00:01
So it’s a specialized vessel, having a specialized
function. Well, last of all, let’s look
at pancreas. When you look at the pancreas,
it has two different components. It’s an
exocrine gland that in fact, there’s 90%
or even more of its histological components,
an exocrine gland that secretes pancreatic
enzymes. And those enzymes go into a duct
system, and the duct then goes and deposits
these secretory products into the duodenum
to help with the digestion of the food in
which we ingest. Well, the other component
is the endocrine component. It’s the component
that occupies a very very small percentage.
00:45
And you can see in sections of the pancreas as
you see here on the left-hand side, a section
through the pancreas showing one of these endocrine
components that appears the pale staining
little ball of cells. The darker staining
on the periphery are the exocrine components,
the serous secreting exocrine acini. But focus
on the central paler stained component.
01:14
That is the endocrine component. It’s very vascular,
even though you don’t appreciate here for
reasons I mentioned earlier, the vessels that
capillaries tend to collapse down, but they
are fenestrated capillaries again. Well, these
endocrine components are called islets of
langerhan, or more recently, we refer to them
as pancreatic islets. And they can be of
different sizes. Some can occupy only a hundred cells.
Some can be very, very large. So there’s
this variety and structure in the size of
these islets just like I explained there was
a variety in the diameter and size of the
thyroid follicles we looked at the very start
of this lecture. On the right-hand side is
another preparation used to try and distinguish
the three major cells types in these islets.
I’m not going to point them out here and
try and distinguish them, but you can see that
there are differences, there are different
sorts of cells. Some are eosinophilic, some
are basophilic and some are not so basophilic.
02:25
So if we look inside one of these pancreatic
islets indicated in the left-hand side, and
then look on the right-hand side and try and
identify the cells, basically, you can class
the cells as either A, B, or D cells or alpha,
beta, and delta cells. And really, they refer
to the hormones that they secrete. And in H&E
sections as you see here, you cannot distinguish
these real cell types. So I wouldn’t expect
you to. But I’d like you to remember that
the A cells secrete glucagon, which controls
glucose levels that we’ll talk about at
another time. The B cells by far occupy the
most cell numbers in these pancreatic islets.
03:14
They secrete insulin. And the D cells secrete
somatomedin and a couple of other components
that we are not quite sure of their exact
function yet. But certainly, the endocrinologist
will talk to you or describe to you what exactly
these B cells do secrete. But focus on the
A and the B cells, those that secrete glucagon,
and those that secrete insulin. Both those
hormones have very, very important widespread
functions throughout the body. In summary,
it’s important that you understand the histological
difference between each of these endocrine
glands that I’ve described in this lecture.
Know what sort of cells are in each of these
four endocrine glands or tissues, know the
hormonal products each of these glands secrete,
and their general effects on their target organs.
And know also a little bit about specialized
components of each of these glands, such as
the blood supply in the adrenal cortex, and
how it affects the adrenal medulla. And also,
the different way in which the thyroid gland
operates. It secretes and stores its product
and it reabsorbs it. So when you look at the
structure and function of all these glands
that I’ve described, you should be able
to point out all their differences, structurally
and functionally. But remember, together,
collectively, they are very important components
of the endocrine system. So thank you for
listening to this lecture. I hope you now
have a good understanding of these very, very
important endocrine glands.