Comparison of mammalian skin glands.
The APSU (apo-pilosebaceous unit) is a common type of skin gland found in the armpit and groin of humans. It consists of a sebaceous gland, a hair follicle, and an apocrine sweat gland. Apocrine glands secrete by pinching off part of a secretory cell and releasing it into the duct. This is very different from typical (eccrine) sweat gland that secrete by exocytosis and are found all over the skin of humans. The MPSU (mammolobular-pilosebaceous unit) is thought to be a derived APSU with apocrine mammolobular secretory cells replacing the sweat-gland cells. A mammary gland contains one or more MPSUs and a nipple (in most cases, though some mammals like monotremes lack nipples).
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evolution, development, evodevo, mammary gland evolution, ectodermal appendages, skin appendages, apo-pilo sebaceous unit