Spermatogenèse

Spermatogenesis occurs within seminiferous tubules, muscle-wrapped structures located in the testes. These tubules contain a peripheral layer of spermatogonial stem cells surrounding a hollow center. Supporting Sertoli cells regulate the process, ensuring stem cells self-renew while producing sperm progenitors throughout a man's lifespan.

Spermatogonial stem cells divide asymmetrically through mitosis. One resulting cell continues as a stem cell, maintaining the stem cell population, while the other becomes a precursor that develops into a spermatocyte. This asymmetric division ensures continuous sperm production and contrasts with oogenesis ovulation and fertilization, where only one egg forms per progenitor cell.

Spermatocytes enter meiosis and divide twice, producing four haploid cells called spermatids. Each spermatid contains a single chromosome set of 23 chromosomes. These haploid cells then undergo differentiation, losing cytoplasm and developing flagella, ultimately becoming mature motile sperm ready for release.

Mature sperm have a distinctive head containing minimal cytoplasm and a highly condensed nucleus, plus a motile tail called a flagellum. They lack organelles like ribosomes, endoplasmic reticulum, and Golgi apparatus, but contain numerous mitochondria around the flagellum for energy. Below the head is the acrosomal vesicle containing hydrolytic enzymes for egg penetration.

Capacitation is a maturation process occurring after spermatogenesis, exclusively within the female genital tract. Components like mucus trigger critical changes including cholesterol removal from sperm membranes, allowing bicarbonate ions and calcium ions to enter. These changes increase tail motility and enable sperm to penetrate the zona pellucida surrounding the egg.

Heat exposure in the scrotum significantly impairs sperm production; prolonged sitting or metal welding increases infertility risk and reduces sperm motility. Additionally, certain drugs adversely affect spermatogenesis, including hormone antagonists for prostate conditions, cancer treatments, and specific antibiotics. Medical professionals now emphasize warning men about these reproductive health effects.

Spermatogenesis produces four functional haploid sperm cells from each progenitor cell through meiosis, with continuous production throughout life via stem cell self-renewal. Oogenesis, by contrast, generates only one functional egg per progenitor cell. This fundamental difference reflects the distinct reproductive roles of males and females in human reproduction.