final point that we want to make with regard
to this section of histology is to look at some light micrographs stained with hematoxylineosin
to give us a clue as to not only the different types of epithelia that are commonly seen in a
typical tissue or organ system but recognize when we see these normal histology slides we want to
be able to recognize a couple things one is where is the epithelium from what organ is it from
number two what cell types are more than one are present in the epithelium and as we alluded
to at the beginning of this chapter where the stem cells are for those epithelial cell types if
known first one is basically an epithelium that's known as simple cuboidal highly characteristic
of much of the tubules that make up the kidney this happens to be a view of a collecting duct
with a classic cuboidal epithelium and fairly well recognized cell boundaries that constitute the
lining epithelium this is an example of a simple columnar epithelium that's highly characteristic
of much of the small and large intestine but unlike the kidney simple cuboidal epithelium
that we saw in the previous slide this epithelium has many different cell types two of which
are illustrated on this particular micrograph where much of the villus that constitutes or
comprises the small intestine for example is lined by an absorptive simple columnar epithelium
with microvilli or a brush border and inner that's shown at the arrow but at the arrowhead you can
see a couple of examples of unicellular gland-like cells that form the goblet mucous secreting cells
that also characterize this particular epithelium now let's move from a simple columnar
to a simple squamous epithelium squamous epithelium simple squamous epithelium is high
highly characteristic of the endothelial cells that line all blood vessels but it also forms
the parietal layer of the kidney glomerulus as indicated by the presence of the arrow at
the arrow heads are proximal tubules that again contain a simple cuboidal epithelium
that's characterized by numerous microvilli then let's move from the simple epithelium to
a stratified epithelium but before we get to stratified we need to to stop part way and talk
about a pseudostratified columnar epithelium this is highly characteristic of much of the
respiratory system including the trachea and the bronchi and in part the bronchioles and it's
pseudostratified in the sense that all of the epithelial cells that make up this epithelium lie
on the basement membrane basement membrane down at the curved arrow but only some of these epithelial
cells actually reach the luminal surface so it's not stratified in the true layered sense for
that reason so lying only on the basement membrane and not extending to the luminal surface
are basal cells and they make up the stem cells that are capable of regenerating the other
cell types in the pseudostratified epithelium the two cell types that do reach the luminal
surface are goblet cells and the ciliated columnar absorptive epithelials so what you're seeing here
for the most part in the lightly stained areas are the columnar epithelial cells and adjacent to them
are a couple of examples of the of the goblet of the goblet cells or the mucous secreting cells and
you can see that the cell surface specializations that characterize this epithelium are dominated
by true cilia that are much taller than the brush border formed by the microvilli and the on the
simple kilometer epithelium of the small intestine next what's shown in here is a highly specialized
epithelium that basically is found in the urinary system and this is the transitional epithelium
stratified epithelium that that is associated with the bladder it's transitional because the
shape of these cells can change depending on how full the bladder is so we presume that because of
the presence of the rounded pillow-like epithelial cells that are lining immediately adjacent to
the luminal surface that this is an example of a bladder that is empty whereas the epithelial
cells on the luminal surface would tend to be much flatter and more squamate basically in
a condition that from a full bladder next is a stratified squamous epithelium and
certainly the best known location of this is the epithelium of the epidermis that makes
up an outer lining of skin so note again that stratified squamous epithelium contains more
than just keratinocytes which certainly are its major cell type that are squamous in nature note
also that stratified squamous epithelium contains melanocytes as well as antigen presenting cells
in the form of longer hand cells probably what's illustrated at the arrowhead is a lighter staining
melanocyte because they lie directly on the within the basal layer of this epithelium note
that this epithelium has not only a prominent basal layer but it is the basal layers in the
in the basal stratum that make up the stem cells that regenerate all of the other cell types in
this epithelium particularly with regard to the keratinocytes finally let's look instead of at
a stratified squamous epithelium let's look at a stratified cuboidal epithelium found in very
restricted locations typically only in the ducts of salivary or even sweat glands and you can
see an illustration here of a number of the of the stratified cuboidal ducts that
are typically found in sweat glands and then finally here is a salivary gland it
consists of an epithelium that's a combination of cirrus cells and mucous cells and obviously there
are different degrees of mucous and cirrus cells present in either the in the three salivary glands
the protogland is a pure serous gland whereas the submandibular and sublingual glands tend to be
mixed glands i wonder what you're looking at at the tip of the arrow are the lightly stained
mucous cells they typically don't stain well in in h e stains the darkly stained cells
that are adjacent are basically the serous cells and they stain much more prominently with
basophilic dyes in this histologic preparation
CHAPTER#1- CELL BIOLOGY & EPITHELIUM. 6- Epithelium
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