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.