Spermatogenesis

Spermatogenesis takes place within the seminiferous tubules and involves the replication of stem cells to enable continuous sperm production over the male life span. The process involves mitotic replication of spermatogonia and the subsequent reduction of chromosome number in primary and secondary spermatocytes to the haploid state. The haploid spermatids undergo a complex differentiation process, termed spermiogenesis, resulting in compaction of the nucleus to form the sperm head, the development of the acrosome and sperm tail, a reorganization of the cell organelles, and a shedding of excess cytoplasm. The entire spermatogenic process is highly regulated, and the progression from spermatogonia to sperm takes a fixed duration that differs among species. The only germ cells in contact with the extratubular environment are the spermatogonia. This is because the rest of the germ cell types are lodged within the intratubular immunologically privileged environment controlled by the Sertoli cells that support the developing germ cells structurally and form the blood-testis barrier. The extratubular compartment contains blood vessels that are surrounded by Leydig cells that produce and secrete testosterone, which, together with the gondadotropic hormones FSH and LH, are critical for the production of sperm.