On the Morphology of the Transitional Zone of the Seminiferous Tubule and the Rete Testis in Man

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Abstract
The transitional zone between the seminiferous tubules and the rete testis in man was examined by means of light and transmission electron microscopy. There are 3 types of junctions: end-to-end-junction, end-to-side-junction and side-to-end-junction. In the terminal segment, the epithelial layer consists of modified Sertoli cells. Sometimes there are single spermatogonia among these modified Sertoli cells. The lumen of the terminal segment is narrow, the lamina propria shows considerable thickenning. At the end of the terminal segment the modified Serotli cells project into the lumen of the tubulus rectus forming a structure which resembles a lip. Compared with the Sertoli cells of the seminiferous tubule, the Sertoli cells of the terminal segment are modified in a typical manner; the nuclei are oval-shaped and do not show indentations of the nucleolemma. Perinuclear cytoplasmic inclusions are lacking, in the apical region there are numerous lipid droplets and telolysosomes. In the whole cytoplasm there is an increased number of microfilaments and microtubules. The lamina propria consists of a basal lamina and of myofibroblasts which are arranged in an irregular structural pattern. Between these myofibroblasts thick bundles of collagen fibrils surround the terminal segment in a ring. In the proximal part of the tubulus rectus there are islands of ectopic modified germinal epithelium arranged round a center of connective tissue.