welcome to this video this video is going to be all about the digestive system everything that your Anatomy teacher might ask you on a test about the digestive system chapter in your textbook we're going to start off with an overview of the digestive system its processes and its organs now if you go into a health care field you're typically going to hear this called the gastrointestinal system or the GI system and that's the same thing okay so you can see from my sketch here I have the organs of the digestive system now some of these are considered accessory organs and some are actually part of What's called the alary canal alary literally means food so it's probably no surprise that this is going to be the organs that the food actually passes through now we also have accessory organs these are ones that the F food is generally not touching as much there are some exceptions like in the mouth but these are organs that typically are going to be important in making um different kinds of secretions for digesting and absorbing the foods that we eat so let's go ahead and we'll use um kind of like a red pink for um all of the elimary canal organs and we will use um I guess blue for all of the accessory organs so let's start off with the oral cavity I'm just going to put a box around it so this is a little sketch of a mouth with some salivary glands and things like that so we'll put a number one on here and this is called the oral cavity oops now there are some what we call Accessory organs within that area and these are things like salivary glands see these you have three um three different kinds of salivary glands teeth there's some teeth and the tongue so these are considered accessory or or so we'll put um teeth tongue and salivary glands these are primarily going to mix up the food to form what's called a bolus or a ball that can then be pushed down to the stomach so the next place that the food goes is into the throat can maybe just put a circle here I guess and that is the FX is a fancy word for it but this is just what you know as your throat Now by this time the food has formed into a little ball that's been all mushed up and we call that a Bolis which literally you can see right there right it means a little ball of food that can be pushed down um into the esophagus when you swallow and the esophagus is this long tube it's about a foot long and um it oops is going to get the food get the Bolis into the stomach which would be the neck structure the stomach is going to um do a lot of churning a lot of me what we call mechanical digestion where it just makes the food gets smaller and smaller then the next structure is um the small intestine so I'm just going to put a five here for small intestine and then I'm going to show you the three parts of the small intestine the first part I'll go ahead and color like this this is the first curve of the small intestine it's only about 12 in long and it's called the dadum the dadum some people call it duodenum and I have looked and looked and I really do find that um people say it both ways and I think it's fine whatever you like better okay now the next section um it's actually much longer than I'm putting in my sketch here but that's the junim the junam and that's where most of the absorption finally occurs then the last section of the small intestine is called the ilium and it ends up at the large intestine so that's the ilium which brings us to um so here I can put an like this so I guess for the dunum we saw we did solid right and then for the gunum we did slashes and for the ilium I did uh dots how's that and the stomach was also dots wasn't it and the esophagus was slashes and the ferx was um solid there okay so then the last structure would be the large intestine you're going to to often hear this called the colon like if you've heard of colon cancer it's cancer in this area of the body and it starts with um what everyone's heard of the appendix and that's attached to the seeum this is the entry point so we'll do a solid and we'll do seeum and appendix and then um the whatever's left over at this point is going to end up in the feces except for water so the food is passed up the ascending colon across the top which is the transverse down the descending around the bend of the sigmoid colon and then finally when it straightens out right before the anus it's the rectum so we go um a TR or sorry ascending colon transverse colon descending colon sigmoid and then finally to the rectum those are going to be all the portions of the large intestine um over back on the accessory glands when the food enters the small intestine it gets uh squirted on with a a bunch of important enzymes so the pancreas makes most of your digestive enzymes I'll just go ahead and color this see how it kind of sits in that first curve of the small intestine and then it has um an an ability to secrete its um enzymes right into the dadum Isn't that cool so that's going to be the pancreas makes most of the enzymes that you need to digest your food and then look here we've got about the liver the liver is going to make a substance called bile that will help break up fat droplets into little droplets it's a form of mechanical digestion it's not actually changing the chemical composition of the fat yet you need pancreatic lipase to do that so the liver oh so the pancreas I colored solid right and then the liver we put some hashes like that so the liver makes bile but the gallbladder this little guy right here we can do this one solid too this structure it's actually on the underside of the liver the gallbladder stores and concentrates the bile let's look at the oral cavity the parts of it and then the structure of a tooth we will start by coloring the lips red on this mouth over here so these are the lips and then we can make the gum line kind of a softer red almost like a pink so this is also called the gingiva so we'll call that the gingera and then um the pallet is the roof of the mouth and hanging from the pallet is um the back of the palette is a little structure called the uvula you can see it when you look in the mirror and it hangs down at the back of your mouth and its job is to move upward and protect your nasal passages from food entering them when you swallow then I'm going to use yellow and color these tonsils at the back of the throat these are the Palatine tonsils if you've ever had strep throat these are what get the white patches on them and they're meant to go guard the entrance to your digestive system from pathogens that are trying to enter then there's the tongue right here tongue and the tongue is anchored to the floor of your mouth with something called the frenulum it's a little uh strip of connective tissue that connects the tongue to the bottom of your mouth now we can look at the teeth so when you are little you get 20 baby teeth so babies get 20 deciduous teeth now they're called deciduous because they fall out that word deciduous means fall off and that's why trees that lose their leaves in the winter winter are called deciduous trees these baby teeth start coming in at about uh 6 months of age and then they get all of their um 20 deciduous teeth and then when they're about five or six those start falling out and then their adult teeth come in and my boys they started getting their adult teeth when they were about five I guess that's when their first tooth fell out but um they think they were a little bit on the young side but they come in about 6 years and then uh some people will even get a third set of MERS by the time they're like 21 but I'll put about 18 for that last set So speaking of MERS let's go ahead and look at the 32 teeth that an adult could have so you first got what are called incizors here's one and here's one so these are called the incizors and their job is to cut the food these are the first ones that little babies get and then there is that real sharp tearing one called the canine one on either side and this is going to tear the food and then there are um a couple of what are called premolar in the textbook that my students are currently using but you'll also see these called um by cuspids and then the last three are called the molers and the very last one is also called the wisdom tooth not everyone will get those last ones and some people's mouss can't really even fit them and so then they'll get them uh surgically removed so the molers their job is to grind the food up next let's look at the structure of a tooth so over here um you can see that I've started a little drawing of a tooth and the part that is visible above the gum line is called the crown of the tooth so this is the part that's above the gum line and I'll color the gum line here for you so that you can see what I'm talking about so this is the gum line right here with that gingiva remember so the part of the tooth that's above that's the crown and then the part where the gum line is is called the neck of the tooth and then the part that is not visible above the gum line is called the root so this is below the gum line now the tooth is protected by very very strong mineralized structures so mineralization protects the tooth and I'm going to show you the three types of mineralization in the tooth and that mineralization it's basically like turns part of the tooth into a rock basically is made of calcium hydroxy appetite crystals now the these are the same similar kind of uh structure that we find in a bone it's just that a bone has a lot more collagen fibers in it to give it flexibility this mineralization makes the tooth very very hard harder than bone so we'll start with the top layer that is um called enamel you've probably heard of that the hardest structure in your body and it's basically 100% mineralized so it's like like a rock and then below that and that's that's going to be covering um the crown of the tooth and then below that we're going to have the Denon I'm going to color the Denon which is a little bit softer than enamel I'm going to put that here so this is below the enamel and I'm making it all in blue this is called Denton so we'll put Denton here and that's going to be about 70% mineralized so do you see that it's softer than enamel but still a hard tissue that um helps to protect us and then the other parts that aren't calcium Hydrox hydroxy appetite would be um proteins and things like that okay then there is one more layer of um mineralization protection and that's um right here do you see on basically along the root and I'm making this in green and this this is also hard this is called centin and centin is about 50% calcium hydroxy appetite so let's put cement in here so it's 50% mineralized and that is um the green maybe I'll put a green line right here and then a blue line right here and then the enamel is um on the white top part of the tooth all right so now once you you understand that that important protection for the tooth is provided by mineralization let's look and see what's so special on the inside of the tooth and that is in the pulp cavity where we have the blood vessels and the neres so I'm just going to put these lines right here do you see how those actually go out the bottom of the tooth so this is where the blood supply for the tooth can both enter and exit so I'm putting red and blue lines to represent arteries or actually capillaries and vules and things like that small arterials so we have blood vessels and then I'm going to use this yellow because you have a lot of nerve endings in here too that's why a cavity can hurt or if the um tooth starts to erod then the the nerve endings here are very sensitive and we call that area the pulp cavity so the pulp cavity is vulnerable because it is basically 0% mineralized it's very soft and um so I can go like this to remind you that this is the pulp cavity like that and put an arrow right here to that pulp cavity so this is where we're going to find the blood vessels and the nerves for the tooth the teeth fit into the mandible and the maxilla in what are called um Alvar sockets and so the mandible and the maxilla that's your lower jaw and your upper jaw and they have Alvar sockets for each tooth that forms an immovable immovable gomphosis joint and we'll that's something you would have learned about when you studied the skeletal system periodontal ligaments hold the tooth to the Bone and these ligaments like all ligaments uh made out of collagen fibers so you can see these collagen fibers are anchoring the tooth to the surrounding mandible and maxilla bone within the Alvar socket so these are the periodontal ligaments they anchor the teeth so maybe you've heard of scurvy when someone doesn't have enough vitamin C because vitamin C is necessary for the production of collagen and the sailors if they got scurvy their teeth would become loose in the sockets we'll look at the salivary glands on this page you have three sets of salivary glands this first one I'm coloring is called the pared gland name makes sense because it's means beside the ear paraded right here and it has a duct that releases saliva into the top of your mouth kind of back by your second Moler and so then that saliva will drip into your mouth and be mixed with um saliva coming from the bottom of your mouth and moved around by your tongue which is right here oh I was going to put this means beside the ear that's where it gets its name and then you have the submandibular gland and it gets its name because it's under the mandible or below and we'll make this one also yellow right here do you see it one of those on each side of your mouth and it is going to release its saliva here and then you have under your tongue a salivary gland called the sublingual which another name that makes perfect sense sublingual means under the tongue now this one has sometimes eight to 20 different ducks that go out into the bottom of your mouth so you have lots of different places where saliva is entering your mouth these salivary glands are controlled by cranial nerves from the parasympathetic nervous system so um parasympathetic control over salivation for s for stimulating it the parasympathetic nervous system is part of your rest and digest so it's going to help you make saliva so that you can start to break down your food and there are two cranial nerves there's cranial nerve number seven which is the facial and uh cranial nerve number nine which is the glosso Fingal that means tongue and throat so those are the two [Music] nerves that are most associated with stimulating salivation it contains an enzyme called salivary amase now the reason we say salivary it seems kind of obvious right you make this enzyme amas in your pancreas too the job of it in the saliva as it is also when in the small intestine is that it begins the breakdown of starch which is a carbohydrate so starch digestion begins in your mouth and this is a carb if you had forgotten that's a carboh hydrate and it ALS saliva also contains another enzyme called lysozyme this enzyme is basically found in all bodily secretions and it's able to kill bacteria by damaging cell walls there's another really neat ingredient found in saliva and it's a specialized kind of antibody called IG G that stands for immunoglobulin a and this particular kind of antibody is specialized for hanging out on your mucus membranes and defending your body against food born illness and things that might come in on your respiratory tract as well so this is an antibody that specialized for defending your mucus membranes ran out of room there just defending mucous membranes now this saliva there's also going to be water and mucus in it and some electrolytes as well uh it's going to get mixed up as you chew so I'm going to take a red kind of a pale red and color these two chewing muscles so the technical term that we use for chewing is mastication and your two most important chewing muscles are your temporalis and your masser so right there I just drew the temporalis so um mastication includes the temporalis which I've colored I think I'll use black here to show you so that's the temporalis and then also the masser here we go color this this is the masser you can see how both of these based on where they insert can close the [Music] jaw right there you can see how both of those pull the jaw closed mastication means chewing and then once you've chewed up the food you have mechanically digested it meaning you break it into smaller pieces and thanks to the salivary amate you've begun a chemical I should put a chemical breakdown so it's a chemical digestion and now you're ready to swallow and I'll put that word right here which the fancy word we use is deglutition and this word means to swallow and we swallow a Bolis which just means ball of mashed up food and then that's going to go down the esophagus and into the stomach and we'll look at that next so it's going to produce this thick uniformly mixed up um substance called Kim and this K is going to end up being very acidic and then it's going to go down into the small intestine and then those substances will be chemically digested the rest of the way let me show you how this works first of all you've got the esophagus here that's coming down from the ferx and the esophagus uses a process called peristalsis which is a rhythmic cont contraction to push the food along the elimary canal and when the food arrives at the diaphragm it has the esophagus actually has makes a hole through it I'm going to highlight this this right here is a skeletal muscle called the diaphragm it's very important in breathing so just under the diaphragm is where the stomach begins and it has a circular or sphincter shaped muscle that guards its entrance and its exit so see how there's a circular muscle right here and then there's also one that guards the exit to the stomach and that way the stomach can make sure that it mixes everything up uniformly and gets it to the right pH before it allows it to leave this top sphincter is called the lower esophageal sphincter sphincters are always circular shaped smooth muscles and sometimes it's called the Lees now a lot of textbooks will call this um the gastro esophageal sphincter but clinically you're going to be hearing it called the lower esophageal sphincter much more and it's going to prevent regurgitation of acidic kind the esophagus is not designed to deal with that acid the way that the stomach is so if someone does have a problem and this is happening when it shouldn't be for a variety of reasons then they might have gastro esophagal reflux disease or gird okay then you also have a guard at the end and this one is called the pyloric sphincter that word pyloric means gate way or gatekeeper and so this is going to guard the small intestine so this is going to prevent Kim from leaving before it's good and mixed and the pH is very low it's about two which is neutral is seven so that's super acidic okay so you see how we have these two guard rails okay now I've been telling you how it mixes it up right so let's use a red and let me show you um just using some lines that the stomach has three layers of muscle sort of like our abdominal muscles we have the rectus abdominis the internal obliques the external obliques we actually have the transverse abdominis too well similarly the stomach has layers upon layers of muscle some of them the fibers run longitudinally like this so we call these longitudinal layers or a sorry it's a longitudinal layer and then there is a layer that runs around the stomach like this and we call this the circular layer and then there is even a third layer that runs at an angle like this and just like on our abdominal area we call these angular ones the oblique so this is the oblique layer pretty cool huh so you have one two three layers of smooth muscle on the stomach and then when they contract they can make the stomach it shorter or wider or angled and that's going to make sure to get it all mixed up into that uniform kind see how the stomach has a curve right here we call that the Lesser curvature and there is a mesentary that attaches to this lesser curvature and so we call that the Lesser momentum let's color that right here so this actually attaches up to the liver from the stomach wall and this mesentary helps hold things in place and also is a place for blood vessels as well so this is the Lesser momentum you can maybe see where I'm going with this because we're also going to have one that's greater oh and that word MUM means apron so it's like an apron that covers this top part of the stomach coming down from the liver bigger curve of the stomach so we call that the the greater curvature and coming down from the greater curvature is the greater momentum and so this is another mesentary this one's really good at getting filled with fat so as we get overweight we can store a lot of fat in this greater momentum this apron like mesentary hang down over your intestines so this is the greater momentum or apron next I'll name the different parts of the stomach so the very entry point that's right near the heart is called the cardia of the stomach and then there's a little part that actually my picture doesn't show this very well but it's called the fundus and this is the part of the stomach that um protrudes above the opening which I didn't really show very well in my picture but the fundus is goes up above the lower esophageal sphincter and then the bulk of the stomach is all called the body that's going to be most of it right and then this part that is um the inferior portion is called the pyloric antrum and then the last part is called the pyloris and that's where we find the pyloric sphincter regions you've got the cardia which is the entry point then you've got the fundus which is the highest portion then the body that's most of it I'll put the bulk then the antrum the pyloric antrum that's the lowest P part it's almost like um opposite to the fundus in a way and then you've got the p lus which is the exit point so it's opposite of the cardia in a way right cardia is the entry point pylorus is the exit point if you were to cut your stomach open and look inside when it didn't have food in it you would see a lot of wrinkly ridges called rug and what these rug do is they allow the stomach to be able to distend because as the stomach fills up then it can um get bigger and bigger and those rug sort of flatten out this is why we can really eat a big meal even though we might feel a little bit overly full afterward right so these are the rug I want to describe to you the classic phases of digestion the first one is called the spalc phase of digestion that word spalc means head so this one happens before you even start eating the stimuli for this first phase since it's all in our head right is going to be the sight of food the smell of food and even just thinking about food and then what happens is our parasympathetic nervous system kicks in and sends signals down the Vegas nerves the vagus or cranial nerve number 10 is known as The Wanderer and what this is going to do is start causing your stomach cells to make stomach acid already so we have cells called parietal cells in our stomach wall W that word parietal means wall because these cells are in the wall of the stomach I'll do it like this so This represents a cell in the wall of the stomach and this cranial nerve stimulates this kind of cell to make acid we'll put it like this it actually releases hydrogen ions and then those mix together with uh chlorine in your stomach and produce combine to form hydrochloric acid so your stomach is getting ready to the food for the food to arrive it's already producing acid to actually help out even further your cranial nerve will stimulate another kind of cell in your stomach wall and this one is called a G cell it's called a G cell because it makes a hormone that will travel in your bloodstream and that hormone is called gastrin and that gastron is going to also stimulate the parietal cell so do you see how we have multiple stimuli for those cells to keep producing hydrogen ions and then they can combine with chlorine to make hydrochloric acid this is why just thinking about having a really good meal if you think you're going to get it and then something happens to delay it you might actually have a little bit of acid indigestion because your stomach was producing acid in anticipation of that delicious meal then we come to the gastric phase of digestion and this one is going to be uh what happens when the food actually enters the stomach so the stimuli is a Bolis of food and especially protein it's going to be the best at stimulating this gastric phase there's another kind of cell lining the stomach wall called a chief cell and this chief cell is going to release an inactive uh precursor to an enzyme that's called pepsinogen Pepin oen now whenever you see peps or oen at the end of something in anatomy and physiology it means that that molecule is inactive it's not doing its job yet it's just waiting in the wings and what it's waiting for is acid and so it can be converted into its active form called pepsin see how we took the O gen off the end and the conversion of this is hydrochloric acid it makes it happen so we can go from an inactive pepsinogen to the active enzyme pepsin and then what do we need that pepsin for well that word pepsin means protein pepsin is going to convert the Protein that's in that food that enters the stomach and it's going to break it down into smaller peptides so it gets the chemical digestion of protein started we have to have acid for that so if you don't make enough stomach acid or you take too many stomach acid blockers you might actually have trouble breaking down the protein in your diet one other thing that that acid um is really important for is not just that it's going to help us um chemically digest protein by activating pepsinogen to pepsin but it also is good at killing bacteria so we can say that that acid has two important jobs in our um digestive activities one is to keep us safe from food born illness and the other is to begin the chemical digestion of protein by the way parietal cells secrete um one other uh substance and it is called intrinsic factor and intrinsic factor is necessary for the absorption of vitamin B 12 I'm going to put this over here since I don't quite have room where I'm talking about it so intrinsic factor is necessary for vitamin B12 absorption and if you have a deficiency in vitamin or in intrinsic factor then you're going to not have enough vitamin B12 and the person will end up with something called pernicious anemia because vitamin B12 is necessary for red blood cell production we will talk a little more about that later but I did want to put it on here to get us started then we come to the third phase the intestinal phase of digestion and the stimuli for this one is the acidic Kim that's the mixed up stuff from the stomach that enters into the dadum which is the first part of the small intestine so a IC kind entering the dadum so now we have two more special cells come into play and both of these cells are in and part of the intestinal wall the stomach lining is specially designed to deal with a IID but the small intestine isn't so it's important that we have a way to inhibit to much acid um in the small intestine because it will get damaged so the these cells in the dadum wall will make secren and secretin is going to inhibit see how I make that straight line that means inhibit so secreton will inhibit further acid production from the parietal cells do you see how my picture shows that so that's one job but then it's going to do something else to help the dadal wall keep from getting burnt up and that is that it's going to stimulate the pancreas to make bicarbonate which is um you know like baking soda and it will um help to make the pH become more neutral in the dadum so that the enzymes will be able to work in the intestine and not get denatured and also so you don't get ulcers in your dadum okay so that's important right we've got these two actions of secreton to calm things down I want you to think about it as inhibiting acid now the last kind of important cell we'll talk about on this page I'll make this in green and these deodal cells they release a hormone called kcyy it's a big word so we're going to give ourselves some room to write this coloin or CC K isn't that easier calling it that and it also has two jobs one of its jobs is to also affect the pancreas but instead of having having the pancreas make the baking soda bicarbonate it actually causes it to release all of its important digestive enzymes that can break down carbohydrates proteins and fats so that's going to be one important job and then the other thing that cck does that's very important and notable here is it stimulates the gallbladder to release bile and bile is an emulsifier that will break big fat Globs down into little fat Globs so that the enzymes from the pancreas can chemically digest it and how these enzymes work all together is what we'll talk about next Once the acidic Kim starts coming down into the dadum we are going to see the liver and the pancreas and the dadum work together to finish chemical digestion first of all the liver is the important start point for bile the liver makes bile and then the gallbladder stores and concentrates that bile I'll go ahead and color over here the gallbladder here's the gallbladder and then this whole big structure is the liver and little cells in the liver called hepatocytes work together to make bile which I'm using green to represent this and then the bile drains down away from those cells until it gets to what is called the common hepatic duct so that's right here common hepatic that word hepatic just means liver duct and that then from there it can um go up into the cystic duct which is this part right here and be stored in the gold bladder then the hormone that we've already talked about cck col ayyan that's the one that will stem the release of the bile and that bile then will drip down the common bile duct which is this area right here it kind of goes behind the stomach there so and then that will go um so this is the common bile duct and then that bile passes through a little sphincter right here that is called the hepato cuz that's liver pancreas IC because it's also going to empty things from the pancreas ampula and that word ampula when you see that that means a [Music] widening little widening where then those chemicals um that the bile can empty into the dadum so it's able to come out into the dadum by passing out this little bump inside the dadum called the major duodenal papilla the purpose of that bile is to do what's called emulsify lipids that's kind of a big word big fancy word but but all it means is that it will break big droplets of fat into little drops of fat and then the enzyme called lipase will be able to work more effectively on it because it will have a bigger surface area the pancreas doesn't make bile it makes the enzymes that can break down chemically the foods that we eat so those emulsified lipids that we talked about they are going to get broken down by an enzyme called lipase and whenever you see Ace on the end of something you know it's an enzyme and we're going to write lipids right here and I'm going to actually add the word emulsified so this has been broken down into little drops mechanically and then will chemically be broken down by lipase into fatty acids and glycerol because triglycerides have three fatty acid tails and a glycerol head and I'll just represent those with these dots right here now imagine that the dadum which we have over here I'll go ahead and outline it in purple so it's just the first 10 or 12 in of the small intestine and it is lined with um cells called entos sites that have microvilli on them so I'll draw it like this and this is going to then be labeled an entro site the word entro means intestine so this is an entro site in the small intestine and actually would be in the dadum and probably junam as well well and I'll give it a little nucleus so those fatty acids and glycerol are able to be absorbed right through these cells and then they enter vessels of the lymphatic system called Lacs and I'll draw them in yellow because they're not a blood vessel they contain lymph so we call this a lacal and it is a lymphatic vessel and so the end result is that those um fatty acids and glycerol are absorbed into the Lacs and then from there they get dumped into the bloodstream near the heart so the heart gets first dibs on these fatty acids which it loves to use to make ATP polypeptides can also be broken down in the dadum and rather than being a full-on proteins we can thank pepsin because remember pepsin is active in the stomach and it breaks large proteins down into poly peptides that then can be made even smaller by pancreatic enzymes into small peptides not yet down into amino acids so they're not ready to be absorbed yet and the enzymes that do this are called proteases there are a variety of them probably the most famous is called Trion so I'll go ahead and write that one and so then we have these small peptides not quite ready to be absorbed yet though they they need a little bit of help they can't be absorbed straight into the Lacs like the fatty acids instead they require the help of brush border enzymes that are in the small intestine so we're going to call these brush border enzymes and these are found on the entos sites and they are required to finish up the digestive processes for both proteins and as we'll see carbohydrates I'm going to wall off the part about the liver up here so let's draw an entro site right here kind of at an angle like this you'll see what I'm doing here in a second we're putting the microvilli on it and give it a nucle and this is a cell that's lining your dadum or your gunum so the small intestine and um there's always capillaries associated with these cells so that things can either pass through them and get absorbed or like in the case of the fatty acids there's also Lacs there are enzymes and I'll make these brush border enzymes orange and these enzymes are capable of breaking the small peptides down down into amino acids so I'll write small peptides and then amino acids here so those enzymes make that happen those brush border enzymes and now we have something that is small enough that can be absorbed through the entos site and enter the bloodstream so see how the pancreas enzyme started it with proteases and the brush B enzymes of the dadum finished it off I'm going to take a moment to outline the pancreas in blue I forgot to kind of draw your attention to it and right here this is the main pancreatic duct and so the pancreas in these asinar cells here will make so these are asinar cells that make the enzymes and then those are able to come out that major dadal papula and enter the dadum where then they can start breaking down the um proteins and the lipids and the carbohydrates asinar cells of the pancreas are where the enzymes are made all right back to work down here so we're going to look now at carbohydrates and polysaccharides that are smaller now than starch are um able to be broken down further so we're going to say than saliva because there is pancreatic amas in your saliva as well polysaccharides are broken down into oligosaccharides which are smaller by none other than Amala which we've talked about before but it's also made by the pancreas so then it can drip drip drip out into the dadum to help break down uh starches and other kinds of carbohydrates but notice now these oligosaccharides they are um not yet broken down enough to be able to be absorbed into the bloodstream so just like the proteins they need a little bit of help from brush B enzymes let's go ahead and show how that works okay let's draw an entro site at an angle so you can see what I want to show you and we'll put the microvilli on there and give it a nucleus and draw a brush border enzyme right here like this but this is going to be a brush border enzyme that is good at breaking down disaccharides like lactose sucrose or maltose in fact some examples of brush border enzymes that are important in the dadum for carbohydrates are called lactase you can guess what that breaks down sucra that breaks down sucrose which is table sugar and then maltase which breaks down maltose which is um another kind of disaccharide and then that is going to so I'm going to go here and put that you have disaccharides which are two put together just a little bit smaller than Mo oligosaccharides so disaccharides are broken down into monosaccharides glucose fructose or galactose those are the options there and now they're finally small enough to be able to be absorbed into um capillaries in the sub mucosa like that so in both cases whether it's amino acids or monosaccharides they going to be absorbed into capillaries and that's you can see that I've drawn those in red and then same here absorbed into capillaries now really remember that that is different because if you're taking a traditional am class you will probably get a te question on your test making sure you know that lipids fatty acids they get absorbed into Lacs which are lymph vessels these are capillaries another thing that the pancreas does under the influence of secreton is to add bicarbonate to um the dadum so the pancreas also secretes bicarbonate because remember you've got that um acidic Kim and it has um endocrine little circles like eyelets of cells um so it also secretes hormones into the blood we'll talk about those later insulin being the main one but I'll put Etc since I'm running out of room there's also glucagon and somatostatin here I want to show you the four main layers of the GI tract they aren't always like exactly the same whether it's from the stomach or the small intestine or the large intestine but a lot of it is similar and so we can have some main takeways what I'm drawing here first is the mucosa these are lined with ENT ocytes and this is a mucus membrane so I'm going to put over here number one first layer is the mucosa the mucosa is made up of simple columnar epithelial cells and usually they have microvilli on them so I'll draw these you might remember the entos sites will usually have microvilli we'll write it like this so these are going to sometimes have brush border enzymes on them which are enzymes that help aid in the digestion the chemical digestion of the food so we'll put some have brush border enzymes to help out because the pancreas has most of the enzymes but we do need these brush B enzymes so if someone has a disease like celiacs it can affect their ability of their brush border enzymes to be um healthy and have enough of them so this is going to be the inner layer where the nutrients need to be absorbed through the cells and there the next layer we're going to talk about is the sub mucosa and that is going to have that's going to be where those capillaries and Lacs are for absorption so we have to have that absorption happen through the entas sites though and then a couple other kinds of cells you find here are going to be goblet cells for example they got named because they have a very goblet look to them and they make mucus this is a mucus membrane so that shouldn't be a surprise and there are antibodies that line our mucous membrane and these are called IGA or imunoglobulin a antibodies and these are specially designed to protect mucus membranes so we have these on all of our mucus membranes and they are very plentiful in breast milk so that babies get to have their mucus membranes protected even when they're still little and pretty vulnerable so we'll look at the sub mucosa next going to use green and make a line around so now this is going to be the second layer as we're looking out and we can put some capillaries in here into the sub mucosa layer sub meaning under so it's under the mucosa and then also some Lac teals these are where the um triglycerides the fatty acids will eventually get absorbed let's go ahead and add some brush border enzymes onto this mucosa lining so you remember that that's these are inyes that have these on them and we can put some amino acids and some fatty acids and some um monosaccharides and these are the nutrients that then can be absorbed into oops I want to do that can be absorbed into the capillaries or if it's a fatty acid into the Lacs if it's a monosaccharide into a capillary so we have different kinds of absorption there now I'm going to just um color this in real faint so I don't go over anything so this is the sub mucosa under mucosa so if you were to take a crosssection of a piece of intestine this is these are the layers you would find so we'll do layer number two sub mucosa this is where we find the blood vessels to absorb amino acids and monosaccharides and the Lacs that can absorb fatty acids you also find lots of massed cells here these are a kind of white blood cells white blood cell um and they're going to help again to defend your body against um foodborn illness okay then the next layer out is going to be um a layer of muscle this is one of the layers of the muscularis externa this innermost layer is circular so I'm going to draw it like this this just represents circular smooth muscle that can squeeze down on whatever food is in the lumen and help to move it along so we call this the third layer the muscularis externa and you've got um circular which we just drew and uh longitudinal is most typical now the stomach also has that oblique layer but most of the GI tract just has the C circular and longitudinal layers so I'm going to draw another layer out here to represent the longitudinal layers this one's a little harder to visualize because so these muscle fibers would be coming at you so the truth is that the best way to show it is like little circles that you would see these would be like fibers coming at you since it's a cross-section if it doesn't make perfect sense to you really don't worry about it what you need to know is that there are two layers there's a circular layer and there's a longitudinal layer in most parts of the GI tract okay so got circular and longitudinal and the purpose of these is to perform peristalsis which is going to move the food stuffs along in a forward fashion so I'm going to say moving it along and then there's another kind of important contraction that occurs that's called segmentation and this is when it kind of moves it forward and then backward and then forward and then backward and the overall effect is an important mixing effect where the contents that are in the Lumin are able to bump up against the walls of the mucosa over and over again okay then we'll do um the Sosa and pull this back let's go ahead the Sosa is also known as the visceral parium so this is a membrane that surrounds it's kind of glistening looking and it surrounds the outside of each coil of intestine and not only that but it will often double over on itself to form what we call a mesentary so that there is a pth pathway for blood vessels and nerves to get to and from all the different places inside of the parium it's like little highways you could almost think of it and this area I really like how I drew this let me fix this so this first I guess I should label it for you right okay so this is the Sosa also known as the visceral parium When You See It fold it over like this this is what we call a mesentary and that's really important because it anchors all the coils in place and it also is a path for vessels and nerves and especially in the really prominent ones like the greater momentum and the Lesser momentum it's a great place to store fat and so as people maybe gain weight you'll notice that their greater mum will be thicker and thicker and the greater momentum is actually where someone has a lot of visceral fat that's where their um fat is stored but we also would have blood V vessels so it's going to give a pathway for those blood vessels and nerves to come and go we will wrap up our discussion of the digestive system with looking at the colon the start of the colon actually has a valve that marks the end of the small intestine and we call that valve the ILO seal valve it's really a sphincter muscle ilocal valve and it's going to prevent feces which are forming in the colon from going back into the small intestine the first part of the large intestine is called the seeum right here and it is a blind pouch at the start of the colon I'm going to put this right here now hanging off of this is a very interesting structure known as the appendix most people have heard of this right the appendix We Believe has a lot of immune functions and it can hold a reservoir of good bacteria to repopulate after you've had bad diarrheal disease so the appendix hangs here and we believe that that it serves immune functions and if people get appendicitis in my mind it's a little bit like someone that is getting you know swollen tonsils a lot your appendix is a lymph tissue but it's just in your colon instead instead and some people can have repeat and chronic appendicitis where it's inflamed chronically without um Perforating meaning uh exploding out basically into the peritoneum and usually they'll have it removed but it can be um a chronic problem too now before I move on I want to show you this smooth muscle that bunches the colon up into distinctive segments that are called um HRA so that's what that line is going to represent it's the Tania coli let's put that right here Tania coli and these are bands of smooth muscle that bunches the colon into segments and we call those segments HRA like little uh bands of sausage basically as the colon goes up we call it the ascending colon and then it turns the corner right here at What's called the hepatic flexure cuz that's where the liver is so this curve right here is called the hepatic flexure then the transverse colon goes across the top until it gets to the splenic flexure which is this turn right here the splenic flexure where the spleen is the large intestine is retrop paranal which means it's attached to the body wall Back Body wall and that's a good thing because we wouldn't want to get a twisted bowel right and so this helps to keep it from twisting up it's kind of held in place the mesenteries help with that too got the descending colon and then the sigmoid colon will do an orange see how it's considered to be kind of shaped like an S curve and I'll make the rectum Here Pink So This is the rectum and then you can see that there's some muscles right here that are important anal sphincters first is the internal anal sphincter and this is involuntary so if your bowel is full then um this smooth muscle is going to relax and you're going to feel very much that you need to have a bowel movement and if you're not potty trained you will but as we become potty trained then we also so are able to voluntarily learn to control the skeletal muscle that is the external anal sphincter and so this one will be able to hold it in until you have opportunity so this is skeletal which makes it voluntary we have a similar arrangement for the urinary bladder with an internal and an external urinary uh and urethral sphincter that help us learn to be able to only void when we want to void it's very important in reabsorbing water if your large intestine is compromised let's say you have a foodborn illness then you will might get very severe diarrhea to the point of death so it's going to reabsorb water and electrolytes to help keep us um having an appropriate blood pH and blood pressure then we also have B ions of normal flora that's just bacteria and some yeast so microbes that live within us more cells that live within us and on us than that make up our own body and these normal flora have some important jobs one they actually protect us from being colonized by actual pathogens so they're for the most part harmless and they keep pathogens away they also are able to help produce and some vitamins for us such as some vitamin K and then we can absorb them into our bloodstream and going along with protecting us from pathogens they actually are important they talk to our nervous system and help to modulate in a good way usually unless you have disbiosis um modulate our immune responses and if you have autoimmune disease or now they're finding that autism there might be an issue with the way that the normal flora communicate with our brain or the populations that we have there