hello everyone this is our third video about the digestive system and for this video these are our learning objectives in the last video we ingested a piece of food and we swallowed it the bolus went down the esophagus until we reached the end of the esophagus where we find the lawyers of a govt sphincter now after the bolus passes through the lower esophageal sphincter it reaches the stomach and here we see the stomach the stomach has several functions which include the storage of undigested food mechanical breakdown food and chemical digestion leading to the production of time our stomach is located in the left upper quadrant of our abdominal cavity and that's the place where we find the pancreas as well so when a person complains of pain in the left upper quadrant the person can be having an issue in the stomach or the pancreas as well the stomach is anatomically divided into cardia folders body and pylorus fundus is really the part of the stomach that's dairy up it's higher than where the esophagus connects to the stomach it's really this up part right here we see here the lesser curvature and attaching to the lesser curvature we find the lesser omentum the mesentery that attaches the liver to the stomach we also see here the greater curvature in attaching to the greater curvature we have the greater omentum another thing you can see in this diagram is the blood supply to the stomach and the one I would like you guys to remember is the left gastric artery because that's the one you guys are learning how to identify in the lab and if you recall the left gastric artery breaks off the celiac trunk and the celiac trunk is the first unpaired artery to branch off the abdominal aorta so what is a stomach the stomach basically is a muscle sack that stores food and very little digestion happens in this comic the main function really is to start food so for example if you go to these all-you-can-eat restaurants and you eat an only stop for like two hours I don't know how long all these food that you're putting into your mouth and swallowing all this food is stored in the stomach temporarily and you keep eating and all this food is there when we have digestion happening it slowly but little by little they stomach will release this bolus of food mixed with acid and that is called chyme the kind will be is slowly released into the duodenum and then the duodenum will take its time to do the digestion so this process of digestion will go on for many hours but when you were at the restaurant and you were eating on stock all that food need to be stored somewhere and that was stored in the stomach so the stomach is this muscular sac that churns mix and holds all this partially digested food in this soup of partially digested food this gastric juice is called chyme in the wall of the stomach we got three muscular layers we have the longitudinal layer a circular layer in an oblique layer now if you recall a typical histological cut off the digestive tract we had two layers we had just the longitudinal and the circular layer but now in the stomach we have a third layer the obliquely the reason why they're named this way is because of the direction the fibers run so they're all arranged in different angles and because of these three layers with fibers in different angles our stomach can make very interesting movements so if you recall we have chemical digestion and mechanical digestion in both of these digestions happen at the stomach there is more muscle layers of the stomach really really start mixing the bolus of food around and with that help breaking it into smaller piece when we look at the stomach lumen we find these wrinkles and these wrinkles are called roogie in roogie are basically folds we think the wall of the stomach and one of the functions of this rugae is to have like a gripping action that helps to mix the bolus of food even better because you can imagine if you had just a smooth surface the bolus of food we just slide from one side to the other but the fact that we have these folds it grips the bolus of food into the places and it helps with mixing another function of this rugae is that if necessary they can stretch and consequently our stomach strikes and gets bigger in case you eat more than what you should have now if you don't eat as much or if you eat very small portions of food the stomach can like shrink and then you get more of this roogie at the entrance of the stomach we have the lower esophageal sphincter and at the end we have the pyloric sphincter and what's the function of always filters and valves in our body the function is to ensure one-way flow so these filters are ensuring one-way flow the pyloric sphincter allows what in the stomach to go into the duodenum but it doesn't allow what is in the duodenum to go back to the stomach because the pyloric sphincter ensures one-way flow the pyloric sphincter works very effectively and it allows one-way flow and thirsty the lords of a Jewish sphincter is not as strong so it's weak and because of that not only stuff kingbolt from the esophagus into the stomach but in some cases is stuff from the stomach can go back up into the esophagus in that what I explained that we call acid reflux or heartburn another thing that's important to point out is that in the portion of the stomach that's closer to the esophagus we have very weak base houses and as we get closer to the pyloric sphincter this peristalsis movements gets stronger and then what happens is that since the pyloric sphincter is basically closed and it delivers a small amount of kind into the duodenum every time that time is pushed into the pyloric sphincter most of it it will bounce back into the pylorus region of the stomach in this mechanism that of course in our stomach even though it is peristalsis it receives the name of retro potion because is the movement of coming back in that's characteristic of our stomach and it's very important because it creates a very good mixing action in the pyloric part of our stomach in further fragments and mixes gastric contents when we look at the histology of the stomach we see that the mucosa of the stomach is made of simple epithelium which means that it is one layer thick now on top of this one thick layer of cells we having nice mucous layer and that creates a protective layer of mucus and that makes a lot of sense because our stomach is very acid the pH and our stomach is between 1.5 and 3 so this mucus is kind of basic and it forms a protective barrier so the answered of the stomach does not damage the stomach itself as you can imagine producing these mucus we have lots of mucus cells which are called mucous epithelial cells now if we look very closely at the mucosa of our stomach we find this tiny little entrances and these entrances are called gastric pits and the gastric pit is kind of a little canal that goes deep into the mucosa deep down the gastric peat we find the gastric gland in the gastric glands specialized cells that secrete acid enzymes in a hormone called gastric if you pay attention to the gastric pit area we see that we have cells called mucous next cells and these are cells found on the neck of the gastric pit these cells are the name why's they produce mucus but the mucus produced by the cells serve to lubricate the food that enters the stomach now deep inside the gastric pits we find very important specialized cells in the reason why these cells need to be hidden is because they are simple columnar epithelial cells like all other cells that line the lumen of our stomach and so they are kind of hidden inside these pits to be protected looking at the gastric gland we see that we have three major cell types we have the parietal cells the chief cells and the G cells parietal cells secrete mainly hydrochloric acid and the hydrochloric acid in the lumen of our stomach helps with the chemical digestion of the bolus of food and it also helps with killing of any pathogen that goes down into our stomach the chief cells are responsible for secreting pepsinogen in a pepsinogen when exposed to the acidic environment of the stomach it gets converted into Pepsi so pepsinogen is the precursor of pepsin and pepsin is the enzyme that's capable of digesting protein in our stomach now the mixture of the bolus of food with all these gastric secretions is called kine and that creates something like an acidic soup made of the contents that we ate and gastric juice that's basically what we see when we throw up right when we throw up is like a liquidy food and that's the content you weight plus the gastric juice hence that's the kind now these cells are the ones responsible for secreting a hormone called gastric and that's why they are called G's cells because they secrete gastric gas string causes stimulation of the chief cells in a simulation of the parietal cells as well as contraction of muscular layers of our stomach so because of the gastrin function I like to think of G cells as gangster cells because they stimulate they they activate chief cells parental cells and muscular contraction as well so they are gangster cells they make everything that's around them to work so when we see food and we think about eating the vagus nerve cranial nerve number 10 activate these gangster cells with Jesus and then leads to the activation of chief cells in parietal cells in our so contraction of the stomach muscle layers but we don't want our G cells to go crazy and just continuously stimulate the production of hydrochloric acid and enzymes because that would lead to a hole in our stomach so a habit is that we have chemo receptors in our stomach and they detect the pH change and then we have this chemical control of the pH we have within our stomach and if we have too much hydrochloric acid so the pH is too low these G cells are not assimilated and consequently they do not produce gastrin which will not lead to the activation of parietal cells and chief cells in the stomach we have the preliminary digestion of proteins and we continue digesting high carbohydrates because the carbohydrate starts being digested by the salivary amylase right that we had in our mouth but we basically do not have an absorption of nutrients in our stomach and the reason why nutrients are not absorbed through the stomach very well is because of the presence of this thick protective layer of mucous lining the lumen of our stomach so this thick mucous layer is what protects a stomach from digesting its own walls however some drugs can be absorbed through the stomach wall and that's the case of aspirin aspirin makes little holes in the mucous layer of the stomach and little tiny holes in the mucus layer allows the aspirin to be absorbed and that's the reason why when we read behind the aspirin bottle it says that if you take too many aspirin it may cause stomach bleeding and ulcers now you know the reason after the stomach we have the small intestine so come present in the stomach will pass the pyloric sphincter and enter the small intestine now respond testin is approximately 20 feet long and it's so divided into three portions we have the duodenum jejunum and ileum in an easy way to remember this order is to remember DJ ileum the small intestine is the major organ of digestion and absorption 90% of the nutrients are absorbed in the wall of the small intestine hence we can't live without a small intestine and if we start thinking about disorders affecting the small intestine such as Crohn's disease in inflammatory bowel disease we can easily see malnutrition as a result of these diseases I love this mo intestine there are some accessory organs that will add to the secretion in these organs our pancreas liver and gall bladder secretions from pancreas liver and gallbladder are added to the small intestine is specifically to the duodenum region of the small intestine in the duodenum which is the first 10 inches of a 20 feet long tube is where most of the digestion happens and if you look here you can see that the duodenum have this very band C shape and the purpose of that is to trap the chyme there until digestion happens then when muscular contractions happens that force is the climb along that bend and then it keeps moving and goes on into the jejunum and then ileum and eventually it passes the ileocecal valve enriches the cecum which is the first part of the large intestine now since I told you that is the first 10 inches off a 20 feet long tube I must tell you how long are the other two parts of the small intestine right so the jejunum is approximately 8 feet long and the ileum which is the last part is approximately 12 feet long but I'm not expecting you to remember the length of the small intestine or the length of any part of our body so here we can see the stomach and the duodenum when contents from the stomach are released into the duodenum they basically get trapped in the band right here and they sit there temporarily and that gives time for it to mix with the juices that comes from our pancreas and gallbladder so we have the co release of pancreatic juice and value here at the duodenum and that has a huge role in digestion that happens here in our small intestine when we look at the wall of the small intestine we can explain why most of the absorption happens here so we see those layers that I mentioned at the beginning we have the mucosa the submucosa and a muscular layer in the serosa but what's different that we see here in Des Moines testing is these folds on top of folds on top of folds in this folds on top of folds is one increases the surface area by a lot so look at this remember I mentioned that we have this big folds and this big folds are called circular folds or PI K circulars now the plank a circle areas are covered with finger like projections and these finger-like projections are called villi basically these villi are extensions of the mucosa is sticking up at the surface now if we look at one village and we zoom in we see that the village is lined with simple columnar epithelial cells with goblet cells and on the apical surface of this columnar epithelial cells we find tiny micro villi which creates something like a brush border so in our intestine we have folks called plucky circle Ares or circular fold on top of the plucky circulars we have finger like projections called villi in the cells that make up the villi have tiny little projections on their apical surface that are called micro villi the main goal of this folds on top of folds is to increase the surface area for absorption in clinic to when the surface area of all these folds were calculated it was compared to the surface area of a tennis court so big it is so all the surface area is what really contributes to the absorptive ability of our small intestine now in the middle of each village we have lamina propria and in the lamina propria we find both vessels so this capillary network that we see here and we find something called like to you which is this green tube we see going up in the middle of each village this green tube called like tu is part of our lymphatic system so what happens is that most nutrients are absorbed into the blood vessels however lipids such as fatty acids cholesterol in fact soluble vitamins such as vitamins a d e and k they are not absorbed into the blood vessels they are absorbed into lymphatic vessels called lacteals so this very length is absorbed through the like to use which is part of our lymphatic system and then this very length travels along the lymphatic vessels and then it drains into the left subclavian ring near the junction with internal jugular vein so in each Delos we have both types of vessels we have blood vessels and lymphatic vessels to ensure that we absorb all types of nutrients each part of our small intestine has a specific function and that has a direct relationship to the differences we absorb in these three small intestinal regions as you can see here the three parts of our is mountain have like a circle Aries and in the plaque a circle areas we find villi and in the apical surface of the epithelial cells that form the villi we have Micro filling now if you look here we see that in the duodenum region which is the first part of the small intestine we have glands at the base of this villi these glands are called duodenal submucosal glands or Brunner's glands the duodenum submucosal glands are just found in the duodenum we do not find them in the jejunum nor in the ileum these glands are responsible for secreting large amount of mucus that neutralize the acidic chyme coming from the stomach and the acid neutralization is very important for the digestive enzymes present in the duodenum to work properly now looking at the jejunum you can see that the circulars and the villi are much more pronounced and that's because the jejunum is involved with most of the nutrient absorption so the bigger there you have the more absorption you'll be able to make and that's why we find in the jejunum very prominent like a simple Aires and villi now looking at the ileum which is the last portion of the small intestine we notice that the pike encircle Aires and the villi are reduced but most importantly we have the presence of lymphoid nodules called peyer's patches so the reduction in the folds correlate with the fact that most of the nutrient absorption already happened at the jejunum now the presence of this link void tissue is related to the fact that the ileum is very close to the large intestine so the job of Disney static tissue is to find the bacteria that's normal in the large intestine the large intestine is not very clean we have lots of e.coli in our large intestine and we actually need them there but they need to stay in the large intestine they cannot in today's mall in testan so we have these fierce patches guarding our small intestine from the bacteria that normally lives in our large intestine here we see the large intestine and the large intestine is divided into cecum a sending colon transverse colon descending colon sigmoid colon and rectum functions of our large intestine includes production and absorption of vitamins absorption of water and electrolytes and then with death the large intestine compact waste into feces lastly the large intestine stores feces prior defecation so we have most of the nutrients absorbed at the jejunum portion of our small intestine in the water and electrolytes are absorbed here at the large intestine now as I mentioned before we find bacteria in our large intestine in this bacterial community is collectively called intestinal flora these bacteria have a very important role they break down food residues and make available important vitamins such as vitamin K which is very important in blood coagulation these breakdown of food residues by bacteria present in our large intestine generate gases and this is the major source of flatulence one of the most notable bacteria found in our large intestine is called ecoli the word coli implies these bacteria lives in our column which is our large intestine most of the time ecoli bacteria doesn't cause problems but it can cause problems and the most common problem it can cause is urinary tract infections in women the cecum is the beginning of our large intestine and we see here in the cecum the vermiform appendix which is basically attached to the bottom of the cecum the appendix is a tube that continues to the cecum and the appendix is part of our immune system the sitcom leads into the a singing column and then we have the transverse column followed by the descending column then the sigmoid column then the rectum and the anus all these pouches that we see here along the large intestine are called Hofstra in Hofstra houses feces so when the large intestine contracts you move feces from one half strim to the next house from and so on another thing that's interesting about the large intestine is that the longitudinal muscle layer is reduced to this little strip and all these pouches that we see are made of circular muscle layer so the longitudinal muscle layer has the same function it had before which is aid in terraced houses but now it receives its a different name which is teeny colon if you look right here next to the teeny coli we have these all mental appendices which is basically pieces of adipose tissue hanging and it's just more places to store fat so we have Sikkim ascending colon transverse colon descending column and then we have the sigmoid colon let's basically this area that looks like another s at the sigmoid column is where the feces can be stored after the sigmoid column we have the last portion of the large intestine which is the rectum and after the rectum we have Danes when we look at the histology of the large intestine we see the typical structure of our digestive tract we have a new cosa submucosa muscular layer in serosa we do not see villi so there is an absence of villi because there is not much absorption happening at the large intestine we have simple columnar epithelium lining the lumen of the large intestine in between this epithelium we find goblet cells which secrete mucus and we find intestinal glands that secrete intestinal juice we can easily see here what I mentioned about the longitudinal layer being reduced to a strip it is not as why'd as the circular layer is just a strip and it receives the name of teh Nikola now when physicists entered the rectum which is the last portion of the large intestine it triggers the urge to defecate in the anal canal we find mucous glands which makes sense because you want to lubricate those faces as they're forced out of the anus if you look closely here you can see that there are two I know is fingers there is an internal and you know a sphincter and an external anal sphincter the internal I know is finger is a smooth muscle and the external noise finger is a skeletal muscle same thing turn away no is finger is a smooth muscle it's not under voluntary control its involuntary we cannot control it so once feces enter the rectum the defecation reflex happens and the internal anal sphincter relaxes but if that was the end of the story we would defecate every time feces enters the rectum but that's not the case so how do we hold it we hold it because the external anal sphincter is a skeletal muscle and since it is a skeletal muscle it's under voluntary control we can control it so what we really need to do is to squeeze the external anal sphincter and that way we don't defecate when it's not appropriate so even though the internal nos filter relaxes because of the defecation reflex the external anal sphincter is squeezes around it in forcing turnovers victim to close as well and with this we finish the third video about the digestive system and there is one more video left where I cover the liver the gallbladder and the pancreas please make sure to watch that video and also please let me know if you have any questions bye