It is important to understand
how glands release
their secretory products and I said earlier
in this lecture, we are going to concentrate
only on exocrine glands. Well, there are three ways.
In this diagram, there are three representations
of the way in which exocrine glands or secretory
cells secrete their products. Firstly, there
is merocrine secretion. Now this secretion,
this form of secretion, this mechanism of secretion
is probably the most common. The secretory
cells make their products and they store their
products within little membrane-bound granules
at the apex of the cell. And when they stimulate
to secrete, these little granules containing
the secretory product moves to the apical
surface of the cell, the membrane fuses with
the cell membrane and the product is released
into the luminal space by a process we call
exocytosis. So that's merocrine secretion.
Another way in which the cell gets rid of
these products is by apocrine secretion. Apocrine
secretion is where often the secretion product
is stored at the apical surface, but then
the apical surface or a component of that
apical surface breaks off and so what is released
into the luminal space is the secretion product
that also is a small part of the cytoplasm
of the cell. And this is common in some of
the glands in the eyelid and probably in the
mammary gland. And the remaining form of secretion,
the remaining way in which cells release a
product is called holocrine secretion. This
is where the cell synthesize its product,
accumulates the product within the cell cytoplasm,
but then undergoes programmed cell death.
So the whole cell is lost into the luminal space.
Holocrine secretion, we will see when we look
at skin, when we look at the sebaceous gland
in skin where holocrine secretion occurs.