apocrine

Apocrine refers to a mode of secretion and to certain glands or tissues in which secretory products are released with budding of the apical portion of the cell. In classic histology, apocrine secretion involves decapitation of part of the cell and release of cytoplasm rich in secretory material; however, many glands historically described as apocrine primarily release their product by merocrine (exocytotic) mechanisms, and the label apocrine is sometimes used for glands with apocrine-like features rather than strict apocrine secretion.

Apocrine glands occur in several sites. In humans, the best known are the apocrine sweat glands, located mainly in the axilla, groin, and perineal regions, and associated with hair follicles. They are larger than eccrine glands and produce a viscous, protein- and lipid-rich secretion that becomes odorous when acted on by skin bacteria. Their activity increases after puberty and is modulated by androgens and other hormones. Eccrine glands, in contrast, are distributed widely and primarily secrete a watery fluid for thermoregulation.

Other apocrine glands include ceruminous glands of the external ear, which combine with sebaceous glands to form ear cerumen, and mammary glands, which secrete milk through mechanisms that involve apocrine-like cytoplasmic shedding for fat droplets. The term apocrine also appears in pathology, for example apocrine metaplasia of breast ducts, a change in which epithelial cells acquire apocrine characteristics and cytoplasm-rich, eosinophilic appearance; it is evaluated in the context of fibrocystic changes or breast neoplasia.