the digestive system continues with the GI tract organs specifically the intestines and so remember we have both the GI tract organs here and the accessory organs so here's where we're at in the intestines and we'll start with the small and dude sorry a boy here he is dying for me to tell you if you're in the Sacramento area this weekend he is a DJ DJ ill he drops the fattest beats and see so there's no one over there Vijay ill or DJ ileum it's just a fun way to help you remember the three parts of the small intestine the duodenum the jejunum and the ileum I don't know anything about dropping fat beats give me a break so duodenum jejunum and ileum will be what we're talking about right now and you can see the duodenum here followed by the jejunum and the ileum now there are differences to these parts of the small intestines but there's also a lot that's the same so let's see here small intestines are about 21 feet long in your living body they are longer after death unless in a cadaver they tend to shorten up again and this is where we will do most of our chemical digesting and absorbing so the duodenum is thought of as the mixing station because it's here at the hepato pancreatic ampulla a little swollen region where the liver and pancreas attach that bile and digestive juices from the pancreas arrive so the bile will help break down the lipids the pancreatic juices are enzymes that will help break down the other major macromolecules in your food also in the duodenum are what are called duodenal glands or Bruner's glands and though secrete this alkaline substance that will help with the acidic slop that arrives from the stomach remember that the stomach mixes the bolus of food with gastric secretions a hydrochloric acid and mucus and digestive enzymes and it makes this slop that will get squirted into the duodenum so the duodenum will protect itself with mucus and the pancreas will secrete some baking soda like alkaline substances into the duodenum but the duodenum also makes its own baking soda like alkaline substances all with the intent of protecting the intestine from the acid by neutralizing it so also here now that these chemicals are all mixing with your food is where we will have our primary site of chemical digestion but you'll only begin absorbing some things here in the duodenum because in fact the jejunum is this sit-ins do area of the small intestine where things will slow down there will be time for the absorption of nutrients from the food and then you move on to the ileum there are a few structures you would find there like tires patches there tend to be more of those in the ileum the ileocecal valve is what will separate the small intestine from the large intestine and some absorption will happen here as well so those are some of the major differences in function and structure between D and J and I but let's look at what they all have in common the small intestine has three modifications in the GI tract wall to help increase surface area by a lot like 600 times that will help increase the rate of digestion and the rate of AB origin of nutrients so those three structures are number one fly case circulars sometimes just called circular folds and those are faults of both the mucosa and submucosa so these are these big folds I can see one here here here here you can see these with your unaided eye there are totally visible macroscopic structures that you can see and feel inside the human small intestine and if we look closely we can see this yellow region is mucosa and the bluish grayish region beneath that is the submucosa so we can see yes indeed these circular folds like a circular include both you cos'è and submucosa villi on the other hand are tiny like about a millimeter long so they're just at the edge of something that you can see with your unaided eye and those only include the mucosa so those are these tiny little structures on the very surface of the intestines and they're pretty large in the duodenum but then they begin to get smaller they shorten and they get more and more narrow the deeper you go into the intestine and on the surface of the villi are micro villi those aren't shown in this image they're too small but they're sometimes called a brush border you know like the end of a toothbrush or a paintbrush they're just small fine little cellular extensions and they are on these simple columnar epithelial cells that line the intestines and they help to push digestive enzymes onto the surface of the intestines while also helping with absorption so we'll see some of these again after we take a look at this actual human intestine with a camera that's somehow capturing these tiny villi but you can also make out just barely the rising and falling of the circular folds in this image so we're getting a little bit closer in here now so we can make sure we can spot the villi these finger-like projections and we said they're both mucosa we said they're only the mucosal layer more specifically we can see on the villi that they do include the epithelial layer and then underneath that is the lamina propria but they don't actually include the entire Yuko salir because here left behind is muscularis mucosae that thin little strip of muscle that we talked about in another video helps do some small contractions you know in case you get a tiny little bit of material stuck in here it's not meant to do some big segmentation mixing it's just small localized contractions but it's not part of the villi the other thing we can see when we look more closely at the villi are what are called intestinal glands or intestinal crypts or crypts of Liebherr kun those are shown here so these are kind of like finger like projections going the opposite way of the villi and if we look closely at these what you'd see is a bunch of cells in here of different varieties there would be stem cells they're helping to replenish the cells that are broken away or burned away over time there would be Paneth cells Paneth cells provide some antimicrobial defense if any bacteria falls into one of these crypts a pana cell will likely encounter it and destroy it but then also trigger the release of antimicrobial products to help with all the other bacteria that might be trying to invade your gut and there'd be some goblet cells making some mucus to protect the lining of the intestines so those are the two major structures you can see here but this is always a good time to make sure you are becoming more confident in telling apart the four layers of the GI tract wall and you'll recall that my suggestion is first knowing that there's always a big thick muscular layer called the muscularis propria or muscularis externa look for that it will be either 2 or 3 layers thick depending on whether you are in the stomach or not and it's usually easy just to find that first muscularis propria if you can find that it'll be easy to find the outermost layer of the GI tract wall what's you lie to be serosa if you are in a slippery part of the GI tract like the small intestine or adventitia if you're trying to anchor the GI tract wall down like in the rectum anus esophagus bearings - now to sort the rest of what I see here I'm gonna go back and look at muscularis propria and try to find something that looks like a tiny tiny little muscular layer just like that and that's gonna be muscularis mucosae if I find that it's got mucosa in its name so I know I found the mucosa is all of this which just leaves the submucosa tucked in between those muscular layers and I've got my four layers of my GI tract wall up to the side here a few other structures we talked about that you'd find in the GI tract wall but we do those in another video so let's finish our deeper dive into the GI tract wall by looking at a single villus now we can better see the epithelial lining which is simple columnar epithelium and if we zoom in really tight we can see the tiny little micro villi on the surface of these cells and if you think way back to unit 1 early days of this course we talked about the difference between cilia and microvilli and flagella and remember microvilli are actual extensions of the entire cellular membrane so there's no organelles stuffed up in there you know it's just some cytoplasm some of the microtubules for structural support but it is those micro villi that help with nutrient absorption and they help secrete some enzymes onto the surface of the intestinal wall to help with chemical digestion we'll also see some goblet cells sprinkled about and this large green structure here is a lacteal so thinking back to the lymphatic chapter remember that most of our nutrients will pass through the epithelial cells and right into the bloodstream right into the blood capillaries lipids cannot do that lipids start to get broken down a bit by like the vile salts that we'll talk about later but these lipids are like fats and oils they don't travel well in water and they don't break down easily so what happens is they get mixed with these proteins the proteins are going to allow the lipids to be able to move about in the waterís aqueous solution that most of our body is without clumping up and killing you in one way or another so that's good but these lipoprotein chunks are too big and unable to enter into the blood capillaries so instead as we talked about briefly previously they'll go through these little epithelial flaps and enter the lacteals lacteals will form bigger lymphatic vessels and bigger lymphatic vessels and eventually they'll let the lymph will get dumped into the bloodstream so the fats will eventually make there okay let's look at a little histology of the small intestine this image here has some gross anatomy - I can't really tell apart the jejunum from the ileum here although if I could find the ileocecal valve that would be a clue I was in the ileum same thing here at the duodenum your best clue would be the duodenum ampulla this region where the hepatic this is another name I think for the hepato pancreatic ampulla must be or if you could find the pyloric sphincter from the stomach you would know you are in the duodenum but we're not gonna try to use all these little clues to hella part the gross anatomy well we're gonna kind of use a similar method to identify the portions of the small intestine histologically meaning their mucosa layer is pretty much the same you know they all have villi waving up and down up and down up and down that's not gonna help us but the duodenum has these extra structures here and the ileum has these extra structures here and that jejunum has nothing there's our clues so let's look at the histology they all have the like a circular like here's a single playa one big fold and then these are the villi and if you get a little closer and you have some real nice tall bill I it was our villi and if you get really close here it's just too villi now we can make out for example individual goblet cells sprinkled amongst the epithelial tissue so no help here but then if we look at the duodenum we'll find a couple things number one those intestinal glands or crypts of libra kun are found right here all in this area but they're all gonna have that still no help well you really got to look for is the duodenal glands aka the Bruner's glands are the sub mucosal glands they are here in the submucosa and those are making these baking soda like secretions very alkaline to help neutralize stomach acid they're the only part of the small intestine that will have those glands the jejunum is the sit-in stew area you still have intestinal glands or intestinal crypts or crypts of Liebherr kun well you have no Bruner's glands and there are no peyer's patches if you move into the ileum again you'll have those crypts but you'll have highers patches remember those are malts mucosa associated lymphoid tissues helping with immune surveillance found mostly in the submucosa maybe pushing their way up a bit into the mucosa ok we finished the large intestine a little bit less complex a five foot long tube and its main structures are the cecum right here which of course would have the ileocecal valve being the sphincter separating the ileum and the sink cecum then you have the colon which is all this and the rectum and anus so you can see why the colon is almost synonymous with large intestine although there are other structures in the large intestine besides just the colon like other things we haven't named yet like the appendix hanging off of the seco we talked about that structure in the lymphatic system chapter there are also these pouches here and here and here the whole colon really is just a series of pouches those are called hofstra and there's this smooth muscle band of tissue that connects to those hofstra and that's the tinea kohli this tendinous band in the colon is gonna kind of help move stuff through the colon the hofstra and the 10-8 the tinea kohli are helping move stuff through your colon and there are lots of other structures if you wanted to see more you can jump ahead to a more complex image here where we can see the valve and some of the more basic structures you'll talk about in the lab like these flexors Affleck's are just being kind of a pivot point of the colon but for our we've seen enough although we should also mention there are four parts to this : the ascending colon goes up transverse colon goes across descending colon comes down and where things start to really curve around a bunch that's the sigmoid colon functions of the large intestine well what is that you have some leftover carbohydrates that get fermented by bacteria in your large intestine but one of the byproducts of that process is the gas the flatulence that we know about we're also absorbing water here the slop that enters your large intestine is very watery and in fact you've encountered this slop before because if you have a diary episode then the large intestine is getting fleshed out very quickly so you're not absorbing much water you're just getting the gnarly stuff from the early portions of the large intestine moves right through what you want to happen is just enough water gets absorbed that you have a well-formed piece of feces not too runny not too hard while absorbing that water the large intestine also absorbs vitamin K and vitamin B and some electrolytes to get feces at the end mostly water a bunch of dead bacteria and stuff that your body couldn't digest it's gonna compact that store it for a while and then defecate so let's look quickly at just one part of the large intestine and it's histology being the colon will still have these intestinal glands aka cribs or crypts of Libra koon well still have goblet cells making some mucus and we'll still have the simple columnar epithelium that we see in the stomach and small intestine and large intestine you may find some lymphatic nodules these are sprinkled throughout your GI tract but there tends to be some seen in the colon what you won't have is villi so there's a nice flat top surface here to the lumen of the colon rather than the up and down up and down up and down shape that would suggest you were in the small intestine and we won't talk much about the rectum it's just a storage location the anal canal with the opening being the the anus has two layers of muscle we should talk about - sinkers there's an internal anal sphincter sphincter and external like this so these are usually closed the internal anal sphincter being closed is closed due to involuntary control done by your body meaning that you can't control the internal anal sphincter you can control the external anal sphincter so as you go about your day these are closed if you feel the urge to defecate then you need to listen because eventually that internal anal sphincter which you can't control is going to relax on you and then your only chance is to consciously grip down with your external anal sphincter and try to push that other sphincter back close but it doesn't want to be closed so the clock is ticking you're tensing a muscle now it's just like working out your biceps you know you can only lift weights for so long you can only close the anus for so long okay cuckoo cool that was a great finish and in our last video we will finally talk about the accessory organs salivary glands pancreas liver and the gallbladder see you there