Spermatogenesis (sperms formation)

The seminiferous tubules contain large number of germ cells called spermatogonia, located in 2-3 layers. In the 1st stage of spermatogenesis, type A spermatogonia divided 4 times (mitosis) to form 16 more

differentiated cells called type B spermatogonia, at this stage spermatogonia migrate centrally among sertoli cells.

For a period of 24 days, each spermatogonium that crosses the barrier into sertoli cell layer becomes by mitosis a large primary spermatocyte. At the end of 24 days, each primary spermatocyte divide to form 2 secondary spermatocytes, this division is called the 1st meiotic division, in this process each of the 46 chromosomes become 2 chromatids, so each secondary spermatocyte have 23 chrom.

Within 2-3 days a 2nd meiotic division occurs in which the 2 chromatids in each of the 23 chrom split apart forming 2 sets of 23 chrom, one set passing into one daughter spermatid.

The importance of these meiotic divisions is that the eventual sperms that fertilized the ovum provide one half of the genetic material to the fertilized ovum and the ovum will provide the other half.

These stages from spermatogonia to spermatid are androgen dependent.

During the next few weeks after meiosis each spermatid is nursed and reshaped by its sertoli cells and changed into a sperm by losing some of its cytoplasm, formation of compact head and formation of a tail, maturation of spermatid to spermatozoa depends on estrogen (does not depend on testosterone) acting on sertoli cells. The entire period of spermatogenesis takes 74 days.