Sweat Glands: Eccrine and Apocrine

Abstract

RAnvier (1879) distinguished two main classes of gland in mammalian skin, the “holocrine” glands (such as sebaceous glands), in which cellular disintegration provides the secretory material, and the “merocrine” glands, in which the cells do not lose their structural integrity. The terms “eccrine” and “apocrine” [Kϱίνeιν, to separate (secrete); έϰ, out of; ά;πo from] were introduced by SChiefferdecker (1917) to describe two types of simple tubular exocrine gland within the merocrine category. Eccrine glands were considered histologically to be those which discharged a fluid secretion without loss of cytoplasmic material, while the apocrine glands were in fact “semi-holocrine”, with the luminal secretory cells forming protuberances which ruptured and discharged into the lumen with some of the cell contents. The “necrobiotic” stage in apocrine gland secretion was thought by SChiefferdecker to be succeeded by a phase during which a simple fluid secretion was produced while the cells returned to a low cylindrical form and recommenced their growth. Thus apocrine secretion appeared to share features of both holocrine and merocrine glands. This histological distinction between the eccrine and apocrine glands is not universally accepted:some consider the evidence that a necrobiotic phase occurs in the sweat glands of man or any other species to be equivocal (JEnkinson 1967). Further, electron microscopy has indicated that the histological differences are not so precise as was originally thought. An alternative terminology was suggested by BLigh (1967) which differentiated sweat glands in all species by their association or otherwise with hair follicles. By this definition “epitrichial” (associated with a hair follicle/sebaceous gland unit) and “atrichial” become synonymous with apocrine and eccrine glands respectively.