Apokrin

Apokrin, or apocrine, refers to a mode of glandular secretion in which the secretory product is released together with a portion of the secreting cell’s apical cytoplasm as the plasma membrane buds off. This contrasts with merokrin (eccrine) secretion, where products are released by exocytosis without loss of cytoplasm, and holokrin secretion, where the whole cell disintegrates to release its contents.

Apokrine glands are classically associated with the skin, particularly in the axillary and anogenital regions, and are connected to hair follicles. The secretions are typically thicker and richer in lipids and proteins than those of eccrine glands and can acquire odor after bacterial action, especially after puberty when hormonal changes occur. Nerve supply and hormonal signals influence their activity; sympathetic, adrenergic pathways play a significant role in their stimulation, in contrast to the cholinergic control more common for eccrine glands.

In humans, apocrine glands are less involved in thermoregulation than eccrine glands. Their secretions are often described as odoriferous precursors, contributing to body odor through bacterial metabolism. In the breast, lipid components of milk have been described as having apocrine characteristics, though lactation involves multiple secretory mechanisms and merocrine pathways are also important for many milk components.

Historically, apocrine describes this secretion mode at the cellular level. In modern anatomy and histology, the term is used to denote glands and cells that exhibit apocrine features, including apocrine changes observed in certain breast tissues.