Spermatogenesis

Spermatogenesis is the production of spermatozoa (mature male germ cells) from spermatogonia (primordial male germ cells). It is the type of gametogenesis that occurs within the testes of mature male individuals.

Section of a seminiferous tubule in a rat testis. Gray's Anatomy (1918) figure 1150. Source: Wikimedia Commons

Description

Prenatal Development

In the testis, primordial germ cells proliferate and differentiate into prospermatogonia in the early fetal period. Prospermatogonia become mitotically quiescent during the fetal period. They and their progeny are connected by intercellular bridges.

Puberty

At puberty, prospermatogonia resume proliferation and mature into spermatogonia.

Spermatogenesis proper

Throughout post-pubertal life, spermatogonia ("primordial sperm cells") differentiate into primary spermatocytes and enter meiosis, producing spermatids that mature into spermatozoa. Spermatogenesis has three stages:

• Spermatocytogenesis is the development of spermatocytes from spermatogonia. Spermatogonia are self-renewing diploid germ cells that proliferate via mitotic cell division. Throughout postpubertal life, spermatogonia differentiate into primary spermatocytes that will undergo meiotic cell division.
• Spermatidogenesis is the development of spermatids from spermatocytes. Primary spermatocytes enter meiosis, producing secondary spermatocytes (meiosis I), and then spermatids (meiosis II). In about three weeks, a primary spermatocyte gives rise to four spermatids.
• Spermiogenesis is the maturation of spermatids into spermatozoa. Spermiogenesis includes compaction of chromatin, reduction of cytoplasm, development of the acrosome and formation of the flagellum (tail), and takes about a month.

Schematic diagram of spermatocytogenesis and the beginning of spermatidogenesis. Source: Wikimedia Commons

Germinal epithelium of the testicle. 1.basal lamina; 2.spermatogonium, 3.primary spermatocyte; 4.secondary spermatocyte; 5.spermatid; 6.maturing spermatid; 7.Sertoli cell; 8.tight junction (blood-testis barrier). Source: Wikimedia Commons

Spermatozoon: Head, neck, and connecting, principal and end pieces of the tail. Source: Wikimedia Commons