Spermatogeneesis

Spermatogeneesis, commonly called spermatogenesis, is the process by which male germ cells develop into mature spermatozoa. It occurs in the seminiferous tubules of the testes and begins at puberty, continuing throughout life in humans.

The process comprises two phases: spermatocytogenesis and spermiogenesis. Spermatocytogenesis involves mitotic proliferation of spermatogonia to maintain the stem cell pool and produce primary spermatocytes, which enter meiosis to form haploid spermatids. Spermiogenesis transforms these spermatids into mature spermatozoa through chromatin condensation, acrosome formation, flagellum development, and cytoplasmic remodeling. Spermiation then releases mature sperm into the tubule lumen.

Regulation: The hypothalamus secretes GnRH, stimulating the anterior pituitary to release FSH and LH. FSH acts on Sertoli cells to support germ cell development and produce factors such as androgen-binding protein; LH stimulates Leydig cells to secrete testosterone, which promotes meiosis and spermiogenesis. Retinoic acid, temperature, and the blood-testis barrier also influence the process.

Mature spermatozoa have a compact nucleus, an acrosome with enzymes, a midpiece packed with mitochondria, and a flagellum for motility. They are released into the epididymis for storage and gain motility and fertilizing ability through capacitation after ejaculation.

Clinical relevance: Disruptions of spermatogeneisis can cause male infertility. Factors include genetic defects, hormonal imbalances, environmental exposures, and testicular injury. Treatments vary by cause and may involve hormonal therapy or assisted reproduction.