Sebaceous glands are microscopic glands in the skin that secrete an oily secretion known as sebum. They are widely distributed all over the dermis of skin, except for the palms and soles. They are especially abundant in the scalp and face. They are also very numerous around the apertures of ear, nose, mouth and anus.
Structure of sebaceous glands:
Sebaceous glands are small and sacculated in appearance. They are made up of a cluster of about 2-6 piriform alveoli. Their ducts open into the hair follicles, with the exception of lips, glans penis, inner surface of prepuce, labia minora, nipple and areola of the breast, and tarsal glands of the eyelid, where the ducts open on the surface of the skin.
Nature of sebaceous glands:
Sebaceous glands are holocrine in nature, which means that they produce their secretion by complete degeneration of the central cells of the alveolus. The degenerated central cells are then replaced by proliferating peripheral cells.
Role of sebum:
The secretion of sebaceous glands is under hormonal control, especially the androgens. The sebum, which is the secretion of the sebaceous glands, lubricates the skin and protects it from moisture, desiccation and harmful sun rays. Sebum also lubricates hair and prevent them from becoming brittle. In addition, the sebum also has some bacterial action. Sebum makes the skin water proof, thus reducing the loss of water from skin surface.