CBSE · Class 12 · Biology · Human ReproductionExplain the process of spermatogenesis in human males with the help of a schematic representation. Describe the different phases involved in the formation of spermatozoa from spermatogonia.

Introduction to Spermatogenesis\nSpermatogenesis is the biological process through which immature germ cells develop into mature spermatozoa in the testes of male humans. This process begins at puberty and continues throughout the adult life of the male, ensuring a continuous supply of male gametes for reproduction. The entire process takes place inside the seminiferous tubules of the testes.

Phases of Spermatogenesis\nThe formation of spermatozoa from spermatogonia can be broadly divided into four distinct phases:

1. Multiplication Phase (Mitotic Phase):

   • The primordial germ cells or primary spermatogonia (which are diploid, containing 46 chromosomes or 2N) multiply by repeated mitotic divisions.
   • These cells are located on the inner wall of the seminiferous tubules.
   • Some of these cells differentiate and grow in size to become primary spermatocytes, while others remain as reserve stem cells.

2. Growth Phase:

   • The primary spermatocytes increase in size by actively accumulating nutritive materials from the surrounding Sertoli cells.
   • Although they grow significantly, their chromosome number remains diploid (2N = 46).

3. Maturation Phase (Meiotic Phase):

   • Each primary spermatocyte undergoes the first meiotic division (reduction division), resulting in the formation of two equal-sized, haploid cells known as secondary spermatocytes (containing 23 chromosomes or N).
   • Following this, the secondary spermatocytes rapidly undergo the second meiotic division (equational division) to produce four equal-sized, haploid cells called spermatids (N).

4. Spermiogenesis (Metamorphosis):

   • The non-motile, round spermatids undergo a structural transformation to become mature, motile spermatozoa (sperm). This transformation is called spermiogenesis.
   • During this phase, the Golgi apparatus forms the acrosome, the centrioles form the axial filament and tail, mitochondria arrange themselves around the middle piece to provide energy, and much of the cytoplasm is discarded.

Hormonal Regulation\nSpermatogenesis is regulated by hormones secreted by the hypothalamus and the anterior pituitary gland. Gonadotropin-Releasing Hormone (GnRH) stimulates the release of Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH). LH acts on Leydig cells to secrete androgens (testosterone), which stimulate spermatogenesis, while FSH acts on Sertoli cells to secrete factors that help in the process of spermiogenesis.