which epithelia are named and classified.
I mentioned earlier that there are some cells
such as the goblet cell that secretes a mucous
type product. But there are also other cells
that secrete a serous type product and I will
explain what those two types of products really
are in a moment. In this slide, you can see
two images, two histological sections taken
through two different exocrine glands. One
is dominated by mucous secreting units.
The other is dominated by serous secretory units.
And you see here, they stain very differently.
In the case of the mucous secreting unit or
mucous secreting cells, the blue tinge or
the light staining is due to the component
of the secretory product. Mucous secreting
cells or mucous secreting units, we call them
asini as well which I will explain later on.
They secrete proteins that are glycosylated
with an anionic oligosaccharides. And because
of that, these proteins, the secretory products
are water soluble. So depending on the fix
that you use, often, the secretory products
are lost from the cell. Here in some way,
there have been a little bit retained. On
the right-hand side, you see serous secreting
cells. These are proteins and if the tissue
has been preserved very well, you can see
little tiny granules containing these protein
secretory products stored in small vesicles
at the apex of the cells. Often you will see
the rest of the cell, the rest of the cytoplasm
basophilic and this reflects the enormous
protein factory inside the cell that is making
the secretory product. Go back to the mucous
secreting unit. The cells there have nuclei
that are squashed against the base of the
cell so they appear flattened.
The serous secreting cells have nice rounded nuclei and
often that is a good indication or a good
way to identify the difference between mucous
secreting cells and serous secreting cells.
Sometimes a gland can have both secretory
units. Here you see a serous secreting unit,
very pink staining, here you see a mucous
secreting unit. And here is an example of what
I've described before where the secretory product
is water soluble and lost during the normal
tissue processing where you use to examine
sections of tissue stained with hematoxylin
and eosin. Down below, if you look very carefully,
you can see three profiles of duct system.
These ducts, remember, carry the secretion
product from the secretory cells to an exterior
location. And these locations can be often
some distance from where the gland is housed
within the body. And we will see an example
of that when we look at the pancreas.
It has a long duct that opens into the duodenum some
distance away. Well, when we look at large glands,