Spermatogenesis
In this article, you will learn about the spermatogenesis in detail. This article provides you the basic outline of spermatogenesis. The preoptic nucleus and the arcuate nucleus in the hypothalamus release the hormone called GnRH (gonadotropin-releasing hormone).
This GnRH triggers the gonadotrophs present in the anterior pituitary gland to secrete FSH and LH.
Spermatogenesis happens in the seminiferous tubules of the testes.
The seminiferous tubules of the testes are primarily made by the cells called Sertoli cells, sustentacular cells, nurse cells, supporting cells.
These Sertoli cells are joined together by the tight junctions, adherent junctions, and gap junctions
These tight junctions, adherent junctions, and gap junctions serve as the blood testes barrier. Because the sperm cells when exposed to the blood, can trigger the immune response and can lead to the production of antigens against the sperm cells. So, these tight junctions are important.
The testes also contain the specialized mitotic cells called spermatogonium. These cells are present in the basal compartment inside the seminiferous tubules. The basal compartment is separated from the luminal compartment by the tight junction proteins, adherins, and gap junctions.
The spermatogonium divides mitotically and produces two cells A and B (2n and 2n). The (first 2n cell) A cell again converts to the spermatogonium. That is recycled.
Now, the spermatogonium and sustentacular cells secrete chemicals that open the tight junctions, adherins, and gap junctions.
Now, this B cell (another 2n cell) enters the luminal compartment and now is called a primary spermatocyte.
This primary spermatocyte undergoes meiosis 1 to form two haploid cells called secondary spermatocytes.
This secondary spermatocyte undergoes meiosis 2 to form four haploid cells called spermatids.
This spermatid will get converted to spermatozoa. These spermatozoa contain the head, midpiece, tail, etc. This process is called spermiogenesis.
The process of converting the primary spermatocytes to the spermatozoa is called spermatogenesis.
Regulation of spermatogenesis:
Sperm production is regulated by the very important hormone called testosterone.
The LH produced by the anterior pituitary comes and binds with the receptor on the Leydig cells of the testes. This activates the nucleus and releases the enzymes which convert the cholesterol into testosterone.
This testosterone reaches the lumen of the seminiferous tubules and also to the blood. From blood, it reaches many tissues and aids in secondary sexual development.
This testosterone inside the lumen of the sem. Tubules cannot be suspended freely. So, the FSH comes into action. This FSH binds to the receptors on the Sertoli cells and produces the ABP (androgen binding protein).
This ABP binds to the testosterone and helps to undergo its action inside the seminiferous tubules. The ABP is needed because testosterone is a water-insoluble/ lipid-soluble hormone. The lumen of the sem. Tubules are filled with water.
This testosterone is responsible for spermatogenesis and also for spermiogenesis.
The head of the sperm contains the acrosome and the midpiece contains the mitochondria and the tail is needed for motility.
When there is high testosterone in the blood, this sends negative feedback to the hypothalamus and ant. Pit. Which in turn leads to inhibition of GnRH and LH. So, inhibition of testosterone production for a while.
When there are too many sperms inside the seminiferous tubules, the receptors on the Sertoli cells detect this and secretes Inhibin into the blood which sends negative feedback to the hypothalamus and the ant. The pit which in turn results in the inhibition of FSH. So, inhibition of ABP production. Without ABP testosterone cannot suspend inside the lumen of the seminiferous tubules. This leads to inhibition of spermatogenesis.
Leydig cells - testosterone production
Sertoli cells – nourishment to the sperm cells
Testosterone – helps in spermatogenesis and spermiogenesis and male secondary sexual characters
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