have region the gi tracts and then have chemical digestion mechanical digestion absorption and special terms so if we start out with the mouth the chemical digestion is going to be we're going to have lingual lipase and that starts fat digestion it's salivary amylase and that starts starch digestion the mechanical digestion is mastication and it's chewing and absorption nothing really i mean you can absorb things like vitamin b12 you can absorb that on your tongue but i don't necessarily think that would be a big it's important enough to mention special term is bolus so what you end up with is a bolus of food and the bolus is just a lump of food okay the pharynx and esophagus will be next and no chemical digestion no mechanical digestion no absorption they're strictly for transport and we would have deglution which is swallowing and peristalsis which is that the contraction and relaxation of the smooth muscle that helps to move things through the through these tubes actually through most of the gi tract and peristalsis pushes the food through your gi tract okay so we have bolus mastication deglution peristalsis and we have the effects of two enzymes lingual lipase and salivary amylase in the mouth all right so um let's do another one region [Music] i'm just going to chemical digestion um physical mechanical sorry mechanical digestion absorption and then special terms all right and here we're going to start with the stomach in the stomach we have um we have gastric lipase but that doesn't really do much in adults but it is there so i'm going to put more for babies as i mentioned before the ph is really critical in activating certain enzymes and causing them to to become functional and also turning other ones off and in babies their ph in their stomach is higher it's less acidic and that's when gastric lipase works best and that's it doesn't really do too much we also have pepsin which is released in an inactive form pepsinogen and pepsin is for it breaks down protein breaks down [Music] protein into peptides so breaks down big proteins into smaller pieces um we have hydrochloric acid and that is uh released in the stomach by chief cells parietal cells excuse me so in the stomach we have chief cells and chief cells release gastric lipase and pepsin parietal cells release hydrochloric acid and also intrinsic faction intrinsic factor excuse me okay hydrochloric acid denatures proteins intrinsic factor is necessary to absorb b12 from b12 from food from your gi tract i guess would be a better way of putting it think of it this way if let's say b12 looks like this and the receptor that binds b12 looks like that it doesn't fit so when b12 is bound to intrinsic factor now it fits in the receptor so if you don't have intrinsic factor you can't have b12 you can't absorb b12 so you have to there's other ways you can do it you can absorb b12 they have little micro dots of it that you can put under your tongue you can get injections b12 is essential and if you are a notifications if you um eat meat you get plenty of b12 meat dairy any of that stuff if you're vegan or vegetarian you probably don't and so you have to make sure you you eat foods that have b12 in it or take supplements okay so intrinsic factor is made in the parietal cells and the the chief cells and parietal cells are cells that are found in the stomach in a region called gastric glands okay we also have another enzyme called alcohol dehydrogenase and this is going to break down alcohol the kind of alcohol we drink um mechanical digestion we have churning and that's vigorous mixing waves absorption we absorb water we also absorb certain drugs like aspirin we absorb some alcohol um not much else just tiny amounts of different things but not much else okay so i would say the big things here would be water drugs and alcohol not all drugs but a lot of drugs we can absorb through the stomach special terms um let me think special terms um um i can't think of any special terms for the stomach the uh so let me just talk a little bit about the inside of the stomach so the stomach if you look down at the stomach it would just kind of have like little holes in it and those holes are actually like if you look at a piece of stomach with a microscope and wouldn't look at at slices of tissue you'd see if you're looking right down into the stomach it would look like that little holes those little holes are gastric pits and i'm just going to talk real briefly about the histology but gastric pits okay are these structures that are covered mucous cells and the mucous cells are going to unsurprisingly release mucus the reason the stomach doesn't digest itself is because it has about two two millimeters or so of mucus a layer of mucus on it that prevents the hydrochloric acid and the pepsin from digesting the stomach so these are gastric pets and mucus being released from those and then down here we have gastric glands which are just like a whole bunch of different cells that are going to secrete different things okay and so in here we're going to have um i'll do one more row of gastric glands we are going to have chief cells and make chief cells t cells are little guys and they're purplish in color we're going to have parietal cells and they tend to be big puffy and pink and i'm going to make them blue here and chief and parietal cells are going to make up the bulk of the cells in these gastric glands the other type of cells that you do see are g cells okay and g cells secrete gastrin gastrin is a hormone it's the get it out of here hormone so gastrin when presence of food is detected in your stomach gastrin is going to stimulate first of all stimulate other areas of your gi tract to start moving things along because if there's food in your stomach that food has to go somewhere and if you have food in your small intestine it has to move out to make room for this food because it's coming soon if there's food in your small in your large intestine that has to move as well to make room for the food in your small intestine so everything has to move and so with gastrin you're going to have more secretions more contractions and it's going to stimulate the movement of food from the broken down food from the small intestine into the large intestine and from the large intestine whatever's there into down like in the sigmoid colon and rectal area ah special term chyme chyme is partially digested food so when that bolus of food gets to the stomach it's going to be broken down into chyme so it's sort of like soupy and it has chunks of stuff in it yet i mean a pathologist can look at what someone if somebody passes away they can look at what the stomach contents are usually they get a ladle and ladle it out and look at it and you can see chunks of things and get an idea for what their last meal was so it isn't completely digested so by the that is what's going to go into the small intestine and if we look at the the stomach the connection between the stomach and the duodenum is the pyloric sphincter okay and as is the food spends a couple hours in your stomach and then it's going to move into the pyloric sphincter um or move through the pyloric sphincter about a tablespoon or so at a time it doesn't just open up and it all drains into the small intestine it's going to be released a little at a time and the small intestines are really built to have the most surface area possible so that that little bit that's being released swirls around and touches all this surface area so that you can get optimal digestion and and absorption because most digestion happens in the small intestine very little happens in the stomach and mouth very little happens in the the large intestine that's mainly from bacteria and none at all happens in the pharynx and the esophagus