The sebaceous glands are an integral part of the pilosebaceous unit and are found over the entire body surface with the exception of the palms and soles. The gland itself is made up of several lobules, which are separated by vascular connective tissue. These lobules all empty into a short duct which then empties into the upper part of a hair follicle at the level of the infun-dibulum. More than one sebaceous duct may drain into the upper part of the hair follicle.
The hair follicle, the hair, the sebaceous gland and arrectores pilorum muscle and (in certain regions) the apocrine glands make up the pilo-sebaceous unit (Fig. 4.2).
Apocrine glands are found predominantly in the axillary and anogenital regions, although they are also found in the ear canal (ceruminal glands) and eyelids (Moll's glands). They are derived from epidermis and develop as an outgrowth of follicular epithelium. They represent compound sweat glands with a secretory coil that extends deep through the dermis into subcutaneous tissue and drains via a long straight secretory duct, usually into a hair follicle. The function of apocrine glands in humans is not altogether clear but in other mammals they are responsible for sexual attraction, and scent production is responsible for axillary and inguinal odour. They become functionally active and larger at puberty. The secretion is opalescent and malodorous.
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