Spermatogenesis

Spermatogenesis is the process by all males spermatogonia develop into mature 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, and for humans takes approximately 64 days. Spermatogenesis is highly dependent upon optimal conditions for the process to occur correctly, and is essential for sexual reproduction. 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. The entire process can be broken up into several distinct stages, each corresponding to a particular type of cell:

Cell type ploidy/chromosomes chromatids Process


spermatogonium (types Ad, Ap and B) diploid/46 2N spermatocytogenesis (mitosis)

primary spermatocyte diploid/46 4N spermatidogenesis (meiosis 1)

secondary spermatocyte haploid/23 2N spermatidogenesis (meiosis 2)

spermatid haploid/23 1N spermiogenesis

sperm haploid/23 1N spermiation

 

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. Most chromosomally abnormal zygotes will not survive for long after conception; however, dollenme plant reproduction is a little more robust, and viable new species may arise from cases of polyploidy.

 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 and involves the acquisition of a tail and hence motility.