Digestion and Digestive Tracts

by Jason Amores Sumpter
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animals ingest their food through their mouths. Now, hopefully it will come as no surprise that something is essential as ingestion of food will be affected in a very significant way by natural selection. So that is why there is a wide variety of forms and functions in, uh, in terms of mouth parts you can see here, this is the skull of a deer, and they have these nice grinding teeth which are useful when your inner before and you need to grind up plant matter. Where is this saber tooth cat here Not going to be doing a lot of eating of plants. And hopefully you can tell what these bad boys air for. And of course, Darwin's moth, which has a very specialized feeding tube for a very special flower that has a very deep neck tary that Onley it can reach now. Because natural selection has such a powerful effect on mouth parts, you'll often see some interesting examples of adaptive radiation with mouth parts. Adaptive radiation, remember, is when a new organism diversifies and gives rise to a bunch of different variations. Um, due to trying to fill different niches. A great example of this is the finches that Darwin saw on the Galapagos, which all had these different types of beaks, depending on their food source. They all came from this one common finch ancestor, but on the islands, due to all the niches to fill their mouth, parts evolved. Thio have the form fit the function now nutrients. They're going to be absorbed in a four step process. The first step is ingestion bringing food into the body specifically into the digestive tract. Then you have digestion, which is the breakdown of the food through both chemical and mechanical or physical means, like chewing, right, grinding your mechanically digesting the material. And it should be noted that humans perform what's called extra cellular digestion, as do lots of other animals. However, some organisms will perform intracellular digestion where they actually bring the material into their cells to be digested. Whereas we do it in the Lumen or the, uh, you know, hollow space inside of our digestive organs, which, of course, is outside of the cells. Now. You also need to do something with the nutrients you extract from digestion, and that is absorption where you absorb them into the body to you make use of them. Lastly, you're not going to use everything you take in. There's gonna be some waste, so you have to eliminate it. Eliminate that undigested material in some manner that we need not discuss here. Now there are going to basically be digestive tracts that fall into two categories. Incomplete digestive tracts where there's a single opening that food enters and waste exits. And this a nice example of this is the gastro vascular cavity of Nigeria and platinum mentees, which you can see two night area. Here we have, ah, hydra and some type of Medusa jellyfish like Creature, and they just have this one. I'm just gonna write GVC for gastro vascular cavity. So basically food is going to go in there. It's going to get digested. That's that's what's happening. This food's getting digested, and then it's gonna exit through the same opening. We, on the other hand, have what we commonly call an elementary canal but is technically referred to as a complete digestive tract. That is to say that it has two openings. Are food enters through the mouth, works its way through this digestive system, which we're going to go through momentarily, so it's going to make its way through the esophagus here, into the stomach, right here from the stomach. It enters the small intestine, wiggles all its way through the long, small intestine until it hits this area, the large intestine where it finally is formed into feces and will exit through the anise. So that is the whole of the process of digestion through a complete digestive tract. Let's actually flip the page and take a closer look at this whole organ system.