Spermatogenesis is the
sequence of events in the seminiferous tubules of the testes that produce the male
gametes,the sperms. During development, the primordial germ cells migrate into
the testes and become immature germ cells called sperm mother cells or spermatogonia
in the inner surfaces of the seminiferous tubules (Fig. 2.6 a). The
spermatogonia begin to undergo
mitotic division at puberty and continue throughout life.
In the first stage of
spermatogenesis, the spermatogonia migrate among sertoli cells towards the
central lumen of the seminiferous tubule and become modified and enlarged to
form primary spermatocytes which are diploid with 23 pairs i.e., 46
Some of the primary
spermatocytes undergo first meiotic division to form two secondary
spermatocytes which are haploid with 23 chromosomes each. The secondary
spermatocytes undergo second meiotic division to produce four haploid
spermatids. The spermatids are transformed into mature spermatozoa (sperms) by
the process called spermiogenesis. Sperms are finally released
into the cavity of seminiferous tubules by a process called spermiation.
The whole process of spermatogenesis takes about 64 days. At any given time,
different regions of the seminiferous tubules contain spermatocytes in
different stages of development (Fig. 2.6 b). The sperm production
remains nearly constant at a rate of about 200 million sperms per day.
at the age of puberty and is initiated due to the increase in the release of Gonadotropin
Releasing Hormone (GnRH) by the hypothalamus. GnRH acts on
the anterior pituitary gland and stimulates the secretion of two gonadotropins
namely Follicle Stimulating Hormone (FSH) and Lutenizing
Hormone (LH). FSH stimulates testicular growth and enhances the
production of Androgen Binding Protein (ABP) by the sertoli cells
and helps in the process of spermiogenesis. LH acts on the Leydig cells
and stimulates the synthesis of testosterone which in turn stimulates
the process of spermatogenesis.