[Human spermatogenesis: basic research and clinical issues].

Histological evaluation of human spermatogenesis suffers from the hazy border line between normal and pathological germ cell development. This border line needs better definition for histological fertility diagnosis and the early detection of germ cell tumors. Testicular biopsies from more than 2,900 patients with fertility disturbances and more than 1,900 patients with testicular tumors were investigated by means of semithin sectioning, different immunocytochemical methods and transmission electron microscopy. Cellular systems of the human testes possess a degree of autonomy from the body. Their morphological and functional heterogeneity reveals characteristics of cells that are not terminally differentiated. In the testis of an adult, fertile man not only the proliferation of spermatogonia, maturation divisions of spermatocytes and differentiation of spermatids take place, but also abortive germ cells, as well as apoptotic and degenerative cells appear. Disturbances of spermatogenesis are defined by the evaluation of quantity and quality of germ cell alterations. Compensatory and non compensatory defects of spermatogenesis may be distinguished. Deficiency of spermatogonial cell types, multilayered spermatogonia, megalospermatocytes, malformed spermatids and single tumor cells in the face of sufficient development of mature spermatids are considered compensatory defects of spermatogenesis. Dominating malformed germ cells or tumor cells accompanied by an arrest or lack of spermatogenesis, however, represent non-compensatory defects of spermatogenesis. In addition, normal organization and function of the microvasculature, Leydig cells and compartmentalizing cells in the intertubular space are prerequisites for spermatogenesis. The neuroendocrine function of Leydig cells may be responsible for regulating the blood flow rate and the permeability to hormones and nutritive substances. Finally, for patients a successful definition of the border line between normal and pathological events of germ cell development may be essential for early detection of germ cell tumors. Therefore, anatomical sciences not only contribute to basic research, advanced diagnostics and therapeutic concepts related to diseases of the male gonad, but also to the improvement of assisted reproduction.