On this slide, it shows you on the left-hand
side a drawing of a hepatocyte.
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 fenestrated, 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.
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.
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.
On the right-hand side, you can see a light
microscope section and stained
of the liver hepatocytes.
And as I explained earlier, between these
hepatocytes are the bile canaliculi.
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.
It has got little pores in it. And then there's
a fenestrated endothelial cell labelled 3.
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.
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.
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.
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.
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.