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Upper gi tract. Um And these are the Tylo's that will be covered in today's lecture. Um that should help you basically guide your re revision. Um So, at the end of this lecture, you should be able to describe the um the anatomy of the gi tract. Um And also understand how the structure relates to its function um across like the different gi regions. Um And then also recognize the roles and mechanisms of um gastric secretions. Um And I, I'll also be talking about uh like pathological changes like those seen in Barrett's esophagus. Um and what their clinical significance is. So I'm gonna be going through the um gut wall, the esophagus, the stomach and lastly gastric secretions. So, to start off with um digestion is the process of breaking down macromolecules to allow absorption. Um and absorption is the subsequent movement of these molecules across the intestinal uh epithelium into circulation. Um And most digestion begins in the mouth, but it's uh completed in the small intestine. So, the gi tract is um embryologically divided into three sections. So that is the full gut, the midgut and the hind gut. And, and each has their own arterial um supply. So the full gut is supplied by the celiac trunk. Um The midgut is supplied by the um superior mesenteric artery arteries, sorry. Um And the hind gut is supplied by the inferior mesenteric arteries. Um And this slide basically just shows how each of the three sections um uh like what each of the 33 sections are composed of in the gi tract. So, understanding how um it's broken down, uh essentially helps you to localized pathology um and understand uh referred pain. Uh So, in terms of what the gut wall is actually made up of, there are four key layers of the gi tract. Um Waller firstly is the mucosa which is responsible for absorption and secretion. Um And then there's the submucosa um which has like different glands in it. And uh the Meisner plexus, which I'll talk about later. Um And then the muscularis um which is responsible for uh like motility and uh peristalsis um via its two different types of muscles, the circular and longitudinal muscles. And then finally, you have the cirrhosa which is essentially like a protective outer layer. Um And there are the enteric nervous system um which I'll discuss a bit later, but um is within this gut wall and it's composed of submucosal and myenteric plexuses. Um And this basically allows it to uh coordinate um the reflexes of the gut um independent of the central nervous system. So, just to break it down even further, the mucosa is this top layer that you see here. Um And then the submucosa and then the muscularis. So the muscularis is composed of the circular layer here. Um And then the outer layer is the longitudinal layer. Um and these are very important in how peristalsis occurs. And then finally, there's cirrhosa. So the oral cavity is very important in the initial stages of digestion. And the master muscles allow for like biting and chewing. So, essentially mastication. Um and then you have the salivary glands which secrete uh aqueous secretions and digestive enzymes. Um amylase which digests carbohydrates and lipase um which digests fat. Um And then you also have the tongue which plays a role in both like mechanical digestion. Um and then bonus formation. So, the formation of the food bonus uh with the intrinsic muscles being used for fine motor control and moving the food around in the mouth. Um And this also assists in uh lubricating the food with the saliva. And then you have the esophagus, which is the food trial next. Uh So it's a conduit for food drink and any swallowed secretions from the pharynx to the stomach. Um It's lined by this nonkeratinized um s squamous epithelium. Um and this essentially protects it from wear and tear from acid and acid reflux. Um And it also is lubricated via these mucous secreting glands and saliva. Um There are two esophageal sphincters, uh the upper upper esophageal sphincter, uh which opens reflexively and then uh the lower esophageal sphincter uh which is stimulated essentially by like it's vaguely stimulated. Um And the lower esophageal sphincter prevents acid reflux from the, from the stomach. Um So, yeah, the upper esophageal sphincter um is uh voluntary and then the lower is involuntary and then you have um the Barrett's esophagus, which is a clinical condition, um which happens when the Z line which is uh here. Uh This Z line is essentially where um the, the, the epithelium of the esophagus meets the epithelium of the stomach. Um And when this, when this deadline is intact, um that's normal. Um However, when the esophageal epithelium um goes from being stratified squamous to being replaced by a simple columnar epithelium. Um This is called metaplasia. Um And that is bars of esophagus. Uh And this can lead to things like um eso esophageal adenocarcinomas. Um And this is caused by chronic acid reflux primarily. So, um it's seen in, in gourd um and it, so the, the Z line is a very important landmark um to remember. So how is reflux actually prevented um in the body? So, there are a few different mechanisms. Uh firstly, the um the diaphragm pinches, the lower esophagus. So, like physically prevents the acid from going up too high. Um And then you also have uh the angle of his, which is the angle of the um gastroesophageal junction in relation in relation to the actual stomach. Um And then also you have the ligaments which suspend the um the G OJ at an acute angle. Um And there's also like gastric emptying is prompted. Um And esophageal peristalsis also helps clear the like the acid um as quickly as possible uh to, to prevent um chronic reflux. So the stomach performs uh many different functions. Um but its main functions are to break food into smaller particles. Um And this is conducted via acid and um Pepsin. Um So it essentially holds food temporarily um and releases it in a controlled state into the duodenum, having uh digested it a bit. Um And the stomach also secretes intrinsic factor which is needed for um B12 absorption. Um And the acid um kills parasites and different bacteria in the, in the, like in the um in the food uh that is passing through. Um And the, the different an anatomical regions have distinct um secretory profiles. So, the cardia and the pyloric region uh predominantly secrete mucus. Um And then you have the body um and the fundus here which secrete mucus and hydrochloric acid and pepsinogen, which is a pre precursor to Pepsin. Um And then you also have the Antrim which secretes gastri, I'll be talking a little bit more about all of these later. Um And then you also have invaginations into the mucosa with uh tubular glands. So, the way in which food actually travels down your gi tract is through peristalsis.