Transcript for:
GI Tract Overview

all right so in this video we're going to be going over the gi overview model okay so we're going to be going over the gi tract itself so gi tract also stands for the gastrointestinal tract okay and what that is is kind of a series of these connected hollow organs for which food is going to travel through the body from one end out towards the other okay where digestion and absorption occur at different stages throughout all right so i don't know about you guys but when i start eating okay i put the food in my mouth okay so the food is going to begin as it enters our mouth into this area we can call our oral cavity okay so the food is going to enter our oral cavity and this is where the first few stages of digestion occur okay so in the oral cavity we have both mechanical as well as chemical okay so the mechanical digestion is going to involve the teeth which we can see here the tongue as well as the roof of our mouth which we can call our hard palate okay so mechanical digestion is occurring kind of chopping up and breaking down that food okay like i said we also have chemical digestion okay this is going to be from the saliva okay so in our mouth we do have salivary enzymes okay so we have salivary amylase which is going to break down the carbohydrates in our food as well as salivary lipases which are going to break down the lipids in our food okay so this also continues the process of digestion okay um so as soon as that food is chopped up and mixed with those chemicals okay so those salivary enzymes it is no longer considered food but is now rather considered what is called a bolus okay so after both the mechanical and that chemical digestion we have the food mixing with those enzymes all right it is now called a bolus okay so that bolus of food is going to be swallowed entering into the structure this tube that kind of sits behind our nose our mouth in our trachea called our pharynx okay and we'll learn about that this block as well so that bolus is going to be swallowed and enter into our pharynx okay this guy right here which is called our epiglottis is going to shut to make sure that that bolus or any of that bolus doesn't get down into our trachea and cause us to aspirate okay so that epiglottis is gonna come and sweep down and shut that way the bolus of food can continue down our pharynx till we get to this guy alright so this is a nice long muscular tube all right called the esophagus all right so this esophagus is made up of two different layers of muscles that work together to help propel the food down the esophagus into where we eventually get to the stomach okay so again this is the esophagus the esophagus uses a type of movement called peristalsis to propel that bolus from the pharynx through the esophagus to the stomach okay so at the very end of that esophagus we have this little kind of narrowing this narrowing is called the lower esophageal sphincter okay so this is a sphincter which is a group of circular muscles that's going to help contract or dilate to allow food to enter or stop it from exiting the stomach okay so once we have that bolus dumped into the stomach we're going to tighten that lower esophageal sphincter in order to prevent the food from being regurgitated okay so right here would be the lower esophageal sphincter okay now that bolus is going to empty from the esophagus into what we know as the stomach okay so we have a bunch of different parts of that stomach all right kind of right here right below that lower esophageal sphincter we have an area called the cardia this kind of part that dips up up here so this area is the fundus this larger area right here is known as the body of the stomach and then this area that kind of swings back up sort of that j shape would be the pylorus okay so that bullet is going to enter um through the lower esophageal sphincter from the esophagus into the stomach okay once it is in the stomach that bolus is going to mix with a bunch of these other gastric juices that are in or exist in the stomach okay so we have hydrochloric acid we have some other enzymes like pepsin that are going to help break down the proteins in the stomach okay so we're going to have this further chemical digestion once that bolus hits the stomach all right we do also have mechanical digestion as the stomach is composed of three different layers of muscle all right you have the circular longitudinal and oblique muscles that are going to help also further kind of churn the stomach contents to mix that bolus with those gastric juices okay once the bolus is then mixed with those gastric juices it is no longer called a bolus but rather it's called chyme okay so that chyme is going to be propelled as the stomach contracts through the pylorus through this little sphincter called the pyloric sphincter all right to dump into our first part of our small intestines which is called our duodenum okay so that chyme when it's ready is propelled by the stomach into the first part of the small intestine called the duodenum right and if i move it up like this now we can see the entire small intestine so all of this is parts of the small intestine as well as this initial part right here okay so that chyme is going to be dumped into the small intestine okay so the small intestine can actually sense some of the contents of that kind okay so say if we have a really fatty meal okay and that chyme is really fatty it has a lot of lipids okay that duodenum or actually special cells in that duodenum called eye cells are going to send a chemical called cck which stands for cholecystokinin right so it's going to send that cck up to the gallbladder which is this kind of pear-shaped green structure that sits underneath the liver okay so the duodenum the eye cells of the duodenum send that signal up to the gallbladder to release its contents which we will eventually know is bile okay so that bile's job is to come down through the cystic duct to the common bile duct to eventually dump into the duodenum all right and from there that bile is going to help emulsify which means to break down or to chop up that really fatty chyme okay so the duodenum is going to secrete that cholecystokinin or cck from those eye cells okay we have another accessory organ right here which is kind of this bubble gum looking structure kind of hidden right that is just below the stomach that is called our pancreas okay so our pancreas also secretes other enzymes in order to further break down that kind that is now in the duodenum okay so it has these pancreatic enzymes that are going to help further break down the chyme and it also has a certain chemical called sodium bicarbonate okay so because of the stomach contents right because of that hydrochloric acid and some of the other acids in the stomach right the chyme is now acidic as it enters the duodenum all right this can be dangerous right so we have the sodium bicarbonate being released from the pancreas in order to coat and protect the duodenum from that acidic chyme okay cool so the pancreas as we'll find out in the pancreas video has both endocrine and exocrine functions okay so the exocrine are again secreting chemicals into a duct okay so through this duct into the duodenum okay so that would be the exocrine function and the endocrine functions you might have known as insulin and glucagon okay so the pancreas also secretes insulin and glucagon by different types of specialized cells okay but again for digestion we're not as concerned with that all right so quick little recap right from the esophagus that bolus is going to travel through the lower esophageal sphincter dumping into the stomach from there that bolus is going to mix with all these gastric juices and enzymes okay once it mixes and the stomach churns that bolus is now called chyme okay once that chyme is ready it'll be propelled through the stomach through the pyloric sphincter into the duodenum all right so again that chyme can be rather acidic because of the stomach contents right so the pancreas releases sodium bicarbonate to help neutralize that acidic chyme okay it dumps it into the duodenum okay if the chyme is really fatty so after a really fatty meal okay special cells in the duodenum called eye cells will release a chemical chemical called cholecystokinin okay which is abbreviated as cck up to the gallbladder to release its contents which is bile through the cystic duct through eventually the common bile duct and then eventually going to the duodenum itself as well okay so now we're having the nutrients being digested okay but finally it's time for absorption okay so the small intestine is the area of the body where the majority of the absorption occurs alright so we talk about digestion that's breaking down the food okay but absorption is absorbing the nutrients or taking in the nutrients from those broken down food particles okay okay so we talked about how the majority of digestion has already occurred but now that we're in the small intestine so from the duodenum on um we're really more worried about absorbing right those nutrients from the food being broken down in digestion okay so majority of absorption is occurring in the small intestine okay so the small intestine can be broken up into three different segments all right we have the duodenum which we already talked about this is the shortest segment wraps around this way and then kind of cuts back where it changes right around here to the jejunum okay so everything over here would be the jejunum whereas it turns and everything right around here would be then called the ilium okay so we kind of did this thing where we put our hand right across it all right so everything on this side that would all be let me switch hands right so all of this would be the jejunum and everything wrapping back here where it continues down and eventually meets the large intestine would be the ilium okay so we have a fun little way of remembering it called dj ill so when we're thinking about the small intestines we remember this guy called dj ill okay so d referring to the duodenum right j referring to the ili or the jejunum sorry so duodenum and then j for jejunum and then ilium right for ill okay so we have d j ill okay so like i said before the majority of absorption occurs inside the small intestine okay eventually you know that chyme is going to reach the point where it's ready to dump into what we know as the large intestine okay so from the ilium the food is pushed through this little valve that we can see right here okay this valve is called the iliocecal valve okay we have this little out pouching inside the large intestine known as the cecum okay so the ilium is dumping that chyme into the cecum okay through a valve we know as the ileocecal valve so again between the ilium and the cecum of the large intestine okay from there the large intestine is going to continue and run up across and back down has this weird kind of shaped kink and eventually going out towards the rectum and the anus okay so the majority of absorption occurs right absorbing of the nutrients from the food occurs in the small intestine whereas once we get to the large intestine it's going to be absorbing or reabsorbing the water okay so that chyme is going to enter into the large intestine it's going to travel up through the large intestine where it's reabsorbing all the water and this helps solidify our feces or our stool okay so there's a few different parts right of the large intestine so the first part of course this outpouring would be the cecum which continues up as the ascending okay so again ascending going up a sending colon it's going to cut across named the transverse colon it's going to come back down so now it's the descending colon all right eventually we get to a point that has this weird kind of s shape which you can't really see right because we have the small intestines in the way but that s shape so that last part of the large colon is called the sigmoid colon okay so after it passes through the large colon okay or the large intestine right the water's gonna be reabsorbed that stool is gonna be hard and ready to exit out the body okay we've absorbed all the nutrients we can up into this point okay so that stool or those feces is going to be stored in this area called the rectum right so this is our rectum which will eventually be poured pushed out through the anus which would be right here okay we do have certain types of muscles okay surrounding the anus all right they're called sphincters again you know um opening or constricting and relaxing in order to allow things to go through them okay we have the internal anal sphincters which are these longer ones right here so these would be the internal anal sphincters and then we have these external anal sphincters closer towards the anus okay or the exit of the rgi track okay so the internal anal sphincters are actually involuntary which means we do not have control of them okay whereas these external anal sphincters are voluntary so we do have a little bit of control okay so when we have to go those involuntary anal sphincters are going to relax and allow the stool to continue down but luckily we do have a safety net which will be those external anal sphincters okay and then of course those feces or that stool that has no more nutrients that we can absorb is going to exit out through the anus right here okay and that is sort of the pathway for which the food takes all right so we do have a few accessory organs that we can see okay one right here on that large intestine is actually the vermiform appendix okay so most of you guys probably have heard of an appendix or at least know what it is or um what can kind of be a complication right so we have this thing called appendicitis okay that appendicitis can definitely be dangerous because the appendix actually holds some bacteria that are important to our gut flora okay so this appendix gets inflamed and get to the point where it actually ruptures okay so if this organ all right that has you know a bunch of this bacteria ruptures and all that bacteria enters our peritoneal cavity all right we can have you know severe inflammation infection uh something called peritonitis all right we should be inflammation of that peritoneal cavity and this can eventually uh quickly lead to death okay so that's why it's super dangerous um when you have an appendicitis that's why i usually go and rush the er to get it removed right away before it does burst all right kind of running back up the gi tract we can see a few organs um so this big guy and let me tilt it up hopefully you guys recognize that as your liver okay that's going to help detoxify the blood all right underneath we already talked about that gall bladder that releases a stored bile okay so the liver is what creates the bile whereas it is stored in the gallbladder okay so remember in the duodenum right if it's really fatty chyme okay those eye cells and the duodenum are going to release that cck going up to that gall bladder to release its contents which is bile through the ducts eventually dumping out into that duodenum to help emulsify that fat okay we already talked about the pancreas and that it secretes um both other pancreatic enzymes as well as sodium bicarbonate to help um kind of neutralize the acidic chyme on the other end of the pancreas we have this guy called the spleen okay so the spleen is going to pretty much help break down old red blood cells okay and that's pretty much everything you need to know um a quick little overview of the gi tract okay cool so of course you know there's more to all these models and you'll see those in the rest of the videos okay