Where solutes go, water follows. And absorption of water in the process of digestion is no different. As nutrients and solutes are absorbed by the small intestine, water will actually be pulled in as well through osmosis. This is useful because it will actually reclaim water that was lost in saliva and mucus, as well as digestive juices. It also absorbs the water that came in with or from the digested materials. And of course, water can't move very easily through membranes, although it can get through membranes because it's small enough. It is assisted by these channels called aquaporins that allow for efficient passage of water. And you can see an example of an aquaporin right here, letting all these little water molecules pass through this membrane. So, we're basically at the end of our journey now. We've gone from the mouth, down the esophagus, into the stomach, through the small intestine, which involves going through the starting point, the duodenum, then through the jejunum and the ileum. Don't need to worry too much about the segments of the intestine. But finally, after the small intestine, we make it to the large intestine, which is this structure that kind of frames the small intestines. Right there, that is the large intestine. Now, it's actually shorter than the small intestine, which is why I think the naming convention is a little weird, but it's wider, which is where it gets its name from. And its main function is to absorb water. When you think large intestine, think water absorption. It also is there to help compact feces, which in part is due to absorbing water from them. So, the beginning of the large intestine is called the caecum. And it's kind of just like a little sac, you can see it right here, it's this little area of the large intestine. And in some animals, like herbivores, this structure is actually going to be specialized for cellulose digestion. So, you can see in the rabbit's digestive system here, right here is the end of the small intestine, beginning of the large intestine, so food, you know, move through the large intestine this way. And here is our cecum. See how big it is compared to this teeny little one in humans? That's because rabbits are herbivores, and the cecum is going to be a specialized structure that allows them to digest plant material better. Now, after the cecum comes the colon, and this is like the main section of the large intestine. This is the real show. And what's super cool about the colon is it's home to a microbiome of bacteria, and these are actually essential to your life. This is cutting edge research right now actually, and people are finding out more and more every day just how important these bacteria that live in your colon are. And of course, the colon is going to be this whole big portion here. And you can see that it has special names, you don't need to worry about knowing all the different parts of the colon, you just need to know that the colon is where, is the main portion of the large intestine, and it's where these, where these bacteria live. Now the last part of the intestine is the rectum. Let me jump out of the image here, so you can see behind me. We have the rectum. That is where feces are stored, for elimination, or as they wait for elimination, I should say. You know, it's not always a great time to have bowel movement, especially if you're an animal in the wild and you need to look over your shoulder and make sure nothing's going to eat you or something. So, you know, this is a useful structure to allow you to wait until the moment's right. Now, it should be noted that some organisms actually have what's called a cloaca. And this is a special orifice that excretes both urine and feces. And this is because urine will flow from their kidneys into their large intestines and then all that nice lovely stuff comes out the same end. So, yeah. Cloacas are pretty gross. That's, you know, going to be something that you find in birds and snakes and stuff, it's just it's icky. The last thing I want to talk about is the appendix. I was going on and on about how cool gut bacteria are. Well, the appendix is this little extension on the cecum, you can see it right here, this just this teeny little nub, and it basically houses useful gut bacteria. It's like a backup. It's a store of gut bacteria. So, for example, if you, you know, due to illness or something, lose a lot of the bacteria in your gut, the appendix can help replace them. It also contains some tissue related to immune function, but you don't really need to worry about knowing the details of that. Basically, just know that it's not the useless structure that people used to think it was, in fact, it's thought to be quite important for housing those gut bacteria, which again, you need to live. They're actually essential to your life. That's all I have for this video. I hope you guys like gut bacteria as much as me. I'll see you next time.
39. Digestive System
Digestion
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