The term spermatogenesis is formed from the Greek words sperma meaning sperm and genesis meaning origin. It means sperm production. The process by which sperm are produced in the testicles of sexually fertile males is called spermatogenesis. Sperm arise from germinal epithelial cells located in the seminiferous tubules. Somatic or Sertli cells provide nutrients to the sperm. Spermatogenesis process takes 60-70 days.
Spermatogenesis is a continuous process. It is described under 4 headings-
1. Multiplication phase: Spermatozoa contain primary germinal cells. Primary germinal cells divide repeatedly to form new cells in the process of mitosis. As a result, the number of cells increases. This is called the numerical growth phase. The resulting cells are called spermatogonia or sperm mother cells.
2. Growth phase: Each spermatogonium grows in size by receiving nutrients. Its nucleus is also enlarged in size. In this condition the cells are called primary spermatocytes.
3. Maturation phase: Primary spermatocytes divide by meiosis to form haploid cells. These are called secondary spermatocytes. Each secondary spermatocyte divides by meiosis to form two spermatids. As a result, 4 spermatids are produced from one primary spermatocyte.
4. Spermiogenesis: The process of transformation of spermatids into spermatozoa is called spermiogenesis. Viable and motile sperm are called spermatozoa. Changes in spermiogenesis are:
(i) Nucleus of spermatid shrinks to form sperm head.
(ii) Acrosome is formed from the glomerulus of spermatid and rests like a cap on the head of the spermatozoa.
(iii) Mitochondria of spermatids form the nucleus of the sperm.
(iv) Centriole of spermatids forms axial filament and tail of sperm.