Electron Microscopic Observations on the Sweat Glands of the Horse

Abstract

Sweat glands in the abdominal skin of the horse were observed with the electron microscope. In good accordance with the light microscopic findings of ITO et al. (1961), it was shown by electron microscopy that the secretory epithelium of this gland consisted of two distinct secretory cell types, viz. the vacuolated cells and dense cells. The former is the main constituent of the secretory epithelium, columnar or cuboidal in shape, and filled with a great number of clear secretory vacuoles. This cell type is also characterized by well developed microvilli, tips of which are often expanded and separated to bring about a part of the secretion (microapocrine secretion). Besides this mechanism of secretion release, large projections often extend into the lumen and may be presumably detached from the cell body (macroapocrine secretion). The GOLGI apparatus and the rough-surfaced endoplasmic reticulum are well developed, and presumable transitions between the GOLGI vesicles, vacuoles and the secretory vacuoles were observed.
The second cell type of secretory epithelium, the dense cell is small in size and the electron density of the cytoplasm is considerably high. Cells of this type contain large round mitochondria but no secretory vacuoles. Plasma membranes of the dense cell are strongly folded on lateral and basal cell surfaces, but the microvilli on the apical cell surface are poorly developed, Probable significance in functional activity of the dense cell is discussed and a possibility that this cell may be a degenerating form of secretory cells is presented.