Glandular Tissue, Animal Tissue, Defining Glands, Classification of Glands

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GLANDULAR TISSUE

The glands are generally made up of either single cells or by the aggregation of cells. These are of two types:

1. Unicellular: Made up of single cell. e.g. goblet cells.

2. Multicellular: Made up of many cells.

All the glands are formed by the folding of epithelia. Their cells are mostly cuboidal and secretory in function.

Exocrine glands: These are those glands which retain their connection with parent epithelium and all the secretion is poured up on the surface. This connection is called duct of the gland.

Classification of glands on the basis of branching of ducts:

(1) Simple glands: Where duct is unbranched and secretion is directly collected and conveyed to the surface. e.g. intestinal glands, sweat glands (man) etc.

(2) Compound glands: Where duct is branched and branches come from various secretory units. e.g. liver, pancreas, salivary glands etc.

On the basis of shape of secretory unit:

(1) Tubular: Where secretory unit is tubule like. e.g. sweat glands are simple tubular while gastric glands are compound tubular.

(2) Acinus: Where secretory unit is spherical or rounded. Liver is compound acinus gland.

(3) Alveolar: Where secretory unit is flask shaped. e.g. sebaceous glands of mammals.

(4) Tubulo-alveolar: Where secretory units are both tubular and alveolar type. e.g. mammary glands of adult, Cowper's glands etc.

On the basis of secretion and function:

(1) Holocrine glands: Entire cell fills with secretory product and then is broken up and sacrified. When overstimulated, gets plugged to form blackheads and ultimately pimples. e.g., sebaceous gland of mammals.

(2) Apocrine glands: The secretory product is accumulated in the apical part of cell or gland. This part breaks off from the remaining part of the gland which remains intact. e.g. sweat glands in the armpit and around anus.

(3) Merocrine or epicrine glands:

Most of the glands of the body are of merocrine type. They are also called epicrine glands. Their secretion is diffused out from the gland and hence gland remains intact. e.g. true sweat glands of human body.