Another cell that is resident in connective
tissue is the mast cell. Now, mast cells migrate
into connective tissue from the blood. They
look like a monocyte if you saw them in a
blood smear. So you really cannot differentiate
them in blood, from monocytes. But in connective
tissue you can, because once they move into
connective tissue, they start to make granules.
They synthesize granules inside them. You
see these granules inside the cell at the
very bottom electron micrograph picture and
also in the top they appear as reddish granules.
All these granules when they are released,
they release heparin and also histamine. Histamine
is important because it alters, it changes
the permeability of blood capillaries and
once that blood capillary has altered permeability,
it becomes very leaky. So tissue fluids starts
to accumulate and we experience a condition
of oedema sometimes, swollen tissue, swollen
connective tissue spaces. Heparin is an anticoagulant.
And both heparin and histamine released from
mast cells, is in response to a number of different
stimuli, such as allergic reactions, high fever,
certain conditions like that. But they
too, along with the macrophage are also very
important connective tissue cells.
Well, the adipocyte is another common cell
in connective tissue. Sometimes you see them isolated
or in very small groups as you see this edge of
this section of a salivary gland, happens to
be the pancreas, but let's not worry about
that at this stage. These fat cells are clear
staining and one day they occur in large groups
they are called adipose tissue shown here
on the right hand side. Adipose tissue is
our storage of energy. The fat cells store
triglycerides and those triglycerides are
used as an energy source when we cannot get
energy from other sources in certain conditions.
And the adipose tissue is very very vascular.
Here you see some little erythrocytes passing
through a blood capillary. We call this adipose
tissue, unilocular adipose tissue because
there is just one big fat droplet inside the
cell and the nucleus inside the plasma is
pushed to the side. And because the fact its
dissolved during normal tissue processing,
then the cytoplasm appears merely as just
a white and clear hole in the section.
There is another sort of adipose tissue and that
is brown adipose tissue. And that is characteristic
of the embryo, developing fetus and the newborn.
And that is really to control heat loss, so
a thermo regulatory mechanism. It maintains
body temperature. And in hibernating animals
that wakeup after a long winter sleep, that
brown fat is broken down and used to create
warmth and maintain body temperature. We do
not see brown fat in normal adult tissues.
It is only really a characteristic feature
of the newborn as a heat insulating role, to
make sure the newborn does not
lose excessive body heat.