Simple Pharmanotes: Spermatogenesis.

Process of formation of mature sperm is called “Spermatogenesis”.
It takes place in places of the reproductive system, it starts in seminiferous tubules of Testes and ends in epididymis.
The location of the testes is critical as a lower temperature (usually 2-3°C lower than the average human body temperature) is essential for the process of spermatogenesis.
Spermatogenesis begins in male after puberty and it is continued till death.
It takes 65 to 75 days to complete.
It occurs in the following three stages,

Spermatocytogenesis is the first stage of spermatogenesis which involves the division of single diploid cells into four haploid spermatocytes.
The seminiferous tubules of kidneys are lined with special stem cells, producing immature cells called “Spermatogonia.”
The stem cells divide mitotically of which, the first half develop to form sperm cells, whereas the rest remain as stem cells to provide a continuous flow of stem cells in the tubules.
These cells then migrate towards Sertoli cells.
Sertoli cells are the elongated cells that are randomly scattered throughout the seminiferous tubules and provide nutrients to the developing spermatogonia.
Spermatogonia that cross the barrier to the Sertoli cells enlarge to form large primary spermatocytes.
After a resting period, these primary spermatocytes move towards the lumen of seminiferous tubules and undergo meiotic division I to produce two haploid secondary spermatocytes.
The number of chromosomes thus reduces from 46 to 23 in each spermatocyte.

Secondary spermatocytes rapidly enter meiosis II to produce haploid spermatids.
Hence, four haploid spermatids are formed from single diploid spermatogonia.
Spermatidogenesis is very fast and is barely seen in histological studies.
Out of the 23 pairs of chromosomes in the spermatogonia, one pair is of sex chromosomes i.e. X (Female) / Y (Male).

Spermiogenesis is the last stage of spermatogenesis where the spermatids undergo changes in the shape and structure to form a mature sperm cell.
The spermatids retain the structure of epithelioid cells for a short time but soon change into an elongated structure called spermatozoa.
A spermatozoon consists of a head and a tail.
The genetic material within the spermatozoon becomes highly condensed and is packed within the head. About two-thirds of the head is surrounded by a thick cap called the acrosome.
The acrosome is formed mainly of the Golgi Body and contains enzymes like hyaluronidase and other powerful proteolytic enzymes that later help the sperm to fertilize the ovum.
Under the influence of testosterone, spermatozoa gain maturity.
The mature spermatozoa are now released from the Sertoli cells into the lumen of the seminiferous tubules, but they still lack motility.
The non-motile spermatozoa then enter the epididymis with the help of testicular fluid secreted by the Sertoli cells and peristaltic contraction.
In the epididymis, mature spermatozoa gain motility and are then stored until the next ejaculation.

Commonly Asked Question.