spermatogenesis

Spermatogenesis is the process by which spermatozoa are produced from spermatogonial stem cells in the seminiferous tubules of the testes. It is a continuous process that begins at puberty and, in humans, takes about 64 days to complete from the onset of spermatogonia to mature spermatozoa. The process requires a specialized cellular environment and coordinated hormonal regulation within the testes.

Spermatogenesis proceeds through several stages. Spermatogonia undergo mitotic divisions to produce primary spermatocytes, which enter meiosis I to form secondary spermatocytes, then meiosis II to generate haploid spermatids. Spermiogenesis then transforms these round spermatids into elongated spermatozoa, and spermiation releases mature sperm into the lumen of the seminiferous tubules.

Hormonal regulation is governed by the hypothalamic-pituitary-testicular axis. Gonadotropin-releasing hormone stimulates LH and FSH from the pituitary. LH acts on Leydig cells to produce testosterone, which supports germ cell development, while FSH acts on Sertoli cells to nurture developing germ cells and to secrete inhibin B, which provides feedback to reduce FSH. Retinoic acid also helps initiate meiosis in germ cells. The testes are kept cooler than core body temperature, which is important for efficient spermatogenesis.

Sperm structure and maturation accompany the process. Mature sperm have a head with a condensed nucleus and an acrosome, a midpiece rich in mitochondria, and a flagellum for motility. After spermiation, sperm gain motility and fertilizing capability during transit through the epididymis.

Clinical relevance includes male infertility arising from impaired spermatogenesis or sperm function. Factors such as genetics, illness, heat exposure, toxins, medications, and hormonal imbalances can affect production. Diagnosis often involves semen analysis, and treatment may range from lifestyle changes to assisted reproductive techniques.