 The esophagus is the tube that allows food to pass from the pharynx into the stomach. So the majority of the job of the esophagus is just to allow the passage of food, pass food to stomach. And that would be great. There is, at the superior end of the esophagus, there is a constriction of muscle, and it's called the superior esophageal esophageal sphincter. It's a constriction of skeletal muscle tissue. Now think about it, skeletal muscle tissue is under conscious control. So this is a sphincter that can be closed off when breathing. You actually close it off when you're breathing so that you don't send air down your esophagus. This happens if you do send air down your esophagus. This is another thing, digestive system. I've got a lot of skills when it comes to digestive system. I can gleek with the best of them, and I'm actually a pretty decent belcher. In fact, there's a new word for belch, eruptation. Did you know that? eruptation is the act of belching. And I mean that word, like, dude, that's not an anatomy word that we have to know. It's more of a physio word for a process that's really cool. The esophagus, if you get air in your esophagus, then you can go through the process of eruptation. You can eruptate, which is super exciting, and sometimes startlingly loud. That's when the air comes back out your esophagus. Now, if you have a superior esophageal sphincter made of skeletal muscle, what do you think you also have? You do. The esophagus leads to your stomach, and you actually do have an inferior esophageal sphincter, and that is made of smooth muscle. Why is that significant? Smooth muscle is involuntary muscle. That sphincter is not strong enough to keep your stomach contents waiting back up your esophagus, so there's help. Think about your anatomy. The esophagus passes through the thoracic cavity or the mediastinum, passes down the middle through the mediastinum, and then enters the abdominal cavity. And when it enters the abdominal cavity, like the stomach is in the abdominal cavity. So somehow it has to get from mediastinum into abdominal cavity, and it does that by passing through the diaphragm. The diaphragm is a skeletal muscle. So if I were to make the diaphragm, it's kind of a, I don't know, like a funny shaped muscle. It's kind of a rounded muscle. And we'll talk about the diaphragm more with the respiratory system because it's the muscle that contracts, it generates breath. So when you contract your diaphragm and shorten those fibers, it's a skeletal muscle, and that actually the contraction closes off your esophagus and prevents stuff from coming back up in normal, healthy conditions. The esophagus tube is stretchy so that you can take massive bites like, oh, half of an enchilada or an entire enchilada, and you can put the whole enchilada in your mouth and swallow it, and your esophagus can expand to accommodate that entire enchilada as it gets sent to your stomach. So it's stretchy, and it's the tube itself. We're going to talk about this more when we do digestive histology in the next lecture, but the tube itself is surrounded with muscle. On the superior end of the esophagus, that muscle is skeletal muscle. On the inferior end of the structure, the muscle is smooth muscle. So that's a really interesting characteristic, and we could look histologically at different sections of esophagus, and we should be able to tell the difference between the smooth muscle and the skeletal muscle. All right, so let's talk about our stomach because that's where we're headed next.