Quantitative morphology of the ovine seminiferous epithelium

Ultrastructural features and morphometric values of ovine Sertoli and spermatogenic cells are reported with special reference to the 6 stages of the seminiferous epithelial cycle. Seminiferous tubules occupy about 83% of the testicular parenchyma. Average tubular diameter (about 275 μm) and epithelial height (about 95 μm) do not vary significantly during the cycle. From preleptotene to late diplotene the cellular volume of primary spermatocytes increases nearly five-fold; the nuclear volume increases threefold in the same period. Secondary spermatocytes are observed exclusively during stage 4 of the seminiferous epithelial cycle. Due to partial cell necrosis and autolytic events, ovine spermatids lose a considerable amount of their cytoplasm during acrosome and maturation phases prior to spermiation. Sertoli cells occupy between 27.6% (stage 3) and 36.6% (stage 1) of the tubular epithelium. The average volume of a Sertoli cell varies between 6 380 μm3(stage 2) and 7 195 μm3(stage 4), the absolute surface area between 10 550 μm2and 12 305 μm2. The irregularly contoured Sertoli cell nucleus contains a vesicular nucleolus and occupies about 7.5% of the cell. Mitochondria (about 5%) and smooth endoplasmic reticulum are other prominent organelles, but three-quarters of the Sertoli cell are taken up by cytoplasmic matrix with a well-developed cytoskeleton. Ovine Sertoli cells contain large basal lipid droplets, but no typical lipid cycle can be observed.