Cells of Connective Tissue, Reticulo-Endothelial System, Animal Tissue

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Cells of Connective Tissue

(1) Fibroblasts: They are most numerous and flattened having irregular cells with branching processes. They produce collagen fibres and are particularly active during wound repair. Activity is impaired in scurvy. The old inactive fibroblasts are called fibrocytes. Reticular cells are similar to fibroblast and form reticular fibres. These cells represent embryonic mesenchymal reserve cells or stem or mother cells and form all other cells of the connective tissue.

(2) Macrophages: They are also called histiocyte or clasmatocyte. They may be fixed or nomadic in nature. They are phagocytic in nature and form a part of mononuclear phagocytic system. When foreign body is large, they unite together and form 'giant cells'.

(3) Plasma cells: They are derived from B-Iymphocytes when needed. Nucleus is eccentric and has a 'cartwheel/arrangement of heterochromatin'. They produce antibodies and may be seen as 'Russel bodies'.

(4) Mast cells: They are also called mastocyte. They are characteristically located around blood vessel. Nucleus is small and cytoplasm with large number of coarse granules showing metachromasia. These cells form pseudopodia. They produce heparin-an anticoagulant, histamine-a vasodialator, serotonin - a vasoconstrictor. These cells are ultimately associated with inflammatory, allergic and hypersensitivity reactions.

(5) Fat cells: They are also called lipocytes or adipocytes. They are filled with large globule of lipid and have signet ring shape. They produce and store fat.

(6) Pigment cells: They are also called melanocytes or chromatophores. They produce melanin.

Mesenchyme cells are undifferentiated cells and are potent to give rise all other types of cells.

Reticulo-endothelial system: It is an important defence system of body. It is composed of phagocytic endothelium of blood vessels, Kupffer cells of liver, microglia of brain, reticular cells of lymph nodes and spleen, rnacrophaqes of areolar tissue, dust cells of pulmonary alveoli and monocytes of blood. They destroy the foreign particles by phagocytosis.

1. White fibrous tissue:

(a) Composed of bundles of collagen fibres.

(b) Only fibroblasts cells are-found.

(c) They constitute tendon.

(d) They bind muscle to bone.

2. Raphe: A linear fibrous band formed by interdigitation of the tendinous or aponeurotic ends of the muscle. It is similar to ligament but stretchable. e.g. linea alba, mylohyoid raphe etc.

3. Yellow elastic tissue:

(a) It constitutes ligaments.

(b) It provides strength and elasticity.

(c) It joins bone to bone.

(d) It provides considerable movements of the parts joined by it.

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