Connective tissue is made up of a large amount of intercellular matrix of fibres or both and living cells. On the basis of nature of matrix connective tissue is of 3 types. They are connective tissue proper, skeletal tissue and fluid connective tissue.
Connective tissue proper – It is made up of a semisolid matrix and cells. Seven variety of connective tissue proper is recognized. They are: (1) Areolar tissue, (2) Adipose tissue, (3) White fibour connective tissue, (4) yellow elastic tissue, (5) Reticular tissue, (6) Pigmented tissue and (7) Mucous connective tissue.
(1) Areolar Tissue:
Areolar tissue is composed of semisolid matrix containing fibres and cells. The fibres are of three types: – white fibres, yellow fibres and reticular fibres. The white fibre is non-elastic and made up of protein collagen. Yellow fibre is elastic and made up of protein elastin and reticular fibre is net-like and made up of protein reticulin. Various types of cells are found in the matrix. The cells are of following types –
It is an active cell. It is a mature form. It produces white and yellow fibres.
It is also called macrophage. It is a large irregular cell. It phagocytosis. In lungs, it is called dust cells and in liver called Kupffer cells.
(iii) Mast Cells:
These cells secrete anticoagulant heparin, synaptic mediator, and histamine and vasoconstrictor serotonin.
(iv) Plasma Cells:
These are small oval cells. They secrete You-globulin protein or antibodies.
They are leucocytes. They leave the blood vessel and enter the aerolar connective tissue. These cells increase their number during allergic condition such as asthma, parasitic infections etc.
These are spherical cells. They carry antibodies.
Areolar tissue is found below the skin, between glands, vessels and around the muscles.
2. Adipose Tissue:
It is composed of fat cells and few fibres. The fibres may be collagenous, elastic and reticular. The fat cells or adepocytes contain a large fat droplet which fills the entire cell and displaces the cytoplasm and nucleus to periphery. Adipose tissues are of two types – White Adipose tissue and Brown Adipose tissue. White adepocytes and monolocular as they contain single fat droplet whereas yellow adepocytes are multicellular as they contain many fat droplets.
Adipose tissues are deposited in omentum, mesentery, perinephric region, sub-cutaneous region.
(a) Adipose tissue gives shape to the limbs and body and protects visceral organs from sock and injury.
(b) Oxidation of fat in adepocytes generates heats to regulate body temperature; hence, it is called metabolic reserve bank of the body.
(c) The sub-cutaneous adipose tissue acts as shock absorber, e.g. sole of feet and palm of hand.
(d) The blubber of whale below the skin acts as thermo insulator.
3. White Fibrous Connective Tissue:
It is made up of parallel of collagen fibres and a few fibroblasts which are arranged in rows. The white fibrous tissue which attatches muscles or muscles are called tendons. Some white fibrous tissue connects bones called ligaments.
4. Yellow Elastic Tissue:
It is made up of diversely arranged yellow elastic fibres and a few fibroblasts. It forms ligaments connecting bones. It is found in ligamentum flava of vertebrates.
5. Reticular Tissue:
It is made up of net-like reticular fibres and reticulo-endothelial cells. It is found in bone marrow, spleen, lymph nodes, etc. these cells are phagocytic.
6. Pigment Connective Tissue:
Some connective tissue cells contain pigment granules. The black pigment melanin containing cell is called menanocyte. Other pigments found in lower animals are xanthine (yellow pigment), guanine (white pigment) and erythrin (red pigemnt). Pigment connective tissues are found in dermis of skin, piameter and choroid coat of eye. The pigments absorb light and protect the internal tissues from harmful effect of sunlight.
7. Mucous Connective Tissue:
It is also called jelly-like connective tissue. It is made up of a gelatinous substance called Wharton’ this jelly. It is found in the umbilical chord of embryos and vitreous humour of eyeballs.