January 14th, 2015
Spermatogenesis is the process of formation of sperm cells in the male body. Spermatozoa are produced when rounded immature sperm cells go through successive mitotic, meiotic divisions, and then undergo a metamorphic change, which results in spermatozoa.
There are tiny tubules in the male testes that contain diploid cells, known as spermatogonium. Upon maturing, these cells become sperm. This means spermatogenesis is all about quadrupling or turning each of the diploid cells into four different haploid sperm cells through meiotic cell division. The process includes the full development of spermatogonia into sperm cells. When puberty sets in, gonadal cords turn from a solid state to develop into a lumen, gradually transforming into spermatic canals to become 50-60 cm.
Termed convoluted seminiferous tubules, they are covered by a germinal epithelium with two cell populations, including germ cells and sustentacular cells.
The life span of sperm cells is short, and thus the production of these cells is constant, with a daily output of over 200 million sperm cells. Though the process is continuous, the production of sperm takes about 64 days in males.
The process of spermatogenesis begins with spermatogonia, also known as primordial germ cells, which become mitotically active only after a male attains puberty. With an increase in gonadotrophin hormones, there is huge mitotic cell division. As a result, spermatogonia enter into meiosis phase and turn into primary spermatocytes that can further divide into secondary spermatocytes or self-renew.
Spermatids are produced when secondary spermatocytes are further divided to form four spermatids. Spermatids undergo many steps of sperm biogenesis to finally produce fully differentiated sperm cells. Throughout the spermatogenesis process, spermatogenic cells are connected with sertoli cells through cyptoplasmic bridges in the seminiferous tubules, providing nutrients and signals necessary for every stage of sperm production.
As spermatids develop, they tend to travel toward the lumen from the seminiferous tubule basement membrane. Upon achieving maturity, sperm cells are released into the lumen of seminiferous tubules from sertoli cell cytoplasmic bridges. The peristaltic contractions of seminiferous tubules transport mature sperm cells, which are not able to swim, into the epididymus, where they are stored.
With the accumulation of the large mass of sperm and the active fluid secretion by sertoli cells, the sperm are pushed along the seminiferous tubules due to pressure. The sperm continue to become mature in the epididymus and gradually achieve the ability to swim before ejaculation.
Spermatogenesis ensures that a male will continue to produce millions of sperm every day for his entire life, with the sperm production process starting from puberty.