all right engineer so in this video we are going to talk about endoderm before we go ahead and get started please make sure you hit that like button comment down in the comment section and please subscribe if you guys want to support us please down in the description box we have a link to our facebook instagram and patreon if you guys want to donate we would truly appreciate it all right ninja nerds let's get into it all right ninja nerds so let's talk about the endoderm first thing we have to talk about is how we actually develop the endoderm i know you guys know this because we've talked about it countless times we're going to really kind of blow through this if you guys remember we start off with what what was this our bi laminar disk the bilimiter disk consists of what layers the epiblast which was your top layer and above that is the amniotic cavity and then the hypoblast which is below the epiblast and then below that is the actual yolk sac remember what happens you get kind of a what a little primitive streak that forms right here in the epiblast and then those actual epithelial cells or epiblast cells will start moving down through that right and whenever they do that those epiblast cells as they move through that primitive streak what do we say they do well they first move down and whenever they move down they replace the hypoblast and turn this into endoderm then they make a new layer between the epiblast and the hypoblast what is this layer this is your mesoderm and then eventually what happens is the epiblast cells themselves differentiate and form what's called ectoderm so we start off with our bilaminar disc forming a triliminer disc this is called what step this is called gastrulation right and there's also the process of making the nodochord we've already discussed this like 10 million times and i know you guys know it but just to quickly recap it the difference between that is that the epiblast cells move through the primitive node and then make that tubular process that extends towards the prochordal plate now if we kind of take and look at this triliminer disc that we made i want us to look at this in two different types of sections one is we're going to look at this in a cross section and then the other way we're going to look at this is a sagittal section okay why that's important is it's going to give you kind of some anatomical understanding of the development particularly of the gut tube which is derived from your endoderm so here's our cross section and again we're just going to label it here ectoderm mesoderm endoderm all right and then here is going to be your neural tube which is in that maroon color and then black is the notochord above here is your amniotic cavity and then below here is going to be your yolk sac what happens we already know this you go through a process called lateral folding and that lateral folding process is where the edges of the ectoderm start moving this way some of the mesoderm moves this way and then the endoderm kind of moves this way and it kind of like hugs itself and when it kind of hugs itself what happens it makes this type of configuration this kind of cross-section of the embryo and what we see here is something very interesting if you take a look here what do we have here we got our neural tube right here here we have our par axial mesoderm here we have our intermediate mesoderm and then here you have your lateral plate mesoderm somatic layer lateral plate mesoderm splenic layer this blue layer kind of hugging around this entire kind of component of the embryo is going to be your ectoderm and then what is this kind of green structure here that's kind of made like a tube here this is going to be your endoderm now why this is important is you can kind of see the configuration of that gut tube you're only seeing a cross-section of it so because you only see just a portion of it throughout the actual length of the gi tract it's actually better and easier to see the endoderm and how it actually is really looks in a sagittal section it's a lot easier because you can derive these different components of the endoderm and really section it off into what's called foregut mid-gut and hindgut so just you understand cross-section lateral folding gives you this kind of component which is good for looking at the cavities right and one section of the gut tube which is derived from the endoderm but the sagittal section is a lot better for understanding the derivations of the endoderm so here we have a sagittal section again what is this layer here ectoderm what is this layer here and i'm sorry mesoderm and then what is the actual green layer this is your endoderm and again here is your yolk sac and here is your amniotic cavity how i want you to think about this in this configuration is that this is the cranial end and this is the caudal end okay now at the cranial end if you guys remember there's kind of like a fusion point of the ectoderm and the endoderm and they make two different types of membranes we'll talk about them a little later called the buccopharyngeal membrane and the cloacal membrane this becomes the mouth that becomes the doodoo hole right the anal canal so what happens in this configuration is a lot easier to see you go through folding so now again same process amniotic cavity is going to come around mesoderm will fold and then the actual endoderm will fold this is called cranio caudal folding pretty straightforward right and what it does is it gives this really nice kind of an anatomical figure of the endoderm the gut tube this right here when we look at it this gut tube is really what i want us to look at and look at what it derives into right and this layer here is our endoderm that's what i want us to focus on now again the gut tube is connected to the yolk sac right and we'll talk about that a little bit later as well all right but again big thing i want you to remember is bilamin under the trilaminer is gastrulation that's how we get our endoderm from the hypoblast and if we look at the endoderm how it actually forms the gut tube and the cross-section and sagittal section via the lateral folding and cranial caudal folding you get a cross-section at one point of the gut tube but if you want to look at the entire length of the gut tube the best anatomical way is the sagittal section when it goes through craniocaudal folding so now let's take and look at this gut tube pull it out and see what it actually divides into so now what i want us to talk about is some of the derivatives of the endoderm okay first thing i want us to do is let's go ahead and take and look at this actual gut tube what section is this this is our sagittal section from this gut tube right you have three components i'm going to kind of slice them off here and slice them off here this right here is called your foregut it's at the actual most cranial portion so here's going to be the cranial end of the embryo and here's the caudal end of the embryo okay here is going to be the mid-gut and here is going to be the hindgut we'll talk a little bit later there's also another structure called the cloaca and we'll talk about what that actually becomes but for right now i want you to imagine here's this gut tube i'm just kind of yanking it out of this and only isolating that gut tube and so now we have the gut tube from cranial to caudal and what i want us to do is understand what happens to the foregut what happens to the mid gut and what happens to the hindgut foregut is going to be at the most cranial portion think about what aspects of the gi tract you're going to make at the top well we have what structure here the esophagus and even the pharynx so first you have a little bit of the pharynx so you start pharynx is the beginning part then you have what else the esophagus what else the stomach and what else the actual first two parts of the duodenum right so you're going to have the first two parts of the duodenum or duodenum however you want to pronounce it that's fine okay but that's the beginning parts of the foregut so so far we know what the endoderm has actually made again endoderm is this it's going to be basically forming the epithelial lining of our gut tube and what structures of the gut tube so far the foregut we have these organs now we come to the mid-gut just continue down it's really easy if you think about the path of the gi tract take a piece of food and follow it all the way down pharynx esophagus stomach first two parts of the duodenum what's left the last two parts of the duodenum okay so the last two parts because there's four parts of the one right so last two parts of the duodenum or again do a denim whatever and then what's after that then you go jugenim so you have your jugenum and then what what happens after that then you have your ilium and then keep going what do you have after that so again you got jugenum ilium is going to be closest to the cecum then after the cecum you have the ascending colon so you have your ascending colon and then what else so you have ascending colon and you get to the transverse colon what aspect of the transverse colon so for that aspect of the transverse colon it's going to be the first or the proximal two-thirds of the transverse colon so proximal two-thirds of transverse colon all right sweet so we've talked about so far foregut mid-gut which is basically going to be the what derives from the epithelial lining of your gut tube these things so far now come to the most caudal portion of that gut tube which again is endoderm lined this is your hindgut what do we have left follow it transverse colon you have the proximal two-thirds what's left the distal one-third so now i have the distal one-third of the colon what part transverse colon then we have the descending colon and then we have the sigmoid colon right so you have descending colon sigmoid colon what's after the sigmoid colon the rectum and then your anal canal but we'll talk about what aspect of the anal canal in a second but again i want you to remember sigmoid colon and then the last part is going to be the rectum and the anal canal we'll get we'll kind of go a little bit more on the anal canal because it's actually a very specific part of the anal canal okay so so far we pretty much say what the endoderm derived into all the epithelial lining of the gut tube from the foregut mid-gut hindgut now let's talk about some other things which are very interesting which are budding off of the gut tube or developing from what's called the primitive pharynx so we've talked about the development of from particularly what happens to the endoderm right remember endoderm is the epithelial lining of that gut tube we talked about all the things that developed from that 4 gut mid gut hindgut there's another thing if we go up to the top right of the top here of the foregut there's an area called the primitive pharynx we're going to cut through that portion and what happens is if you cut through it it kind of looks like this so this is kind of going to be like the area of what's called our primitive primitive pharynx okay because obviously the pharynx itself will develop from that foregut but what happens is this primitive pharynx starts kind of having again what is this layer here remember we said that there's a portion where the ectoderm and the endoderm fuse together what is this called we're going to abbreviate it but this is called our bucco pharyngeal membrane that's where the mouth is going to be right then what happens is here's the ectoderm lining the outer part here's the endoderm lining the inner part and the mesoderm in the middle what happens is you start to form these kind of like vesiculations here and this gives way to what's called the pharyngeal apparatus again we're going to go through the pharyngeal arches and what they develop into their development in another video but for right now what i want you to know is that the pharyngeal apparatus is basically going to have endoderm on the inner aspect of it so here this is all that endoderm lining the inner aspect of the pharyngeal apparatus which is derived from the primitive pharynx on the inner aspect so here here's your ectoderm here's the mesoderm here in the center on the inner aspects you see these portions here where it kind of comes in right here these kind of form little pouches called pharyngeal pouches and we'll talk about these later but they can form like different components like a dorsal and a ventral pouch we'll talk about those pouches a little bit later but for right now what i want you to remember is that these pouches a couple of them they will actually derive from the first pharyngeal pouch the second the third the fourth into these structures here what are some of those structures all right so if we have this first pharyngeal pouch right so here's our first pharyngeal pouch second pharyngeal pouch third pharyngeal pouch and fourth pharyngeal pouch these pouches we're not going to go into the different components of these but they will derive into these structures here that we have below the first pharyngeal pouch will actually form two components here one is called your middle ear right or basically your tympanic kind of cavity here and then the other one is the auditory tube or also known as your auditory tube which is also known as your eustachian tube so auditory tube or eustachian tube that's derived from the first pharyngeal pouch the second pharyngeal pouch will form what's called your tonsils and you got a ton of these dang things to give you a hit of some of them you got your tubal tonsils you got your pharyngeal tonsils also known as your kind of like your adenoids you have your lingual tonsils and you also have your palatine tonsils okay all of these are derived from your second pharyngeal pouch now the third and the fourth one these can be a little bit more complicated we'll go over this in more detail and again the pharyngeal apparatus video but your third and your fourth pharyngeal pouch derive into a couple different structures one is they derive what's called to the superior parathyroid gland this one into the inferior parathyroid gland and they also derive into what's called your parafollicular cells or your c cells so again you got your superior parathyroid gland inferior parathyroid gland and your c cells and also from the primitive pharynx you also have this kind of bud that comes off of it this buds from that primitive pharynx and this is going to make your thyroid okay so again just to remind you again the third and fourth pharyngeal pouches here are going to give way to your superior parathyroid your inferior parathyroid and your c cells your parafollicular cells there is another one if you guys want to remember this this kind of actually is in the neck and then it moves down into your chest it's called your thymus gland so if you actually want to add in one more don't forget about that good old thymus but these are going to be all derived from your third and fourth pharyngeal pouch the thyroid is derived kind of a budding off of the primitive pharynx all right but these are the things that are going to be derived from parts of your pharyngeal apparatus now i want to talk about some organs that actually bud off of the foregut so we talked about again some of the structures that derive from the endoderm-lined pharyngeal apparatus which is again derived from that primitive pharynx the next thing i want you to know is that going again back to that foregut okay so again this is going to be our foregut we already talked about the structures that are coming from the foregut actually again imagine the endo endoderm is the epithelial lining of this gut tube coming off of this gut tube some of the endoderm cells kind of move into these little pouches and also help to make other structures git associated organs let's call them what are these like little pouches or buds that come off of them one is called the respiratory bud or the respiratory diverticulum the other one is called the hepatic bud or the hepatic diverticulum and then the other one is called the pancreatic bud or the pancreatic diverticulum these obviously their names pretty much give you the answer from these buds the endoderm can move into these little buds and help to make what structures your respiratory tract right so your respiratory tract obviously your trachea your bronchi the parenchyma of the lungs all that good stuff the hepatic diverticulum is also going to be helpful for making the liver and even the gallbladder the biliary system now even a little bit of the hepatic diverticulum gives way to the head again we'll talk about these in later videos too but the head of the pancreas can also come from the hepatic diverticulum and then the remaining body and tail come from the pancreatic diverticulum but either way all of these buddings coming off of the foregut give way to these structures so again this is also endoderm derived all right all right so the last part that i want to talk about is how we actually can take endoderm and derive other structures particularly the bladder the urethra and the inferior aspect of the anal canal we're going to talk a little bit about the inferior anal canal we'll talk about it again in a second remember we have the sagittal section so here's cranial and here is caudal and again we already talked about these membranes where the ectoderm and the endoderm directly fuse what are these areas here this is called jor bucco pharyngeal membrane and again what do we say what happens when this actually breaks down what does this become the mouth and then this one is called your cloacal membrane and the cloacal membrane once this breaks down this actually becomes two structures your drainer and your stainer okay here it's going to become the actual urethra and it's also going to become the anal canal right so easy way to remember that is your drainer and your stainer okay so that is going to be something that we have to talk about a little bit so how does the cloacal membrane because we already talked about the buccopharyngeal membrane how does the cloacal membrane form the urethra and the anal canal and actually more particularly there's another aspect that actually comes and feeds into this urethra and that's going to be the bladder so let's take and zoom in on this portion here and look at it if we look at this portion here at the bottom we had four gut mid-gut hindgut and we said that this bottom part here is called the cloaca so here we're going to have that hindgut portion coming into the cloaca what happens is the cloaca has this little kind of structure here called the don't worry about that right now but this portion here called the cloaca guess what happens it starts actually bifurcating so it kind of breaks into two portions one portion is going to move anterially and the other portion is going to move posteriorly so now look how this right here was one hole kind of like sac now it splits into two portions this anterior portion is going to be called the euro genital sinus which one is this one anterior this one here is posterior this is going to be the anal canal basically okay so that is what i want you to remember now once it does this what's going to happen this urogenital sinus will actually lead to the formation of a couple structures again we're going to go into this in more detail in the renal system but for right now what i want you to remember is that the urogenital sinus will help to make what structure the bladder the urethra and in males the prostate gland so again what structures are going to be derived from that urogenital sinus it is going to be the bladder the urethra which obviously in males there's multiple parts to that urethra and then also in males there's going to be the prostate gland beautiful right now the anal canal right which is going to be in the post posterior aspect which was derived from the cloaca that you see how again we have ectoderm endoderm which are kind of connecting with one another well some of the ectoderm kind of moves in and when it does this it actually kind of forms this like nice beautiful separation in the anal canal so you have this kind of pink structure that i drew here this here is called your pectinate line it's called trapectinate line and what the pectinate line is is it separates beautifully the endoderm derived portion of the anal canal and the ectoderm derived portion of the anal canal and that cool so the ectoderm is going to be below the pectinate line the endoderm is going to be above the pectinate line so that is why i wanted to say something specific about the anal canal back there that the two-thirds the superior two-thirds of the anal canal is actually going to be endoderm derived and then the inferior the inferior third of the anal canal is going to be ectoderm derived all right so the last thing that i want to do here is come up with a little mnemonic it's not amazing but it'll give you the basic things that you need to know for the endoderm what structures are derived from it and it's really it's just remembering endo okay so e is the epithelial lining of the git and that includes anything from the pharynx all the way down to that superior two-thirds of the anal canal so that covers all that the other stuff is just remember kind of some of the stuff that's in the neck what are some of those structures that we talked about that were in the neck just to mention a couple of them your thyroid your thymus and your parathyroid glands right those are some of them obviously it doesn't cover the tonsils and it doesn't cover the auditory tube but it gets you some of them the next one is your drainer okay so you gotta remember that good old drainer and that covers what your bladder and your urethra okay and then o is the organs associated with the gi tract so the organs kind of associated with the gi tract and those are things that are derived from those actual diverticulum are buds which was the respiratory tract which was your liver your gallbladder and your pancreas it doesn't give you all of it but it gives you a good amount to remember some of the derivations of the endoderm iron engineer so in this video we talk about the endoderm i hope it made sense and i hope you guys did like it alright ninja nerds as always until next time [Music] you