In today's video we'll be looking at the structure of the liver and its function. So it's really really important to understand first of all how it is organized in the first place. So the liver is actually the second largest organ in the body, the first one is actually the skin. And the liver is so big because it serves so many different functions from digestion to blood glucose level regulation to detoxification, so we'll talk about that in a bit more detail later on.
And the liver can be organized into lobules and a lobule is the structural or functional unit of the liver. So like how in the kidney we have a structural functional unit which is the nephron in the liver it will be lobule. So we see a loads lobule.
forming in a particular structure and then it becomes the liver. And here we've got the different parts of the lobule. So before I show you the actual structure of it, so here is some general idea about what it actually is like. So the center bit here, which is the same as that one, is actually the hepatic venule.
So loads of these hepatic venules is acting like a drain where every bit of blood inside the lobule would ultimately drain into it. and be carried away in the hepatic vein. And we've got the hepatic artery, which kind of generally organizes itself so, kind of across around the sides of it. And that's obviously where the blood, the oxygenated blood travels through the hepatic artery into the lobules. So that is kind of one of the branches of the hepatic artery, or you can call it the hepatic arteriole.
Now this is the hepatic portal vein, which is quite a unique blood vessel. It is the only blood vessel that connects to a blood vessel. organs but neither of them is the heart so it connects it carries deoxygenated blood with nutrients actually from the intestines to the liver so its goal is to transport some of the nutrients to the liver where it can be processed or at least some of the materials that we actually eat so that includes toxins as well so here we can you can see that there are loads of green bits inside the lobby so those are actually spaces which is called the canaliculus.
And the canaliculus is a space that connects to the bowel duct, and as the name implies, that's where the bowel is actually drained, and it travels to the gallbladder and... weights for it ultimately when we do actually need it in digestion then they can secrete the bile. And the cells in the liver is called hepatocytes. Hepet usually refers to the liver so you can have the hepatic veins, the venule, hepatic artery etc. So the cells are called hepatocytes and we've got two different types of spaces inside it so the green bits like I mentioned is called the canaliculus and then the the rest of the black space there is actually what we call the sinusoid.
And I'll talk a little bit more in the next bit here So we're gonna do now is actually to just look at one section of the lobule and just magnify a little bit more and see What it looks like so here. We've got the Just one section of the lobule, right? And usually in exams, if they do ask you to label it, then it probably looks something like this, or at least a 2D version of it anyways. So here we've got the hepatic artery. And one of the ways that you can tell that it is an artery is...
or at least an arteriole, is because of the thicker wall along it and the smaller lumen. Then this one here next to it, this is the hepatic portal vein. And as I mentioned earlier, hepatic portal vein is the vein that carries the deoxygenated blood from the intestines to the liver. And you can tell it's a vein because it's got a thin wall and a slightly larger lumen, at least compared to the artery.
So that's how you can tell it's a vein. Then obviously how can you tell between the hepatic portal vein and the hepatic vein? The major thing that you can recognize is the hepatic vein or the venule is always in the center of it so it always drains towards it. So this one here is the hepatic venule and you can see loads of different venules connecting to this one big drain and it carries the blood off like that. Then this particular part here, that is the bile duct.
And as I mentioned earlier, that's where the bile travels and it goes down like this towards the gallbladder where it is stored. So these cells here, all the white cells those are the hepatocytes like I said they are just a liver cell and they they are really really important because they are the bits that actually do loads of different functions for the liver which I'll talk a bit more later. Now we've got the cuffer cells here so you can see that they're situated within the space inside which I'll talk a bit more later.
The cuffer cells are the resident macrophages and macrophages are basically wet blood cells so they're there to actually serve an immune function. So they basically kill and attack pathogens if they are found in the bloodstream here. So these are cut for cells. And that's especially important because, like I said, they're responsible for many different functions. So if there is a liver infection, then it will be actually having a massive impact on the rest of the body or your health, basically.
So the cover cells are there to make sure they can almost be like the first line of defence in the liver. And then now we're going to talk about the two different types of spaces here. So you can see this one here, it's surrounded by hepatocytes and it drains into the bile duct.
Whereas this one, particularly here, so the blue and the red bits, those are signifying the sort of deoxygenated blood and the oxygenated blood coming in and mixing together. So first of all, I'll talk about this part. I mentioned this word already before, this space is called the canaliculus. So the canaliculus is the space where all the bile is drained into. So these hepatocytes around it, one of the functions is to produce bile.
As you remember, bile is a particular chemical that can surround and emulsifies lipids. So their idea of emulsification is that you're physically breaking a large oil drop down into smaller oil droplets, increasing the surface area to volume ratio and therefore... meaning that more lipase can actually work around these smaller droplets to increase the rate of lipid digestion.
So these hepatocytes will produce the bile and it drains into this one space called the canaliculus and drains in the bile duct. The way that you recognize that this one's the bile duct and not... these other ones is that the bile duct is surrounded or the canaliculus is surrounded by hepatocytes like that there's a specific space that is almost like enclosed so this one space and the duct that is surrounded by hepatocytes it will be the bile duct and the canaliculus so that's the way that you can remember it and then the rest of this space so all of this blue bits and red bits this whole space is called the sinusoid so the sinusoid is a space where the blood from the hepatic artery and the hepatic portal vein actually mixes. So it's actually very rare and probably the only place in the body where the oxygenated blood and the deoxygenated blood can actually mix together. And the idea here is to increase the oxygen content for the cells to actually work.
So the hepatic artery carries the oxygen here and it basically supplies the oxygen to these hepatocytes and well and the cover cell as well but mainly for the hepatocytes to work. And the hepatic portal vein carries all the toxins, amino acids and also nutrients and they need somewhere to mix it together in order for the cells to process. So that is the aim of the sinusoid. Ultimately at the end of processing all of those bits of nutrients and toxins they will all drain back into the this drain here which is the hepatophenyl and then travels down.
towards the hepatic vein where it carries all of the blood back to the heart. So the hepatic artery carries the oxygen and blood from the heart into the sinusoid so it goes up like that, whereas the hepatic portal vein will carry the blood like this into it as well into the sinusoid where they mix together and then all of the remaining blood afterwards will travel into the hepatic sites sorry into the hepatic venule and it travels all the way down like so so it goes all the way in so it comes up this way goes all the way that way and for the space here obviously then it actually exits the particular bile duct so it actually goes this direction so a very very quick summary just on this part we've got the hepatic artery carrying the oxygen of blood from the heart to the liver and the hepatic portofine carries the deoxygenated blood but with all the nutrients and toxins from the intestines to the liver. And the two bits of blood will mix in this space called the sinusoid, providing enough oxygen for all the cells to actually work and process these nutrients and toxins. In this space as well, we've got cover cells. So if there are any bacteria that is carried through, or pathogens in general, they can destroy the pathogens in the sinusoid before they get transported any further, or actually infect the hepatocytes themselves.
These hepatocytes also can surround an enclosed space called the canaliculus, which is where the bowel gets drained into, and then the canaliculus leads to the bowel duct where it travels to the gallbladder, and it's stored. And then the rest of the blood will travel through to here, which is the hepatic venule, and it travels to the hepatic vein, then back to the blood, and then the whole cycle continues again. So that is the structure of a lobule inside the liver.
Now to elaborate a little bit more about the function of the liver, and we will look at this in terms of the hepatocytes because actually it is mainly the cells, the hepatocytes in the liver that does the function. First of all we can think of it as making the hepatitis can make bile, which is in for digestion. They can emulsify the fats, which is the key word that we use.
Never say that bile is an enzyme because it is not. It doesn't chemically break the lipids down, it just physically breaks the oil drops down. down and emulsification itself is a physical process almost.
It's not quite chemical so just be aware. So hepatitis can make bowel which goes on to digestion. In this particular chapter however they will focus on the three functions of hepatocytes that are responsible for homeostasis and here they are.
So the first one is that hepatocytes can convert glucose into glycogen and that is about regulating our blood glucose level. So hepatocytes is sensitive and they can same as a lot of other body cells especially like muscle cells they can respond to insulin and glucagon so when insulin comes in and binds to as to the receptors hepatocytes can actually convert the glucose into glycogen and if it's glucagon binding then if they do the opposite direction they convert the glycogen back into glucose and then releases that so especially in this case where the blood from the hepatic portal vein can drain into the sinusoids you they can then do this particular process when they react to the insulin or glucagon and the glucose traveling from the hepatic portal vein and the artery. Another function of the liver in terms of homeostasis is deamination. So as the name implies, it's deamination, so it's removal of the amine group. And as you may remember, the amine group exists on amino acids.
So what we say is that the liver... the hepatocytes can actually remove the amine group from amino acids and this is especially important let's say old red blood cells or old or excess amino acids that we don't want then we can actually do this process removing the amine group from the amino acid and then there are two different things that happens here. So once you remove the amine group, the amine group itself becomes urea ultimately through the ornithine cycle. And the ornithine cycle, you do need to know in detail, but I'm not going to talk about it in this particular video.
But the idea is that the amine group then becomes ammonia, which then becomes urea, which is a lesser toxic version of that. And then it travels through the hepatic venue and it goes to the kidneys ultimately, which then gets removed. which you learn a little bit more in this particular chapter anyways.
And actually the other part of the amino acid after deamination, the rest of the amino acid can actually be converted into pyruvate, which is, pyruvate is a particular, the key substrate you can say for respiration. So it's actually quite useful. So if you don't have enough glucose to do a respiration, actually one of the things that the body can do is to break the proteins down into amino acids. They go through this process, de-immunization, ultimately generating pyruvate. Obviously not ideal because you're breaking down muscle mass, but this is one of the things that can happen.
Then the final function that we'll talk about today is detoxification. I think that's kind of obvious. The liver is expressed, important in processing any sort of toxins that we have or we ingest into our body. So alcohol, for example, and drugs.
So even medicines that we take like paracetamol or ibuprofen, all of those stuff ultimately needs to be processed by the liver before we get rid of it. And so it's massively important. One of the key enzymes that the liver does have is called the alcohol dehydrogenase. which is an enzyme found in hepatocytes where they process the alcohol or ethanol into a less harmful version.
So that is the one way that they can use the liver, or one way the liver can work to make sure these toxins are rendered harmless. So here's a summary of it. So we've got the liver.
The liver is actually organized into lobules, and the lobules are the individual structural unit or functional unit of the liver. And the lobby looks a bit like this with the hepatic vein or venule in the center of it and loads of different artery the hepatic arteries and the hepatic portal vein will kind of connect together in the sinusoids and also we've got the bile duct here which is connected to the a canaloculus and it drains away all the liquid. So that's the lobule.
And here is the actual structure of a cross section of the lobule or one section of the lobule anyways. So the hepatoarticular carries oxygenated blood through, hepatoboravine carries blood from the intestines with the nutrients and toxins and etc. and they mix together in the sinusoid making sure that there's enough oxygen for the hepatocytes to actually work to process these stuff. stuff in the blood from the hepatic portal vein.
The cut for cells around here also kills any pathogens that enter in here to make sure the liver can function properly and preventing infections. Then the hepatocytes can also produce bile which drains into the canalic list, the space here, which ultimately drains into bile duct and travels to the gallbladder. And the rest of the blood here would drain through the hepatic venue into the vein and back to the heart. And we see We say hepatocytes can have different functions. One of them is to make bile.
Then the other functions regarding homeostasis is number one, to convert glucose into glycogen to regulate our blood glucose level. It can also do deamination, which is the removal of the amine group from excess amino acids in the ornithine cycle. then the removed amine group ultimately becomes urea, which we can get rid of through our kidneys, and the rest of the amino acid becomes pyruvate, which enters the respiration cycle. Then finally, they can also detoxify any toxins such as alcohol and drugs using, for example, enzymes like alcohol dehydrogenase to make sure our liver and our body can maintain its health.
And this is the structure and the function of the liver.