CHAPTER#1- CELL BIOLOGY & EPITHELIUM. 6- Epithelium

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

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