Mouth and Esophagus

by Jason Amores Sumpter
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in humans and other mammals, digestion isn't sequestered to one single organ. It actually occurs in multiple organs as the food moves through the body. And as we'll see, uh, certain organs air specialized for certain types of digestion. Now, the first place where digestion begins is actually in the mouth itself. The food there is gonna be mechanically digested and subdivided. And this serves the benefit of actually increasing the surface area of food particles, which is going to be really useful later on when we get thio, uh, chemical digestion because this increased surface area is going to help increase the efficiency of the chemical breakdown. Now, there actually is some chemical digestion going on here. You see, salivary glands release, uh, substance. Of course, saliva and saliva is a mixture of water, mucus and enzymes. It actually contains something called salivary amylase, and am Alice breaks down carbohydrates, and this salivary amylase is going to break down carbohydrates into maltose and what are called Dextre ins. Now, mall toes is basically to glucose subunits. You can see in maltose right here behind my head. A single one of these is glucose. Now behind me, let me jump out of the way here. This is what you could think of as a Dextre. Now, it wouldn't be quite as long. This is basically saying, you know, that you just are repeating this unit some number of times. Now, you know it's not gonna be the, you know, hundreds long it Z. It shows in this figure a deck. Strine is going to be like a couple units of glucose linked together. So the idea is that salivary amylase breaks down carbohydrates into small units, but not into glucose itself. That's the point to take away now, Mucus. Speaking of glucose and all that good stuff, mucus is actually made from glycoprotein that form a slimy substance when they mix with water. And, of course, there's water in saliva. So you get that nice, slimy mucus and this is gonna be good because it lubricates the food bullets. And the Boulis is basically what, uh, you know, that ball of chewed up food that you swallow is referred to in a technical sense. Now, salivary amylase isn't the only ends. I'm there, actually also gonna have lingual light base, which is basically, uh, a enzyme that's gonna break down fats, right light base light like lipid ace. So this is gonna break down Fats and it's released along with the saliva, but it's actually coming from glands in the tongue, as opposed to these salivary glands that you see here. So these air salivary glands and the, uh, lingual light base is going to be coming from a gland in the tongue. You don't need to worry about the details of that. Here you can see a nice overview of the mouth, and once that food is chewed up or you know that Boulis as we should probably call it, be technical about it. What's that? Boulis is ready to be swallowed. It's going to move through the pharynx to the esophagus. The pharynx is back here. It's kind of like the throat region or, you know, the back of the mouth region, and it's going to connect to the esophagus, which is an organ that connects theme mouth to the stomach. You can see here that's going to lead to the stomach, and you should note that there's actually another opening in here. The opening the larynx, which will, uh, it's commonly called the wind pipe that's going to lead to the lungs. That's where air goes. So these guys actually share a new area together, which is you know why? If you've ever eaten or drank anything for long enough, is a human. I'm sure you've had some water or food, very unpleasantly go down your windpipe. That's why, because they are right there next to each other. Now, once the bullets is in the esophagus, it needs to be moved to the stomach. In part, gravity is gonna help with this, but the esophagus is lined with smooth muscle that's going thio go through these rhythmic motions known as Paris Tulsa's. This is basically a wave like contraction in smooth muscle that has the effect of pushing the food Bullis down through the esophagus. So, uh, it's it's, you know, a little hard to visualize and a static image. But essentially, uh, this right here. These are these smooth muscle contractions that air in a wavelike motion, going to travel down the esophagus and cause that food bullets to move towards the stomach. Now, birds, actually, or some birds, I should say, have an interesting modification to the esophagus known as a crop. And this is you can see this right here. It's this kind of like big, chunky ball that's attached to the esophagus, which is this tube here leading from the mouth. In case you're curious, there's other To be soothing from the mouth is actually the wind pipe right there. So anyways, their esophagus has this big, chunky area on it, and it is known as a crop, and it is modified for food storage. This is, you know how all those birds will go, eat a bunch of food. And then they were regurgitated Thio. They're young, they're actually storing it in their crop, and that is again just part of the esophagus that's been modified by evolution, but that let's turn the page.