Fine structure of the human sweat ducts of eccrine and apocrine types.

The sweat ducts of human eccrine and apocrine (ceruminous) glands were observed with the transmission electron microscope. Both the dermal and epidermal segment of the eccrine as well as apocrine ducts consist of two epithelial layers: luminal cells and peripheral cells. Well-developed microvilli, occurrence of cored vesicles, dense granules, multivesicular bodies and phagosomes in the adluminal filamentous zone, and a strong accumulation of mitochondria in the basal part of the duct epithelium at the dermal segment, as well as an accumulation of small clear vesicles beneath the surface of the luminal cells of the epidermal segment are all prominent in the eccrine duct and concomitant with the special function of the human eccrine duct, i.e., absorption of ions to make the sweat hyotonic and an active endocytosis of some material from the sweat. All of the above enumerated characteristics of the eccrine duct are only rarely or never seen in the apocrine duct. On the other hand, lipid droplets appear in the peripheral cells in a certain level of the apocrine duct near its orifice into the hair follicle, suggesting a kind of metaplasia towards the sebaceous gland. Epidermal duct cells of both eccrine and apocrine sweat glands may keratinize. In the eccrine duct the process in the duct cells precedes the surrounding keratinocytes, while in the apocrine duct the relationship is reversed.