All right, so it's too bad that they ran out of coffee this morning, but I'm going to be talking a little bit about the basic anatomy and physiology of the esophagus and stomach. So how it's organized is we're just going to be working from the top down, I think. So I'll start. So the GI tract, it starts with the, really doesn't really start with the mouth. I tell all of our fellows that it starts after you swallow. So the GI tract really starts with the esophagus. So if something is stuck in the mouth, I tell the residents, call ENT. Don't call us. So the esophagus then turns into stomach, then stomach turns into small intestine, large intestine, then you poop whatever you ate out. On the side, there is the liver, the gallbladder, and pancreas, which are secreting digestive enzymes into the lumen of the digestive tract. So digestion refers to the breakdown of food that you eat into smaller components. That breaking down of the food allows the body to absorb the nutrients and the minerals in the food, and you need this to grow for metabolism, body maintenance, and reproduction. When we think of digestion, there's two components. There's mechanical digestion and chemical digestion. Mechanical includes mastication, which is chewing, peristalsis, which is the forward movement of things through the GI tract, and then segmentation. I'll go over what segmentation means. Mechanical digestion is basically breaking down the food. So part of that starts with the saliva that's in your mouth, gastric acid, pancreatic enzymes, and bile. So in terms of motility and digestion, motility refers to the movement of things through the GI tract. Peristalsis is, again, the forward movement of food through contractions, and segmentation is mixing of food. Here's a picture that kind of illustrates this. So again, peristalsis is moving down. Segmentation is moving things back and forth, so sort of mixing the food or the food bolus, usually in the intestines. So again, motility refers to the muscular movements of the GI tract. Peristalsis is forward. Oh, did I go? Okay. Segmentation, again, is mixing the food with simultaneous contractions. And then secretion is the release of acid or enzymes that mix with food and helps it to break down. Finally, once things are broken down, they can be absorbed in the small intestine into the blood. So we kind of already went through our journey of food through the GI tract. So again, GI tract digestion starts in the mouth with mastication. That's chewing food down, breaking it down. There is salivary amylase, which starts the breakdown of carbohydrates in the mouth. And then the tongue helps to move the food bolus towards the back of the mouth to allow for swallowing. Saliva is produced by the salivary glands in the mouth. It moistens the food to assist in swallowing. So patients who don't have saliva oftentimes or have enough saliva complain of dry mouth, difficulty swallowing. Salivary amylase initiates carbohydrate digestion. And saliva also contains some antibacterial properties. The esophagus is the hollow muscular tube that the food travels down after you swallow. It connects the mouth to the stomach. In adult, the esophagus is approximately 18 to 26 centimeters in length. So it can vary in length depending on how long your torso is and how tall you are. And it mostly just transports saliva and food liquids from the mouth to the stomach. There's different layers of the esophagus, starting from the inside. And this is kind of similar throughout the GI tract. But you start with the mucosa. It's the innermost layer of the lumen. Then there is the muscular mucosa. Beneath that is the submucosa. And then you encounter your circular muscle and your longitudinal muscle. The mucosa of the esophagus, you'll see a stratified squamous epithelium. So looking at this as an H&E stain, it's sort of a flatter layer, flatter type of cell. And this will be in contrast, as we'll see later on, to the cells of the stomach and the small intestine. In terms of the musculature of the esophagus, you have your inner circular layer, which contracts and moves the food and the fluid down the esophagus. And then you have your outer longitudinal muscle layer, which can shorten the esophagus. The first third of the esophagus is skeletal muscle. And this is considered, quote, unquote, voluntary. And the lower two thirds of the esophagus is smooth muscle. So that's more your involuntary muscle. The GE junction is what we use to describe where the stomach and the esophagus meet. So the Z line is specifically where you see endoscopically the change in that mucosa from your sort of paler esophageal mucosa to that more salmon-colored gastric mucosa. The GE junction is approximately where the diaphragmatic impression is. So the esophagus has to travel through the diaphragm. And so your GI tract then goes from your thoracic space to your abdominal cavity. If there is stomach above the diaphragm, that's when you have a hiatal hernia. The GE junction is also where your lower esophageal sphincter is located. Again, this is where the esophagus and the stomach meets. The lower esophageal sphincter should reflexively relax with swallows. And we'll talk about more in the pathology when that doesn't happen. It also contracts to prevent the backflow of stomach acid and food back into the esophagus from the stomach. So it has, just like any other muscle in the body, it has a resting tone. And so when that resting tone is very low, then you can have more reflux back into the esophagus. So this is a picture of the GE junction. And like I described earlier, you see that this is sort of the paler esophageal mucosa. And then this mucosa here, which is darker in color or more what we describe as a salmon-colored appearance, is the stomach mucosa. This is the stratified squamous epithelium. So these cells are sort of flatter in appearance. And then here you have your stomach. So these cells up here are sort of more of a rectangle in shape. The stomach is really a reservoir for food. It's sort of J-shaped. It mixes in acid with the food that you're eating to help to break it down. It also turns the food back and forth to mechanically make it smaller. And once the food is broken down into smaller particles, then it slowly releases that food into the small intestine. There's different parts of the stomach that have different functions. So you can see that the lower esophageal sphincter empties into the esophagus, empties into the stomach. You have your fundus at the very top. And the fundus is what accommodates the food. And so I'll show you in a later picture, there are a lot of folds in the stomach, which allow it to really expand. So the fundus plays a big role in accommodating the food that you're eating. Then you have the body of the esophagus, which makes up the majority of the esophagus. You have the cardia, which is immediately proximal to the lower esophageal sphincter. The body has a lesser curvature and a greater curvature. Here's where we describe as the incisor. It's a common place for ulcers to develop. The antrum is the sort of more distal aspect of the stomach before you reach the pylorus, which is another sphincter muscle, which helps to release food particles from the stomach into the small intestine. Really it's the body that does the majority of the churning of the food, and the antrum is propelling that food towards the pylorus. So the stomach mucosa, again, has a lot of folds, which really help it to expand. The stomach also has a few layers of muscle, which I think is sort of in the next slide. There's different layers of the stomach, again, kind of similar to the esophagus. You have your mucosa and your muscularis mucosa, then your submucosa, your muscularis propria, and then your serosa. There's different cells within the stomach, too, that have different functions. So the parietal cell, as we'll go over, I think in a slide later, is the cell that is responsible primarily for the secretion of stomach acid. Endoscopic ultrasound, which Sushant and Tiffany know much more about than I do, allows you to look at the different layers of the esophagus as well as other areas of the GI tract intraluminally through an ultrasound. So through an endoscopic ultrasound, you can also appreciate the mucosa, muscularis submucosa, the muscularis propria, and the serosa. The stomach epithelium, as opposed to the esophageal epithelium, is columnar. So you can kind of appreciate the difference in how the stomach mucosa looks as opposed to when we looked at the esophageal epithelium. And there's three muscle layers of the stomach, starting from the inside. You have your oblique layer, your circular layer, and your longitudinal layer. So the stomach is pretty thick. And when it comes to doing interventions on the stomach, the stomach wall can tolerate a lot more because it's so thick. So if we have to burn, we can burn more. We don't worry as much, typically, about perforating the stomach as we do other parts of the GI tract that are thinner. So stomach acid physiology, the stomach really secretes a lot of gastric acid. And that gastric acid is secreted by a cell called the parietal cell. So things that stimulate the parietal cell to secrete stomach acid would be histamine. So histamine is released by the enterochromaffin-like cells, these ECL cells. And when the ECL cells release the histamine, the parietal cell produces more stomach acid. That stomach acid, though, negatively inhibits the G cell. So the G cell is one of the cells in the stomach that secretes gastrin. Gastrin stimulates the ECL cells to secrete histamine. And so if there's a lot of acid already, then the G cells are then not stimulated to secrete gastrin. And so if there's already enough stomach acid, then that is what enables your stomach to not keep producing stomach acid. Any questions? That was short.

esophagus

stomach

digestion

gastroesophageal junction

gastric acid