- Gastrointestinal system questions
- Meet the gastrointestinal tract!
- Small intestine 1: Structure
- Small intestine 2: Digestion
- Small intestine 3: Absorption
- Hepatic lobule
- Biliary tree
- Exocrine pancreas
- Endocrine pancreas
- Colon, rectum, and anus
- Control of the GI tract
Created by Raja Narayan.
Want to join the conversation?
- What happens to all the nutrients in the liver? How do those nutrients reach other parts of the body if you say the hepatic vein is nutrient poor?(24 votes)
- I think that when Raja says that the hepatic vein is nutrient poor is because all the nutrient that reaches the liver is processed into energy, stored as glycogen (or vitamins and minerals) or got rid of the organism (in case of drugs, alcohol or something like these things; When I said got rid of I mean making these things harmless and then throw them away). After the absorption and the digestion processes have come to an end and we really need some of the nutrients stored in the liver, it releases them in the bloodstream.(11 votes)
- Why is the portal vein called a vein when it doesn't lead directly to the heart?(7 votes)
- I think of the portal vein as a vessel that leads away from the stomach and intestines, drains in the liver, reaches the hepatic-portal system where it exchanges all the nutrients and leaves through the hepatic vein, which eventually drains in the heart. So it is a "special" vein that leads to the liver, then to the heart.(5 votes)
- Hm, what happens to the nutrients that are in the liver? Shouldn't they be just "refined" in the liver, and delivered to every cell in the body via bloodstream? The hematic vein (the vein that leaves the liver) has poor-nutrient blood. How come?(5 votes)
- i think that is in accurate in the video. the hepatic vein is rich in nutrients but they are packed to be delivered to the tissues(4 votes)
- Can blood type affect the transplantation/regeneration of liver tissue into someone else's body (like if their blood type doesnt match up)?(2 votes)
- In short - yes. Your blood type denotes the presence of the types of antigens and antibodies in your blood, these are important in blood donations, and even more so in organ transplants. With blood donations if the blood donated lacks antigens (e.g. O negative) then it can be donated to anyone, as the body will not reject the blood. However, with organ donations, they must be an exact blood match, and even then, there is still a high risk of rejection, due the tissues being different, this is why people have to go on donor lists and normally look for a relative to donate organs, as then the tissues will be more similar.(6 votes)
- What does "hepatic" mean? When it is used with the above mentioned terms does the definition change? Thank you ahead of time.(1 vote)
- hepatic means it has something to do with the liver. Hepatitis, is inflammation of the liver. Hepatic cancer, is liver cancer. Hepatoma, is a liver tumor.(5 votes)
- At3:40, doctors prescribe drugs that account for drug efficacy caused by cytochrome P450. Why not prescribe cytochrome P450, or anything similar to that enzyme, instead of other drugs since it is able to detoxify multiple toxins rather than a specific toxin?(3 votes)
- At2:40, he says, cytochrome p450. What does p450 stand for?(1 vote)
The scientists came up with a naming system or nomenclature to identify the protein they were working with in the lab. with a particular gene. It doesn't stand for anything specific about the enzyme, it separates that one from 80,000 or so other proteins. It is better than calling it Bob or Sue :) Cyp 450 is well researched because problems with that protein causes problems with the breakdown of certain medications and that is due to a problem or mutation of the gene in that person or animal.(4 votes)
- Doesn't the liver also have to do with blood clotting factors? Is this not one of the main functions or more like a secondary function?(2 votes)
- Formation of blood proteins like prothrombin and fibrinogen are synthesized in liver cells. They are necessary for blood clotting.(2 votes)
- At5:10, aren't there only veins in the circulatory system? Or is the portal vein just a name? I don't really know.(2 votes)
- The circulatory system is made up of arteries and veins. The portal vein is just the name of a big vein that is responsible for most of the venous drainage in the abdomen.(1 vote)
- What causes cysts on the liver and how can you treat them?(2 votes)
- The cause of most liver cysts are unknown. They can be either present since childbirth, or they can develop later in life: they usually grow slowly and can't be detected until adulthood. Some liver cysts can be caused by the parasite Echinococcus, which is usually found in sheep. Most liver cysts don't need to be treated, but if they get too painful to live with, they can be either drained or surgically removed. They especially need to be removed if they stop bile from reaching the intestine.
Hope this helps!
Voiceover: The next accessory organ we're going to talk about in the GI tract is the liver. The liver, and that's this big fatty guy right here. Now, the liver has to be one of the coolest organs in the body. It's the only one that you can take a piece of, this small chunk right here, and transplant into a recipient that has cirrhosis or liver failure, and it can grow to become a much larger organ that can sustain the patient. How wild is that? And so to better understand the liver, we'll start by discussing the main functions it's responsible for. The first thing we need to think about is that it's responsible for metabolism, metabolism, and that involves the breakdown of nutrients or catabolism, and I'll just write cat right here, catabolism, as well as the buildup of larger macromolecules, and that's through anabolism. So, catabolism and anabolism are achieved in the liver. The other function the liver is responsible for is storage of these nutrients. \When we're not breaking them down or building them up, we need to have a place for them to hang out, and so, they're responsible for the storage of our carbohydrates, so I'll just write carbs right here, and also mainly our fats, so these two guys, and they're stored in three different ways. First, carbs or fats can be stored as glycogen. Glycogen is just a polysaccharide, so a linkage of a whole bunch of monosaccharides or simple sugars. The other thing that we can store our carbs or our fats as are lipoproteins, lipo meaning fatty and proteins meaning, well, protein, and then lastly, we can also store these guys as triglycerides, triglycerides, which is one of the forms of fat that we ingest in our food. Now, these are two of the major macromolecules we use for energy. The other major macromolecule class that the liver sees are proteins, but these aren't really stored in the liver. Instead, they're processed into molecules like albumin and then cast off into the bloodstream, where they'll float around and carry out other functions, until they need to be retrieved by the liver to be broken down or used for other molecules. The other major process the liver is responsible for is called detoxification, detoxification, and this is one of those awesome scientific terms where the function is in the name. This is where we take toxins and modify them so they can't harm our body. This is achieved mainly by cytochrome P450 enzymes, cytochrome P450, and these are kind of funky enzymes, because unlike the other ones you've probably heard about before, these don't bind a specific single substrate or molecule. If you remember an enzyme like phenylalanine hydroxylase, that's something that will add a hydroxyl group to phenylalanine and only phenylalanine, but cytochrome P450's will take a whole bunch of different substrates and react with them. That's something that's pretty unique to this class of enzymes. Now, because of these cytochrome P450 enzymes, we have a problem when we take medications. In fact, we have a decrease in drug efficacy because of this detoxification process, and what we mean by drug efficacy is the amount of an effect a drug is able to have, and so, if the liver or these enzymes perceive medications that we ingest to be foreign or like toxins, they're going to try and break them down so they don't cause an effect to our body. So, doctors knows this, and because of that, a specific dose must be given to account for the amount of a drug that's going to be detoxified by the liver. And finally, as we'll talk about in a separate video in better detail, the last thing that the liver is responsible for is bile production, bile production, and as you might recall from our discussion on small bowel, bile is needed for the absorption of fats from our food. Okay, so now that we understand what are the main functions of the liver, how does it get all the nutrients that we ingest and absorb from our intestinal tract to be metabolized or stored or detoxified in the liver? Well, let's take a look at the blood supply to the liver. So, one of the things that makes the liver so unique is that it has two separate blood supplies. The first, that comes in from the intestinal tract, is from the portal vein. The portal venous system is another term for it, and the portal vein supplies the liver with nutrient-rich blood, nutrient-rich. So, where do these nutrients come from? Well, food that's absorbed in the intestinal tract will then go through the circulation and end up in the portal vein, to be delivered to the liver for metabolism, and so we consider this blood to be nutrient-rich, but where does the liver get its oxygen from? Well, that's a separate blood source, and that's actually through what's called the proper hepatic artery, the proper hepatic artery, and as the name suggests, this is arterial blood that will be supplying oxygen-rich red blood cells. So great, these are the two different sources of blood that go to the liver. Well, what about blood that leaves the liver? There's one main vessel that carries blood out of the liver, and that's called the hepatic vein. The hepatic vein is the exact opposite as the two other types of vessels we just talked about. It's nutrient- and oxygen-poor. Blood that leaves through the hepatic vein from the liver will circulate back to the heart to receive oxygen, flow past the intestines to receive nutrients, and then return to the liver, either through the portal vein or through the proper hepatic artery. The other output of the liver, that I guess I should mention right now, we'll talk about in more detail in a separate video, is bile, and bile mainly leaves the liver through what's called the common hepatic duct, the common hepatic duct, common hepatic duct that will take bile.