Liver functions part 1 and 2 Flashcards
How will these lectures be structured?
Role of the liver in erythrocyte maintenance
Learning Outcomes
where in the body
So when we start to look at the liver,
then you’ll notice that we’ve got these green lines that go through the liver and they are known as the bile canaliculi
and they are miniature bile ducts that collect the bile from the hepatocytes that are cells of the liver and brings the bile into the gallbladder.
What you don’t need to know is all the different parts of the liver, that one side is bigger than the other.
What we really need to focus on is its function. So this is really just kind of letting you know where things are and how they’re related,
that these then the gallbladder will empty down this common bile duct and into the small intestine.
And the restriction here of that emptying is carried out by a sphincter called the sphincter of oddi that then allows release into the small intestine
what part of the body area is the liver located
So what about the structure of the liver then let’s start here.
You’ve got your glossary link at the top there,
which should take you to the glossary at the end of the PDF if you need to use it for any terms that you don’t quite understand when I’m using them.
So whereabouts in the body is the liver located?
And you can see the liver is present here just underneath the diaphragm, which runs here and next to the stomach.
And the gallbladder is this little, tiny bit sticking out just underneath there,
it’s a it’s the largest solid organ, about one and a half kilos or just under.
And it is located very close by to the pancreas,
which is kind of tucked under behind here close to the small intestine, which, of course, has to empty into.
The other thing that is close by, of course, is the gall bladder, which also empties into the small intestine.
So. The gallbladder is where we store bile and bile is produced in the liver,
so they’re very close so that it’s easy for that bile to drain out of the liver and be stored in the gall bladder.
Now, I’m not going to go into any particular detail here,
but just to say that the gall bladder is essentially a sac that is surrounded by smooth muscle and it’s about seven to 10 centimetres.
And it stores and concentrates the bile and it periodically releases bile into the intestine so that you can take up lipids from your diet,
they enter the small intestine. And of course, there is an intimate relationship between the liver and the pancreas.
But we’re not really going to talk that much about that because you already discussed the endocrine pancreas with Dr. Johnson.
And you more talk about how they coordinate when you start the GI tract lectures in week six.
Blood supply to the liver
So then if we think about it, we need things that we take up from our diet to go to the liver because the
liver is the place that is going to essentially start that screening process,
it works a bit like a bouncer that goes, yes, these things will benefit the body.
It can continue around the body and these things that we don’t need.
So what you notice is that we’ve got our liver in the middle.
And the liver contains hepatic sinusoids, which we’ll talk about in a little more detail in the next slide or so,
what you’ll also notice is we’ve got the GI tract here. It’s rather a crude picture.
I apologise. And what happens is,
is that our blood from the GI tract travels through the hepatic portal vein to the liver in the centre here along this blue arrow.
The liver also has a supply of oxygenated blood shown here by the red line,
by the red arrow that’s coming from originally the lungs and the heart is coming through the aorta and along the hepatic artery into the liver.
So they’re coming together, these deoxygenated blood from the GI tract and the oxygenated blood from the hepatic artery.
Now, don’t go scribbling because they’ll be this information on the next slide.
The hepatic vein then is where we get amalgamation of both of these blood supplies and
it goes out of the liver and into the vena cava to circulate to the rest of the body,
including cycling back to the lungs. So what you’ll notice, of course, is that if you eat something in the GI tract, it’s first port of call.
The first place it goes to with all its nutrients is the liver.
And that’s because the liver was originally evolved to prevent us from getting large amounts of toxic substances in our body.
So that nutrient rich deoxygenated blood that comes from the GI tract to the liver then joins with oxygenated blood from the hepatic artery.
And we get nutrient rich, deoxygenated blood that’s present in the hepatic vein.
And this nutrient rich blood cycles back around the body and then out as it gets oxygenated to other tissues and organs.
Structure of the liver
So this is the point at which we start to look at the structure of the liver.
And hopefully you have read up on that pre lecture task that I asked you to do so.
And the question was, what is the shape of the structural unit of the liver?
Well, if you look down here on the right hand side, this is our structural unit.
It is called a labule. And what you’ll see is that it forms this hexagonal shape here.
And what’s in the middle here is the central vein. And we’ve got our hepatocytes lining the other sources of blood supply.
And they are a mixture of that that came from the hepatic portal vein, which remember,
this has got lots of nutrients in it, but it is deoxygenated because it’s coming from the GI tract.
And we’ve also got the hepatic artery shown here in red, in the top and the left hand corner.
And that is, of course, oxygenated coming from the aorta.
So these are going to merge in these sinusoid coming here and drain into the central vein,
which, of course, that central vein then drains into the hepatic vein.
So what feature of these units makes them particularly suited to their job?
OK, what we can see here is that we’ve got these very thin walled sections here.
There’s only one or maybe two layers of hepatocytes lining each of these sinusoids.
And that’s particularly important because we have a thin wall, very thin wall on the sinusoid
And of course, that increases the uptake into these hepatocytes that are lining that basement membrane of the sinusoids that
enables them to take things up very rapidly is very much a large surface area because of how many holes there are,
meaning the uptake is quick and that is essential to make sure that it can essentially screen all of the blood that is coming in from the GI tract.
It also is the fact that we have large numbers of these sinusoids that are moving through this liver lobule collating in the middle here.
And of course, that, again, means that we’ve got a large surface area so that this can happen very quickly.
I’d like you to let me know if you can. How long that took you, hopefully only about 10 to 15 minutes.
So if we now look in a little bit more detail about the structure of the liver, we have got hepatocytes.
As I pointed out to you, these little cells of the liver, they’re quite unspecialised.
They don’t have any particular shape or noticeable features in terms of when you look down the microscope at them.
But mainly they are involved in these processes of metabolism secreting things.
So because they are a main storage facility, if you like, they have to be able to secrete things.
So of course, they are involved in secretion of vitamins and glucose, and things like that that they have stored within those cells.
And they’re also really important in endocrine function. OK, production of various hormones and also storage of vitamins and things like that.
So they’re also surrounded by the sinusoids, like we’ve just talked about.
And they are usually a single layer thick maybe two at the most, which we picked out in the last slide.
The sinusoid are very, very permeable capillaries.
They have very patchy endothelium, which we mentioned before. They’re very hole-ie.
And that increases the diffusion across the membrane from the blood into the hepatocytes.
They’re nutrient rich, so they have plenty of nutrients.
They’ve just come from the GI tract and they are full of deoxygenated blood.
If they come from the hepatic portal vein or oxygenated blood if they come from the hepatic artery and they all drain,
as we said, into the common central vein and then eventually into the hepatic vein.
These sinusoids also have kupfer cells that are resident in and between them at the hepatocytes and these kupfer cells,
they’re really macrophages.
And these are generally able to survail the tissue.
You might see that they are called stellate reticuloendothelial cells,
but they obviously have an immune function, OK, which is to survail what’s coming in.
If there are any bugs and things that that you ate or even bacteria, then they should be able to pick those out.
Now, the thing that we haven’t really mentioned already is the bile canuliculi
so you can see here this little yellow green bit here from the portal triad,
which is where all of the bile canaliculi, the hepatic artery and the hepatic portal vein come in at the kind of corner, if you like, at three corners of that hexagon.
And the bile canuliculi, they run out to the portal triad from within and between the hepatocytes here that line the sinusoids,
they travel in the opposite direction.
To the flow of blood in the sinusoids, in the sinusoids the blood travels in the direction towards the centre and the bile canuliculi
the bile is secreted from the hepatocytes into the canuliculi and these travel in the opposite
direction here in green at the bottom of that hexagon going out towards the portal triad located.
And they eventually drain into the common hepatic duct, which takes the bile out to the gall bladder.
Structure of the liver in a histogram
So in terms of that lobule, we can see what it looks like down the microscope, so what you can see here in the middle.
Is that we’ve got our portal Triad here on the left hand side.
There’s a black box that middle bit and that blows up to what we can see here in the foreground on the left.
And you can see your hepatic artery, your bile duct in the kind of purply colour here.
And then you can also see the branch of the hepatic portal vein here and on the bottom sort of left side of that.
So this is just by light microscopy.
We can see these structures and you can see as your hexagon goes around in that central part, that the central vein in the middle here,
which is blown up on the right hand side of the diagram, is quite large in comparison to those little hepatic arteries.
And that’s because it’s collating all of the blood from the different areas and bringing them together in the middle.
Structure of the Gall Bladder
So in that process, if this is the gallbladder Lumen here at the top and this is the muscular lining on the sides
this is the cells of the muscular lining here in orange,
what you can see is that sodium and chloride ions will move out along with water and bicarbonate will move into the gallbladder lumen.
And that means that will get a concentrated, more alkaline solution that’s there.
And the water passes all the way out of the basal natural surface so that it can’t even end up that this
muscular sac ends up swollen and we get the movement of sodium out with water in exchange for the potassium.
So sodium-potassium ATPas that does that moving.
Liver functions
Influence on protein metabolism
In terms of its influence on protein metabolism.
the liver is a major site of protein synthesis.
It generates plasma protein, so proteins such as albumin and other globulins that carry, um, both hormones and regulate the osmolarity of the serum.
Is also involved in the generation of coagulation factors.
Of course, these coagulation factors are only synthesised here in the liver in their long forms,
um, which are inactive and these are activated upon their requirement.
And the final thing is that calcium and iron binding factors are also created here,
which of course means that we can keep concentrations relatively high in the blood.
Um, if we’ve already talked about the one for iron Fe2+, which is of course, transferrin.
This is really important to keep them in the blood because it means they can’t be filtered by glomerula filtration.
Of course, protein breakdown or catabolism will generate urea.
Influence on glucose metabolism
In terms of the influence that there is on glucose metabolism by the liver.
There is quite a big influence here, and most of this is attributed to the maintenance of blood glucose.
So that is break down glycogen um, into glucose and also by glycogenolysis occurring in the liver itself.
glucogenic amino acids are also broken down.
Um. And this will generate Glucose by gluconeogenesis.
Um, there’s lactic acid that’s used in this process,
and we get the release of glucose that goes directly into the bloodstream, meaning that it’s immediately raising and controlling that
in terms of glycogen of course, there are times when there’s excess glucose in the blood, and so there is a need to store it somewhere for a rainy day, so to speak.
So under these conditions, for example, immediately after a meal, there is storage of glucose in the form of glycogen.
And also it’s used to generate triglycerides in combination with some of those fatty acids.
And in this case it means that those can be stored later on.
The liver as storage
One of the liver functions is. One of the liver functions is to work as a storage unit.
And you can see that I’ve tried to help you in remembering this process by providing you with the big Yellow Self Storage Company label.
We’ve already talked about how glycogen is stored in the liver, um, to reduce the blood glucose concentration,
but enable it to be utilised at a later time to increase that blood glucose, um, concentration should it go down?
Also, there is storage of fats in the form of triglycerides.
There is storage of steroid hormones, especially given that this is a major site of cholesterol creation.
So those of you that are again doing biochemistry, we touched on which ones of those vitamins were steroid hormones.
Uh, lots of these generated out in the liver.
There’s also minerals, iron and copper that are also kept here.
Um, this means that these will be released when they’re needed elsewhere in the body, but otherwise they kept out of the way here in the liver.
Role of the liver in lipid metabolism
In terms of the role of the liver in lipid metabolism.
There are some dietary fats that we take up in our diet, and of course, they come into the gastrointestinal tract.
But when this process occurs, it will generate through a number of steps, some lipoproteins.
And you can see these lipoproteins here on the right hand side.
They look like they’ve got phospholipids all around the outside.
And we’ve got triacylglycerols and also cholesterol esters that sit inside here.
And on the outside, those phospholipids are joined by some Apo lipoprotein, like apo B.
Which are key for the action of lipases.
Okay. So here this apolipoprotein is key in the uptake of lipids from your diet.
The uptake of lipids from the diet will only happen if we have the presence of bile acids or bile salts.
So if we look at, uh. Um, cholesterol, for example, you can see here the steroid ring.
This ring structure is the basis of our bile acids.
And what our bile acids do have is they have a hydroxyl group here, which makes this, um, structure, uh, slightly hydrophilic.
It’s able to do hydrogen bonding. And there are some other hydroxyl groups that can be added to these bile salts,
to make them much more hydrophilic, which will enable these bile salts.
And they can sit on the outside of the lipid droplets that’s formed as you get uptake from the gastrointestinal tract.
And what you’ll notice is that the hydrophobic areas are on the inside facing, um, those triacyl glycerols and cholesterol esters and then the.
Outside is the portion of the bile acid that is hydrophilic, and so this allows the lipids to be solubalized in the hydrophilic environment.
In terms of the breakdown of fatty acids, this process of breaking down fatty acids, will generate ATP.
But then also we’ve got storage happening again.
the hepatocytes will keep some of these triglycerides that have got, for example,
glycerol and three fatty acids
they’re stored in this format so that they can be utilised at a later date.
The liver produces Bile
In terms of what Bile is, because we’ve just been talking about bile acids.
Bile is, um, a sort of liquid mixture of water, bile acids, bile salts, uh, bile pigments, cholesterol lectin and several other ions.
But what you can see is that by far and away the biggest component of bile,
all these bile acids and it’s kind of a yellowy brownish or slightly green tinged liquid that has, um, a little more of an, a sort of basic, pH.
In comparison to that really low pitch of the stomach.
Okay. And so therefore it’s able to neutralise the, um, products that come from the stomach into the small intestine.
Each day, hepatocytes secrete up to one litre of bile.
Um, and these bile acids that are in bile are really essential to emulsify fat droplets
and facilitate the uptake of fats and cholesterol in the absorption process,
and it solubalises them.
Into structures that are similar to those, apolipoprotein we talked about earlier that allow them to circulate in the blood.
But these are sort of chylomicrons later on, you’ll find out a little more about the role of these structures in digestion,
because you talk about this with, um, Doctor Vicki Revelle later on in the module.
So in terms of bile, the main thing that causes that brownish colour is BiliRubin.
And of course, this is the product of Haem breakdown, which we mentioned earlier.
And the Haem breakdown gives that sort of brownish tinge.
The Bilirubin is the breakdown product of that, and will increase the solubility.
That’s the most important thing. Um, it can be altered, uh, by bacteria that are in your gut, um, in your faces.
And, uh, but most bile, um, salts or bile acids can be recycled, especially, um, if they have not been, um, completely altered by several steps,
which again, if we did, if you joined me for biochemistry, you will have found out about in that module too.
Bile Acids
So in terms of our bile acids the sodium or potassium salts, of these bile acids are known as bile salts.
Okay. So for now, we’re going to, uh, just look at these in a little more detail.
And as I said, they’re really key and emulsification of the fats into those lipid globules.
If you think about when you cook some sort of meat, usually all of the fat drips out of it into, um, a layer at the bottom of the pan.
And if you put some, uh, washing up liquid in with that,
it will create sort of a film around the outside of each little droplet of the, uh, lipids of the fats.
And that is almost exactly what these bile acids do.
They create these little droplets, which can then essentially be enabled to be taken up in our GI tract.
So usually this allows a suspension, um, temporarily, um, of these lipid globules in the aqueous solution.
And that increases their solubility. So this cholesterol here on the left represents what the base product is of these bile acids.
And then in the liver we generate bile acids by using cholesterol.
And you can see here that it’s got a carboxylic acid group up here at the top.
And what happens is, is that this can have, um.
A, uh, an amino acid such as glycine or taurine added to this bile acid.
And this will make it a conjugated bile acid.
Um, and if you notice here that in the process of generating, um, our conjugated bile acid or secondary bile acid, you would also see that there’s the ability for dissociation of this molecule in the, uh, hydrophilic environment.
And so therefore we generate that C double bond O and an O minus um and this can associate with a sodium for example, that’s got a one plus charge.
And so in this case where it’s dissociated it’s known as the bile salt.
I don’t want you to worry too much about the differences here.
We’ll talk about bile acids in general. And it will mean either of these two things.
But this is really the essential part to enabling this covering of these lipid droplets.
Because then this area where we’ve got our NH-CH2COO-Na+ that will do hydrogen bonding and enable this to be dissolved or solubalysed in the hydrophilic environment, this is what enables that to happen.
And then the other parts, the sterile ring for example, will be facing inwards where it’s um facing towards those triacyl glycerols and cholesterol esters
Detoxification by the liver
So what happens in terms of detoxification in the liver?
Um, there are many, many metabolites.
Think you for all your hormones and things like that. They’re not always going to be there to be reused over and over again.
These often get broken down and replaced.
And so this process means there has to be detoxification and lots of the metabolites of things like alcohol and things like that.
They need to be detoxified.
And this happens in the liver where there is excretion of drugs like antibiotics in particular the sulfonamides as well,
And these can be chemically changed in the same kind of process that those bile acids were that we just mentioned.
There can be a chemical change where something will get added to it.
And so therefore it will be easy to excrete because it becomes more, um, water soluble, hydrophilic.
chemical changes or secretion of hormones and things like that may happen as a response of this as well.
So, for example, the liver is able to produce an enzyme that we already know, um, degrades vitamin D2.
Into, Into Calcitriol .
And so therefore this is going to generate further hormones and, uh, other hormones are affected by things like this are oestrogens and aldosterone.
Secretion of bile:
So in terms of secretion of bile, we’ve got unconjugated bile acids that might be recirculated or that are generated in the liver itself.
Newly generated, um, bile acids that are unconjugated are generally considered to be primary bath acids.
Okay.
And what happens is, is before that process of conjugation to generate our conjugated bile acids, they don’t have those more hydrophilic structures.
And they can actually be quite toxic to the hepatocyte itself.
So that conjugation process needs to happen to make them a little less excited so they dont go and wreak havoc inside the cell and instead calm it down a little bit.
So the conjugated bile acids that, um, are secreted usually into the bile canaliculi, from our hepatocytes. And these will move down the bile canaliculi and out into the, um, gallbladder via the common bile duct.
Okay. Now there are going to be other things that are also secreted into the bile canaliculus
And some examples of those are sodium and chloride, bicarbonate ions, water etcetera etcetera.
So these migrate in this process of cholesterol to cholic acid and glycocholic acid
This, um. Conjugation step is key here because if there is not conjugation that’s been happening, then these bile acids will be toxic.
So this is where liver damage can be particularly problematic.
If there’s something that doesn’t happen, um, to allow conjugation to happen then you will end up with some quite toxic products.
Secretion of bile: cells
So the bile migrates from the canaliculus down here in this way, opposite way to the way that your, uh, circulation is travelling.
So here’s our, um, portal triad, and we’ve got movement of blood in this direction,
but the canaliculus are transporting the bile in the opposite direction down to the bile duct.
Enterohepatic circulation
So our enterohepatic recirculation that happens here is where we get bile salts and bile acids that are
generated in the liver that get secreted down through the bile canaliculi they collect in the gallbladder,
as we discussed in the previous lecture, bite.
And then when it’s the time, then this gets released down the bile duct to the sphincter of odi and into the intestine.
A lot of these bile acids that are in the liver are recycled about 95%.
Only a small amount are newly synthesised.
Okay. So these secondary bile acids that are recirculating, they may be modified on their journey in the GI tract.
But as they reach part of the large intestine, they are able to be reabsorbed, and then they will circle back into the hepatic portal vein and back round to the liver.
So this process happens, um, most of the time with most of these being recycled.
So there’s only a small amount of primary bile acids being generated at any one time.
In the terminal ileum. That 95% is where the reabsorption happens.
Remember, the other 5% that that aren’t recycled will get excreted in the anus, okay?
Whereas the other, the other 95% will circle back to the liver to be reused later.
Hormones that regulate digestion
In terms of hormones that regulate this process and the secretion of bile.
There are two main hormones that is secretin which is released in response to acid that comes into the duodenum.
So if you have a meal with any any amount of food, you’re going to get release of acid into the duodenum.
And this stimulates, um, biliary ducts cells to secrete bicarbonate.
So it’s that reconstitution of that really sort of stiff, um, concentrate in the gallbladder.
It increases bicarbonate and water release so that the volume expands massively and that increases the flow down, to the sphincter of odi
Because imagine how hard it is to squeeze all that out of the gallbladder.
If it’s a bit like mud and sludge.
cholecystokinin is the other hormone that controls this process, and this is released in response to fat, specifically fat.
In the duodenum. This leads to the contractions of the gallbladder and the common bile duct so that it will push by peristalsis,
the bile all the way down and actually stimulates the delivery into the duodenums
Bile secretion
So how does that process look? So here we’ve got our liver and we’ve got our stomach here with the pancreas sitting right next to it.
And we’ve got our gallbladder here with our um.
Bile duct running down here. We’ve got the sphincter of ODI at the end there.
So here what happens is, is that during fasting, bile accumulates in the gallbladder.
And of course it’s concentrated down. However, chyme that comes out of the stomach and enters the duodenum here.
And there’s going to be some acids and partially digested fats.
which will stimulate the release of secretin.
So bile acids via the blood Stimulate the parenchymal secretion.
Um, secreting comes along, um, and stimulates the liver to secrete bile.
And then bile stored down here in the gallbladder.
Waiting for the stimulation from the secretin to start the release from the gallbladder
therefore that secretin is starting the generation and allowing accumulation to happen in the gallbladder.
Bile secretion and the structure of the organs
In terms of when that’s released.
It’s this hormone called cholecystokinin thats release, it’s only released when fat comes into the top of the duodenum
So secretin may well be generated as there’s a bit of acid that comes out of the stomach.
But until there’s actually signs of fat in this meal, that’s when cholecystokinin is released.
So chole Meaning liver, and cysto meaning gland.
So liver gland, i.e. gallbladder, and kinin means movement.
So this point that cholecystokinin is stimulating the gall bladder to empty and it stimulates the movement down.
Um the common bile duct. So cholecystokinin
causes contraction. And it also causes the relaxation of that sphincter of odi.
And that allows all the bile that’s coming down to enter the duodenum and to enable the coating of the fat that have just entered the duodenum.
Um, as they come moving down in towards the duodenum
There’s also some vagal stimulation that happens to help the contraction of the gallbladder, to give it more rhythmicity.
Otherwise, um, this process can be very stiff.
So it wants it to be squeezing all the way down in a rhythmic way.
Liver as a gland
Now. Liver is also a gland. Uh, it synthesises a number of different hormones, including angiotensinogen
And the synthesis and release of thrombopoietin which is similar to erythropoietin, and it acts on mega carrier sites to generate platelets.
And there’s also the synthesis and activation of vitamin D.
If you don’t remember what angiotensinogen is, well it is cleaved by renin and it produces angiotensin one.
And this is really important in blood pressure maintenance.
If you’re not sure what I’m talking about right now.
Relationship between structure and function
In terms of the relationship between structure and function that we mentioned so much in physiology.
Um, there are some arguments that instead of looking at the liver as a lobule that we should be looking more in this orientation.
So here is our central vein that was in the centre of the liver lobule before.
And we’ve got our portal triad here which was said to be on the periphery.
But actually those portal triad vessels run in the direction down to zone 1
which means that you’re much more likely in zone one to get a high concentration of oxygen and nutrients.
So of course, we want enzymatic reactions to be going on in this area.
However, out here in zone three, we’re much have much less of those resources with us.
So this area is much more suited to the storage function of the liver.
And there’s a lot of, um, argument and you hopefully have read in the um,
page that was recommended in the Silverthorne book about why this model is actually preferred in the liver.
Relevance of blood pressure to the liver
So in terms of how this works, also with blood pressure in the liver, you’ll remember that we had our portal triad.
We’ve got our branch of our hepatic portal vein here in the blue. and our branch of the hepatic artery
And what the important thing to remember is the arteries also got valves.
So this artery has got a much higher blood pressure than our vein over here.
Okay. So the arteries got a blood pressure about 80mm of mercury.
And the vein has got a pressure of about ten millimetres of mercury.
And that mixes together, of course.
so our hepatic portal vein is going to have plenty of Components that have come from the GI tract, whereas our hepatic artery.
Has come from the rest of the body. So it’s going to be oxygen rich and these are going to move together and they’re going to come together and increase the pressure in the sinusoid.
So this becomes about 7 to 8mm of mercury.
Hey, if the hepatic portal vein blood pressure rises, then so will the sinusoid blood pressure.
Okay. And this is something that can be a little problematic.
You can see here that in the central vein this is as low as five millimetres of mercury.
So it’s really controlling how high that blood pressure is over this progress through the liver.
Now, if we’ve got high blood pressure in the, um.
Hepatic artery. This will lead to a Ascites of the belly.
And this always makes me think of my dad when I sit here and I talk about this, because fluid moves into the peritoneal space,
and often you will see especially slightly older men with this sort of pregnant belly looking stomach
And so this is exactly what happens, um, under these circumstances, to make that swelling happen,
because it’s accumulation of fluid in the peritoneal space
role of the liver in erythrocyte maintenance
On the functions of the liver and gallbladder.
As you hopefully remember, part of the function of the liver is to, um, enable red blood cell turnover.
Um, that happens courtesy of our macrophages.
This is in addition to its primary job, which is to produce bile and therefore aids the digestion of lipids.
Other jobs that are attributed to the liver include storage of certain vitamins,
um, which we’ll talk about shortly, and detoxification of lots of products,
not just things you eat, um, as part of your diet from elsewhere, outside the body, but also your own waste products.
And finally, as we already know, there is production of some hormones.
So we’re gonna start, um, in this journey and look at these in turn briefly.
So first of all, the liver is able to take part in the life cycle of the erythrocyte
It contains kupfer cells or stellate reticuloendethelial cells, as they may be called in some books.
And it houses the cells which are able to break down the erythrocytes that you can see over here.
And they create iron, globulin and bilirubin as a result of that.
And if you remember, this is our haemoglobin over here. And each one of these little Plates are shown more closely on the right
And this is our haem group with un iron at the centre of that.
So this iron is taken away. The globulin here is broken down and we generate bilirubin as a product of that.
The iron is then stored as ferritin, and, hemosiderin and it’s transported courtesy of transferrin.
To the, long bones, where erythropoietin will stimulate the release of these to the bone.
To enable iron to be released for erythrocyte generation again.
So you’ll see this everywhere that there’s plenty of recycling going on.
And this generates, iron, globulin and bilirubin that can be used in different ways.
Now a breakdown product or bilirubin is stercobilin, and this gives your faeces that sort of browny tinge to them.
However most of these components are recycled.
Jaundice
So the last thing that we’re going to talk about is the fact that usually if somebody has got something wrong with their liver,
they will develop a yellowish colouration to the sclera of their eye and also to their skin, which is known as jaundice.
And this is because of the accumulation of bilirubin. And if you remember, that’s the breakdown product of haemoglobin.
This can also lead to very light stools, um, and dark urine, because the bilirubin is getting stuck in these fatty tissues and not being excreted.
Now there are four types of jaundice.
The first one is called pre hepatic jaundice.
Um and this is where there’s excess production of bilirubin.
So there’s a high amount in the blood. But there’s also a high amount in the urine as well.
Usually this is a sign that there’s haemolytic disease.
And that might be something like malaria sickle cell anaemia or thalassaemia.
The second type of hepatic jaundice is called intrahepatic jaundice.
This prevents the proper function of the hepatocytes, because there is a build up within the liver of bile.
Congenital liver disease and cirrhosis can be causes of this intrahepatic jaundice because it’s, um,
happening within the liver itself, whereas extra hepatic jaundice is something that is outside of the liver, outside of its control.
This is when there is a change in or a drop in the function, um, due to the accumulation of bile, it’s blocked in places like the um gallbladder.
So for example, gallstones or perhaps cancer of the pancreas, which actually the pancreas is very, very close to that bile duct.
And nodules here can obstruct that vessel, which is often the first thing that that person knows about that cancer.
And the final, uh, type is one that is restricted only to newborns.
It’s known as neonatal jaundice. Um, and this is where there’s poor function of the liver when they’re very first born.
And usually this can be, um, rectified by exposing them to blue light.
It’s just waiting for their kidneys and their liver to start working.
Please do look at the learning outcomes and I will see you next week for some problem based learning.
Which values would be abnormal? What is the relevance of these physiologically and what signs and symptoms might the patient be experiencing?
A recap:
A recap:
Problem Based learningactivity
Problem Based learningactivity
Gall stones
there can be some problems in this process of bile secretion and recycling
Gallstones can block the common bile duct near to the hepatic duct
And cause a back up of bile into the liver.
It can also be further down the common bile duct, or in fact, even in the gallbladder.
And any of these places are particularly problematic.
But these ones further down in the common bile duct are particularly bad because as the gallbladder increases in volume,
this volume that happens in the response to Cholecystokinin
well it’s got nowhere to go, and it will back up into the liver and start to cause damage.
So with this in mind, what do you think will happen?
What will block the bile duct? And what would you expect to see if you looked at a liver panel here? (liver panel is a liver test)
Um. Consider the model Of the acinus
Which of those cells would be affected first and what outputs would change?
We will discuss this in the tutorial when I see you next.
