Cells: Mast Cell and Adipocyte

00:02 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.

00:29 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.

00:43 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.

02:45 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.

03:22 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.