Sebaceous glands

They are scattered all over the integument in association with the hair follicles. They are absent from the hairless portions of the body like the palms of the hands, the soles and sides of the feet. These glands, however, occur independently of hair follicles at certain places like the eyelids, margins of lips, external auditory meatus, nipples, anus and around the external genitalia, and at these sites the glands are more superficial.

The sebaceous glands are numerous and large on the scalp, forehead, ears, face, the sternal and interscapular regions. In the hairy portions of the skin, the ducts of these glands open into the hair follicles, while in the non-hairy portions, they open directly on the surface of the skin.

One or more sebaceous glands may be attached to one hair follicle. Meibomian glands, mammary glands and smegma glands of the penis are modified sebaceous glands. Perspiration in hot climate and in hot weather stimulates the production of sebum. Further, the sebaceous glands are more active at and after puberty, during menstruation and pregnancy.

Structurally, these are small glands composed of a number of rounded sacs, the alveoli. Adjacent alveoli form a mass like a bunch of grapes. All these alveoli open into a short duct near the hair follicle. An alveolar wall is formed by a basement membrane supported by a thin layer of fibrillar connective tissue. Lining the inner surface. of this basement membraneis a single layer of thin, secretory cells with round nuclei.

During secretory activity, most of these cells become polyhedral and large, and are filled with fat droplets. Large cells distended with fat, with shrinking nuclei, can be seen in the centre of the alveoli. The nuclei disappear and the cells break down into fatty detritus which mixes with the horny scales of other cells. This oily secretion of glands is then thrown out into the hair follicles and upon the surface of the epidermis.

The ducts of the sebaceous glands are lined by stratified squamous epithelium which is continuous with the external root sheath of the hair, and with the malpighian layer of the epidermis.

Structure of Epidermis
Structure of Dermis
Sebaceous Glands
Sweat Glands

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