The following points highlight the six main cells of areolar tissue along with its function. They are:- 1. Fibroblasts Cells 2. Histiocytes Cells 3. Basophil Cells 4. Plasma Cells 5. Pigment Cells 6. Mast Cells.
1. Fibroblasts Cells (Fibrocytes):
Fibroblast is an active cell. Fibrocyte is an inactive one. These cells are usually elongated containing an oval nucleus and are often branching. The younger cells are more rounded, whereas the older ones are more elongated. They remain upon and in between the fibres. When they lie upon the surface of an aponeurosis, they are arranged side by side and look like an endothelium.
In the cornea the fibroblasts remain joined together through their branches. Fibroblasts are non-motile and are not phagocytic.
i. Produce white fibrous tissue under normal and pathological conditions.
ii. They are also responsible for the formation of amorphous ground substance.
iii. It takes a great part in replacement fibrosis during repair of inflammation. Following tissue injury there is an increase in cytoplasmic ribonucleoprotein (RNP) granules in fibroblast, observed electron microscopically.
2. Histiocytes Cells (Clasmatocytes):
These cells belong to reticulo-endothelial (R.E.) system and have functions similar to them. They are large and irregular containing one or more nuclei and a basophilic cytoplasm. They are actively motile and phagocytic and engulf foreign substance and bacteria.
The proteolytic enzymes present in the cells destroy the digestible ingested materials.
3. Basophil (Basiphil) Cells:
They are large, spherical or oval cells, actively motile and containing a single nucleus and a granular basophilic cytoplasm. They are commonly found in those places where fat is being deposited. Occasionally they burrow into the blood vessels and appear as the basophilic leucocytes (mast cells) in the blood stream. Their functions are same as that of the mast cells.
4. Plasma Cells:
These are large, oval cells with non-granular basophilic cytoplasm stained by Leishman’s method and a round eccentric nucleus. The chromatin in the nucleus is arranged like the spokes of a wheel. These cells have an abundance of granular endoplasmic reticulum and so can be stained with pyronins (pyroninophilia) which demonstrate RNA. Fluorescent antibody techniques indicate that these cells form antibodies.
They help in synthesis of γ-globulin.
5. Pigment Cells:
Some of the connective tissue cells are found to possess pigment granules and such cells are more common in the skin, choroid coat of the eye, pia mater, etc. the black pigment is called melanin and the cells, melanocytes. In some lower vertebrates, the pigment may be yellowish and such cells are called the xanthophores.
The pigment granules generally remain collected round the nucleus. But change of environment, i.e., light, moisture, etc., causes dispersal of the pigment granules out into the cytoplasm. Due to this mechanism certain animals can change their skin colour and use this device as a protective camouflage. This redistribution of the pigment is caused by a hormone secreted by the posterior pituitary (melanocyte-stimulating hormone, MSH).
6. Mast Cells:
They are large round or oval cells. The cytoplasm contains coarse granules which can be stained with basic dyes, the nucleus being stained pale. Under electron microscope, little granular endoplasmic reticulum or free RNA has been observed inside the cells.
Mast Cells Probably Elaborate:
(a) The anticoagulant heparin,
(b) Probable synaptic mediator histamine, and
(c) A vasoconstrictor serotonin.
The areolar tissue is distributed in varying amounts throughout the body. It occupies the intercellular spaces of other connective tissue and serves as a support and also as a packing material. The cells in it serve the purpose as described above.