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 Spermatogenesis

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مُساهمةموضوع: Spermatogenesis    الأحد أبريل 05, 2015 10:09 pm


Spermatogenesis

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Spermatogenesis is the process in which spermatozoa are produced from male primordial germ cells by way of mitosis and meiosis. 
The initial cells in this pathway are called spermatogonia, which yield primary spermatocytes by mitosis. 

The primary spermatocyte divides meiotically into two secondary spermatocytes; each secondary spermatocyte then completes meiosis as it divides into two spermatids. 

These develop into mature spermatozoa, also known as sperm cells. Thus, the primary spermatocyte gives rise to two cells, the secondary spermatocytes, and the two secondary spermatocytes by their subdivision produce four spermatozoa.

Spermatozoa are the mature male gametes in many sexually reproducing organisms. Thus, spermatogenesis is the male version of gametogenesis. 

In mammals it occurs in the male testes and epididymis in a stepwise fashion. 
Spermatogenesis is highly dependent upon optimal conditions for the process to occur correctly, and is essential for sexual reproduction. 
DNA methylation and histone modification have been implicated in the regulation of this process 

It starts at puberty and usually continues uninterrupted until death, although a slight decrease can be discerned in the quantity of produced sperm with increase in age 

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The process of spermatogenesis as the cells progress from primary spermatocytes, to secondary spermatocytes, to spermatids, to Sperm


Purpose

Spermatogenesis produces mature male gametes, commonly called sperm but specifically known as spermatozoa, which are able to fertilize the counterpart female gamete, the oocyte, during conception to produce a single-celled individual known as a zygote. 
This is the cornerstone of sexual reproduction and involves the two gametes both contributing half the normal set of chromosomes (haploid) to result in a chromosomally normal (diploid) zygote.

To preserve the number of chromosomes in the offspring – which differs between species – each gamete must have half the usual number of chromosomes present in other body cells. Otherwise, the offspring will have twice the normal number of chromosomes, and serious abnormalities may result. 

In humans, chromosomal abnormalities arising from incorrect spermatogenesis can result in Down Syndrome, Klinefelter's Syndrome, and spontaneous abortion.


Location

Spermatogenesis takes place within several structures of the male reproductive system. 
The initial stages occur within the testes and progress to the epididymis where the developing gametes mature and are stored until ejaculation. 

The seminiferous tubules of the testes are the starting point for the process, where stem cells adjacent to the inner tubule wall divide in a centripetal direction—beginning at the walls and proceeding into the innermost part, or lumen—to produce immature sperm. 
Maturation occurs in the epididymis.


Duration

For humans, entire process of spermatogenesis takes 74 days 
Including the transport on ductal system, it takes 3 months 
Testes produce 200 to 300 million spermatozoa daily



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Spermatogenesis
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