Electron microscopic study on human eccrine sweat glands.

In this electron microscopic study on human axillary eccrine sweat gland, the so-called dark and clear cells composing the secretory epithelium were designated as “superficial” and “basal” cells respectively, because of their different location in the secretory epithelium.The cell bodies of the tall superficial cells occupy the superficial portion and line the main gland lumen with their apical surface, whereas the slender basal parts are extended in between the basal cells to reach either to the myoepithelial cell or to the basement membrane. The superficial cells are characterized by poorly developed microvilli protruded into the gland lumen, well-developed abundant tonofilament bundles oriented in various directions, poorly developed intercellular interdigitations as well as basal infoldings, and the accumulation of the secretory vacuoles in the apical cytoplasm.The rounded basal cells occupy the basal portion of the secretory epithelium without bordering directly on the main gland lumen. They enclose, however, the intercellular canaliculi between them which seem to empty in the main gland lumen; their wide basal surface rests either on the myoepithelial cell or the basement membrane. The basal cells are characterized by a number of closely packed microvilli protruded into the intercellular canaliculus, lacking secretory vacuoles, large content of glycogen granules, extraordinarily well-developed agranular endoplasmic reticulum, and extensive and complicated intercellular interdigitation and basal infolding both of which show vigorous vesiculation of the plasma membrane.The transformation between both secretory cell types was never proved. The occurrence of two secretory cell types with distinct cytological differences suggests the existence of two loci of different kinds of sweat production in the secretory epithelium of the human eccrine sweat gland.The concordance in certain cytological features of the basal cells with the salt-gland cells of some animals and birds supports the view that the basal cells are probably the production site of sweat which is high in water, Na and Cl content. The agranular endoplasmic reticulum closely packed in the whole cytoplasm of the basal cells is supposed to participate in the transport of water and the solutes from extracellular spaces to the intercellular canaliculus.The agranular endoplasmic reticulum in the basal cells sometimes contain a small amount of glycogen granules within its dilated cisterns, a finding which suggests that the agranular endoplasmic reticulum may probably play a role also in intracellular glycogen metabolism.The secretory vacuoles elaborated from the Golgi vacuoles in the superficial cells are discharged into the main gland lumen by means of either eccrine or apocrine mode of secretion. In the process of the latter, it was discovered that the paired demarcation membrane was formed at the neck of the papillary apocrine projection. The opinion of the present authors concerning the formation mechanism of the apocrine projection was also presented.The ultrastructural properties of the membrane bounded lipid droplets found in both cell types were described and the formation of large monolocular lipid droplets and the correlation between the lipid droplets and the dense bodies elaborated in the Golgi area were also discussed.