all right ninja nerds in this video today we're going to be talking about mesoderm before we get started though make sure you hit that like button comment down in the comment section and please subscribe all right neither jared let's get into it all right ninja nurse when we talk about mesoderm first thing we have to talk about is how we make mesoderms so we have to kind of start back and go over just briefly the gastrulation process so gastrulation is what you're going from a bilaminar disc and we'll talk about what those two layers are made up of to a tri-laminar disc and we'll talk about what those three layers are made up of so we start off with our bileminer disc right and we're generally around week two you consist of two layers this top layer like above here where you can't see would be the amniotic cavity right this blue layer here is called your epiblast layer okay so this is your epiblast layer then this green layer which is actually going to be just below the epiblast layer and then again you can't see but there's a little cavity underneath of it called the yolk sac this is going to be called your hypo blast layer what happens is during week two you develop this kind of little split this little slit here in the epiblast layer with a big old knob there so some of the cells start kind of disappearing or moving and creating this little space this space here this one here is called your primitive streak and then this one here is called your primitive node what happens is is certain types of growth factors like fibroblasts fibroblast growth factor type 8 gets released and what it does is it causes some of these epiblast cells to start moving and what they do is some of these epiblast cells start migrating through this primitive streak and as they move through this primitive streak they move downwards and they move laterally and they also move cranially towards this thing here called the prochordal plate when they do that as these epiblast cells move in here they replace this layer here what was this green layer here called this is called your hypoblast it'll specialize and turn into a new layer called the endoderm we'll talk about that in a second then you'll make a new layer between this hypoblast and this epiblast and this layer that we're going to talk about in next is called your mesoderm one last thing that we'll talk about in a second is how we have other cells epiblast cells moving through that primitive node and making what's called the nodochord all right so we took our epiblast cells moved through the primitive streak and made three new layers what are these three new layers again first layer is you replace the hypoblast layer and this turns it into endoderm then you make a new layer what is that new layer between the endoderm and this epiblast layer for now this is called your mesoderm okay what happens is remember i told you that only the epiblast cells here were moving through the primitive streak what happens is they start moving through the primitive node and they make this tubular process as they move towards the head and this is going to make what's called the notochord another thing is some of these epiblast cells they start differentiating and specializing and they turn this epiblast layer into a new layer called the ectoderm so now what happens as we move down here now the primitive streak and primitive node are gone we now have the endoderm that's now there right so it's still there we have the mesoderm and what else did we say happens here remember we said we get a little tubular process that develops between the mesoderm that's called your notochord and then remember the epiblast cells they differentiate last and become ectoderm ba-boom shakalaka next thing that happens you get this notochord what this nodochord starts doing is it starts secreting proteins and growth factors and what it can do is it can trigger the ectoderm to form what's called a neuralation pathway which makes a neural tube but the other thing it can do is it can trigger this mesoderm to kind of specialize and form special types of differentiation so what is the notochord going to do the notochord is going to be releasing different types of growth factors and proteins like sonic hedgehog protein that's not fake and what that can do is that can trigger the ectoderm to trigger what's called the neuralation process you're going to start making neural tubes or it can stimulate the mesoderm to start differentiating so it'll cause the mesoderm to differentiate what do i mean by this let's come down and look so now as we come down here what did i say these growth factors that the notochord is releasing it triggers the nergulation that's that maroon color tube right there but the other thing is look how the mesoderm changed you see how it changed and now it turns into like completely different chunks of mesoderm here what are these chunks of mesoderm we're actually going to have to talk about them from medial to lateral so what i'm going to do is i'm going to number them the one that's most medial closest to the notochord and the neural tube is this one here okay the second one we're going to go out a little bit laterally is going to be this chunk here and then the last one is going to be these two little chunks that are coming off of that second one so the first chunk that i want you to know the most medial one is what this is called your par axial mesoderm okay very important one to remember most medial one second one is this is pretty easy intermediate mesoderm it's called your intermediate mesoderm okay and then the last one which is as you move most lateral what is this this is your lateral mesoderm lateral plate mesoderm actually this is called your lateral plate mesoderm now we actually have to kind of specialize and talk about this in just a second so we kind of lay the groundwork technically this 3 we're going to divide into 3a and 3b the 3a layer that's kind close contact with the ectoderm is actually going to be called the somatic layer of the lateral plate mesoderm okay 3b that's moving down to become in contact with the endoderm is called your splanchnic layer of the lateral plate mesoderm okay so we talked about the development of the mesoderm and then the differentiation of the mesoderm now we need to do is the easy part talk about what happens to all of these mesoderm chunks and what they derive into all right so now what i want to do is i want to take each one of those mesoderms one two three and then technically three a and three b and talk about what they develop into let's start with one what was one again you guys remember most medial one what was that called that was called your par axial mesoderm it's the most medial one now what happens with the paraxon mesoderm is very interesting so let's talk about the fate of it what does it become in the most basic sense well here we have our starting point here is going to be our par axial mesoderm right what happens is it starts to develop a little cavity in the center of it okay it starts to form like a little cavity in the center of it and what happens is not only does it form a little cavity but they also form these big chunks so if you were to take the neural tube out like if i imagine i just yank that neural tube out like a son of a gun okay i'm going to yank that neural tube out and when i yank the neural tube out if you look on the sides of the neural tube what would i have if you imagine the notochord is out of the plane of the blackbird like it's going to come punch you in the face on the sides here is going to be these chunks of mesoderm what is this chunk of mesoderm here called this is called your par axial measure right what happens is the par axial mesoderm actually kind of like forms these little chunks called somites so it forms these little like segmented chunks called somites then what happens is those somites develop little cavities inside of them okay so they develop little cavities inside of them so first thing that happens is you have a big cord of mesoderm called par axial mesoderm that's on the sides of the neural tube and the nodochord and what happens it segments forming somites then it forms little cavities and what is that little cavity there called that cavity is called your somato seal and again what are these chunks here called these chunks are called somites so what happens is you start off with par axial mesoderm segments into somites forms a space in it called a somatoseal then what happens is that somatosteal continues to extend and extend and extend and separates this somite into chunks technically into two chunks if we were to actually go from this point it technically separates into a chunk like this and a chunk like this this top chunk here is actually going to be what's called the dermatomyotome and then this chunk here is actually going to be called the sclerotome then what happens is this dermatomyotome differentiates even more and guess what it differentiates into three particular layers what are these three particular layers i'm going to color code them the most superior and as you would see actually like more dorsal aspect here so in this view it's superior but actually in real life it's dorsal because this is the ventral surface this is the dorsal surface this color right here this maroonish color that is going to be called the dermatome so that chunk of tissue right there is called the dermatome then if you move a little bit more ventrally in the middle here what is this pink color here this is called the myotone and then finally the most ventral here let's do this one in this baby blue color here what is this one this is called your scleratone sclerotome so you start with paraxial mesoderm then into chunks called somites develop a cavity called a somatoseal develop into two chunks called a dermatomyotome and a sclerotome chunk it out even more into three types dermatome myotomed sclerotome and this configuration from dorsal to ventral then what happens to all of these different things the dermatome if we follow over here guess what it makes well think about it think about simply when you're looking at this this can migrate to the neural tube and surround and make connective tissue around the neural tube i just want to connect what kind of connective tissue is going to make it's going to make your meninges so it's going to cover not the actual brain it only covers the neural tube which makes up particularly the spinal cord so it's going to cover that and make your meninges particularly what meninges your spinal meninges so this will make your spinal meninges what else dermatome what does that sound like dermis so guess what else it's going to make it's going to make the skin particularly what aspect of the skin is it going to make it's going to help to make the dermis and technically if you really want to go the next step what's the tissue below the dermis the subcutaneous tissue so it's also going to make the sub q tissue okay the subcutaneous tissue so when we talk about the dermatome what is the fate of the dermatome the fate of the dermatome is going to be making your spinal meninges and the dermis and subcutaneous tissue go to the next one the actual the most like kind of the intermediate one here right that's your myotome what's the myotome going to do think about the name myo muscle it's going to make muscle tissue what's going to happen is we'll talk about it later in the muscular system it forms two types of muscular structures one is called your ep axial muscles at the axial muscles and we'll go into more detail of these later in the muscular system but this is going to be kind of your dorsal muscles on the back like your erector spinae and stuff like that and then your hype axial muscles and these are basically going to be your trunk and in your limb muscles so when we talk about this one which one the myotome what is the fate of the myotome the fate of the myotome is going to be making skeletal muscle of your trunk the back and the limbs okay what kind of muscle skeletal muscle all right the last one here is your sclerotome this is going to be the most ventral part of it right and even a little bit more medially the scleratome what is its fate the sclerotome is actually going to form the vertebrae so it's going to form the vertebrae what part of the vertebrae what are the different parts of the vertebrae if you go through it quickly the body the spinous processes the vertebral arches right it's also going to form the intervertebral discs i'm going to put ivds the intervertebral discs and what else the ribs it's also going to help with the formation of the ribs so when we talk about what happens with the par axial mesoderm we have to just say what happens to the dermatome the myotome and the sclerotome and that's going to be the fate of the par axial music now that we talked about that let's go to the next diagram and talk about the intermediate mesoderm all right so we talked about the par axial mesa they're making the somites and making the dermatome myotomes glares home all the derivatives of that now let's go just laterally so we talked about the first one the par axial mesoderm right just on the side of the notochord in the neural tube go just lateral now we're going to talk about the second one this is our intermediate mesoderm thank the lord this is actually a very straightforward and simple one we'll go into these pathways these systems in more detail individual videos for right now just basic if you take the intermediate mesoderm what it develops into is primarily two things one is your renal system so it's gonna help to make your kidneys right so it's gonna help with making the kidneys and it's also going to help with the ureters so two things you're going to get the kidneys which we'll talk about later we'll talk about the pro pro nephroes the mesonephros the metanephros we'll talk about all that and the second thing you're going to get is the ureters so it's going to help with your renal system the second thing that it's also going to be involved in is the gonads okay when we talk about gonads we're either talking about the testes or we're talking about the ovaries but again remember how we had the kidney it had an excretory ductal system which is the ureters these have to have an excretory ductal system so whenever you get into like your ductal system for the testes so for example your epididymis your vas deferens all of those structures that are involved in excreting the substances made by the testes are also going to be derived from the intermediate mesoderm in the same way the fallopian tubes is the part of the kind of the ductal system which is carrying the egg and the egg will then also be carried into the uterus not the vagina the vagina actually develops from another structure called the endoderm but for right now when we keep it simple it's either going to make the renal system kidneys ureter and then gonads which is going to be the testes or the ovaries and then the ductal system epididymis vas deferens and the ductal system for the females fallopian tubes and uterus okay that covers the intermediate mesoderm now let's go into the last one which is the lateral plate mesoderm all right let's talk about the last part of the intra-embryonic mesoderm and this is going to be the lateral plate museum so we talked about the first one which was the par-axial music we talked about the second one which was the intermediate mesoderm now let's hit this bad boy the third part which is the lateral plate mesoderm so now we're going to talk about the lateral plate mesoderm and the fate of this lateral plate mesoderm all right remember we said that there's two parts the one that's going close with the ectoderm 3a which we kind of denoted over there that's the somatic layer and then 3b which is the one moving with the endoderm that is going to be the splendid layer i wanted to show you guys how this actually happens so imagine i'm taking this embryo here we're looking at this in a particular section when i look at this embryo i'm taking a chunk like a slice of it but i'm particularly looking at this in what's called a a longitudinal type of axis okay what i want us to imagine here is this process called lateral folding so there's a process called lateral folding in the longitudinal axis and then there's another one called cranial caudal folding in a different type of axis okay what i want us to imagine is imagine this kind of ectoderm coming around and hugging the mesoderm in the endoderm and what happens is the endoderm also is going to kind of come around and hug itself and the endoderm makes this gut tube and then what happens is the ectoderm will then come together approach one another and eventually this will fuse okay and then this will help to kind of make the skin right and some other structures that we've talked about in the ectoderm what i want you to think about is this mesoderm though remember we had that lateral plate here here's our intermediate mesoderm from here we're going to have a branch going with the ectoderm what's that layer hit it tell me this is the somatic layer another name for it is called the somatopleric layer just so that you in case you read that one then you have 3b the layer that's moving with the endoderm what is this one called this is the splanchnic layer also sometimes referred to as the splanchnocleric layer so again just so that we're clear here this layer close with the ectoderm is called the somatic layer another name just so that you're clear it's called the somatopleric layer and then this one here the deeper one right near the endoderm this is called the splancnic layer also referred to as the splanchno pleuric layer of what the lateral plate mesoderm now it's pretty straight forward one of the easiest things to understand what these layers derive into is thinking about body cavities so right away i want you to think whether we're in the pleural cavity where the lungs are whether we're in the pericardial cavity or the peritoneal cavity what is the layer that's clinging to the wall of that cavity that's your parietal pleura parietal pericardium and your parietal peritoneum who makes that the somatic layer and then this layer clinging to the gut tube that's the visceral layer of the pleura the pericardium and the peritoneum so these are going to help with the linings of our cavities so i just want you to remember this will make the parietal layer of your body cavities and this one will make the visceral layer of your body cavity that's the easiest one to remember the next thing is also important is that this lateral plate also forms some kind of retroperitoneal kind of organ some of them one of them is your adrenal cortex so it also helps with forming another structure here called your adrenal cortex it also helps with the formation of lymph nodes right so lymph nodes and don't worry i got a nice little mnemonic to remember all this stuff for you guys the next one is the spleen and then another thing is this actually kind of moves around the gut wall the gut tube and makes the smooth muscle around that gut tube so it's also going to make the smooth muscle of the gi tract so it'll make the smooth muscle of the git it also we'll talk about this in more detail will help with the development of the cardiovascular system so it'll help with the development of the cardiovascular system and this is the coolest one this one's really interesting it also helps with the development of particular structures that are made by a red bone marrow you know what type of stem cells come from this you have what's called myeloid stem cells right and your myeloid stem cells are what helps to make your neutrophils basophils eosinophils it also has the lymphoid cell line that it helps with it making and your erythroid what's your rhythm for your erythroid stem cells are going to be for your red blood cells so that is what this actual layers are helping for but particularly to make sure that we understand the layer that's actually involved with all of these structures here is which layer well i already kind of gave you an information here which one is actually the smooth muscle of the git this is going to be the visceral layer so all of these structures are made by what this is all made by the splancknic layer so all of these structures are developed by the splancnic layer all right sweet that means that everything else over here all these structures that i'm going to talk about are made by the somatic layer what are these structures pretty straightforward you see this structure here right and smack dab in the middle think about this the somatic layer moves around here so it moves anteriorly and it's going to form some structures in here what do you think is going to form right in the mid kind of like the part of your chest your your sternum right so it's also going to help with the formation of what structure here the sternum and obviously our sternum is made up of a couple different components right the manubrium the body and that xiphoid process the other thing which we'll talk about later is you also start to develop these things called limb buds right and then what happens is you'll see later that these limb buds which make our limbs upper and lower limbs this lateral plate mesoderm moves into that and helps with making some of the actual structures within the limbs what structures what's going to help with making structures within your limbs and what is this this is going to be your bones this is going to be particularly what structures this is going to be all the bones and the cartilage that are going to be developed within what your limbs so your upper limbs and your lower limbs beautiful okay that covers the lateral plate mesoderm now let's finish this off with a quick little mnemonic to help you guys to remember all this tons of stuff we talked about all right engineer so i did my best to come up with a mnemonic that will help us to remember the tons of things that the mesoderm derives into which is a lot of stuff i know so this is the best i could come up with in a mnemonic for mesodermal cell differentiation into a bunch of structures so mesodermal cells is going to be our kind of our starting point so m is going to be for your myeloid stem cells okay e is for your erythroid stem cells s is for the spleen this one's kind of a cheat i couldn't figure out another way so o remember gonads d for the dermis e is for the entire trunk right r is for your renal system m is for the meninges a is for the adrenal cortex l is for the other stem cell the lymphoid stem cells c is for the cardiovascular system but to go a next step inside of the cardiovascular system because this is going to help with a lot of parts of the cardiovascular system remember that it also makes the endothelial lining within the heart and the blood vessels so don't forget the endothelium of your blood vessels l is for the linings the lining of your body cavities what are those the visceral and the parietal layers right so that's going to be for that part and then l is going to be for what else the limbs and then s is going to be for what this is going to be for the smooth muscle of the git and if you really want to add in one more that we added lymphoid stem cells just remember lymph nodes as well because we said that was also derived from it so this is a helpful mnemonic i hope helpful for the mesoderm all right engineers so in this video we talk about mesoderm i hope it made sense i hope you guys did enjoy it and ninja nerds as always until next time [Music] you