what is Gametogenesis ?

Gametogenesis is the process of formation of male and female gametes in the testes and ovary respectively. It is of two types: 1. Spermatogenesis – males 2. Oogenesis – females Spermatogenesis In testes, spermatogonia produce sperms by the process of spermatogenesis. This begins at puberty. Steps in Spermatogenesis

• The spermatogonia present at the inner side of seminiferous tubules multiply by mitotic division and increase in number. Each spermatogonium has 46 chromosomes.
• Spermatogonia undergoes the first meiotic division to form spermatocytes. i.e secondary spermatocytes having 23 chromosomes.
• The secondary spermatocytes under the second meiotic division form haploid spermatids.
• The spermatids are transformed into spermatozoa through a process called spermiogenesis. In spermatogenesis, the sperm heads remain embedded in Sertoli cells.
• These are released from seminiferous tubules by the process of spermiation.

Hormonal Control of Spermatogenesis

• Spermatogenesis is initiated due to increased activity of gonadotropin-releasing hormone (GnRH) by the hypothalamus
• An increase in the amount of GnRH acts on the anterior pituitary and stimulate the secretion of two gonadotropins, LH and FSH.
• LH acts on Leydig cells and stimulates them to produce androgens.
• FSH acts on Sertoli cells and stimulates the secretion of some factors which help in the process of spermiogenesis.

Sperm A sperm is a microscopic structure that is composed of a head, neck, middle piece and tail. The sperm head has an elongated haploid nucleus. The anterior portion of sperm is covered by a cap-like structure acrosome. Human male ejaculate about 200-300 million sperms during single coitus. The seminal plasma along with the sperms forms the semen. The function of male sex secondary ducts and glands is maintained by androgens.

Oogenesis The process of the formation of mature female gametes is called oogenesis. It starts from the embryonic development stage. At this time millions of oogonia are formed in each fetal ovary. Steps in Oogenesis

• The gamete mother cells start dividing and enter into prophase-I of meiotic division and get temporarily arrested at this stage. These are called primary oocytes.
• The primary oocyte gets surrounded by a layer of granulosa cell and is called the primary follicle.
• By the time of puberty, about 60,000- 80,000 primary follicles are left in each ovary.
• The primary follicles get surrounded by more layers of granulosa cells forming the secondary follicles. These transform into tertiary follicles which has a fluid-filled cavity called the antrum.
• The tertiary follicles change into the mature follicle called the Graafian follicle. This ruptures to release secondary oocyte from the ovary by the process of ovulation.

Structure of Egg