NCERT · Class 12 · Biology · Human ReproductionDescribe the process of spermatogenesis in human males with the help of a suitable flowchart or detailed description. Explain the hormonal control involved in this process.

Introduction to Spermatogenesis\nSpermatogenesis is the biological process through which immature germ cells develop into mature spermatozoa in the male testes. This vital reproductive process begins at puberty and continues throughout the life of a human male. The entire process takes place inside the seminiferous tubules located within the testes.

Phases of Spermatogenesis\nThe formation of spermatozoa from spermatogonia occurs in four major phases:

1. Multiplication Phase: The primordial germ cells or spermatogonia (diploid, 2n = 46) present on the inside wall of seminiferous tubules multiply by mitotic cell division and increase in number. Some of these cells function as stem cells, while others act as primary spermatocytes.
2. Growth Phase: The primary spermatocyte actively grows in size by accumulating nutritive materials from the surrounding Sertoli cells, preparing itself for the upcoming meiotic divisions.
3. Maturation Phase:
   • The primary spermatocyte undergoes the first meiotic division (meiosis I), which is a reductional division, resulting in the formation of two equal-sized haploid (n = 23) cells known as secondary spermatocytes.
   • The secondary spermatocytes promptly undergo the second meiotic division (meiosis II), which is an equational division, producing four equal-sized haploid cells called spermatids.
4. Spermiogenesis (Transformation Phase): The non-motile, round spermatids are transformed into mature, motile spermatozoa (sperm) through a structural metamorphosis known as spermiogenesis. During this phase, the Golgi apparatus forms the acrosome, the centrioles form the axial filament, mitochondria form the spiral sheath in the middle piece, and excess cytoplasm is discarded.

Hormonal Control of Spermatogenesis\nSpermatogenesis is regulated by the hypothalamic-pituitary-testicular axis:

• Hypothalamus: Secretes Gonadotropin-Releasing Hormone (GnRH) at puberty, which acts on the anterior pituitary gland.
• Anterior Pituitary: Releases Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH).
• LH: Acts on the Leydig cells (interstitial cells) to stimulate the synthesis and secretion of androgens (testosterone), which in turn stimulate the process of spermatogenesis.
• FSH: Acts on the Sertoli cells to stimulate the secretion of certain factors that help in the process of spermiogenesis (the conversion of spermatids to spermatozoa).