肝脏

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 I'll just write catch right here catabolism as well as the buildup of larger macromolecules and that's through anab ilysm 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 a 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 our 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'll add a hydroxyl group to phenylalanine and only phenylalanine but cytochrome p450s 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 gonna try and break them down so they don't cause an effect to our body so doctors know 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 as 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 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 its 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