Animal tissues and their functions pdf

Animal tissues and their functions pdf

Aug 09, 2022, 16:45 IST

Origin and functions of Animal tissues

EPITHELIAL TISSUE

• The word ‘epithelium’ was introduced by Ruysch.

• It is the most primitive or the first evolved type of tissue.

• It consists of cells of different shapes, held together, by a small amount of an intercellular substance called matrix.

• The epithelial cells rest on a basement membrane, which serves to bind the epithelial cells and provide nutrition to them. Check our More Biology Doubts

Basement membrane is a delicate, non cellular layer consisting of extracellular substance. It is differentiated into outer basal lamina and inner reticular lamina. Basal lamina (lamina basalis) consists of lamina lucida in contact with the basal surfaces of the epithelial cells and lamina densa just beneath lamina lucida. The former consists of a cell coat or glycocalyx of basal surface of epithelial cells. It has proteoglycans, glycoproteins, adhesive proteins, integrins and hemidesmosomes. In kidney glomerulus, lamina lucida lies on both the sides of basal lamina due to juxtaposition of capillary cells and podocytes and absence of reticular lamina. Lamina densa consists of a delicate network of collagen, heparan sulphate, proteoglycans and laminin protein. Basal lamina is present around Schwann cells and muscle cells. Reticular lamina consists of dense matrix and collagen fibrils which bind the lamina densa to underlying connective tissue. The matrix has abundant proteoglycans.

Diagram exhibiting microvilli, cilia, cell junctions and basement membrane.

Functions of Animal Tisses

Basement membrane anchors epithelial tissue to the underlying connective tissue.

It provides a selectively permeable barrier for glomerular filtration.

It provides a medium for material exchange between epithelial cells and vascular supply underneath.

It determines polarity, metabolism, cell division, repair and movement of other tissues.

Connective Tissue

It consists of two basic elements: cells and non cellular matrix. Connective tissue cells, unlike epithelial cells, are separated by a considerable amount of matrix. Matrix further consists of ground substance and fibres.

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