have to do active exhalation where I have to like use all of my muscles to really force myself to Exhale um the air and that can happen in a couple of different diseases or if I'm just really really trying trying to get rid of the air um I will say that this is not um too important for you to memorize in terms of high yield to just kind of look over this uh the mucous membranes are kind of important for protecting against pathogen because when you're breathing in uh you might you know inhale some pathogens into your mucus membranes in your uh you know in your lung Parts like your trachea your broni they kind of have this mucous membrane that protects against these pathogens um lysozymes lysozymes are in your nasal cavity in your salifa and they're attacking gram positive pep glycans so you don't want to breathe in like um gr positive things so that's what the lmes are doing and mass cells are antibiotics on surface that uh are involved in inflammation allergic reactions if you become an allergist then you know mass cells will become half of your life dealing with those okay finally we have the bicarbonate buffer and the bicarbonate buffer is something uh that's very important to understand and it kind of goes back to what I was explaining over here um with the medula obligant stuff but the bicarbonate buffer is uh this equation and you just want to remember lat's principle which is that um you know when you have too much carbon dioxide right when you have too much carbon dioxide you're going to push this equation this way and when you have too much H+ right you're going to want to push this equation this way okay so when I have too much H+ my pH goes down right my pH goes down and then I increase my respiratory rate because I want to get rid of this carbon dioxide right so when I have too much H+ this equation goes this way I have too much carbon dioxide and I need to breathe faster to get rid of this carbon dioxide and when I increase my pH basically this H+ is going down so I'm going to uh force my carbon dioxide to produce more H um to produce more protons and now I don't want to breathe faster because I have less fewer carbon dioxide molecules and so I'm going to decrease respiration to make sure the carbon dioxide doesn't leave my body if um if that explanation of Le shers principle doesn't work for you just just memorize this because that's kind of what you need to know I won't say that it's high yield but you probably will get a question or two on this so it's kind of good to know okay next we have the cardiovascular system and this is actually um the very first unit that we had in med school so I I really like this uh topic so I would say that it's a lot easier to understand the blood pathway if you're looking at a diagram when I first looked at this I was trying to understand from this and it was very confusing so um I would say that it's best to look at a diagram and understand it um I think this should work so okay so the idea here is that there's these two veins that uh drop blood into the right atrium right this is the superior vena and the inferior vena and that goes into the right atrium and that sends blood all the blood from your body goes through this into the right atrium right now the right atrium sends blood through the tricuspid valve into the right ventricle right just remember that this is all deoxygenated blood coming from your inferior and Superior vnea into your right atrium then your right ventricle through the tricuspid valve now it's your right ventricle the vent right ventricle is going to send it through the pulmonary artery right and it's going to go left and right um left and right through your pulmonary artery to your lungs right so it's going to go to your lungs this is your lungs right here and so this is all the deoxygenated blood is going through your pulmonary arteries to the lungs and then it becomes oxygenated and it comes through it comes through through the um pulmonary vein back to the left atrium okay so blood o now the newly oxygenated blood from your lungs are going from your um pulmonary artery are going through your pulmonary vein to send oxygenated blood to your left atrium now your oxygenated blood from the left atrium is going through the mital valve to your left ventricle and the astute Observer will notice that this left ventricle has a really thick wall right a thick myocardium and the reason for that is because this left ventricle is sending blood the oxygenated blood to the aorta right throughout the entire body and so this has to be a really thick wall because this ventricle is responsible for sending blood to the entire body so it's going to be really really uh harsh push through the aortic valve into the aorta which aort is the very first artery after the heart and then sends blood to the rest of the body through a variety of arteries that then go into arterials that then go into capillaries that then go into veins and then finally go to the heart right um let me repeat that so it goes through arteries then arterials then capillaries then venules and then veins and then back to the heart through the superior and Vena Superior inferior venina Capa all right hopefully that Mak sense um so this is basically I just covered all of this and if you understand that then that's a huge um huge important thing in the card cardiovascular system now you should know the electric conduction I can show you image for that too okay um so the electric conduction happens from the saay node so happens from the ESS node over here and then goes to the AV node right and then um I don't know if this is the best I think it might be easier to just read this so it goes from the SA node which is the pacemaker of your heart to the AV node and the AV node is kind of slow so it's like um it'll wait for the electrical signals that's going from the SA node to the AV node and kind of slows it down and then goes to the bundle of His and then the pingi fibers right so you can either remember this or you can remember the stab big pickle uh pneumonic I kind of just remember this and you should know that the SA node is the pacemaker of the heart now what if the SA node stops working right because your heart is just responsible for beating all the time no breaks because if it takes a break uh you die right so if this happens then there's backup pacemakers and that's the AV node the bundle of His the pen G fibers and so these are responsible for creating electrical signals that constantly tell your myocardium to keep beating your heart okay next we have blood pressure blood pressure can be systolic or diastolic and um systolic is when you're Contracting your heart and so there's higher blood pressure because you're Contracting your heart trying to push blood outside your heart and diastolic is when you're relaxing your ventricles and so the blood pressure is going to be lower um should know that the AV valve closes during syy and the SV valve closes during di but it should make sense if you understand the blood path way okay um next we have the normal blood pressure and normal blood pressure is usually 120 over 80 when you increase the blood pressure you increase this uh chemical called A&P and that's responsible for decreasing the blood pressure when you decrease the blood pressure you increase this chemical called adstone or an ADH which we already talked about they're hormones and that's kind of responsible for bringing the blood pressure back up next if you increase the osmolarity like remember I said you increase the ADH which sends out a lot of those uh solutes through the urine cardiac output is how much blood is being sent outside by your heart per minute and it's equal to the heart rate which is how many how many beats per minute times the stroke volume which is how many how much blood are you sending out right and that gives you your cardiac output which is how much blood are you sending out per minute and the SV sorry the stroke volume is how much blood you're sending out per beat if you multiply the two you get hard but okay let's talk about the vascular real quick which I kind of talked about already arteries are these thick muscular elastic um uh blood vessels that are responsible for recoil that allow recoil and help Propel the blood forward why are they thick and muscular well because they're sending blood through the rest of the body and so they have to be like very very um thick and so if you look at any pathology slide you can kind of tell the difference between arteries and veins because arteries just have these thick walls arterials are smaller muscular arteries this is when they start to separate into smaller blood vessels and then we get really really tiny blood vessels which are capillaries they're so tiny that they're actually just only one cell thick and the reason why they want this is because you want to kind of slow the blood flow down and you want um the capillaries near these tissues so that there can be exchange of gases the oxygenated blood is giving oxygen from the hemoglobin to the tissue and the tissue is giving its carbon dioxide that's a result of cellular respiration to the hemoglobin so that it can go back to the lungs through the heart next we have veins which are thin walls and inelastic they can stretch to accommodate blood but they don't have recoil so they're not like going back and squeezing the blood through they're not helping to pump as much um there is surrounding muscles that do help but not as much as the AR arteries which are really really trying to propel the blood forward and then there are venes which are very small veins and the ven will go back to um the superior and inferior V cable okay um actually sorry I don't know why this is in Reverse but it should be uh capillaries to yeah so it should be from capillaries you go to venal and then you go to veins so I guess if I was uh going to write this it would be heart goes to artery goes to arterial goes to capillary goes to venules and then goes to veins so veins and this is the inferior inferior in Superior and inferior vena that go then goes back to the heart um I hope that makes sense okay um okay next is blood blood is considered a connective tissue uh it's made of erthrocytes uh which are red blood cells it's very important to know that all the cells in your body have a nucleus and have um have a nucleus except for the red blood cells okay they don't have a nucleus they don't have mitochondria they don't have organel they're just kind of responsible for containing hemoglobin and hemoglobin is the important protein for carrying oxygen uh ocytes red blood cells are are formed in the blood when the bone marrow next we have hematocrite hematocrite is the percentage of blood that's composed of red blood cells so it might be like 55% or something should know that not all the blood is red blood cells there's also that liquid that the red blood cells is within now we have Lucy which are white blood cells and this is very very important in the immune system and we'll get get into this a little bit more later but um lucos sites include granulocytes which are neutrophils eosinophils basophils we have a granulocytes which are lymphocytes lymphocytes are like B&T cells that provide specific immunity so when you have a virus it makes a specific antibody or specific reaction to that virus whereas neutrophils eosinophils and basophils they respond the same to all different types of inflammatory reactions or viruses or bacteria um monocytes and macras are kind of responsible for digesting the forign matter so you can think of macras as kind of eating something eating a bacteria and it's important to remember that neutr eils and basophils provide non-specific immunity okay next we have thrombocytes or platelets thrombocytes are important for cell fragments and coagulation they're very very important um for coagulation coagulation is kind of when you create a blood clot and so let's say you have some sort of bleeding in your um in your uh endothelium right you have some sort of crack and so your blood uh starts to leak out of that blood vessel you want platelets to come and plug up that that hole and that's called coagulation now there can be a problem with this which is that if you have too much coagulation you could create a blood clot and you could that blood clot could embolize and that could cause a stroke if that goes to the brain for example right um and so sometimes when uh somebody is uh having too many platelets respond to these types of events you give them anti anti-coagulation medication to make sure that they don't have this sort of um stroke or embolism or thrombosis event um you don't need to know too much about that though okay uh for the purpose of MCAT by the way you'll have to know that when you go to Med scho okay blood type antigens antigens are surface proteins on red blood cells it's very important to know this because when you have a transfusion right when you're giving somebody your blood you don't want um you don't want to have like kind of uh you don't want to be giving red blood cells which will have a bad reaction in their body because they'll create immune cells against your red blood cells so you want to look at the antigens that are produced the antibodies that are produced and who you're able to donate to so and Rh factor is also something you want to consider so if you are um for example blood type AB that means that the antigens that are being produced against your red blood cells are a and both A and B against your red blood cell surface and you're not going to be producing any antibodies and so you can only donate to other people who have AB because um if you give to anybody else they're going to have antibodies against either the a or the B right but you can re from anybody because you don't have antibodies against anything uh you're okay with receiving anything because you have both A and B antigens and so your immune system thinks that A and B are your own self um antigens and so it's not going to attack a or b or AB or o but let's say you're o that means that you don't have any antigens on your red blood cells but you have anti-a and you have antib so you have these immune cells these B cells that are producing antibodies that if it these a then it's going to attack it if it's c b then it's going to attack it so you can't receive from anybody besides o right because if you receive from somebody with blood type A or blood type B you're going to produce uh immune you're going to sorry you're going to produce antibodies against that um but you can receive only from o but you can donate to anybody because you don't have any antigens on your red blood cells and so nobody is going to produce any sort of immune reaction against you that's how you think of this this took me too long to understand next you have coagulation coagulation is when the endothelial lining of the blood cell blood vessel is damaged the so this is what I was talking about coagulation by the way um I introduced it a little too early and so when your endothelial lining of blood vessel is damaged Co collagen and tissue factor is going to be exposed and this is how you produce fibrin and thrombin right and fibrin and thrombin are responsible for kind of um clotting up that place so that you don't have loss of these um these blood cells and uh these clots are broken down by plasmine okay So eventually you're going to have to break down this plot once the endothelial lining has healed and how do you break them down with plasmine okay finally we have fluid balance we're almost done but fluid balance is hydrostatic pressure and osmotic pressure um osmotic or oncotic pressure is when you have these solutes that kind of suck in pressure and hydrostatic pressure is the pressure created by the fluid and so if you think about um kind of like this bucket where you have a lot of solutes I'm sure you've seen something like that this right and like two solutes here the water if there's like equal amount of water on this side and this side the water is going to want to come um to this side right from the site with fewer solutes the site with more solutes because um these solutes kind of have this oncotic or osmotic pressure hydrostatic pressure let's say like I did the same thing but there's way more fluid on one side than the other right then there's going to be hydrostatic pressure which is going to send the water from more to less and that's kind of the idea okay oxygen is carried by hemoglobin and carbon dioxide mostly exist in the bloodstream as bicarbonate or hc3 and we have this bicarbonate buffer and that's kind of something that I've already went through so just remember that okay next we have the immune system which is pretty pretty exciting stuff uh this is very high yield and a lot of information um so yeah make sure you understand everything so far just pause the video if you need to um yeah okay so we're talking about the immune system innate immunity and adaptive immunity so innate immunity is defenses that are always active but not specific um so by not specific it means that the specific antigen that's invading your body um the innate immune system is going to have the same response to all of that so example is on your skin your mucus your stomach acid your tears all of those are examples of innate immunity adaptive in immunity is when defenses take time to activate and are specific to The Invader so specific to the um specific to the species of bacteria for example okay let's talk about the innate immune system so we have non-cellular and cellular immune defenses and the cellular is actually very high yield but non- cellular uh innate immune system includes skin mucus Lymes complement system and interferons so the skin is the physical barrier and a lot of people don't think about the skin as a actual part of your immune system but if you think about it your skin is preventing a lot of bacteria from invading and so there's a physical barrier and there's also antimicrobial enzymes like defensin um the mucus if you remember the mucco escalatory elvil elevator that we talked about mucous enzymes kind of trap pathogens and in your respiratory systems in your lungs um the mucus is being propelled upward by Celia via this mucco cyar escalator lyses are in your Tei and your saliva and this contains some sort of antimicrobial compound so if you think of something getting into your eyes for example like some dirt or something you can you have these tears and that contains um antimicrobial compounds same thing when you're eating something and you're salivating that Sal saliva is helping to protect your your body compliment system is essentially this very uh cool system it's kind of like this complex um complement complex that punches holes in the cell wall of bacteria and it makes them osmotically unstable and that leads to their Lis um it also triggers this thing called opsonization which is kind of like a tagging system um that helps other um immune cells destroy the bacteria so compliment system is this very powerful system that the immune system uses in order to destroy bacteria okay the last thing is interferons and when a cell is virally infected um this gives it gives off interferons and that interferes with the viral replication and dispersion that viruses need in order to invade the host organism next we have cellular inate defenses so cellular inate defenses include macras mhc1 and two dendritic cells natural killer cells and granulocytes remember I said that this is high yield so definitely know this macrofagos are things that ingest pathogens and present them on mhc2 they secrete cyto kindes um mhc1 is present in all nucleated cells they display endogenous antigens to the cytotoxic tea cells um so essentially this is a very important concept and it's essentially true that every single cell in your human body that has a nucleus so not red blood cells they have mhc1 right mhc1 is like this receptor and it displays the endogenous antigen so the antigen from inside your own body to the cytotoxic cd8 T cells and these te- cells will then kill off the cells that display um an antigen that's not endogenous right so um mhc1 again is on all your nucleated cells and they display in indous antigens to your cytotoxic cd8 cells if these cd8 cells notice that there's something wrong with these endogenous antigens or that there's not enough of these mhc1 molecules or there's something wrong with this then this T Cell will kill off that cell mhc2 is only pres present in these antigen presenting cells so very specific cells like macras dendritic cells B cells epithelial cells right there's very specific types of cells that uh display mhc2 and these mhc2 display exogenous antigens so things like um parts of bacteria or things like that to CD4 cells and definitely know this is this one is cd8 and this one is CD4 and this is all nucleated cells and this is only professional antigen presenting cells dendritic cells are antigen presenting cells in the skin so remember we talked about how mhc2 is on dendritic cells so this is a dendritic cells are on the skin natural killer cells attack cells low on MHC including virally infected cells and cancer cells so something that happens sometimes is that a virally infected cell might have fewer mh1 so the natural killar cell will come and notice that there's something wrong that there's fewer mac1 and will notice that that's true and will assume that that's a virally infected cell and kill your own cell sometimes that's true with cancer cells as well so natural killer cells will kill those cells as well granulocytes include neutrophils eosinophils and basophils these are called granulocytes because they have these granules um and they are activated by bacteria uh neutrophils are activated by bacteria and they do this thing called phagocytosis which is like eating the the bacteria eosinophils are activated by parasites and allergens and they increase the histamines so they're very um prominent if you go to an allergy clinic you'll notice that you know there's a lot of uh there's a lot of whenever you look at the pathology slides and the allergy patients you'll see a lot of eosinophilia um and then there's basophils and basophils are activated by allergens as well and they inhibit blood clotting okay the next thing is the lymphatic system the lymphatic system basically you have um you have a lot of blood in your body I think it's like five liters of blood right um let's just make sure that's numers how much blood in the body there's okay 1.5 1.5 gallons or so right and so not all of that is uh in your circulatory system all the time it or not all of that is in your blood vessels all the time some of that drains through the lymphatic system and this is basically part of the circulatory system that has one-way vessels with these lymph nodes and uh lymph nodes can be on your like neck your um your cheeks right lymph nodes uh and then they're uh important for these immune responses so let me show you an image of the lymphatic system what's an image okay so if we look here we can see that you know there's the whole blood system and the excess blood that's going throughout your body about 5% of that is getting drained through the lymphatic system and the lymphatic system contains these little um these little nodes right you can see these These are nodes uh over here and those are called lymph nodes and if you've ever heard of a lymphoma that's a cancer of the lymph node and that results in like some sometimes like swollen um lymph nodes that you can feel on your neck um so the lymphatic system is really important to for the um for the immune responses and it connects the cardiovascular system it connects to the cardiovascular system via the thoracic duct in the posterior chest so in the back of your chest you have the thoracic duct and it connects to the cardiovascular system and it basically equalizes the fluid distribution transports fats and fat soluble compounds and kyom microns and um sometimes when the lymphatic system is overwhelmed and it can't drain the excess fluid from your tissues you'll have edema which means that you'll have like um fluid swelling in your body and you'll you'll basically see all this like like your arm might be really big or your legs might get really big because there's um fluid build up okay the next thing is the Adaptive immune system and so we have humoral immunity and humoral humoral immunity is essentially antibody produ C by B cells and it kills antigens when they're floating around in the fluid or the humor and so this is the Adaptive immune system as as um in contrast with the innate immune system so the Adaptive IM immune system has B cells antibodies B cells make antibodies right B cells are made in the bone marrow and they're activated in the spleen or the lymph nodes and they express antibodies on their cell surface now um a special type of B cell is plasma cell C and plasma cells form antibodies plasma cells are activated B cells so B cells are made in the bone marrow they're in the spleen and lymph node and they have antibodies on their cell surface when you activate a B cell you have a plasma cell and plasma cells create antibodies now a antibody will Target an antigen and an antibod contains two heavy chains and two light chains and um uh you'll have a constant region and a variable region right and so the tip of the variable region is the antigen binding region and so this tip is uh specific to that antigen hyper mutation can occur and this is not super important for you to understand fully right now but hyper mutation is mutation of that antigen binding site on an antibody and that results in varying affinities of the antibodies for specific microbes so there's five different isotypes migm igd IGG IG IG and in different different reactions you'll see a different um response and different isotypes that are responding to that to that inflammation um but it's just important to know that hyper mutation is kind of responsible for some of that variability in the an antibody opsonization again remember it's when it's like this tagging system it's when antibodies Mark pathogens for Destruction utenation is when pathogens Clump together and uh they form insoluble complexes uh and that's caused by OB izing pathogens so things that um you know Mark pathogens for Destruction they'll also Clump them together and finally we have memory B cells and this is kind of why um sometimes when you um well this is actually this is the way that like things like the covid vaccine are based on is that you uh have these B cells that remember the the initial exposure and then the second exposure to the pathogen it doesn't have to go through this whole process of making new antibodies and responding to the to the pathogen now just kind of remembers because they have these memory B cells and so the secondary response is now really rapid and vigorous and that's why for example the covid vaccine they first give you like this anoculus um like strain of whatever like uh maybe the the cell wall or sorry the the viral capsid or something right and they'll give it to you in a vaccine and then your B cells they respond to it and now you have memory B cells and then if you actually get the covid um virus then your memory V cells will be able to respond to that and much faster way and much more vigorous way than if you had not gotten the vaccine okay cell mediated immunity is on t- cells and cell mediate immunity is uh response to cells once they've already been infected by the antigen so once once you have a cell and the antigen or the virus or the bacteria has invaded it you want this cytotoxic immunity which will basically kill that cell because that cell has been infected right and so um sorry and so T lymphocytes are made in the bone marrow they mature in the thymus and they coordinate immune system and directly kill the infected cells this is called cell mediated immunity you can have positive and negative selection positive selection means that you're maturing only the te- cells that can respond to the presentation of antigen on MHC so you're making sure that the tea cells are only responding to the to the uh to the antigens right from the MHC you don't want you don't want like these tea cells to be killing off your self antigens like the healthy cells right and so positive selection means that you're maturing only those t- cells that are able to respond to um to the antigens that are like bad antigens right negative selection means you cause apoptosis in the t- cells that are self-reactive right so positive selection means you're promoting uh growth of good te- cells and negative selection means you're destroying t- cells that are self-reactive next we have helper t- cells these are CD4 t- cells and or th these are very important they coordinate kind of like the rest of the immune system besides the cytotoxic immunity and there can be th1 or th2 th1 is responsible for creating this interon gamma um so ifn gamma and th2 activate B cells um in parasitic infections um okay so cytotoxic te cells or CD T cells I've already told you about this suppressor t- cells are these interesting set of t- cells so I've talked about helper t- cells cytotoxic te- cells and finally there's suppressor t- cells suppressor t- cells kind of do the opposite of what I've been talking about they kind of down regulate the immune response after your infection is over you don't want to be in this like hyper state of um of like killing things all the time so T regulate T suppressor t- cells or t- regulatory t- cells they kind of um promote self tolerance and if they're defective then you can get some autoimmune conditions memory T cells does something very similar to what memory B cells do autoimmune condition is when um you know self antigen like your own um body something in your body is recognized as foreign and so the immune system attacks that allergic reactions is like a non-threatening exposure that results in an inflammatory response so like an example is if you eat peanuts and uh your body thinks that that's like a antigen that's that's a really harmful antigen whereas it might not be then that's an allergic reaction and immunization is what I talked about is that you want to induce active immunity passive immunity is kind of when you're transferring the antibodies to the individual rather than letting the individual develop their own antibodies um these last way uh shorter in time period so immunization might last like for example a whole year whereas passive immunity might just last a few days or something um example of passive immunity is when a mother gives her child a breast monk okay next is the digestive system so uh yeah I actually really like this topic so digestive system we can have intracellular or extracellular digestion intracellular is like oxidation of glucose and fatty acids through cellular respiration to make energy and extracellular is just the process in which nutrients are absorbed from your food um mechanical digestion is different from chemical digestion chemical digestion is like you're cleaving bonds within a within a peptide or protein or uh glycogen mechanical digestion is when you're breaking physically your large food molecules into smaller food molecules so when you're like crunching a a piece of broccoli that's mechanical digestion um peristalsis is you know the rhythmic contractions of your gut tube so if you actually like listen um listen to somebody's stomach and uh like if you tap and listen you can actually hear the Rhythm rhythms of the gut tube and so you can this is increased paracelis by the parasympathetic nervous system and decrease by the sympathetic nervous system remember parasympathetic nervous system is all about um is about all about rest and digestion and paralis is kind of the process of digesting right there's these Rhythm contractions as you're digesting the food through the gut tube and so that's why Paralis is increased by the pns okay um the digestive pathway is um a lot easier to understand I think than the the heart pathway the blood pathway you have your oral cavity or your mouth it goes through the fings FX is where you have both food and air then it goes into your esophagus then it goes into your stomach your stomach is going to release a lot of HCL a lot of acid and it's going to be really really uh acidic so that you can break down that food it's going to go to the small intestine then the large intestine then the rectum okay you have your oral cavity and oral cavity is where you have mechanical digestion like I said when you're chopping down on a broccoli you have amas and lipas which kind of starts the process of um digestion of food and you might be like how do we have those enzymes in our mouth it's actually from the saliva that you're salivating when you're eating something um that saliva has EMAs and liace that starts to break down some of the fats food is formed into a Bolis and then it's swallowed that's just what we call the food at that point ferx connects the mouth to the esophagus and epiglottis prevents food from entering the larynx so if there's an issue with your epiglottis you might have food in your LS and that's a really bad problem um you might like aspirate some food and that can cause you know that's like when you have a baby who's aspirating a peanut for example and then you know that's a really big problem uh the esophagus is uh a something that you know is like this this pipe and it propels food to the stomach uh using peristalsis the top third has skeletal muscle and is under somatic control and you should remember what somatic control is from earlier in this video and the bottom third is smooth muscle and the middle third is a combo of both the middle and the bottom are under autonomic control so if you think about it next time you're eating you might think about like oh um am I in control of the of like the the digestion of my food and at what point am I not digesting and that that can be a cool experiment for you okay like I said the stomach has a very acidic environment it has four parts the fundus body Anum and pyloris uh the sorry the fundus body Anum pyloris the enzyme pepsin is very responsible for breaking down protein so I remember this by p and p um secretory cells that line the stomach include mucus cells Chief cells parietal cells and G cells so mucus cells are something that produces mucus right uh and mucus protects the stomach wall from the acid so you don't want the stomach to actually get damaged from all the acid that's producing so that's why you need mucus and mucus has a lot of bicarbon it which is as you'll remember is basic and so it'll protect the stomach wall the next thing is Chief cells Chief cells release pepsinogen which then is formed uh is cre is is sorry is converted to pepsin which which breaks down proteins parietal cells parietal cells are very very important and they release HCL so they actually release the acid and they also re release intrinsic factor and so um if you don't have parietal cells this goes beyond what you need to know then you might not produce enough um intrinsic factor and you'll get less vitamin B12 absorption and you'll get this thing called anemia of chronic disease um and finally we get G cells G cells secrete gastrin and that's a peptide hormone that increases the CL secretion and increases Gast motility so it'll help you kind of um move the food down and uh G cells basically uh tell parietal cells to secrete more HCL okay um now food particles that have been processed in the stomach are now called Kime so if you remember from the mouth it's called Bolis and now it's called Kime Kim and exits through the pyloric spinter which is like kind of the last part of the stomach and is this um this like you it's a sphincter and it goes into the Dum and the or the dadum and the dadum is the first part of the small intestine okay um next we have these hormones it's kind of important to know this so ADH and aldosterone is going to increase your thirst because basically it's it's sensing that there's um less volume of fluid in your extracellular space and so it's going to tell yourself like you need to drink a little bit more water next is glucagon and gin glucagon and gin both tell your body that you're hungry and you need to eat some food and leptin and chosy sorry chinin increases satiety um the dadum is the first part of the small intestine a basic um it's it's very basic uh it kind of needs to be because that acid might come from the stomach and so you don't want the dadum to be um to be uh I guess like damage from that acid right so um so you have disaccharides you have aminopeptidase and dipeptidase and you have enteropeptidase unfortunately these are not too difficult to understand disaccharidases they are brush border enzymes that break down all these disaccharides into monosaccharides uh aminopeptidases and dipeptidases they're they're protasis basically peptidases and anop peptidases activate the trypsinogen and pro carboxy peptidase I'd say that like kind of the important thing to understand is that there's you know enzymes in the Dum that helps chemically break down your uh food now the hormones in the dadum are secretin and chosy secretin is a peptide hormone and it stimulates the release of pancreatic juice and that pancreatic juice is basically helping you to break down your food it's slows this slows motility a little bit kosyan stimulates bile release from the gallbladder um and that kind of helps again and chosy and also release helps you release pancreatic juices and also if you remember increases the Tidy okay the next thing we have is absorption and defecation so the jum and the ilium are part of the small intestine and are primarily involved with absorption and the small intestine is lined with these things called Villi and Villi contain micro Villi and that kind of uh helps you digest some of the things so Villi uh the capillary bed helps you absorb water soluble nutrients and the lacle helps you absorb fat soluble things and it sends to the lymphatic system so you can remember that fat soluble are ad and water soluble are all other vitamins um yeah and water soluble because they're water soluble they can enter the plasma directly the large intestine absorbs water and salts and form feces the seeum is basically I think it would might be helpful if I show you digestive Tru okay might be helpful if I show you this so all right so you have you know your tongue your mouth it goes through the fering and the epig latus make sure it doesn't go through the larynx then you have the esophagus right and it goes through your thorax and then um through your diaphragm your esophagus goes and it goes into the stomach right this is kind of like the pyloric sphincter over here right and it goes into the the small intestine small intestine has the um the what is it the dadum the deum the ilum and then you have your large intestine which is like this thing right and the large intestine is uh is the last part before you get to the rectum and the anus maybe we should do this one okay so you can see that you have the appendix over here you have the large intestine and and then you have the rectum and then the anus right your liver is over here and it's going to have bile it's going to create bile that bile is going to be stored in the gallbladder and then released into the dadum your pancreas is right over here sort of um deep to the stomach right and this pancreas is going to release pancreatic juice and the the this duct over here that that um this the part that uh goes into the dadum from the gallbladder and the pancreas this part over here is called the ampula of batter okay all right now we have uh the structure of the colon so the the colon is this is ascending transverse descending right and then sigmoid okay uh and then you have gut bacteria gut bacteria is responsible for producing vitamin K and biotin um finally let's talk about the accessory organs that I mentioned so we have the pancreas and the pancreas produces pancreatic juices that contains bicarbonate amas peptidases lipases so it's just all these things that help break down your food and bicarbonate helps protect your duodenum from the acidic stomach the liver produces bile albumin clotting factors right processes Nutri nutrients so if you drink a lot of alcohol somebody might tell you like oh you're making your liver do a lot of work because it's the thing that's kind of detoxing um alcohol drugs liver receives blood from the abdominal portion of your digestive tract via the hepatic portal vein um and then we have the gallbladder and the gallbladder stores and concentrates bile so it's it's storing this bile that's produced by the liver and the cck right kosyan stimulates vile release into the biliary tree which merges with the pancreatic duct and um if you remember when these two merge with the pancreatic duct and the bilary tree that goes into the dadum via the ampula of vatter okay uh and hopefully you remember that this is endoderm these are endoderm organs because they're endoderm all right making good progress so we're almost done with this whole section next thing is um kidney and skin so um let's see if I can find a good diagram for you okay um sorry this might be too complicated let's start with the simple one so very simply uh you should know that there's the kidney and the kidney goes into the uror then you have the bladder right the bladder over here and then you have the uthra which is how you eject this urine right kidney is is producing this urine for the uror and um I heard this really good quote um from my teacher a couple months ago which was that the kidney is not thinking about the kidney as producing urine is the wrong way to think about the kidney the kidney is really responsible for maintaining your whole body's homeostasis and and fluid and making sure like the amount of sodium and potassium and bicarbonate and everything in your body is right right so it's it's doing all this um understanding of what your body needs and what it needs to excrete and then makes the urine in order as a byproduct in order to maintain homeostasis and so that's kind of a good way of thinking about what the kidney do um and so the kidney has um this thing called The Bowman space let's see if I can show you here so okay um moment space give diagram okay so you have the let's look here so you have the kidney right and the kidney has these little nephrons let's show you that instead okay so then the this is a nefron which is kind of like the functional unit of a kidney and it's kind of responsible for um the whole process of absorption and of secretion and absorb reabsorption uh and so whatever goes through here is going to be released as urine and there's going to be cells uh throughout that are going to be trying to reabsorb the nutrients that are going through here and also trying to secrete things right so we call this the tubular fluid and then it's going to be released by the urine and we're going to have cells all throughout that are right next to these that are trying to reabsorb the the nutrients from the tubular fluid and put it back into the bloodstream so I'm going to call this the bloodstream over here so that's called reabsorption and then there will also be cells that are just secreting um secreting uh like ions and nutrients into the tubular fluid to be excreted via urine so if you understand that you'll know that um first there's this glus right glus is the first part which kind of uh this is the glomerulus and this is all blood over here right and so the glomerulus through this process because there's you know all this liquid and all these nutrients so this is going to pass through the glomus right and this space in between the uh blood and the glomerulus is called The Bowman space okay so goes through the B Bowman's capsule right so this sorry this thing over here the blood is called Glarus and this thing over here is called the Bowman's capsule so my bad so the blood is called the glomerulus and this and the capsule is called Bowman's capsule and the space between the blood and the Bowman's capsule is called the Bowman's space and you should know that the it goes from the glomerulus to the Bowman's capsule via you know hydrostatic pressure and oncotic pressure and Etc so now that it enters here it's it's tubular fluid right it's tubular fluid that will eventually be released as urine but we don't want this to go as urine as is so there's going to be a process of reabsorption and secretion into and out of this tubular fluid and so the first part is called the proximal convoluted tubal next we have the Henley's Loop Henley's Loop is consisting of descending thin descending and thick ascending limbs of the Henley Loop next we have the distal convoluted tubu just like we had a proximal alluded to here proximal means near and distal means far and then we have the collecting duck right we have the medular connecting duct and the um yeah we have the what is it the cortical collecting duct and the meary collecting duct okay so that's kind of the nefron anatomy that you need to know sorry if that was uh not as well explained as I wanted to um we have the kidney the kidney contains a cortex and M medula and so this is kind of what I was talking about is this part is the outside of the which is the cortex and then we have the inner part which is the medula and so the nefron goes um from the cortex to the medula and kind of back to the cortex and then back inside the medula um uh urine is collected in the bladder and excreted through the urethra the nefron is the functional unit of the kidney kind of like I said uh the renal portal system is how blood flows through the um all the way to the glary L blood goes from the renal artery to the afrine arterial to the glomeruli and then it it um then goes to the ephrine arterial so like all this filtration happens in the glomi through this whole thing right but this blood from the glomi go to the eph arterial then the vas erecta which surrounds the nefron and then finally goes out the kidney through the renal vein filtration is that process in which um the Bowman's capsule movees solute from the blood and that's called filtration right remember that the Glarus contains all this Blood here I'll show you so this is the glomerulus over here this blood and let do red so this is the Glarus over here right and this is the Bowman's capsule over here see over here is Bowman's capsule and so you can see that you know this the solutes in the blood over here need to go to the Bowman's capsule here and that process is called filtration okay secretion is when you have um movement of solutes from the blood into the tubular fluid and reabsorption is when you're going from the tubular fluid or the filtrate in from to the blood from the filtrate to the blood is called reabsorption um the kidney is very responsible for main regulating pH of the blood and kind of doing all these things with the bicarbonate and H+ aldosterone is um act aldosterone is synthesized in the adrenal cortex and it kind of is responsible in this aspect in this area right and aldosterone is responsible for making sure that uh potassium is secreted into the urine and and sodium and water are reabsorbed from the tubular fluid that's what aldosterone does and so what it's basically doing is increasing H2O reabsorption by increasing the sodium reabsorption and if you understand that then you understand that your your um aldosterone is basically encouraging ing your nefron to preserve water and so there's no change in blood osmolarity because you're also reabsorbing sodium but you're also increasing blood pressure because you're increasing the amount of water that's being reabsorbed finally we have ADH or vasopressin and ADH is a peptide hormone that's synthesized by the hypothalamus again and released by posterior pituitary and it increases the permeability of the collecting duct to H2O which increases H2O reabsorption so what you're going to get is very concentrated urine and I kind of explained this already okay um now let's talk about the nefron a little bit more so this is this is going to be talking about um what parts of the nefron secrete and reabsorb what so the proximal convoluted tubal is going to try to reabsorb everything that it can that's important so you don't want to get rid of glucose in your urine you don't want to get rid of amino acids you don't want to get rid of vitamin salt some water is going to be reabsorbed um so all of these things are going to be reabsorbed from the proximal conol tubo secretion you'll have secretion of H+ k+ NH3 UA the descending Loop of the loop of the descending limb of the loop of Henley is permeable to H2O and not salt and so basically um this this tubular fluid it's going to be going down and down and what's happening is that um the filtrate moves into more and more concentrated medula right because water is being reabsorbed so water is being reabsorbed so moved out of this um out of the descending limb and so we're getting more and more concentrated um tubular fluid down here right in the descending limb and what's happening in the ascending limb is that it's permeable to salt and not water so because we're coming up with this really really concentrated thing now the salt is going to be reabsorbed passively so we're going to reabsorb the Salt until basically um basically the salt has been reabsorbed here so it's it's not as concentrated when it goes back up into the distal convoluted tual so you might ask like oh what was the whole point of that because basically we went down and we we brought back water and then we went up and we brought back salt and so we're kind of we didn't really change the osmolarity of that fluid that much and the reason is because of this thing called countercurrent multiplier system which is that um that whole process creates maximal reabsorption of water all right next is the distal convoluted tubal and that responds to aldosterone and that creates um salt reabsorption and waste product excretion and finally we have the collecting duct the collecting duct is um responsible responsive to both aldosterone and ADH it has variable permeability and it basically makes sure that the right amount of H2O is being excreted based on the body's needs okay next we have the blad and the bladder is uh has a couple of different has a muscle and then two sphincters that you should know about so the bladder has this D truser muscle and it's under parasympathetic control and it's this muscular lining of the bladder um and then we have the internal and external urethal SP sphincter the internal one is uh smooth muscle and the external one is skeletal muscle the internal one is parasympathetic control and when you really need to pee it's voluntary control and that's external urethal sphincter okay so the next thing that we need to talk about is the skin and um uh this is not as high yield as some of the things that we've already talked about so I'm just going to encourage you to memorize some of these Concepts the epidermis the longer Han cells the melanin right the epidermis you should know what these layers are they don't come up too often and most of the practice exams but it is somewhat good to know um what these what these layers mean so if you look at maybe skin epidermis layers um yeah let's see for okay this is a pretty good diagram that we looked at in med school also when we were learning about the skin and um you can see the Keratin here the granules here and you can kind of see that this is the stratum corneum this is the stratum lucidum this is the stratum granulosum this is the stratum spinosum this is the stratum basali and the important thing about the stratum corium is that there are no nuclei right you can see over here there nuclei but here it's just a dead keratin layer okay uh and so you just kind of want to look at this and make sure you memorize uh some of these layers over here the longer Hound cells are macrofagos that are antigen presenting cells in the skin and melanin are produced by melanocytes that's what gives you your skin color and protects your skin from DNA damage that's caused by ultraviolet radiation um uh Caucasian people are actually the most uh susceptible to skin cancer because they have the least of this melanin um the same thing you should probably know what the dermis layers are and it's it's a lot easier if you kind of search up dermis layers I wish that I did this when I was starting for the MCAT but looking up images can really help you so you can see that there's the papillary layer and the reticular layer and there's the subcutaneous fatty tissue below that right and so you can see that there's nerves and capillaries over here and so just make sure you memorize this a little bit it's not too difficult but it'll help you a lot and finally we have Thermo regulation oh sorry hypodermis is what I was talking about which is this subcutaneous fatty tissue so um you can see that fat and connective tissue it connects skin to the body and then we have thermal regulation so you should know that you know sweating When you sweat when you your sweat evaporates that's cools your body down you have pyo erection which is helps you warm up shivering is also something that you're like shaking in order to warm up then you have Vaso dilation Vaso dilation helps you stay cool and Vaso constriction helps you stay warm um okay so now we're on to the muscular system so this shows up a little bit more often than the skin and um first we have to talk about skeletal muscle skeletal muscle is important for all these different things it's under somatic control so you can control it it's voluntary it's multinucleated um there's support and movement blood propulsion Thermo regulation strided right it's important to know that this is striated there's red fibers and white fibers and you should kind of know what the difference are red fibers are slow twitch and white fibers are fast twitch right this is oxidative phosphorilation and this is anerobic metabolism next we have smooth muscles and smooth muscles are respiratory reproductive cardiio vascular and digestive and hopefully you know that this is involuntary right you don't control some of these things right you don't control your heart beating uh you don't control like your stomach releasing acid so these are these are autonomic control they're uninucleated um and you should know that they can have myogenic activity even without any neural input so your brain doesn't even have to be involved for some of these things um okay next is cardiac muscle cardiac muscle is the contract tactile tissue of the heart right it's under involuntary control you're not controlling your heart uh it's uni nucleated but sometimes it's binucleated and this is the muscle of your heart it can display myogenic activity and the cells are connected with these things called inter calculated discs which contain Gap Junctions this is helpful for moving across that electric signal and now we're going to talk about the skeletal system overall skeletal system remember is derived from the mism which the you have the axial skeleton and you have the appendicular skeleton and the axial skeleton is Skull vertebral column rib cage hyoid bone and the appendicular skeleton is bones of the limb pectoral girdle pelvis you could have compact bone which is very strong and dense you can have spongy bone which is um lattice like you can have the bone marrow the bone marrow is remember filled with these he hematopoetic stem cells and it's responsible for producing a lot of the red blood cells um the yellow part of the B bone marrow is fat you can have these long bones it's not super high yield to understand this but make sure you understand some of these things another thing that's kind of high yield is ligaments and tendons ligaments attach bone and Bone tendons attach bone to muscles um let's see I think this is very high yield which is that bone remodeling so osteoblasts build bone so I just remember Osteo blast build bone and then osteoclast resorb bone and resorption here means that it's breaking down the bone to produce calcium and so parathyroid hormone is something that's responsible for increasing resorption of bone because there's too little calcium in the blood and so it's going to increase the blood calcium by resorbing this bone vitamin D also increases the resorption of the bone and also increases blood calcium and then calcitonin if you remember does the opposite it increases bone formation and decreases the calcium in your blood these are all kind of ways to regulate how much calcium is in your blood um next we have cartilage and that's kind of this uh firm and elastic tissue uh next we have joints joints can be immovable movable and there's synovial fluid which kind of lubricates these joints um let's look at more okay uh now I want to talk about sarir which is kind of like the very high yield concept here sarir are these basic contractile units that have strided muscle they're called strided because if you look at them under a microscope you can see like these lines right unlike smooth muscle and so you have thick myosin and thin actin filaments okay so the thick myosin and the thin actin filaments are responsible for this contractile unit and on the thin filament you have so on this thin actin filament you have troponin and you have tropomyosin okay that's found on the th thin filament and it regulates these interactions so I can show you the diagram here and so you have the myosin right you have the actin filament which is this blue thing over here and you have um diagram Tron and diam okay so you can see that you know there's this act in there's the tropomyosin there's the troponin and um okay actin troponin tropomyosin myosin calcium so basically what's going to happen is um see I'll get into the contraction and relaxation later but just know that there's troponin and tropomyosin on this thin filament and act and regulates this actin myosin interaction we should talk about what what the parts are here so there's the Z line there's the M line there's the I band there's the H Zone and then there's the a band just know what each of these mean z line is the boundary M line is the middle I band is only the actin filaments and hband is only the myosin filaments right this is the I band over here this is the H Band over here um next this is the sorry this is the I band over here this is the H Band over here and a band is the part that contains both right um okay sarir attach end to end and become myof fibral and each myosite contain many myofibrils so you can imagine that you know there's another sarom here and because they're attaching nend to end they're forming myofibrils and each myosite can contain many myofibrils next we have the psychop plasmic reticulum and this is kind of um a similar version to the endoplasmic reticulum except calcium plays a really big role in the sarcoplasm culum cemma is the cell membrane of the myosite and T tubules connect to the cemma and they carry these signals okay and we're going to kind of understand a little bit more about this with this part so contraction contraction and relaxation begins at the neuromuscular Junction and it's where there's a e ephant neuron release of acetylcholine that binds to receptors on the sarcolemma remember the cell membrane and causes de polarization and so depolarization then goes down to the T tuul and triggers release of calcium calcium binds the troponin causing a shift of the tropo tropomyosin and exposure of The trosin Binding site on the actin filament and then there's shortening of the sarir and then this is called a sliding filament model so when your sarir shortens then you're basically um yeah you're basically sliding this F let me let me try to find the diagram that might help you um cetal cling in muscle contraction diagram okay this might be good all right so you can see that um over here you can see that there is this acetyl choline that's entering right this acetyl Coline goes down through the T tual and it's getting released into the cytoplasmic reticulum right uh it goes and binds over here and it binds to troponin on actin filaments and now the tropomyosin is going to physically move aside right because the calcium has bound to the troponin so the troponin is going to stop blocking this and so now we're um going to be able to cause a contraction okay uh I'd encourage you to kind of read through this diagram and make sure you understand everything and also kind of just read through this and make sure you understand everything but I highly encourage watching kind of a YouTube video to understand this because when I first learned it it was really complicated to me okay um almost done last page so this is genetics and evolution and I really like this topic so the first thing is alal alal are different types of uh forms of genes right so the gene might be eye color but the AL might be brown or blue or green or gray right and if you have a dominant Al then you only need one copy for it to be expressed and recessive require two genotypes is the combination of alals that you have at a given Locus so homozygous genotype means that you have the two of the same and heterozygous means you have two different phenotype is when you have an observable manifestation of a genotype so the genotype me might be big a little a and the phenotype might mean green eyes or something right dominance can be complete or incomplete or co-dominant so complete means that there's only one dominant alal co-dominant is that there's more than one dominant Alo and incomplete means there's no dominant alal right so um you might be able to express both uh both alals you might be only able to express one alal or you might not be able to express either Alo completely and so that's what um dominance means penetrance is the proportion of IND idual who are carrying a specific Al that also Express the associated phenotype so sometimes people who have a particular Al might not actually Express the phenotype that's associated with that genotype right and so the percentage of people who actually do Express that phenotype when they do have that genotype is called penetrance and expressivity is the variable phenotypic outcome of a genotype so say somebody has um the genotype for like extra fingers on their hand um they can either have like nine fingers on their hand or they can have six fingers on their hand and that's expressivity genetic leakage is the flow of genes between species via hybrid Offspring genetic drift is when you know the composition of a gene pool changes as a result of chance so I'm sure you've done like those uh experiments of when you have like 10 people in a population and you see like how do the how do the genotypes differ and eventually genetic drift will happen right and so you'll get one Al one gene that just dominates that's called genetic drift founder effect is when for example you have like a a bird that goes to a new island and its genes are like kind of the thing that is responsible for creating a lot of the new genes there's a lot of inbreeding as a result of founder effect and then you should know that this is the taxonomic rank it's not very high yield to know this but it's still not that difficult to memorize if you remember King Philip came over from great Spain okay next we have mle's laws um there's the law of segregation and law of independent assortment the law of segregation says that um the two alals for a gene segregates during anaphase one and the Law of Independent Assortment means that these alals that are separating don't have any impact on one another so um if you have an Al for little a that doesn't affect the O for little B on a different on a different chromosome um this is not true for linked genes if you have little a and then little B on the same gene then that's going to have increased likelihood of being together in The Offspring right but if you're on different chromosomes it doesn't have any impact on each other okay the next thing is we have experiments that have shown that DNA is the genetic material sometimes this shows up because in a passage they'll explain to you an experiment that's very similar to one of these experiments and they'll ask for the outcome and if you know these experiments you'll kind of know what the outcome to expect is the Griffith one showed that there's transformation was possible so these um these bacteria could still were like basically picking up DNA from their environment from the virulent strain in their bacteria and were basically transforming their DNA the it's also if you search up on YouTube these experiments you'll find like two or three minute explanations and those are really really helpful Avery McLoy McCarthy basically showed that the degradation of DNA led to a cessation of bacterial transformation but when you degraded proteins it did not so it showed that DNA was the thing that was being um transform not the proteins and lastly we have Hershey Chase which show that um when you radiol label the DNA the only thing that was the only thing that was being found in the bacterio phage infected bacteria so you inputed a lot of bacteria phages and you saw that there was only radiol Lael DNA in that bacteria okay um this is different types of evolution so you should know this Divergent parallel and convergent and then um we have nucleotide mutations this is all very very very high yield for you to know nucleotide mutations can be point mutation frame shift mutation and the results can be silent which means that you know there's a mutation but it doesn't have any effect on the protein on translation of that protein there's missense and nonsense nonsense is when you have a stop code on and so your amino acid chain might stop too early and you don't actually uh translate everything that you need to right there's also miss which means that one amino acid has replaced another amino acid so you might need like Bine over here but you get I don't know glutamine or something right insertion or deletion can result in this thing called frame shift uh mutation right and so that that's like moving the three-letter reading frame um um sorry sorry so frame shift mutation is when you have um moving the three-letter reading frame and you can get an insertion or deletion into the amino acid so it's important to know and a mistake that I just made is that this insertion or deletion is referring to the amino acid chain and this frame shift mutation is talking about the MRNA that's producing that amino acid chain so if you have like for example a t c right and you add like an a over here then that's an an insertion of a nucleotide and that's going to cause this to be a a [Music] t and then C is going to be on the next one right and so this is going to be a frame shift mutation and that's very dangerous because basically everything in the in the DNA or the RNA molecule is going to be um changed because you're now CH moving that three-letter reading frame and so these are the results in the protein and so you can get silent which is no effect on the protein you can get missense or nonsense and then finally you can get insertion or deletion which is the insertion of an amino acid into the um amino acid chain okay I hope that makes sense just make sure you review that so that it makes sense next we have chromosomal mutations and this can be like huge segments of DNA on a chromosome that are being affected can have deltion duplication inversion insertion or translocation and I probably would encourage you to just look at an image I can show you that now because these are not too conf confusing to understand but it was very confusing for me uh when I was first looking at it so if you look here these are very easy diagrams to kind of understand what's going on this is a deletion over here this is a translocation over here this is a duplication over here and this is an inversion over here and if you understand these Concepts then it's very easy to kind of know what's going on okay now we have analytical techniques uh the Hardy Weinberg principle is p plus Q equals 1 and P and Q are the two different alals um and how frequent they are now sometimes there's more than one more than two alal maybe there's like 10 alals um so this is true under a certain uh number of conditions and if if you have two alals and you know your population is stagnant and it's not changing and things like that there's a lot of different criteria that you can search up then this equation should be true okay uh recombination frequency is also kind of this important concept and recombination is um the likelihood that two Al are being separated during crossing over in meiosis and so um I never really understood this concept until I started med school and basically what's going on in recombination frequency is when you have a single chromosome right you might have multiple genes on it sorry you might have multiple genes on your chromosome right and usually you'd expect that on this chromosome that these genes would stick together in the daughter cell but what might happen is if you remember meiosis you can get crossing over right and so in crossing over these two um alals might swap right and so recombination frequency is how often do do those does that swap happen because you you have crossing over like crossing over over here and so this Gene is no longer attached to this gene on the same chromosome how often does that happen well that's actually directly equivalent to the the closeness of these two genes if these two genes are very close together it's very likely that the daughter cell will get these two alals together right but if these two genes are very far apart these two Al on the same chromosome then crossing over might happen some somewhere in here and so there's going to be recombination and so these two alals might not end up together on the same chromosome in the daughter cell okay next we have Evolution and so evolution is when you you can have natural selection natural selection is kind of the main method of is the is the actual mechanism for evolution um uh yeah I don't think it's that important to know modern synthesis model it's just it's just this idea that mutation and recombination are mechanisms for variation it's not just mutation but you can also get the recombination uh which is kind of like uh the biochemical uh biochemical way that you can create variation you can also have Inclusive fitness Inclusive fitness is that if a population meets certain criteria then the Leal frequencies will remain constant and that's only when there's a lack of evolution so when you learned about like the bird beak and the finches beaks right there was um there was Evolution going on because the environment was changing and uh if that's not true if there's no like change in your environment then you'll have Inclusive fitness which means that the legal frequencies will remain the same punctuated equilibrium again not that important it's when you have very very slow process of evolution and then you have this burst of evolutionary activity you can have these different types of natural selection which you should just read it's not too important to know for the purpose of MCAT but yeah just know what stabilizing directional disruptive and adaptive are um and then yeah I I guess the last thing that we should talk about is the molecular clock model which is when is the degree of difference in the genome between two species that are related to the amount of time that the two species broke off from the common ancestor so uh I had once did a research project in which I was looking at um like this socks 11 Gene within between mice and frogs based on how far apart they broke off from the common ancestor right and can kind of figure out how different the genomes are based on two species based on like when their last common ancestor was and that's kind of the molecular clock model and so the further away their common ancestor was the further back the more genetic uh differences they're going to be but if they're like they very recently had a common ancestor then it's more likely that um their genome looks pretty similar that's what that is okay uh that's everything you need to know for the biology section I really hope that was helpful just make sure you go through everything and understand everything that we went through um and I really really appreciate your time thanks so much for uh for watching and giving me your attention um I'll see you in the next video bye everybody