Hepatocytes

00:01 On this slide, it shows you on the left-hand side a drawing of a hepatocyte.

00:08 And it has boundaries, the apical boundaries, and the lateral boundaries open into the bile canaliculi. You can see them there colored in green and labelled. And the other boundaries open into the sinusoids, and you can see between the endothelium of the sinusoids and the cell border which has got very extensive microvillus extensions, there is a space called the space of Disse. And as I explained earlier, that space allows plasma to readily flow from the capillaries, which are sinusoidal, into that space of Disse, and continually circulate through that space and then return back to the vascular system, returned back to the sinusoids. So the hepatocyte is exposed to that plasma fluid in an environment free of all the blood cells. And the microvilli increase the surface area of that hepatocyte so that it can do its functions more effectively.

01:11 It can absorb and secrete materials. And when you look into the cytoplasm of that diagram, you can see there are a host of organelles that this hepatocyte uses.

01:22 It's a rare occasion that you get a cell that has got both granular, or rough endoplasmic reticulum making proteins, and smooth or agranular endoplasmic reticulum that's detoxifying substances. Mitochondria to provide the energy, Golgi apparatus to package all the proteins that that cell is making. In other words, a factory inside this cell that serves the enormous functions that the hepatocyte does.

01:55 On the right-hand side, you can see a light microscope section and stained of the liver hepatocytes.

02:07 And as I explained earlier, between these hepatocytes are the bile canaliculi.

02:16 And then you can just make out at the light microscope that space of Disse, and you can also make out the sinusoids. Well, here is that diagram repeated on the left-hand side. And on the right-hand side is an electron micrograph of a very high magnification showing you the sinusoidal space, which is labelled 1 there, the lumen of the sinusoid. Then there's a basal lamina which is discontinuous.

02:44 It has got little pores in it. And then there's a fenestrated endothelial cell labelled 3.

02:50 Then labelled 4, you can see the space of Disse between the endothelial cell that's fenestrated and the hepatocyte. And you can notice the microvillus projections from the hepatocytes into that space of Disse domain.

03:09 And now, at electron micrograph level on the right-hand side, you can see some details, all be it faint, of all those organelles that I mentioned earlier, the endoplasmic reticulum, the rough endoplasmic reticulum. You can see little tiny stores of glycogen. The bile canaliculus is in the center labelled 3. And then also there's lysosomes in the cytoplasm to help break down components that the hepatocyte ingests. And then, of course, there's the nucleus, the large nucleus on the bottom right-hand side of that electron micrograph. So it's a very busy cell, and as I said before, it has a large factory.

03:59 This diagram is not meant to be a description of the physiology of the hepatocyte. I put it here just to emphasize two points. And that is, that one of the jobs of the hepatocyte is to recycle when bile salts are used in the gut to help emulsify lipid droplets. The intestine absorbs those bile salts into the lymphatic system, into lacteals that sit in the lamina propria of the villi of the intestine. And they're absorbed eventually into the vascular system when the lymph vessels finally return that lymph back into the vascular system up towards the neck region, shoulder region of the body into the large veins there.

04:51 And then those bile salts then find their way to the liver, where they're re-absorbed by the liver, processed into being very active bile products, and then secreted into the bile canaliculi, then stored in the gall bladder, and used again in the intestine. So there is this recycling process, these hepatocytes have a role in them. And on the right side, you can see another bile canaliculus, the right side of the diagram. And that illustrates the fact that the hepatocyte gets rid of bilirubin. When red blood cells are broken down in the spleen, we try and retain some of the very important components of hemoglobin.

05:41 But we get rid of bilirubin, another component. So the blood containing that bilirubin finds its way eventually to the liver, and then the liver absorbs that, secretes it into the bile canaliculus, and then we get rid of the bilirubin as a waste product because it's delivered then to the intestine and not recycled.