Hey y'all. We're gonna keep this a...accessory digestive organ train a-rollin,
this time with the pancreas. The pancreas is a mixed gland. It is both exocrine and
endocrine, and will investigate both parts here in just a minute. The pancreas
is located in a posterior to the stomach, and it...the exocrine portion is going to
secrete via a pair of ducts into the duodenum or duodenum of the small
intestine. So we can see that here up at the top, and if we look a little closer,
histologically, we can see the mixed nature of the gland. We have acini
surrounding ducts. So we have...we have a branched acinar type gland going on here,
and the acinar excretory portion is going to be secreting digestive enzymes,
and I'll tell you which ones here in just a minute. And then you're also gonna
see if we can think of the pancreas as being kind of like a sea of exocrine
tissue you're gonna see little islands of endocrinology tissues throughout. Currently referred to as pancreatic islets but you still might them
referred to by their older eponymous name "the islets of Langerhans". So when
you hear some fossil like me talk about the islands of Langerhans we're
actually talking about the pancreatic islets; we just learned an older no
longer preferred name for them. So let's look at actual histology here. This is
kind of a low mag shot of the pancreas, and we can see some notable features.
First this conspicuous duct running... What would be a good color here? Maybe...maybe
yellow. This conspicuous duct...oh yeah, that shows
it nice...running through our CO exocrine tissue. So here's the duct going on here.
We can see numerous capillaries. Note right in here those little red discs
that I just covered up with my marker. Here's a better one, little arteriole, or a
little venule, sorry. There's a little arteriole here. So we've got plenty of
vasculature in here, and all of this stuff out in here, this darker same stuff
is exocrine tissue. All of this mess out here. We're actually going to zoom in on
two structures as we move through here. So we're gonna zoom in right here, where
we can see a single exocrine acinus, and we're also going to zoom in over here
where we see one of those pancreatic islets. So this is an exocrine acinus.
It's supposed to be an "A". There we go. And then over here we have an endocrine
islet. So let's zoom in first on the acinus and look at the exocrine
portion of the pancreas a little more closely. Here we can see that single
acinus, so right in here, surrounding a duct. So here's the duct here (sound effect), and (sound effect) like
that. So it's...its components are going to be secreted out into here, and this is
going to secrete digestive enzymes, or bicarbonate, or a mixture of the two.
When chyme first enters the the duodenum from the stomach it's highly acidic, and
so these pancreatic cells are going to primarily produce bicarbonate, a base to
neutralize the acid, then once the acids have been neutralized,
these acini will switch over to secreting enzyme rich, what we call
bicarb...or enzyme rich pancreatic juice. And that enzyme rich pancreatic juice will
contain proteases, lipases, nucleases, and amylases that will break down the
macromolecules in the food into its base components, so that it can eventually be
absorbed later on in the jejunum. So it's the exocrine pancreas, there's not a
whole lot to it. You guys have seen secretory epithelial before. I do think
it's kind of cool you can see this capillary back here, and it's not for
nothing I just think it's really neat. You got the red blood cells lined up two
by two over here. So it's a pretty narrow capillary, you're looking at something
about 15 micrometers wide right there. Well let's look at the endocrine pancreas and see how this is different.
Hear we can clearly see these columnar secretory cells around their central duct.
When we look at a pancreatic islet, we of course see no such
thing because endocrine glands, which is what the pancreatic islets are, don't
have ducts, instead notice...so here I'll just outline the whole thing...it's always
there pretty easy to pick out because they tend to be lighter colored in
staining then the exocrine cells, but also inside here, look here, there's a
little capillary.There's a little capillary right in here. There's another one. I
feel like Bob Roth. There's a happy little capillary. And it makes sense that
we're gonna see a lot of capillaries in here, because this is endocrine tissue,
and endocrine glands secrete their products where directly into the
bloodstream. So out here we can see the sea of exocrine tissue surrounding our
pancreatic islet that I've outlined here in yellow, and I found some cool pictures
on Wikimedia Commons that are of stained pancreatic islets, and in this one...and
I'm gonna have to switch pen colors. So i've got a white background, switch to black.
Up here we have stained the Alpha cells. We find two kinds of cells in the
pancreatic islets, and alpha cells produce a hormone called glucagon, which
raises your blood sugar. So during times of fasting the alpha cells will be
stimulated to release glucagon, which will then tell your liver hey take some
of that that glycogen you're storing and break it down into glucose we need to
raise the blood sugar. The lower image shows pancreatic beta-cells.
Beta cells produce the hormone insulin. When you're not fasted, for example after
a meal and your blood sugar starts to rise, the insulin from these beta cells
will tell your liver hey take the sugar, the extra sugar out of the blood, and
store it as glycogen. And we'll talk a little bit more about the endocrine
pancreas later on, but really that's it for the pancreas. You've got an exocrine
portion that makes bicarbonate, or digestive enzymes, and an endocrine portion that makes the hormone
glucagon and insulin. Well that's it for now. I hope you had fun.
Study hard. We'll see you later.