Liver Functions

hi everybody dr mike here in this video we're going to take a look at the various functions of the liver [Music] now to begin with we need to talk about the liver itself as a structure we know it's located in the upper right quadrant of the abdomen and we know that it weighs around about 1.5 kilograms now this is around about 2 percent of your body weight which is significant obviously making it the largest organ inside of the body now in order for the liver to undergo its many functions it requires a functional subunit and the functional subunit is what we call lobules and lobules are these hexagonal shaped structures inside the liver that do all the work now they're so small that they're between 0.8 to 2 millimeters in diameter but we've got heaps of them we've got between 50 000 to 100 000 of them per liver so many many liver lobules to do all that work now when we look at the liver itself and all of its functions you can broadly categorize the functions of the liver under four main categories so these particular categories are filtration and storage of blood it includes metabolism and detoxification it includes bile formation and regeneration now there's multiple subcategories of functions that fit underneath each of these which we'll be discussing today but these are the four broad categories that i want to talk about when we look at liver function so the first i want to discuss is that a filtration and storage of blood so the liver filters what's coming through our blood and it receives huge amounts of blood remember that the liver has two vessels that come into it it's got the large portal vein and the large portal vein is coming from the git so this is a venous system draining nutrients and other particular substances including blood from the git so it includes the stomach it includes the intestines pancreas and parts of the colon and it's going to the portal vein which goes to the liver itself and this can be around about a thousand mils of blood you also find that you've got the hepatic artery that also goes to the liver and this is a branch off the celiac trunk itself and the hepatic artery has oxygenated blood but it's around about 300 mils of blood that's coming in but cumulatively there's about 1300 mls of blood going to the liver itself and what happens is when it comes in these two particular vessels go to the liver lobule and i've discussed this in another video so if you want to have a look at the liver lobule or portal triad video what you'll find is that at every particular corner you're going to have a portal vein or at least a branch of it and a branch of the hepatic artery and both of them drain into this thing called a sinusoid and the sinusoid drains into a central vein now what you're going to find so they're both draining into this sinusoid now the sinusoid is porous many holes but it's lined by epithelia and this epithelia plays a very important regulatory role as to what gets through and what doesn't get through and in addition to that there's also these macrophage cells that sit at the sinusoids and they're called kapha cells and what they do is they engulf bacteria any invading pathogens anything that shouldn't be going through because what happens is the fluid that's draining from the portal vein and the hepatic artery that's coming through it moves through the pores of these sinusoids and on the other side we've got hepatocytes these plate-like cells that take what's in this fluid that's moved through and it can either metabolize them detoxify them use them to produce bile for example and so forth so cup for cells and endothelial cells with the hepatocytes play an important role in filtering the blood that's coming in from the portal vein and the hepatic artery now when we look at storage of blood because what happens is this blood goes into this central vein and that central vein of all the lobules come together and that then forms the hepatic vein which leaves the liver now the hepatic vein actually merges with the inferior vena cava and the inferior vena cava is obviously going back to the right side of the heart so when it looks at so that's filtration what about storage of blood well what you'll find is that the liver while it's got a high flow of blood coming in and that's a low pressure too by the way so high flow low pressure it can store at any given moment or it does store at any given moment around about 450 ml of blood this is 10 percent or thereabout of our circulating total blood of the body so it's an important storage unit and think about this if remember i said the inferior vena cava is going to the right hand side of the heart so i'll just draw up the heart here for example if there's something wrong with the heart so an individual has heart failure or the mitral oh sorry the tricuspid valve that goes from the right atrium to the right ventricle is stenotic or hardened this blood can back up and back up and back up and back up into the liver itself and the liver can go from holding 450 mils of blood to over one liter of blood which is quite significant so it plays a really important role when it comes to storage of venous blood what about metabolism and detoxification well let's take a look the liver plays a really important role when it comes to the uptake the processing and the distribution of nutrients and these nutrients are going to be proteins fats and carbs proteins fats and carbs and the most important point to begin with is obviously we ingest these through the food that we eat through the whole entire digestive tract whether it's the oral cavity breaking down carbohydrates or the stomach breaking down proteins or the small intestines breaking down fats they all get absorbed while most of them fats get absorbed into the lymphatic system but still get to the liver at some point but carbohydrates and proteins get absorbed through the intestines jump into the portal vein and go to the liver for processing storage or utilization but in addition to that the liver can actually regulate what's happening with those particular nutrients of other structures of the body so for example the liver can regulate what's happening at adipose tissue so if i've got adipose tissue here which is fatty tissue right so let's just say that a bit of adipose tissue the liver can regulate this adipose tissue's ability to release glycerol and fatty acids the liver can also regulate skeletal muscle and its ability to release things like lactate pyruvate and amino acids you may be thinking what about glucose no the stored glucose in the muscle as glycogen can go back to glucose but it cannot leave the skeletal muscle the only glucose that can leave a tissue and deliver itself to other parts of the body is actually coming from the liver and that's that next point while the liver can regulate what's happening at other tissues it itself also plays around with these particular nutrients and can release them into the circulating blood supply to deliver to the rest of the bodies to the rest of the body so the types of things that the liver can release includes glucose and it can release this glucose through a process known as glycogenolysis so glycogen is the stove stored form of glucose lysis means splitting apart so when you take in glucose the liver will store it as glycogen if you need glucose the liver will break glycogen apart and release that glucose into the body so that structures like the brain and kidneys for example can utilize it but that's not the only way that it gets glucose i can get it through something called gluconeogenesis and gluco glucose neo-new genesis the production of the production of new glucose we're making glucose from non-carbohydrate-based sources so we're getting this for example from amino acids like alanine alanine is one of the primary ways that we can produce glucose or through glycogenolysis but also we're doing this through fatty acids as well so the release of glucose but also the liver can release acetoacetate and acetoacetate is produced through beta oxidation so the liver can release these particular nutrient substrates as well which is extremely important so the next thing we need to talk about is why don't we go a little bit more specific and talk about the role that the liver plays for carbohydrate metabolism protein metabolism and fat metabolism in itself so when we first start with carbohydrate metabolism let's have a look carbohydrate metabolism so we know that carbohydrates they're ingested predominantly broken down by the salivary amylase in the mouth and also the amylase from the pancreas in the intestines itself and it's broken down ultimately into glucose now this glucose is going to be taken up by the liver postprandially after we eat because it's in the portal vein and goes into the liver now the liver can store it as glycogen and the liver can store up to 65 grams of glycogen per kilogram of liver tissue so that's a fair bit of glycogen that it can store now if it's hit this capacity what happens well the excess glucose is turned into fat and that fat is stored in adipose tissue and that's an important point because when we go from carbohydrate metabolism into fat metabolism what we find is adipose tissue is actually very poor at creating its own fatty acids and storing it so the liver itself is the primary way to synthesize fat and store it in adipose tissue okay so excess glucose can be turned into fat stored into adipose tissue fatty acid synthesis or taking fatty acids and glycerol synthesizing it so remember what the liver can do is it can take fatty acids it can take glycerol and it can do a couple of things so it can take the two turn them into triglycerides and that's how we store them triglycerides and we store them in adipose tissue or what we can do is take the fatty acids and glycerol and turn it into atp and ketone bodies right so one's obviously going to be storage the other one's going to be utilization for energy and that's that way of utilizing the protein so what about the fat sorry what about protein let's have a look so when we look at protein metabolism it's really important to recognize the fact that when we ingest proteins we go from proteins two amino acids these amino acids are in our bloodstream and get taken up by other tissues and these amino acids from other tissues can turn into structural proteins for example enzymes which are proteins that have a particular function and hormones now this is an important point but excess amino acids go to the liver amino acids go to the liver for processing and metabolism and when they do this the liver metabolizing amino acids or proteins actually release a couple of things the liver releases ammonia glutamate glutamine and aspartate and this ammonia needs to turn into uric acid or urea which then goes into our urine and we pee it out so the liver is extremely important in nitrogen handling nitrogen is made well amino acids and proteins are made up of excessive amounts of nitrogen and that's broken down into ammonia the liver handles it and allows us to pee that out and that's really important but there's other things that the liver does when it comes to proteins and it makes a number of really important proteins that everyone needs to be aware of for example coagulation proteins so the liver produces proteins transport proteins the most important of which is albumin copper and iron binding proteins and also protease inhibitory proteins so protease breaks proteins down and we need other proteins to inhibit them funnily enough so all of these are produced in the liver and are extremely important to discuss okay so what we need to talk about now is we've gone through metabolism of proteins fats carbohydrates when it comes to the liver what about the metabolism of detoxification or compounds that are potentially toxic so the liver can detoxify toxic substances and this is called xenobiotic metabolism so these are foreign particulates that are potentially damaging or toxic and it can include include things like cigarette smoke and pollution and and pesticides and all those types of things and the liver can manage it by detoxification and there's two phases of this detoxification so you can have phase one which utilizes cytochrome p450 which is also known as the sip pathway and you've got phase two which simply takes this toxic compound and makes it a little less toxic so something that can be handled a little bit better and hopefully can be excreted so it turns it into a less toxic form and that's the way that the liver deals with toxic metabolites now another important metabolic process is that of which we metabolize red blood cells so importantly red blood cells have a lifespan of around about 120 days and obviously it's hemoglobin just filled and filled with hemoglobin which is heme which is the iron portion and globin which is a protein portion the globin can be recycled it's protein we can undergo amino acid catabolism and utilize it elsewhere but the heme needs to be handled a little bit differently so the heme from the red blood cells are pulled apart they've taken away and they turn into billy verdin and that billy verdin then turns into unconjugated bilirubin which then in the liver becomes conjugated billy rubin now an important thing that happens here is that the unk the conjugated the unconjugated bilirubin in the liver going to the conjugated bilirubin has a couple of different pathways for example now it turns into something called urobilinogen and the urobilinogen can go to the kidneys for excretion or it can go to the intestines for excretion so if it goes to the kidneys it's coming out in your pee and is one of the reasons why your pee is yellow and if it goes to the intestines and turns into something called stercobilin for example it's going to come out in your poo and it's the reason why your poo is brown so your liver plays an important role of conjugating bilirubin so it can be trans so conjugating means basically binding it to something like proteins and sending it out so it can be excreted through the kidneys or intestines now what can happen is if you have liver damage this process isn't happening and the unconjugated bilirubin this bilirubin can accumulate in your peripheries and it looks as though you're yellow and this is jaundice so when somebody has hepatitis or cirrhosis and they get jaundice as a side effect it's because the breakdown of red blood cells the bilirubin is no longer being conjugated by the liver and then being redistributed but it's going to the peripheries and the individuals turning yellow all right so we've done one and two let's have a look at bile formation this one's going to be quick because i've done an entire video on bile formation and it's a little bit complex but we're not going to talk about the complexities here we're going to talk about the very basics of bile itself if you want to know the details type in bile formation in one of my videos so bile formation what bile does is it emulsifies fat emulsifies fat fat is one big globule you've seen when you put oil in a pan and it all comes together what bile does is it breaks it apart like a detergent and it forms what's called micelles smaller more manageable sized pieces of fat that then enzymes in the body like lipases can chop up and turn into that fatty acids and glycerol so that's really important but bile in addition to emulsifying fat is really important in the absorption of fat soluble vitamins now importantly and i should have included this in the metabolism fat soluble vitamins are metabolized by the liver so if they're fat soluble they need fat to be absorbed and by definition we need to ingest vitamins we can't create them ourselves now the fat soluble vitamins is d e k and a so deca and we need them in our diet and we need the bile as well that's produced by the liver but stalled in that little green gall bladder that sits underneath but behind the liver we need that bile because it helps us absorb vitamin d e k and a so let's have a quick look at those particular vitamins and then we'll go back to bile and finish off what we're talking about there so when we look at these particular vitamins what you're going to find is vitamin a we need vitamin a in order to retinoic acid for appropriate vision embryological development and gene transcription all extremely important but it's stored in the liver and what that means is if you have too much vitamin a it can lead to hepatic toxicity so that's important hepatic toxicity too much vitamin a what about when we look at something like vitamin d vitamin d is extremely important for calcium and phosphate homeostasis and what you'll find is that one of the vitamin d synthesis steps occurs in the liver one of those steps so that's extremely important what about vitamin e so when we have a look at vitamin e which is an antioxidant i don't know write that in but it's a potent antioxidant the liver you utilizes this antioxidant activity for lipid peroxide lipid peroxidation and being able to deal with free radicals which is oxidative stress so the liver utilizes that because obviously it plays an important detoxification role so it utilizes the metabolites of vitamin e and the last one vitamin k so vitamin k is required for coagulation its metabolite is important for the coagulation factors and what happens in regards to the liver is it utilizes vitamin k to make particular coagular coagulation factors like coagulation factor 2 coagulation factor 7 coagulation factor 9 and coagulation factor 10 through vitamin k now last thing when it comes to the vitamins is that the liver does also play an important role with handling the b vitamins as well and utilizing their particular metabolites as cofactors i should say let's go back to bile so the liver makes this bile it's important for emulsifying fats in the small intestines it's important for absorbing those fat soluble vitamins as well and it's made up of bile is made up of water it's made up of ions so ions like sodium potassium magnesium chloride things like that it's made up of made up of bile acids it's made up of cholesterol that's important phospholipids and proteins all extremely important all right regeneration the liver plays a really important role in its own regeneration the liver is such an important structure and we know it's important because of all these roles that it plays and as we've spoken about as we've moved through if the liver becomes dysfunctional you can have a number of issues you can have storage issues of blood and portal hypertension issues with being able to filter out bacteria or infections metabolism issues so handling proteins fats carbohydrates detoxification issues of xenobiotic compounds the formation of bile and the emulsification of fats and the absorption of vitamins and now regeneration so somebody through hepatectomy so the loss of up to 70 percent of their liver they can regenerate which is amazing and it happens really quick so in mice for example they can regenerate up to 70 percent of their liver in seven days and this is extremely important and shows that it is such an important structure that it has developed or evolved the capacity to regenerate which is obviously very important so what we've gone through is a lot the four overarching functions of the liver and hopefully it all made sense

Channel: Dr Matt & Dr Mike

Views: 211,951

Keywords: liver, function, hepatic, regeneration, metabolism, detoxification, xenobiotic, p450, cytochrome, storage, fats, protein, carbs, carbohydrates, glycogen, gluconeogenesis, glycogenolysis, oxidation, energy, blood, reservoir

Id: 2GlWMvFvyU8

Length: 26min 38sec (1598 seconds)

Published: Tue Jul 28 2020