The ultrastructure of four types of human spermatogonia

Abstract

Electron microscopic examination of normal human testes has revealed the ultrastructure of four types of spermatogonia. These are the dark type A (AD), the pale type A (AP), the type B (B), and a new type A (AL). The subcellular criteria used in distinguishing between these four spermatogonial types include the shape of the nucleus, the density of the nucleoplasm, the type of nucleolus and its placement within the nucleus, the structure of the mitochondrial cristae, the association of the endoplasmic reticulum with the mitochondria, the amount of glycogen present within the cell, and the presence of previously undescribed filamentous structures in the cytoplasm of the AL and AD spermatogonia. Each spermatogonium is in contact with the tubular basal lamina; the amount of contact progressively decreases from the AL, a flat cell lying parallel to the basal lamina, through the AD and AP to the B spermatogonia, the latter being a pear-shaped cell with its long axis perpendicular to the basal lamina.