精子形成

Spermatogenesis consists of mitosis, meiosis, and spermiogenesis. During mitosis, spermatogonia stem cells divide to produce identical daughter cells. Meiosis reduces chromosome number, creating haploid cells called spermatids. Finally, spermiogenesis transforms spermatids into mature, functional sperm capable of fertilization through development of specialized structures.

Type-A spermatogonia remain attached to the basement membrane of the seminiferous tubule, maintaining the stem cell population for continuous sperm production throughout life. Type-B spermatogonia are displaced toward the lumen and differentiate into primary spermatocytes that enter meiosis, progressing toward mature sperm formation and eventual ejaculation.

During meiosis I, homologous chromosomes in each primary spermatocyte pair up and exchange genetic material through crossing over, ensuring genetic diversity. This process produces two secondary spermatocytes, each containing half the original chromosome number, preparing cells for the second meiotic division that yields four haploid spermatids.

Sertoli cells, also called nurse cells, provide essential nutrients and physical support to developing sperm throughout spermatogenesis. They regulate hormones and maintain the optimal environment within seminiferous tubules, directly supporting the transformation of spermatids into mature, functional sperm cells ready for male sexual response.

One spermatogonium undergoes mitosis to produce two type-B spermatogonia, each entering meiosis. Each primary spermatocyte completes meiosis I and II to yield four haploid spermatids. Therefore, one initial spermatogonium ultimately produces eight mature sperm through successive cell divisions and spermiogenesis.

During spermiogenesis, spermatids undergo transformations to become mature sperm, including development of the acrosome, flagellum, and mitochondria. These structures enable sperm motility and the ability to penetrate an egg, creating fully functional reproductive cells with the morphology necessary for successful fertilization and reproduction.

Spermatogenesis begins at puberty and continues throughout life into advanced age, producing sperm continuously in the seminiferous tubules. This lifelong production of sperm ensures continuous male fertility, distinguishing male reproduction from the finite egg supply in females and enabling reproductive capacity across the lifespan.