Hello, this will be our epithelium laboratory and this first slide shows simple
squamous epithelium shown by these flat cells near the surface. This is a section
through mesentery and this simple squamous epithelium on this mesentery
sheet is given the special name mesothelium you can also note a simple
squamous epithelium that lines blood vessels. You can see that here and you
can see a little bit of it here and here. When the simple squamous epithelium
lines blood vessels, we give that the name endothelium. They're these little
capillaries, you can also observe some connective tissue cells, so there's
probably a fibroblast here and this is probably a mast cell Here is a profile
of the mesentery as though you were looking down from the surface so you
don't see the nuclei in these planes of section but you can see these flattened
cells and you can see the cell outlines in this preparation of the mesentery.
This particular stain is a silver stain. It's a rather unusual stain. Here a
simple cuboidal epithelium that's lining thyroid follicles, in this case, the
simple cuboidal epithelium and the thyroid has given the name follicular
cells. Here is the thyroid colloid which is actually a thyroid hormone which is
stored extracellularly. We'll talk about the
dynamics of this much later in the course and we'll also talk about the
pair of follicular cells or C cells in the thyroid that are involved in the
synthesis and secretion of calcitonin. Some of these C cells would be located
here, for example, where my pointer is. I would never expect you to recognize that
this is the renal medulla at this point in the course but the collecting ducts
in the renal medulla consists of a simple cuboidal epithelium and you can
see that nicely outlined around any of these cross sections of the collecting
tubules. The blue stain that you see in some of these slides is staining
connective tissue. These are trichrome stain slides
and usually the blue stain is picking up connective tissue. We'll have more to say
about connective tissue later in the course. Here is a simple columnar
epithelium lining the mucosa of the small intestine. You can see the single
nuclei and the ethelium. You can see the brush border which you'll recall
from an earlier presentation. These are microvilli along the brush border. Here
is a goblet cell and then you can see some lymphocytes that are actually
invading this epithelium. Well beyond the scope of what I'm expecting you to know
right now, but the area that I'm in here with my pointer is the lamina propria.
When we talk about the GI tract, we're going to talk about particular layerings
and I don't want you to worry about that right now, for now, I just want you
to recognize this simple columnar epithelium. Here a profile through the
jejunum in the small intestine, also a simple columnar epithelium. You can see
the nuclei. Here you can see a goblet cell, maybe another goblet cell here and
you can get a sense of the brush border and then this region again would be
region of lamina propria. For now if you just understand that the lamina propria
is essentially a connective tissue on which an epithelium sits, you'll be fine.
Here is a profile of a large striated duct, probably taken from one of the
large salivary glands. This striated duct also consists of a simple columnar
epithelium. You can see as I would trace this cell like that a simple columnar
epithelium, the striations, you can see these basal striations. This is an area
where there's membrane infoldings with a lot of interdigitated mitochondria
and once again this would reflect active transport and in these large salivary
glands these striated ducts function to concentrate the secretion of the
salivary gland. We'll have more to say about that later in the course and again
a trichrome stain slide so the blue is picking up connective tissue.
Here's an area in the small intestine, again a simple columnar epithelium. I think we
showed you this slide in an earlier podcast, so here you can see the nuclei,
here you can see the brush border, the lumen of the GI tract here and several
goblet cells are highlighted. This is a profile through the oviduct. It's a
ciliated simple columnar epithelium and here you can see the profiles of the
cilia. We'll have more to say about the oviduct later in the course as well.
How do cilia differ from microvilli? That's one of these questions I'll leave
for you to try to discover on your own. This is a profile through the epididymis.
The epididymis of course is in the male reproductive tract and this is a pseudo
stratified columnar epithelium and these epithelial cells possess a surface
specialization called stereocilia. The stereocilia are a scene like this.
Stereocilia are essentially long microvilli. What would their fine structure be
and then how would these fine structures of these stereocilia differ from that of
cilia? You can also note basal cells in this profile of the epididymis and these
basal cells are indeed stem cells. This is a pseudo stratified columnar
epithelium and we know that it's pseudo stratified because if you look at the
nuclei, the nuclei appeared to be in very staggered layers. Here's a view of the
trachea, again a pseudo stratified columnar epithelium, and a ciliated
pseudostratified columnar epithelium. Here are as a goblet cell maybe another
goblet cell here. Notice the nuclei are at staggered layers and you can clearly
see the cilia on this epithelium. A ciliated
pseudostratified columnar epithelium is often given the name respiratory
epithelium because that's essentially the only place in the body where you find
a ciliated pseudostratified columnar epithelium would be in areas of the
respiratory tract. Here is a profile of the vagina, I would never expect you to
recognize that at this point in the course, but it's a stratified
squamous epithelium non-keratinized or non-cornified. You can see multiple
layers of cells and it's defined as a stratified squamous epithelium because
the top layer of cells is squamous or flat. You'll come to appreciate that
anytime we have a stratified epithelium, we define it by the shape of the surface
layer of cells. So here a stratified squamous epithelium
because the surface cells are flat. Here is connective tissue underlying the
epithelium so in the lamina propria if you want and I don't expect you to
recognize this right now, but this is probably a profile of a small nerve. I
also don't expect you to pick these out right now but these cells might be
melanocytes. Here is another profile of non-keratinized stratified squamous
epithelium. The surface is actually off the histological image so it's down here
but again a stratified epithelium and notice that as you're going towards the
surface, the cells are getting flat so we define it as a stratified squamous
epithelium. Here is a stratified squamous epithelium keratinized. The surface layer
of cells are actually dead that cornified or keratinized so we would
correctly identify this epithelium as a keratinized stratified squamous
epithelium and then again some connective tissue underneath the
epithelium. This is a section through a large duct probably from a salivary
gland and it's reflecting the fact that this is a stratified columnar epithelium.
Notice the surface layer of cells is columnar. There are two layers of cells
in this area so it is stratified. We define the epithelium by the surface
layer so we call it a stratified columnar epithelium. Now you have to be
careful because in some areas here we're getting it like a tangential section
through this duct. This would almost look like a pseudo stratified epithelium and
in some areas you almost think maybe it's a stratified cuboidal epithelium
because the epithelium looks more cuboidal than columnar so sometimes this
is a judgement call but I think like in an area like this there's no question
that these surface cells are columnar so stratified columnar epithelium. Here is a
transitional epithelium. This epithelium is unique to the urinary tract so you
might find this epithelium and the ureters or in the bladder or in the very
proximal portions of the urethra but very characteristic of this transitional
epithelium are these very large dome shaped cells that would project into the
lumen and here's another view of the same thing on this next slide. It's a
stratified epithelium but we call it a transitional epithelium because this
epithelium has the ability to change its shape. It can be very much stratified
like this, I don't have a view to show you, but if the bladder for example is
very distended this epithelium can spread out to almost look like a simple
squamous epithelium so a transitional epithelium it can change its shape
depending on the physiologic state of the organ, the characteristic dome shaped
cells. Another interesting feature about this transitional epithelium oftentimes
transitional epithelium has what are call polyploid nuclei. Look at the size of
this nucleus compared to this nucleus. This nucleus is probably a 4 C nucleus
where this nucleus is probably a 2 C nucleus. Sometimes you can see cells that
are binucleate in transitional epithelium.