The fine structure of monkey sertoli cells in the transitional zone at the junction of the seminiferous tubules with the tubuli recti

Abstract The monkey testis contains an axial rete in a highly vascular central core of loose connective tissue. Seminiferous tubules join the rete along its entire length. The short terminal segments of the tubules are lined mainly by Sertoli cells. There is then a transition from Sertoli cell epithelium to the simple cuboidal epithelium of tubuli recti, which connect the seminiferous tubules to the rete testis. Electron microscopic observations of the Sertoli cell in the terminal regions of the seminiferous tubules reveal a highly lobulated nucleus, a unique nucleolus and a columnar cell body with an irregular free surface bearing processes of varied form projecting into the tubule lumen. The cytoplasm is characterized by a well developed rough endoplasmic reticulum, large numbers of lipid droplets, and an extraordinary abundance of 70 Å filaments. Occasionally these latter are so densely packed that other organelles are excluded from large areas of the cytoplasm. Profiles of smooth endoplasmic reticulum are few in marked contrast to the usual condition of Sertoli cells elsewhere in the seminiferous tubules. Many of the Sertoli cells in the terminal regions of the seminiferous tubules contain spermatozoa in various stages of degradation. Small lymphocytes, never observed in normal seminiferous tubules, are distributed in small numbers among the Sertoli cells of the transitional zone. No desmosomes or other junctional specializations are observed at the interface of lymphocytes with the surrounding Sertoli cells. The cytology of the terminal region of the seminiferous tubules is discussed in relationship to exit of sperm from the tubules, the blood‐testis barrier, and the pathogenesis of immune orchitis.