Areolar tissue: This is the most widely distributed connective tissue in the body of the animals. The main function of this tissue is connective. It usually fixes skin with the muscles and then attaches blood vessels and nerves with the surrounding tissues and fastens the peritoneum to the body wall and the viscera. The other functions of Areolar tissue include formation of the dermis of the skin and submucosa in the wall of the alimentary canal.
It forms packaging material in all organs between the muscles. It also permits considerable stretching of the tissues. Structurally the areolar tissue has a large amount of transparent sticky matrix enclosing numerous fibrous cells and large quantity of mucin. The fibres in the areolar tissue are of two types white and yellow.
The white fibres occur in fasciles (bundles) and are very fine and wavy. They are bound together by mucin. They are nonelastic and unbranched and are formed of a protein called collagen. The collagen fibres are composed of numerous microfibrils which provide tenacity to the tissues.
The Yellow fibres are less in number than the white fibres. They are also much thicker and occur singly. The yellow fibres are branched and elastic with the branches getting interwoven to form a network. Chemically they are composed of a protein called elastin. The spaces left between the fibres are called areolae hence the name areolar tissue.
The cells found in the matrix are of three kinds namely fibroblasts or fibrocytes, macrophages or histocytes and mast cells. The fibroblasts are elongated flat cells with oval nuclei. They secret the material from which fibres is formed. Those secreting the white fibres lie along with them at the initial stages and later move away. Those producing Yellow fibres are never adjacant to the fibres. The macrophages are large amoeboid cells with ovoid nuclei. They freely wander in the matrix and engulf foreign particles microbes damaged cells etc.
Mast cells are oval shaped cells or irregular shaped cells and have abundant dense granules in cytoplasm. It is these cells that produce the matrix. They also produce haparin, histamine, and serotonin. Haparin prevents clotting of the blood. While histamine is involved in allergic reactions, Serotonin plays a role in control of the blood pressure.