24 lecture 5 is on the stomach the stomach sort of looks like a long wrinkled up sausage when nothing's in it it starts at the bottom of the esophagus and it's at the pile org sphincter and the main job of the stomach is to be a mixing and holding area for food it starts a digestion of proteins continues digestion of triglycerides and converts the bolus into a liquid called chyme there's also a few things that can be absorbed there so the three major functions it stores bulk amounts of ingested food mechanically breaks down ingested food and starts to chemically digest ingested food there are four regions four main regions to the stomach the cardia the fundus the body the pylorus it has three layers of muscle which separates it from other areas of the gi tract that only have two and this is related to the mechanical digestion of food it also has a highly specialized mucosa with lots of goblet or mucous cells that help to protect cells underlying from the effects of acid as well as enzymes so the four regions are the cardia the fundus body and the pylorus and when the stomach is empty the mucosa lies in folds that are called rugi there are two abnormalities of the pyloric sphincter that can happen in newborns that are going to either block or partially block the exit of food from the stomach and that has to be treated with either drugs or surgery so here we can see the stomach this is the cardiac region right here this hump is the fundus and then we have the body and the pylorus this area is called the greater curvature and it connects to the greater momentum the lesser curvature connects to lesser momentum there's a sphincter at the top that's the lower esophageal sphincter and a sphincter at the bottom called the pyloric sphincter and this again shows the greater momentum on the greater curvature and the lesser momentum on the lesser curvature as food is being digested it'll move through the stomach the stomach will churn the sphincters are both closed and the stomach turns kind of like a washing machine and helps to mechanically break down the food after a certain amount of time has passed the pyloric sphincter will slowly open and it'll squirt out a couple teaspoons full of this what is now chyme into the duodenum here you can also see the three layers of muscle so in addition to the circular and the longitudinal muscle there's also an oblique layer so during a meal as the stomach fills up there's waves of muscular contraction mix the food with gastric juice then one to two hours after a meal the pyloric sphincter starts to open up and i'm sorry the uh muscle contractions get more powerful and then three to four hours the pyloric sphincter starts to open up and it squirts small quantities a few teaspoons full at a time of the kind into the small intestine that allows for maximal digestion so pyloric stenosis happens when there's either some kind of blockage to the pyloric sphincter pylori spasm happens when um the muscle fibers don't relax they're spasming they're continually contracting uh this stenosis is the narrowing of the sphincter and you tend to see when you see these in infants they'll have uh projectile vomiting they won't be able to keep any because eventually as they're nursing it's not going anywhere it's just building up inside their stomach and it will come out as vomit as i said the his the stomach has a very specialized mucosal histology there's a lot of mucous cells found on the surface and then the epithelial cells go down into the that second layer the lamina propria that forms the gastric pits in the gastric glands the gastric glands have three different type of exocrine glands there's mucous neck cells they secrete mucus chief cells secrete pepsinogen remember if if an uh protein ends in gen or starts with pro it's inactive so this is an inactive form as it's secreted and as well as uh it also secretes gastric lipase and then there's the parietal cells and they secrete hydrochloric acid as well as intrinsic factor the gastric glands also have enteroendocrine cells that produce gastrin these are the g cells zollinger ellison syndrome happens when you produce too much hydrochloric acid and it's generally caused because you're secreting too much gastrin so this is showing here's the lumen of the stomach and this is showing the gastric pits as well as the gastric glands gastric glands are where you're going to find the chief and parietal and g cells of the stomach and the gastric pits you'll have the mucous cells lining these here you can also see that the oblique layer of muscle circular and the longitudinal so hydrochloric acid when when pepsi pepsinogen is released into the lumen the hydrochloric acid can convert it into pepsin intrinsic factor is essential for absorption of vitamin b12 through this through the gi tract um it binds with vitamin b12 and allows it to bind to the protein that will transport it into the absorptive cells gastrin hormone is the get it out of here hormone it stimulates the release of gastric juice increases gastric motility relaxes the pyloric sphincter and constricts the esophageal sphincter so that the food that is the kind that has been produced in the stomach can move into the small intestine here you can see all these goblet cells or surface mucous cells they call them here uh lining the gastric pits and then down in here are the gastric glands where you find the puffy pink parietal cells and the little purple chief cells so the submucosa is areolar connective tissue as i said the muscularis has three layers and the cirrhosis part of the visceral peritoneum at the greater curvature becomes greater momentum at the lesser curvature becomes the lesser momentum again having the three layers of muscle helps to increase the churning the mechanical digestion consists of peristaltic movements called mixing waves and then the chemical digestion is going to mostly be the conversion of proteins into peptides first because the hydrochloric acid is creates a very acidic environment it denatures the proteins and gives a lot more surface area for the enzyme pepsin to work on them pepsin will cut them up into smaller pieces called peptides gastric lipase is important in producing fatty acids and monoglycerides from certain molecules in the butter fat of milk so this is more important in babies than it is in adults babies also have a higher ph in their stomach and gastric lipase works best at a higher ph the stomach wall is impermeable to most substances not much absorption happens here at all but water some electrolytes certain types of drugs especially aspirin as well as alcohol can be absorbed through the stomach lining alcohol dehydrogenase is another enzyme that we find in the stomach it oxidizes ethyl alcohols to aldehydes and ketones it also oxidizes methanol to produce formaldehyde and this is why wood alcohol which some people drank during the prohibition time is so toxic it also oxidizes ethylene glycol which is antifreeze to produce glycolic and oxalic acids oxalic acids um can form crystals and the crystals are what deposit in different areas of the body and cause the a lot of the issues associated with ethylene glycol poisoning the largest quantities of alcohol dehydrogenase are found in the lining the stomach and liver and the activity of this enzyme varies between men and women as well as between racial groups and among populations of people of different ages the gastric ph is going to be disrupted when food enters the stomach unless it's you're drinking lemon juice or something the ph is going to be much lower in the stomach than of anything you would eat so the ph of the gastric juice along with stretching stretch receptors that are going to be activated from distension of the stomach walls send information to the submucosal plexus here nerve impulses the parasympathetic nervous system are going to cause the parietal cells to secrete hydrochloric acid and smooth muscle in the stomach well to start constricting or contracting the increase in acidity of the stomach chyme and the mixing the stomach contents you're going to also have emptying of the stomach that's going to occur because of this and that brings us back to homeostasis in which the ph of the gastric juice and the distention in the stomach are back to normal