Apocrine sweat gland

Apocrine sweat glands are a type of exocrine gland found in the skin that are distinct from eccrine sweat glands in their distribution, structure, and function.

Distribution and Location

Apocrine sweat glands are primarily located in the axillae (armpits), anogenital region, areolae of the breasts, and periumbilical area. They are also found in modified forms in the external ear canal (ceruminous glands) and the eyelids (glands of Moll). Their distribution is closely associated with hair follicles, as they empty their secretions into the upper portion of the hair follicle, above the sebaceous gland duct.

Structure

• Apocrine glands are coiled tubular glands located deep in the dermis or at the junction of the dermis and subcutaneous fat.

• They have a larger lumen than eccrine glands.

• The secretory portion is lined by a single layer of cuboidal to columnar epithelial cells, surrounded by myoepithelial cells that contract to expel the secretory product.

Secretion and Function

• Apocrine glands produce a viscous, lipid-rich, initially odorless fluid. The characteristic body odor associated with these glands results from bacterial decomposition of the secretion on the skin surface.

• Unlike eccrine glands, which are primarily involved in thermoregulation, apocrine glands do not play a significant role in temperature control in humans.

• Their secretion is thought to have a role in pheromone signaling and scent communication, though this function is vestigial in humans compared to other mammals.

• The term "apocrine" historically referred to a mode of secretion in which the apical portion of the cell is pinched off with the secretory product (decapitation secretion), though this mechanism has been debated; evidence suggests that merocrine (exocytotic) secretion may also occur.

Development and Activity

Apocrine glands develop from the follicular epithelium during embryogenesis but remain inactive until puberty, when they are stimulated by androgens. Their activity is regulated by adrenergic (sympathetic) innervation, and they respond to emotional and hormonal stimuli rather than thermal stimuli.

Clinical Significance

Apocrine glands are involved in several dermatologic conditions, most notably hidradenitis suppurativa (a chronic inflammatory disease of the apocrine gland-bearing skin), as well as Fox-Fordyce disease, apocrine bromhidrosis, and apocrine chromhidrosis. Apocrine gland carcinomas, though rare, can also arise from these structures.