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Renin Angiotensin Mechanism.

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,

    1. Spermatocytogenesis.

    2. Spermatidogenesis.

    3. Spermiogenesis.

  1. Spermatocytogenesis:

  • 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. 

  1. Spermatidogenesis:

  • 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).

  1. Spermiogenesis:

  • 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.

  1. Write a short note on Spermatogenesis.
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