39. Digestive System
Digestion
1
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Food and Feeding
8m
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hi in this video will be talking about digestion and the digestive system, the organ system responsible for bringing in food, extracting nutrients from it and getting rid of the waste. Now food is any substance that has nutrients needed by an organism. Toe live. We consider food to be things like pasta, which is chock full of carbohydrates, meat, which has proteins or fats, which can be found in things like dairy products. Now those air all well and good. However, we also need what are known as essential nutrients these air nutrients that we can't synthesize and have to be obtained in the diet. So while we can, for example, make a bunch of amino acids, we can't make all 20 that are used to build proteins. In fact, they're actually eight amino acids that we can't synthesize, and we call these essential amino acids. And in case you're curious and don't worry about memorizing this, these include is a losing, losing licensing Mutthiah Ning phenylalanine three inning veiling and trip to fan and methane in is actually fairly significant and significant in there, since that is going to be the amino acid coded for by the start code on now. It should also be noted in, you know, in case you're curious about these things that infants actually also can't produce history ing this, uh, can lead thio certain infantile diseases that you know, maybe you'll learn about if you go to medical school or something. No vitamins. Our organic compounds that are required in small amounts and are used for a variety of different things, including as co enzymes, which are going to be important parts of enzymes in fact, usually the essential part to carry out whatever reaction it's responsible for. We also need minerals which are inorganic substances required again in just small amounts. Um, however, they're going to be incorporated into proteins, and, uh, you know, the active sites of enzymes, for example, where the reactions take place. And they also can be important components in hormones. Now, minerals also include what we refer to as electrolytes that are gonna be, uh, mineral ions that are super important for maintaining osmotic balance in the body. Because, remember, water follow salutes, and these will also be super important for nerve signals. And, uh, we'll learn more about that in the A section on the nervous system. However, just know that the electrical signals sent through nerves are actually being conducted by the movement of these electrolytes or ions. Lastly, there is also essential fatty acids, and it should be noted that most animals can produce, you know, all the fatty acids that they need. However, there are certain double bonds that we azi humans can't produce. And those are commonly referred thio as omega three and omega six fatty acids. Due to the double bond at the Omega three position and Omega six position. This just has to do with the chemical naming. Um, so, you know, don't worry about trying to memorize any of this. It's just a convention in terms of counting the carbon tale from the end, as opposed thio the beginning. Anyways, omega threes are found in, uh, you know, things like tree nuts. For example. These air often thought of his plant fats. Omega six is are commonly referred to as animal fats, and interestingly, it's been theorized that, uh, issues with obesity can actually be in part due to the ratio of Omega three and Omega six is you have in your diet, and Americans tend to have too many Omega six is not enough. Omega threes or balance is a little out of whack. And, um, you know, you know, America suffers from obesity quite a bit now, if I jump out of the way here, I also want to point out how these vitamins can be used. This is a vitamin called riboflavin because it's got all the flavor, and riboflavin is an essential component of F A D. Yeah, which you can hopefully see. Rival Flavin's structure in this portion of the molecule F A. D is, of course, the essential electron carrier that plays a critical role in the electron transport chain and, of course, cellular respiration production of a teepee. So these essential nutrients are truly essential. We need them to build components that aren't just there for, you know, ah, little added advantage. These build components that are essential to living organisms. Now there's different techniques when it comes to obtaining food. Uh, you know, I've always admired, uh, whales that have this stuff called baleen, which you can see here. It almost looks like a comb. It's these, like bristled, uh, bristled structures that surround their jaws, and you can actually see the baleen in a whale's mouth right there. That's a sperm whale, And what it's doing is it's basically, uh, you know, taking a big bite of ocean water rich in these tiny little organisms called krill. And then it's going to filter those krill through its baleen and basically strain it's food out of the water. This tactic is known as suspension feeding. Technically, it's a type of filter feeding, which is like a filter. Feeding is like a type of suspension feeding. And, um, you know, this is just one of the many ways that organisms can obtain their food. There's also deposit feeding where, for example, a sea cucumber will kind of eat the e. I mean, it's kind of yucky, but the sediment deposited material around it. There is substrate feeding, which is basically when an organism lives on its food source, kind of like a caterpillar on leaf. There's also fluid feeding like insects, sucking your blood or, in a way, less creepy and gross. Example. A nice little hummingbird that eats nectar. Right now we have the dubious title of being mass feeders. Sometimes this is called bulk feeding, and basically we eat large chunks of food, sometimes whole organisms. Basically, we eat big pieces of other things bodies, and that is considered like a mass, and we feed on it. And it's kind of why I like to think of animals is a very crude form of life. You know, we have to just take in this matter from the outside like stick it in our bodies and then process it and waste all this stuff that just comes out of us anyways. And you know, when you compare that to, for example, a plant which you know, absorb sunlight produces its own sugars, much more eloquent way of living. Anyways, that's just my little two cents on that. Let's flip the page.
2
concept
Digestion and Digestive Tracts
5m
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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.
3
concept
Mouth and Esophagus
6m
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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.
4
concept
Stomach
10m
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the stomach is a muscular organ where digestion really starts to get serious. And that's because the stomach actually creates this acidic environment that is ripe for protein digestion. Now, before entering the thesis, um, ACC from the esophagus, the bullets has to move through a sphincter, which is a circular muscle with a hilarious name that maintains the constriction of an orifice. Basically, it's like the gatekeeper for a particular orifice. Now there are two sphincters in the stomach worth noting, and you don't need to worry about memorizing the names. I'm just telling you. So you know you have the cardiac sphincter, which is going to be the sphincter that leads from the esophagus into the stomach. And then the pile oryx sphincter. So this is cardiac. This one is Hi Lorik, and the pile or ex victor leads to the intestine. Now the stomach is full of gastric juice. This is digestive fluids that are secreted by the stomach. And when the food mixes with the gastric juice, it is no longer considered the Bullis. It is now considered Kym, which is Ah, just lovely sounding name for something that I'm sure looks and smells fabulous. No there are some interesting specialized cells in the stomach that perform the important functions needed for digestion. First cell I want to talk about is parietal cell. This is going to be the type of cell that not only secretes but makes hydrochloric acid in this hydrochloric acid is going to help break down food. Uh, in part, it's going to help de nature proteins. If you recall proteins are very sensitive to pH changes. A lot of them are sensitive to acidic environment. So by creating an acidic environment, it's going to help denatured proteins, making them easier. Thio chemically grade, Which is gonna be the job of this enzyme that will talk about momentarily called Pepsi in. And the hydrochloric acid produced by these parietal cells actually activates Peps in. It's stored in an inactive form called Pep Synergen. Again, we'll get to that just a second. This hydrochloric acid is also going to help kill pathogens. Yeah, I mean, you know, you often will be eating bacteria that's on the food you're eating or, you know, like other harmful things. This is civic environment can help kill some of those before they can really cause problems for your body now it should be noted there's a hormone called gastric that's actually secreted in response to food entering the stomach. And this has the effect of causing the parietal cells to increase hydrochloric acid production. And it is production because, as I'm sure you can imagine, hydrochloric acid is not something that you could just store right. It's It's a very powerful acid. You don't want that just sitting around so these parietal cells don't actually store it. They produce it, and you don't need to worry about the specifics of how they produce it. As you can see it, it involves a variety of pumps and channels and exchangers. You know, just very quickly we have this pump here. It's an at pus, meaning it burns ATP to pump thio pump particles, and it's going to bring in a potassium and pump out a proton. And you have this exchanger here that's going thio. Get rid of a bicarbonate and bring in a chloride ion, and then the chloride ion is going to be also moved into the stomach. Lumen, along with your proton and guess what? Proton plus chloride ion. That's hydrochloric acid right there. So don't worry about the specifics there. Just know that these parietal cells, uh, you know, use a chemical process to make this substance on the fly, because again, can't really be store in acid in your body. A little dangerous. Now there's also chief cells. Didn't mean to give parietal cells all the attention. Chief cells are, you know, equally, if not more important, because they secrete Pepsi. Neogen, which is again an inactive form of unending Sime called Pepsi in this inactive form, is actually a special type of enzyme Caldas, Imogen, which again it's a type of enzyme that's gonna be stored in an inactive form. And usually it's because it's safer to store when it's inactive. See, the thing is, pep sin is a Proteus, so it's going to degrade proteins you can't really be storing. Proteus is around yourselves because they're going to degrade all the protein products you make. I mean, cells make proteins for everything. Thes Prodi. Aces are just one of the things they make. And a lot of the proteins they make are essential to their life. So, yeah, Proteus is floating around. They're just gonna be gumming up your day. They're gonna be totally ruining everything you make ruining all your hard work so they have to be stored as imagines we call those Imogen Pep Synergen. And at low ph Pep Synergen actually converts itself into pep sins called on auto catalytic process. Again, don't worry about memorizing all these details. Just know that Pepsi has kept in inactive form, which we call Pepsi neogen, and at low pH, which is provided by this nice hydrochloric acid. It will turn into peps in and start breaking down proteins into smaller poly peptides, and you can see a nice little model of that, their parietal cell and chief cell working together. It's a it's a match made in heaven. Lastly, I want to mention the mucus cells, which secrete mucus to lubricate and protect the stomach from all that nasty acid. I mean, the tissues of the stomach need protection from the harsh stuff that's in the stomach, and the mucus cells provide that. So don't forget, this stomach is a very muscular organ. In addition, Thio secrete ing this hydrochloric acid and the Proteus Peps in its muscular. It's going thio, you know, physically move and churn the Keim in there to help with digestion Now, just like birds had a crop. That or some birds have a crop that modified esophagus. Some birds have a modified stomach called a gizzard. And basically, if you think about it, birds have beaks, so they're not gonna be very good at chewing. And that could be a problem when you want to break down your food so that it's easier to chemically digest, right? We have thanks teeth and mouths to do that. Birds don't have that option, which is why have a gizzard and a gizzard is basically a special stomach that is going to contain stones and sand and grit like, you know, uh, harsh, abrasive materials in there, and it's going to help grind up their food. Right? The stomach again, some muscular Oregon. If you have all this grit and stones and sand in there and the stomachs churning, all that stuff is gonna physically grind the food that as a bird, you know, you swallowed in a big chunk because you couldn't chew it, and it should be noted just because I think it's kind of funny that the way the stones and sand and stuff gets in there is the birds actually swallow them. So just if you ever in a bad mood picturing picture birds swallowing stones and hopefully that'll cheer you up. Now, one other really cool evolutionary, uh, modification made to the stomach is found in class of mammals called ruminants. Ruminants have a special four chambered stomach. One of the chambers is called the Rumen, hence the name. Basically, this four chambered stomach is specialized for digesting plant matter, and part of that actually involves fermenting it. So basically, when food enters through the esophagus, let me jump out of the way here. When food enters through the esophagus, it's going to come into the room in which is the largest chamber and contains bacteria. And protests that produce cellulitis might recall that plant matter could be particularly hard for animals to break down because of the plant cell walls that contain cellulose, well, cellular laces, an enzyme that could break down cellulose. And even though we don't produce it, bacteria and Protess can. So if we keep those dudes in our stomachs or if you're ruminant, if you keep them in your room in, then they'll give you the assist. Still, help you break down that plant matter Now. It should be noted that ruminants will actually often regurgitate what's called the cut. Basically, that chewed up kind of die partially digested plant matter. It's pretty yucky. If you think about it too much, just just don't think about it. Don't think about it. They're going to regurgitate that cut and reach you. It thio grind it down even more to ensure that they can extract as much. Nutrition is possible. Plant matter. It's very hard to get the nutrition out of it, So this is their way of just like really ensuring they're getting all the nutrition they can for the effort they put in into digesting it. With that, let's flip the page.
5
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Small Intestine and Pancreas
6m
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after the stomach, the food or as we should call it now the Kym will enter the small intestine through the pile oryx sphincter, the small intestines long tube in which digestion is going to occur. And also this is very important absorption. This is where you get to finally get the payoff for this and absorb those nutrients and the small intestine are actually are. The small intestine is actually going to be assisted by the pancreas and liver. Who are going to provide some nice secretions that will help with the digestive process. Now, small intestine is often a often leads to some misconceptions because it's actually longer than large intestine. It just has a smaller diameter, and in fact it's really long. It's like 6 m long, which, you know if you think that a meter is like approximately, like a little more than 3 ft, you know, talking about 20 you know, roughly 20 ft here. Obviously, humans aren't 20 ft long, and that's because our small intestine are all wrapped up. Thio minimize the amount of space they take up, but because they're super long, they have a lot of surface area on the surface area is actually even longer. Uh, due to some cool modifications that the small intestine has now first, if we look at the small intestine here, you can see that the tissue on the inside of the intestine has these folds in it, right? That's what these little lines are. Basically, the tissue itself is, you know, uh, made to fold to increase the amount of surface area on the inside of the small intestine. Now, this fold, if you zoom in, is actually covered in what are called Vialli. So basically, this fold has all these little projections on it. Thies, Vialli and these V Liar and turned in turn covered in what are called Micro Valli. So the veal I are gonna the cells of the veal. I rather the terror sites have these little hair like structures on their tips called Micro Vialli. This is going thio result in a crazy amount of surface area. Right? We have the tissue itself folded, those folds air covered in Vialli and those Vialli are covered in microbes. Eli. So we are maximizing surface area here now. Veal. I actually a surround blood vessels. As you can see in this image here, and they also have what's called a lacked hell in them And this structure here. Okay, it's lacked hell, and basically, it's a lymphatic vessel. The lymphatic system is going to be a system involved in both circulation and immune functions, and we'll talk about it at a different time. Just know that it has, uh, projections into these ville I, as do blood vessels. Now, the do wadding, um, is what we call the start of the small intestine. That's where the Kym is gonna enter, and the duodenum secretes hormones in response to the time. Uh, two of these hormones are SEC written, which is a hormone that's going to stimulate bicarbonate release from the pancreas. And that's super important. Because, remember, the kym is filled with acid, and you don't want all that acid sitting in your poor small intestine. So they're going to ask for some bicarbonate from the pancreas to help neutralize the acid. The other hormone is, ah, Cola Cola site or Kainan. It's a mouthful. CCK. That's that's what they call it in med school and stuff that's whatever it calls. It's a lot easier. So si ck is going to be the hormone that stimulates the pancreas to secrete digestive enzymes. See, not only does the pancreas provide nice bicarbonate solution for the time Thio cool off, so to speak, it's also going to secrete a bunch of enzymes that digest the food, uh, coming from the stomach. Now, these include things like nuclear bases, which breakdown nucleic acids. Uh, pancreatic amylase, which, similar to salivary amylase, is going to break down carbohydrates into maltose indexed Reines, as well as pancreatic light paces that break. Try celeb Lyssarides into two fatty acids and a mono a soulless a ride. Now, pancreas will also secrete Prodi aces and two of the important ones to take note of our trips in and Kimo trips in. And these air Proteus, is that break down proteins into smaller poly peptides. It should be noted that they actually will Onley break specific poly peptide bonds. That is Polly Pep. Uh, that is peptide bonds between specific types of amino acids. So just like other enzymes, they are very specific as to what they will act on. What's cool about these is there actually also Zim Mogens like Pep Synergen. So they're released his trip Synergen and Kima trips engine. And this enzyme called in Terra Cockiness, which is produced by the small intestine, is what will activate trip Synergen. And that leads to the activation of other Prodi aces, which will help break down those poly peptides. Now with that, let's flip the page.
6
concept
Nutrient Absorption
19m
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Hello, everyone. In this lesson, we're going to be talking about the functions of the small intestine and how nutrients like fats and sugars are going to be absorbed through the small intestine. Okay, so in the digestive system, the absorption of the nutrients that comes from your food is going to happen in the small intestine. The small intestines main job is to absorb all of the energy and nutrients from the food that you eat. And absorption is going to happen through the epithelium cells that line the small intestine. Now, these air very selective cells there on Lee going toe, let through certain substances and each substance, like sugar or fats or proteins, are going to have their own unique method of getting into these cells. They may have a specific cell receptor. They may have a way that a vesicles enters the cell. They're gonna have unique forms of transport into these epithelial cells. But just know that these epithelial cells in the small intestine absorb very specific nutrients molecules, and they're going to require specific transport proteins to do these particular processes. Now, whenever we talk about the movement of nutrients into the cells from the small intestine, It's actually going to require energy. Now remember, there are two different types of active transport or transport that requires energy. One is gonna be primary active transport where you utilize a teepee, and the second one is going to be secondary active transport where you're going to utilize potential energy of a molecule. Now they're both of these types of active transport are going to be used in the cells, and I'll show you a more specific example of both of these types of transport. But just know the transport is active and it does require an energy source of some type because you're generally going to be moving these substances against their concentration. Grady int. Okay, Now, once all of these nutrients have been absorbed into the cells, these cells are generally going to give this nutrients to the bloodstream and the blood vessels from the micro ville I or the ville I that line the inside of the intestine cells are going to converge at the hepatic portal now the hepatic portal vein or hepatic portal system. So a portal system is basically just a system of blood vessels and the hepatic portal vein is going to be a portal system or a blood vessel system that is going to specifically take things to the liver. And the way that I knew this is because the prefix have pat H e p A t is actually Greek for liver. So if you ever see that prefix, you know, we're talking about the liver and you guys can see that right here. The hepatic portal system is going to be the system that leads these blood vessels to the liver. So this is going to transport nutrients directly to the liver. Now you got to think about why would we want nutrients to go to the liver? Well, generally, remember the functions of the liver. It is going to be able to detoxify any toxic substances that we may consume into our bodies, and it also stores a lot of things. It can store glucose. Remember, it stores glucose in the form of glycogen. It can also store iron, it can store copper, and it also stores a lot of vitamins. So the liver is going to be the first stop that these nutrients get Thio because it stores a lot of this stuff. It's going to store glucose, our main energy molecule in the form of glycogen. And it also destroys toxins. Remember that our liver is our main detoxify air. So if we eat anything that might be toxic, it's going to go straight to the liver, and the liver is going to do its best to destroy those toxins. So generally the things that we absorb in our small intestine are going to enter the blood vessels. They're going to travel through the hepatic portal vein right to the liver so the liver can either detoxify whatever we've eaten, store some of it or send it on its way. Okay. All right, So now let's look at how these epithelial cells actually work. So we're going to go down a little bit and we're going to look at these cells. We're going to talk about how these epithelial cells in the small intestine actually do absorb glucose, because glucose is what we're really interested in interested in because this is gonna be the molecule that we use for cellular respiration, the main molecule. So glucose utilizes something interesting. It utilizes secondary active transport to cross those epithelial cells, and it's going to do this in a very unique way. The way it's able to do this is because of the functions of the sodium, potassium, 80 p ace or as more commonly referred to as the sodium potassium pump. Now, generally, when you think of the sodium potassium pump, you're thinking of neurons because it's utilized to create that membrane potential in neurons. But the sodium potassium pump has another function as well. Now the sodium potassium pump is used in these epithelial cells to create these concentration Grady INTs. So let's have a look at these cells right here. So these cells are going to be our epithelial cells, and that's going to be kind of like a chunk here. Let's say that we took this chunk off these epithelial cells inside of the small intestine and we expanded it so we could see these cells. That's basically what we're looking at Now. Remember, whenever we are talking about these epithelial cells in the small intestine, they're gonna be very specialized cells, and they're going to have two different sides. And these two different sides are going to be called the a pickle side, which is this side with the little tiny micro villa right here. This is the a pickle side. And this is the side that is going to face the Lumen off the small intestine. That means the inside of the small intestine. So basically, the a pickle side is looking into your small intestine, and then we're going to have the bezel lateral side. So bas oh, lateral side of these cells is this side, and this side is going to face the extra cellular matrix and it's going to face your blood vessels. So this is where this is the side that the nutrients is going to exit whenever it's trying to go to those blood vessels. So we're gonna have these two sides of these epithelial cells, and they're going to have tight junctions right here that actually make it so none of the juices inside of your small intestine actually leak into your body. Thank goodness. And they have these two different sides of these cells because of these two different sides air specialized in the proteins that they have in their cell membrane. So on the a pickle side, we're going to have the glucose transporter and on the bezel lateral side, we're going to have the sodium potassium pump. So, in fact, whenever we're looking at this blue structure right here, this is the sodium potassium pump, thes blue proteins that you guys see right here are the sodium potassium pumps. So what did the sodium potassium pumps do remember? They're going to be pumping sodium out of the cell. They're gonna be pushing sodium out of the cell, and they're going to be pushing potassium into the cell. So what that means for our cells is we're going to have high potassium concentrations and low sodium concentrations inside of this self. Now, whenever we're talking about the a pickle side, we're going tohave this protein, which is going to be a sodium glucose co transporter. So these red proteins are the sodium glucose co transporter. The reason there are co transporter is because both the sodium and the glucose are going in the same direction they're moving together. The sodium potassium pump, on the other hand, is an anti porter. They're going in opposite directions. Now the sodium glucose co transporter is going to move sodium and glucose into the cell at the same time. Now, how does this work? Well because there's such a low concentration off sodium inside of these epithelial cells, the sodium is moving with its concentration Grady int, but the glucose is going to be moving against its concentration ingredient. So basically, this is called secondary secondary Active transport, because this type of active transport is utilizing the potential energy of the sodium to move the glucose. The sodium wants to move into the cell because it's moving down its concentration ingredient, and when it does, it drags the glucose with it. So glucose uses sodium energy via its concentration. Grady into pull itself into the cell, and then you are going to have glucose and sodium inside of the cell. Now and then, the sodium potassium pump is going toe. Actively pump that sodium back out of the cell. So now you have actively absorbed glucose into these epithelial cells. Now, something else to note that is not drawn here is we're going to have these other proteins, which I'm going to draw in green right here. This protein is going to actively transport glucose out of this, so so we're going to have glucose exit the cell, and it's going to exit the cell via a glucose transporter. Sometimes these air just abbreviated glute G l u t. But these air glucose transporters, which are going to transport glucose into the bloodstream and out of these epithelial cell So then glucose will enter the bloodstream right here. Now, this would be an example of a glucose transporter. Now, the glucose transporter isn't really going to require any energy because there's a very high concentration of glucose inside of these epithelial cells that glucose is going to use the transporter to just go down its concentration Grady int and exit these epithelial cells into the blood. But it can't simply diffuse through the membrane. So it's gonna have to use these glucose transporters that you guys can see over here. So it's going to need its own protein on the basil lateral side off these particular cells to actually exit the epithelial cells. So that's the basis of how absorption of nutrients works. This was specifically for glucose, but just you guys know most of the nutrients that you absorb is kind of gonna happen this way. We'll talk about Fats in just a second because they're gonna have a special form of absorption. But most substances are going to be absorbed the way that glucose is going to be absorbed. So just to recap glucose, you utilize the secondary active transport because it utilizes the potential energy of the sodium ions to enter the cell. And the potential energy of the sodium ions is built via the sodium potassium pump concentration Grady Int that it makes because it's transporting sodium out of the cell, establishing a sodium Grady int. And then the sodium glucose co. Transporter is going to utilize that potential energy. And then glucose is carried over the basil lateral membrane through a glucose transporter via facilitated diffusion, which doesn't require any energy. Okay, guys. All right, So now let's talk about how fats are going to be absorbed and broken down inside of our bodies, because that is a little bit different because fats are going to be nutrients that we need. But they're very special nutrients because they're going to be nutrients that are hydrophobic. They're going to be broken down and absorbed a bit differently. Okay, so fats are going to be broken down by this very important substance called vile. It sounds really gross, but it's very, very important bile is going to be a substance that is basically going to break down these fats, these hydrophobic molecules, by increasing their surface area and pulling them apart. So bio and lip basis, which you're going to be the special proteins, are going to break down these fat molecules and then these fat molecules can be absorbed by the entero sites. Now, in tarot sites is just another way to say epithelial cells in the small intestine, they're the same thing. So fats are gonna be broken down into these smaller components by vile and lip light bases, and they're gonna be broken down into these smaller components or smaller pieces called my cells. So this is a my cell right here and basically a myself is how these hydrophobic fats hydrophobic lipid molecules are going to form this structure to decrease the amount of surface area that they have interacting with hydro filic, um, the Hydra Filic interior of our cells. So we're going to break these fats up into all these tiny pieces called my cells, and then our epithelial cells can actually absorb those my cells. Now what's the point of bio? What does it actually dio. Well, the cool thing to know about bile is is going to increase the surface area of fat. And this is also called em uls ification. So it's going to increase the surface area of these fats, these lipids, and then it just makes it easier for light paces or these proteins that break down lipids to break them apart. It just makes it easier. So bile kind of takes these fats and stretches them apart. And then the light bases come in and they break the fats apart. Now, whenever a fatty food enters your small intestine, your body needs to understand that it's gonna have to start breaking down this food a little bit differently than it does with glucose. So we're gonna have these special hormones. So you're going to have your small intestine and say, Hey, there are fats in here. We need our bile in our life bases. So we need to make this signal, and it's going to be the CCK signal. And this is gonna be a hormone that stimulates bile production in the liver. And a good example of that is actually down here. So let me go out of the picture so you guys can actually see it. So this is gonna be the diagram of your digestive anatomy. And right here in orange, we're going tohave the small intestine. And once the fats enter the small intestine, thesis E. C K hormone is going to be released from the small intestine, and it's going to travel to deliver, which actually generates and creates bile. And it's going to travel to the pancreas, which can actually start breaking down sugars because it creates insulin and it's going to travel to the gall bladder, which you guys can see is this little structure right here. And the gall bladder actually stores bio for the release into the small intestine. So the CCK hormone is going to stimulate the release and the production of Bio. Now Remember, Like I said, bile is going to be produced in the liver, and it's stored in the gall bladder so you guys can actually see these bile ducks right here in green through the liver. You guys can see it's being made in the liver, and it's actually going to be stored right here in the gall bladder. Now some people will have issues with their gall bladder and your gall bladder can be removed. It is not necessary for you to actually create bile. It's just important to know that with people who have their gall bladder removed, they can't store bile. So they have to not eat as many fatty foods at one time because they won't be able to digest it. So you just have to change your diet a little bit. But people without a gall bladder still function just fine. They just can't eat as many fatty foods because they don't have any bile stored up to actually break down those fats. Now, bile salts are going to be an important component of bile. I just want you guys to know that these are going to be molecules that air and fifth AMFA path IQ. That's always hard for me to say, meaning they're both hydrophobic and hydro Filic basically just know that they helped bile do its job. I m uls if eyeing those fats. So then once the factory most ified broken down, how are they going to enter those cells? This epithelial cells where they're going to enter in this form called these kylo microns, these are going to be a special way that we package fats for transport through the body. And these kylo microns are going to be these lipoprotein associated complexes. So this is a kylo did not spell that right? This is a Kyle omicron right here, which you guys can see right here. And it is going to have lipids right here, and it is going to have proteins. And this is basically just a shipping container for these digested fats. So the digested fats are going to be in here. So those are the digestive fats, and they're going to be stored in these Kyle omicron kind of packages, and this allows them to be transported around the body. So they're going to be transported into the lack. Thiel, just you guys know a lack teal is going to be a vessel, a lymphatic vessel and the lymphatic vessels just simply leads to the blood. So to transport fats, which are very hydrophobic molecules in the hydra Filic blood, we're going to need to actually package them in these kylo microns, or they won't be able to transport in the Hydra Filic blood. So we package them this way and then it is able to go to the lack teal, which will place those kylo microns in the blood. And then we can transport fat anywhere in the body that we need those fats. So that is going to be how fats are broken down and packaged and transported. So fats are going to be broken down by bile and light based proteins, and they are going to be packaged and transported in the sky low microns. So this lesson just went over how the small intestine does many of its important functions. Just remember, the small intestine is utilized for absorption of nutrients, including glucose, vitamins and fats. Now let's go on. And let's talk about the functions of the large intestines and its importance in absorbing water.
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Large Intestine
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we're salutes, go water follows and absorption of water in the process of digestion is no different. As nutrients and salutes 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 mucous as well as digestive juices. It also absorbs the water that came in with the 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 Aqua porn's that allow for the efficient passage of water. And you can see an example of an aqua porn 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 jejune. Um, and the ilium 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, uh, 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 conventions a little weird. But its 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 sick. Um, and it's kind of just like a little sack. You can see it right here. It's a little area of the large intestine. And in some animals like herbivores, this structure is actually gonna be specialized for cellulose digestion. So you can see in the rabbits digestive system here. Uh, right here is the end of the small intestine, beginning of the large intestines of food, you know, move through the large intestine this way. And here is our seek. Um, see how big it is compared to this teeny little one in humans. That's because rabbits or herbivores and seek, um is going to be a specialized structure that allows them to digest plant material better now, after the sick, um, comes the colon, and this is like the main section of the large intestine. This is the rial show, and what's super cool about the colon is it's home to a microbiome of bacteria and these air 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, uh, the colon is going to be this, you know, whole big portion here, and you can see that has special names. You don't need to worry about knowing all the different parts of the colon. You know, you just need to know that the colon is where, uh is the main portion of the large intestine. And it's where these, uh, where these bacteria live. The last part of the intestine is three rectum. Let me jump out of the image here so you can see behind me. We have the rectum, that is where feces air stored for elimination or as they wait for elimination, I should say, um, you know it's It's not always a great time to have a bowel movement, especially if you're a nail in the wild. And you need to look over your shoulder and make sure nothing is gonna eat you or something. So, you know, this is a useful structure to allow you to wait until the moments right now, uh, it should be noted that some organisms actually have what's called a claw waka. This is a special orifice that excretes both urine and feces, and this is because you're in will flow from their kidneys into their large intestines, and then it all that nice, lovely stuff comes out the same end. So yeah, Chloe, ca's air pretty gross. That's, you know, going to be something that you find in like birds and snakes and stuff. It's just it's icky. The last thing I want to talk about is the appendix was going on and on about cool. The gut bacteria are well, the appendix is this little extension on the Sikh, Um, can see it right here. It's 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, uh, 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 the immune function. But you don't really need thio. 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 there. Are there actually essential to your life? That's all I have for this video. I hope you guys like gut bacterias. Muchas me. I'll see you next time.
Additional resources for Digestion
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