HSCI 4590 Histology- salivary glands

HSCI 4590 Histology- salivary glands


Hey y’all, Brown’s back and this time
we’re gonna be talking about spit. How exciting is that? We’re beginning our
unit on accessory digestive organs. Those are organs that aren’t part of the
alimentary canal but that secrete something into the alimentary canal to
assist with the five digestive functions being ingestion, digestion, propulsion
absorption, and defecation, and the salivary glands are going to be
important both for chemical and mechanical digestion. Now, your mouth can,
contains dozens of tiny, little, what we call minor salivary glands. They’re
scattered throughout the oral cavity and they are important but most of your
saliva comes from three pairs of what we call the major salivary glands, so we’re
gonna be focusing primarily on the major salivary glands. Saliva is a really
complex fluid. I said in the intro to this video that’s in your course
module there are over 1100 unique proteins in saliva and it doing a lot
for us and it’s doing that through the secretion of two main factors or fluid
components. So saliva contains a combination of serous fluid and mucus,
mucus being primarily the glycoprotein mucin, U C I N, and these glands are going
to secrete either serous fluid, mucus or some combination thereof. The minor
glands that are scattered throughout the oral cavity are largely only mucous
secreting glands. Your major glands are either serous glands or seromucous
glands meaning they’re secreting a combination of both serous fluid and
mucus. The three glands we’re going to look at are the parotid gland here, which
is located kind of posterior to the mandible in your cheek, the
submandibular gland which, as its name implies, is under the mandible and then
finally the sublingual gland, which as its name implies, is under the tongue.
We’re gonna start kind of in the back and make our way forward, so the
first one we’re gonna look at is the parotid gland. The parotid gland is a
branched acinar gland meaning that it has these acini, these kind of ball
shaped secretory portions, and it has multiple of them that share a central
duct, so it’s a branched acinar gland and it’s primarily serous secretion,
you’re not gonna see a lot of mucus secreting or any really mucous secreting
cells inside the parotid gland, but that serous fluid is going to contain some
very important components, one of those being salivary alpha amylase, which is an
enzyme that begins the chemical digestion of carbohydrates like
starches. If we look in the micrograph on the right, we can see and I’m gonna have
to use a different color, let’s go to maybe a nice blue, over here on the right
the secretory portion is to the right of this blue line I’m drawing, so these
cells over here, these are the secretory cells and they contain numerous
secretory granules inside them, so you can see the vesicles there that contain
the serous fluid that’s going to be excreted and eventually transported into
the ducts, so this structure here that I’m doing a very poor job of outlining
is a duct, you can see the cuboidal epithelial cells that make up the lining
of the duct, there’s the contents and the lumen of
the duct and then there’s connective tissue out here. This connective tissue
is not unimportant, the connective tissue, I couldn’t find a picture that showed
them really well, but this connective tissue can actually contain B
lymphocytes and those are going to be secreting IgA antibodies which are the
antibody form that we find in exocrine secretions. These glands having a duct
are exocrine glands and so it’s unsurprising that we would find IgA in
there, so the parotid gland it is a branch acinar gland, it is serous
secretion only and it’s secretions include things like alpha amylase and
immunoglobulin A. Making our way forward the next gland up is the submandibular
gland. This gland actually produces about two-thirds
of the saliva that your mouth is going to make and it is a compound or branched
tubuloacinar gland, meaning that it is going to have acini, kind of the
little ball shaped structures here at the end, but these are also going to be
connected via tubules that we see here in purple, so it is a tubuloacinar
gland and it is a mixed gland. If we look at our micrograph on the right and I
have a higher mag one coming up we can find mucous secreting cells, here these
are called mucus tubules, so the part I’m outlining here in blue is the part that
would be purple in our diagram over here on the left and then the serous
secreting portions, there are some good examples down here at the bottom, are
largely the kind of half-moon shaped areas that we see out here in the acini, so because the acini tend to have kind of a mucusy portion at the part
where it connects to this mucous tubule, the acinar portion is shaped in section in the microscope kind of like a half-moon,
so we refer to these as serous demilunes, and demilunes just means little
half-moons, so we make little half-moons down here. If we look at slightly higher
magnification we can see a mucous tubule, say your words Patrick,
so this lighter standing stuff, the glycoprotein mucin, which is the primary
component of mucus, doesn’t stain well in histological preparations so cells that
contain a lot of mucin are going to appear pretty transparent, you can see a
cross section through mucous tubule here and here and then you can also see
up here at the very top how the serous secreting portion, part of this thing is
purple, is going to make kind of this half-moon, so this is a serous demilune. Okay, and in addition to alpha-amylase,
the serous secretions of the submandibular gland also contain
lysozyme. Lysozyme is an enzyme that’s found in exocrine secretions,
particularly in saliva and in tears, and it has antibacterial properties, it
actually breaks down the cell wall of bacteria, thus helping to prevent
infection, and then finally, the last and smallest of our major endocrine glands
is the sublingual gland. Like the submandibular gland, it is a branched tubloacinar gland, so at the macroscopic level it’s going to have a
very similar structure. However, as you look at this micrograph, you can see that
it’s dominated by mucous secreting cells, so these kind of columnar cells you can
actually see the outlines between them, right there you can see the cell
membranes, so there is some serious secretion, there is a small amount of
alpha amylase and lysozyme produced by the sublingual gland, however, the vast
majority of its secretion is mucus, so technically it is a seromucous gland
like the submandibular gland, but practically it is a seroMUCOUS gland, it’s pretty much only making mucus. That’s really it for the salivary glands,
so you have your minor salivary glands secreting mucus, your major salivary
glands, the parotid gland, which is a serous gland, the submandibular and
sublingual glands, which are seromucous glands and together this combination of
serous fluid and mucus and all of the proteins that come in it are going to
help us digest our food, going to help bind our food together into a ball so
that we can swallow it and also going to help us taste because taste or chemoception, the reception of chemicals, has to be done in an aqueous environment and
it’s going to assist with preventing the oral route of infection by containing
both antibodies and antibacterial enzymes. Well that’s it for now. I hope
you had fun. Study hard. See you later.

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