Transcript for:
Understanding Cell Structure and Function

okay so we're going to try to go through Chapter three as quickly as possible we're going to be talking about sells their overall structure and function and then we're going to get into some details about the organelles that are contained in the cell so we kind of want to know what a cells doing because that's an important part of how function takes place when we discuss organs and organ systems and things like that okay so this term membrane can be confusing sometimes because it can actually refer to anything overall it just it's a coating it's something that's outside so here you can see the pericardial membrane which is actually made up of epithelial cells that coat the outer it's an outer coating of the heart we'll talk about that more when we when we cover cardiovascular but what we're interested in right now is this thing which is the cell membrane and the cell membrane are made of these phospholipids that's what these guys are and then there are little cholesterol molecules giving it some structure and support outside that and then we have their proteins sticking out their lipid sticking out lots of stuff coming out to make up the cell membrane so that's where we're that's where we're going to start now just as a as a review we're all of the cells are bathed in some kind of fluid and they have fluid inside them the solute inside remember is intracellular the fluid on the outside is extracellular so extracellular but we sometimes call that interstitial fluid because that means that it's between the cells or around the cells now in the blood the fluid that we that we think of that's around these are the blood cells these little guys right here and the fluid that's around that we call that the plasma okay all right so so if we start talking about membrane function it does a lot of things the the cell membrane is is hugely important and it's going to keep coming back that's why I talked about it it's going to keep coming back up because we have to think about how things move it's a bilayer so these phospholipids there are two of them with their tails together and there their heads that remember the hydrophilic head and the hydrophobic tail with the water out here okay on contacting the head region but a lot of things have to move through this a lot of things are blocked by it and so we have to kind of understand the cell membrane as a semipermeable membrane okay so some things can go in some things cannot go in it's permeable to it's it's selectively permeable so it allows some particles move through but not all okay so this allows things like a concentration gradient which we're going to be talking about excessively from one side to the other concentration gradient electrical gradient so the outside of the cell cell seam tends to be positive while the inside tends to be more negative and so all of these things so the cell membrane its cells have to know where they are they have to know where they are in relationship to each other sometimes there are usually there they're attached to one another but a lot of communication a lot of a lot of communication goes through exchange it acts simply as a physical barrier to block to block things from moving through okay all right so if we look at if we if we really back out and we look at a cell membrane it's very very busy okay so it's got a lot of stuff going on so here we can see if we look here this is important we can see these phospholipids and how and we call this a bilayer because here's a layer of phospholipids air and there's another layer of phospholipids so we call that a bilayer it's it's two layers and then there's fluid on the outside like I said and fluid on the inside okay but see here we can see a glycoprotein glyco means sugar okay so it's sugar this is the sugar part here and this is the protein part here okay so it's a glycoprotein and so we see other things we see we see here we see sugars that are anchored in by lipids okay so these are fats remember the fatty fatty acid tails that hang down from the head of a phospholipid well here are fats fatty acid tails that are attached to sugars okay so so there's a lot of so there are a lot of things going on we would call that a glyco lipid because of how its structured we have mem we have proteins that are transmembrane proteins that are going entirely through the membrane the cell membrane okay so these are our transmembrane proteins okay we have this is a lipids as your lipid-anchored protein so that's stuck there by these two little lipid tails and there's a protein out there this could be a signaling molecule they just have lots and lots of different function then we see the cytoskeleton which is attached to this protein which is holding everything together so you can see that all of these structures that make up the cell membrane are important for how it for how it works so this is this little picture over here is showing a protein so this protein is is it's an alpha helix or it's it's moving through there and then so you have part of the protein that's on the inside and part of the protein that's on the outside this is great for communicating so we can have a signal we can activate something on this side and it can actually cause something to happen on that side okay so that's a way that the cell is communicating without letting anything in so nothing is able to go in but if a ligand we're to bind this here it could actually change its shape enough to make something happen here okay and that's we call that a g-protein that's what this one that's what this is an example of there are lots of different types of proteins but G proteins are the most popular in terms of drugs that that affect them and things like that okay so that's that's it and here we see this is a nice little picture of sphingolipids bingo lipids form little rafts down here that can can sort of make a coating on the outside which is a which is further protection okay so we have phospholipids that we just mentioned sphingolipids which is this as an example here then cholesterol of course which are which are these little guys here that sit in between the phospholipids and they can be harvested to make things like steroids okay so that's all part of the part of the cell membrane okay so but it's different for every cell right I mean different cells are doing different things so for instance here's the red blood cell membrane which is about half and half proteins and lipids with some carbohydrates here if you look at something we're going to talk about later called myelin myelin is almost all lipids okay so it's nested with just a few proteins inside the mitochondria which we'll also talk about it's a very busy place doing lots and lots of things so it has a lot of proteins for that kinds of function okay so for that function to take place so there it's it's very heavy on the protein very light on the carbohydrate okay sounds like a diet doesn't it okay so again quick review this is a phospholipid we've seen this slide before it has the polar head which is hydrophilic trying to get that get that solidified in your brain so polar head hydrophilic it likes the water okay nonpolar fatty acid tail does not like the water and so we'll associate with another phospholipid that may be sitting down here and then it's going to have down below it's going to have its polar head okay so that's that's what goes into making up primarily the phospholipid goes into making up the the membrane because if you were to dump these if you were to make a bunch of these which can be done if you were to make a bunch of these and you were just to dump them into a beaker of water they would arrange naturally just like this because the water is going to associate with these outer parts and it's going to push these tails all in together and you're going to end up with something called in my cell now if there's a pore some of the water gets trapped in the middle of it we call that a liposome okay so means body so it's a lipid body okay so and like I said this little term here it's a bilayer okay so when you're wondering and this is just just how it is I mean these are just chemicals you know we've looked at the structure of fats and then it has this little glycerol and then a little phosphate group and that's what makes a phospholipid okay so so that's just it that's the way they will naturally come together you can dump this in a beaker stir it up and you'll see a bunch of these types of things that have formed okay all right so intracellular compartment some terms here the cytosol is the fluid okay so if we draw a cell here we can say that the cytosol is just the fluid part which is going to be water then there are also inclusions which are things like ribosomes glycogen which we've talked about they all just kind of sit in here and then there are organelles okay organelles have their own little membrane-bound compartments in there okay and so the all of these things together so these are membrane bound I'm going to say that again membrane bound there's a nucleus all of these things together make up the cytoplasm okay so don't get I know cytoplasm inside is all sound very familiar keep them separate site of cytosol is the fluid cytoplasm is all of this all of these things together and then there's the nucleus that sits over here and it's it's own little structure doing its own little thing inside the cell okay so yes the cell is a busy place so if we if we look at this we think first of all we think wow that's that's kind of pretty but then we can kind of all cells for the most part we'll talk about some exceptions but for the most part every cell in your body from neurons to your skin cells to liver cells all of the cells in your body have these structures contained in them and they all do specific things this is a little factory I mean you've got your your DNA that's hiding in the nucleus and it's its job is to make proteins well the endoplasmic reticulum is part of that protein making process and then you can see here this is the Golgi apparatus well we have to excrete some proteins sometimes out of the cell so the cell will make the protein and then it will release it and it uses the Golgi apparatus to do that we have these guys here which are the mitochondria and those are making the energy because there's a this is very very busy so the mitochondria are busy making ATP and then the ATP can be used by all the proteins and by everything else that's doing stuff so all cells have most of these organelles at any one time now you can see your micro villi that are growing on the outside and that increases some surface area and we'll talk about that specifically as well not all cells have that but but all cells with like I said the couple of exceptions that we'll talk about all cells have these components in it now the cell might be shaped differently but but they're all going to have those things so if we if we break these down and we look at and this is this is the difference here organelles versus inclusions organelles have membranes so the mitochondria the endoplasmic reticulum the Golgi apparatus lysosomes peroxisomes these is just the digestive system of the cell and the ER and the Golgi are used to make proteins and then the mitochondria is used to make energy these are the organelles and then there are inclusions okay so it gives the example of lipid droplets glycogen glycogen is that chain of glucose molecules that's used to store glucose okay for later use and then ribosomes and we'll talk about ribosomes are in the next section okay and then there are a bunch of fibers okay so so we can kind of see these here we can see the little fibers that are giving some structure and there also something that they also serve serve other functions the these fibers that are in their centrioles centrioles are are what you would call to give it a fancy name they're nucleation sites for for mitochondria but they're they're involved in or not mitochondria but microtubules sorry so there's they they make microtubules which are a type of cytoskeleton tubules okay and so so they they can they produce these microtubules cytoskeleton and they serve other function too but they're just long protein fibers and then flagella the only the only flagella that you'll find in the human body is on the is on the sperm okay so that's the only that's the only human cell that has a flagellum and the flagella is just a tail it's the tail of the sperm okay so this is what we're talking about cilia to keep to keep these separate because a lot of people have trouble with this cilia versus flagella a cilia moves moves things okay so the cilia will move something in it and it moves in such a way for instance on your respiratory your respiratory system the bronchi and the and the trachea have cilia and the cilia are moving particles so here's a particle that gets that gets trapped in the mucus and the cilia will move in this direction and then kind of like this is trying to show so then it's it's over here now but then it kind of bends backwards and it sneaks back over to this side moving this way and then it moves it again okay so it's moving something in one direction so it's moving fluid in one direction okay the flagella spins around and this shows it this shows it snaking okay which is fine because it does that but it's to propel the cell forward okay so it's it's actually propelling this cell for by moving the fluid in that direction okay so that's really the only difference these things are both involved in movement in the case of the flagella it's in humans it's moving the sperm but this is also found in bacteria and and other other smaller organisms okay and it's to propel okay so let's move it forward and then the cilia is to move is to move fluid okay all right okay so so we just looked at cilia and I'm spelling these out for you because it's confusing flagella and now we have this other term microvilli because they all look kind of silly similar I think we can kind of check flagella off we could say okay I've flagella I mean that's that's the sperm and that's this is the flagellum okay we can we can get that cilia remember cilia is fluid movement and movement with my kindergarten handwriting there but now we have this thing called microvilli okay now micro villi don't move okay their job and notice this because that's what you're that's where you're going to get confused I see it all the time you're going to get confused between cilia and microvilli micro villi increase surface area we're not saying anything about movement when we talk about micro villi okay so that's where the trick question is going to come in it's going to say what's a micro villi and one of the choices will be movement and you're going to say no it's not that that's cilia and flagella okay but they have these these microfilaments that kind of move up in there and give them structure and then like in the stomach this gives a lot more surface area so you can have absorption here as well as down here okay so without these we wouldn't have all of this surface area to absorb something I mean something that's flat like this can only absorb that much but if you were to put micro villi sorry and to make sure I use the terms correctly if you were to put microvilli you can get a lot more surface area in that same distance okay between there and there okay so that's its purpose okay and microfilaments and microtubules are giving all of these things structures so you can see these these guys down here they're the microtubules there are the filaments we'll talk about actin when we talk about muscles and then there are their intermediate filaments which sit down here so these things are all you can see now that the saw the cell isn't just this empty little thing it's actually got a lot going on and these are just proteins okay so these are just proteins arranged in such a way that that they're giving that they're giving making these filaments and giving it giving it structure okay so one of the other things I'm just going to say this briefly there are certain things called motor proteins which to me are just amazing little things and this guy will walk along this fiber okay right now all you need to do is know that these things exist however when we're later on talking about how a muscle contracts we're going to see that this is how your muscles contract you have these motor proteins that are specialized to walk along a cell or I'm sorry walk along a fiber in this case in the case of muscle contractions this is an actin fiber and this is myosin okay so we're going to learn that later on but right now just if you just look at this you can see this guy will keep changing its shape every time it binds and it will walk along this filament in that direction okay and of course it requires ATP which is energy to do it okay so now let's start talking about some of the some of the organelles speaking of ATP ATP is energy it's a molecule and I'm not going to say too much about it here but it's a molecule that has a lot of energy built up in in its bonds okay and so the body has figured out a way to use ATP as energy well there's one place well primarily one place that makes great quantities of ATP and that is the mitochondria it's kind of a kind of a joke that the mitochondria is the powerhouse of the cell ok well that's that's fine but it's not very descriptive so we're going to talk about how that energy is being made in a later chapter but right now you can see them here's a mitochondria here's a mitochondria here's a mitochondria they have their own DNA and you have your mother's mitochondria ok so if you think about what happened at conception the sperm moved into the egg and all it did was release DNA it released its own DNA well there were mitochondria that we're in here and these mitochondria have their own DNA ok and so that means is this thing started to divide the only mitochondria that it had access to because the sperm didn't give it any the only mitochondria it had were these that were originally there so you have your mom's mitochondria now the idea is that the mitochondria mitochondrion was originally just a bacteria an organism that that invaded other other other organisms but it was so good at making ATP that other organisms started using it ok and so now it is part of our cell ok so it has its own DNA it can't survive on its own it's not a bacteria anymore but it does have its own D and this DNA is primarily used in some of these processes to make ATP okay so that's the mitochondria and that's what it does in general and we're going to talk about how it does that later on okay so it's arranged in such a way that it has this inner mitochondrial membrane this inner membrane and and that's that's part of how this how this function takes place so this is this is how ATP is generated ATP is generated primarily down here in this area and then it's released okay so it has this unique structure and that structure is made is that way so it can make ATP all right now we have the endoplasmic reticulum now if we look at a cell the endoplasmic reticulum is kind of shaped like this okay alright so the thing is we have a couple of different kinds of the ER we have rough ER which has a bunch of ribosomes sitting on it and it looks rough okay now I know we don't know what ribosomes are right now it's just a word or I'm assuming it is maybe you already know but that's where proteins are made ribosomes are used we call them I call them translators okay so so these ribosomes are used to make proteins so that's where if we sorry I'm going in the wrong order here but the rough ER protein assembly and modification that's what it does okay now something that happens over here so this is rough and it's rough because it has the ribosomes and then over here we have smooth no ribosomes so if it's smooth and it doesn't have ribosomes then it's not making proteins and and protein assembly and modification that's not it roll but if you think about a cell that grows and gets larger and larger it needs more lipids it needs more phospholipids it needs fats and so the smooth ER has processes assembly processes that allow it to make fats it makes these fatty acids sterols lipids so it makes all of these things so so that's what's going on the smooth ER and then those can move out here and they can become part of the membrane or they can become cholesterol or they can become you know the ultimately they can become things like hormones okay so that's what's hormones so that's what's going on in the smooth ER so just keep those separated for right now smooth ER synthesis fatty acid steroids lipids modified forms in the liver kidney and the muscle but this is really the function that you need to to keep separate okay is the rough ER versus the smooth ER and hopefully that'll make more sense when we start talking about protein protein synthesis okay so here's another picture of this and this is not a nicer picture than I drew these little these little blue dots are the ribosomes and then over here you can see in the smooth ER it doesn't have the little dots because it is making fats okay specifically fatty acids what's the difference well fatty acids are specifically the tails okay those are the little tail so you can have something that's considered a fat but specifically the fatty acid is this is this fatty acid tail that can then join to the glycerol to make and what looks like what I drew here was a phospholipid okay that means it's going to have a little phosphate group on it - all right or it can be a triglyceride thing looks like a jellyfish okay all right so that's the endoplasmic reticulum now another thing so if we look at this if you can if you can see this okay this little pink area here that's the endoplasmic reticulum this area right in here that's the endoplasmic reticulum so we're making proteins there we just said that making proteins or fats but those proteins have to go somewhere so they work with the golgi complex or the Golgi apparatus maybe you've heard it term that which is this green thing right here okay this is the golgi they also do protein modification and we're going to talk about what protein modification means it sounds like a pretty mysterious term right now but they also do protein modification but they do it so it's packaged into this little secretory vesicle so if we look at a golgi larger what we see is that these proteins that are being made in here can all be packaged into this nice little secretory vesicle and then if we have our lipid bilayer or cell membrane here then that can actually fuse with it and then release those proteins okay so when we talk about the golgi it's doing something specific and it is modifying and then packaging proteins for secretion okay so that's a major role of the golgi complex because I might ask something like well gosh what if if you have a cell whose specialization is secreting things like mucus or something like that which organelle do you think is going to be very extensive in a cell like that if you have a cell that's whose job it is to secrete things it's going to have a very extensive not just ER but Golgi it's going to have a very extensive golgi complex Golgi apparatus because it's that's what it does secret secretion okay so this is a this is another picture a better picture and it shows the same thing it's it's in this case it's going up but it's but it's going to create these little secretory vesicles here and then those are filled with proteins and then they will fuse with the membrane so if we have the membrane out here it'll fuse with the membrane and then release those proteins to the outside release those substances to the outside okay all right and then last but not least the nucleus the nucleus is that's where your DNA is and that's where you're your own personal DNA is now I did mention that the the mitochondria has some DNA but everything that makes you you aside from the few things that this mitochondrial DNA does that's all contained in the nucleus okay and they're they're arranged in chromosomes okay so we have our 23 pairs of chromosomes that are all existing in the nucleus now if we look at the nucleus so I'm going to draw this was supposed to just be the nucleus I'm going to go ahead and erase that but if we draw the a cell and then we put the nucleus in it what we see is not a bunch of nicely packed chromosomes individually we see them all and wound and all over the place okay so when this DNA and there there are a bunch of them okay but they're filling this up and so when you look at it you don't usually unless the cells about to go about to divide you don't see them as what we're typically used to seeing is chromosomes that look like this okay that's a chromosome that's that's very dense and getting ready to divide usually they're unwound and they look like this and so we call that chromatin okay all right and there's an envelope we call this outer area the envelope of the nucleus and it has holes in it okay so it's got holes which is going which are going to let the newly-formed messenger RNA we'll talk about what this is let's stuff move in and out okay all right so that's that those are these three items nuclear nuclear pores the nuclear envelope which sits around it and then the chromosome chromatin which are the chromosomes that are all unwound and and sitting in there okay so we can see this the nuclear envelope this is a nice little picture nuclear envelope the outside of it nucleolus we haven't talked about that yet but that's where there's a bunch of RNAs being made and then this chromatin it's DNA and with the proteins on it that are that are trans transcribing that that DNA okay so that's what all this is filled in here that's that's the chromatin and then of course these are the nuclear pores okay the nuclear pores that are letting things out okay that's what that's what we see here these arrows don't really line up very well that arrow should be down a little further but that's what it that's what it is okay all right now I'm not going to say too much about this but it kind of puts everything together and it says okay up here we're going to go through all of these in a later chapter so I'm going to have a section just on that but right now we're just going we're trying to get a big picture for what's going on and we're saying okay here's the nucleus that's where the DNA is well the DNA never leaves the nucleus but the purpose of DNA is to make proteins but we just said if the purpose of DNA is to make proteins it's not a protein it's a nucleic acid but if the purpose of it is to make proteins but it exists inside the nucleus remember what we just said we just said that the ER is where protein synthesis takes place and the Golgi apparatus modifies the ER also modifies but these things are modifying proteins so it sounds like the protein work is being done out here and that's absolutely true so that means that the DNA with its contained in the nucleus makes a little copy you know for whatever protein you want to make you just find a section of the DNA that has the code for that protein you make a little copy of it that's RNA and then that then these ribosomes will find that RNA and start making a protein now this little purple thing right here that's a protein being made okay you can see it's starting to be made on this one okay so that's what the ribosomes are doing so little by little we're going to get into the details like I said and that's what that's what all of this is but little by little we're kind of getting an idea okay ribosomes aren't responsible they play a role that's what we know so far in making proteins that happens it happens out here in the cytosol but the ER which is what we're just talking about is an organelle they also will stick to this and they'll make proteins and they'll put them in there and then these proteins if we follow this this protein kind of blebs off that's a real word by the way and then moves down to the golgi where it's modified a little more and then they're packaged into a secretory vesicle down here so they move through this system and then they're packaged into this little vesicle and then those proteins are released so we have an entire picture we don't know all of the details yet but we have an entire picture of how these guys are working together meanwhile now I will say that everything uses proteins so we have proteins going to the mitochondria we have them going to peroxisomes which are involved in digestion and breaking down junk that builds up in the cell same with lysosomes we have proteins that have to go to the mitochondrion so these are all these are all being made and moved to different places but here's the mitochondrion here that is producing what it's making ATP and because all of these processes that take place require ATP okay so that's how they're all working together we're making proteins proteins are the workers I said that lots of times and they all need energy to to be made into and to function in a lot of cases okay so that's what the mitochondrion is doing so now we can kind of see how all of these things we just went over work together and they're actually doing something okay so if we continue with some structure there are some things to remember and that is that when let's say if you're digesting something you just data you just ate a cheeseburger this is supposed to be a cheeseburger okay and you break that down into little pieces those things have to be absorbed if this is your intestine those things have to be absorbed we don't just want them to move between the cells we don't want big gaps in the cells so these things just move through because we want to make sure that they're actually healthy for us okay so we want to make sure that like for instance if it's a if it's a sugar that it's not a big complex carbohydrate we wanted to make sure it's a little monosaccharides okay so we have so it doesn't look like this they are joined together by junctions so most cells that exist in your body have junctions that are holding them together and there are a couple of different kinds gap junctions tight junctions and anchoring junctions the one you have to know by name is this one okay the gap Junction I'm going to have a have a picture of that okay so that's what this is showing this is showing gap junctions and so two things first of all it's a junction okay this is a cell and this is a cell okay so these two cells are joined together okay so that means it's a junction that's what a junction does it holds these two cells together they're attached however a gap junction has a space where things can move from one side of the cell from one cell to another cell so they're a special type of Junction okay and they're a special type of Junction that we are going to talk about and you are going to be asked about on an exam when we talk about the heart okay because gap junctions or would hold cardiac cells together because communication is important in that case and you see gap junctions in lots of other places but the place will mainly be talking about it is in the heart okay so it serves two purposes it allows communication but it's still a junction so it's joining things together okay so we can see we can see more examples of this here's a tight Junction this is not allowing communication and it is saying nope nothing is getting through so this is an example lumen of the intestine and the lumen is just the space of something that's hollow like the intestine and so this is the lumen of the intestine so this is where your food is moving through and you're trying to absorb it well we want to make sure that it goes correctly and that it actually goes through the membrane moves across the cell and then is put in here we don't want it to cheat and just start flowing through there that would be bad because you could get a lot of toxic things or things that haven't been broken down properly and that would be a bad thing okay so we have these tight junctions that join them together so you can see here if you remember the gap junctions the gap junctions had this space but if you look at this guy this has no space so nothing in this cell is going to move into this one okay there's no way for it to move through okay and there's no way for anything to come through in this way it holds them it holds them together okay all right let's see is that everything hopefully that's that gets that point across okay all right so to say a little bit more about this because like I said this stuff needs to be in your in your mind because we have to start that we have to have to have to start thinking about things as a as a process and as a as a machine almost instead of just memorizing you know terms and things to get us to the next section we have to start thinking about these things in a functional way because here you have what we sometimes call endothelial tissue but it's a capillary which is a very small blood vessel okay so you have capillaries all over that's whyyou that's why you blush you have capillaries very close to the surface of your skin but they're very thin and they absorb things things can move through the capillaries very easily that's why you can breathe and things go into your bloodstream because there's this nice little layer that allows things to to move through okay so we call that exchange epithelium but here with these exchange epithelia you can see that this has an actual gap or a pore that allows some things to move through okay now these pores will can actually close or open more to let more and more stuff flow through okay so a lot of times when these things when you have when you're when you hurt yourself and your ankle swells or something like that what's happened is that this guy has shrunk a little bit and it's letting more fluid flow into that area okay and that's causing a fluid buildup and you have swelling edema okay that's what that is all right so so we're going to see this we need to think about it in that way we need to think okay well there there can be tight junctions it doesn't let that do not let anything through and then we can have this exchange where in some cases we can actually have flow through here okay we don't want that in the intestines we do want it sometimes in capillaries we want to allow that fluid to move through there so there are modifications and adjustments that can be that can be made for that okay do you remember the difference between cilia and microvilli little quiz there cilia is fluid movement so hopefully you got it micro villi are for surface area okay so in this case this cell has both okay ciliated epithelium lining the airways okay so it has both microvilli and the cilia okay now it also has these items here there's the golgi there would be there would be the endoplasmic reticulum so it's still a cell it still has all of these things this could be secreting mucus usually you have specialized cells for secreting mucus but that's but that's a an example of a of a cell function okay and then of course you have the mitochondria because everything needs ATP all right okay secretory epithelia i talked about this because one thing that we do is we we do things like we we sweat and we excrete fluids we excrete fluids from mucus in our in our GI system actually in most places your your excreting mucus you have lots of things that are being excreted and it's kind of an interesting idea if you don't actually talk about what it is that's happening by that I mean if you were to ask somebody how do things get excreted okay how to sweat glands work they might think oh well you know there's fluid inside it that builds up and then there's a muscle that squeezes it out well that's not the way it happens that's not the way secretion happens the way secretion happens is these cellular processes will produce something and it fills this little pore and more and more and more of it builds up and it starts to ooze out okay so that's the way secretion takes place okay and so a lot of times there will be specialized cells called goblet cells that will sit in here and they're the main ones that make these fluids and then those and then it's and then it uses out endocrine we haven't talked about endocrine versus exocrine yet but sometimes we have we're releasing things into the blood and so it's kind of the same thing we just build these things and then we release them usually through an still fluid and then they move into this capillary and it loses into the blood okay so that's that's secretion okay so that's secretion when something is is moving into the blood we say that it's being secreted all right and then the last thing we're going to talk about is apoptosis okay cell death and replacement if you have if you know someone or if you have a patient or something that has a stroke a lot of times you have cells that die okay so if a neuron dies like because it doesn't have enough oxygen okay so if a neuron dies we'll say this is a neuron what it necrosis means that it dies and it releases all of the goo and all of the proteins and all of these enzymes that were inside it it releases those and those are toxic and it's supposed to be a skull and crossbones those things tend to be toxic that's very very bad well the thing is cells get old all the time okay they function for a little while and then they stop functioning and whether it's through DNA mutations or whatever buildup of toxins inside them they stop functioning and they don't work anymore they don't just die and leak out all of their stuff all their toxic stuff that would be bad what they do is they go through a process called apoptosis this guy gets a signal says hey dude you're too old you're not working right anymore and then it will just sort of fall apart it'll start to separate and it'll turn into particles and it'll contain all that stuff and then that can be broken up by peroxisomes or macrophages something will come in and then detoxify all that stuff turn it into something harmless and then release it okay so that's what apoptosis is apoptosis this is the term for programmed cell death cell suicide it it does it in such a way where it doesn't kill all of the cells around it because if you have a neuron that dies in that way it could potentially kill other neurons and that's actually a big problem after stroke is that the stroke may kill a certain number of neurons but those neurons upon dying kill other neurons so you have to stop that you have to stop that process and that's one of the that's one of the things with stroke that they're working on is how do we you know limit the damage to just the cells that were initially initially killed okay replacement of cells stem cells we're going to talk about this again later too stem cells are they retain their ability to divide so they're sitting down here and so when these cells die so this cell goes away it's gone then we can have this one divided okay so it'll it'll divide and then this one will go on to take its place okay so this can happen in some tissues that happens indefinitely a lot but there are limitations sometimes to how how many times this can divide before it's done okay all right and then research uses in potential we've we've heard a lot about stem cell studies where if you put stem cells in they can maybe maybe replace lost neurons because right now once these guys are gone they're not really replaced at least not in the central nervous system okay so that's all we have for four cells hopefully that wasn't I know it's long I'm sorry about that but but hopefully it's it's helpful okay