Spermatogenesis in Animals
The development of sperm in the testes is called spermatogenesis. The testis is a glandular organ composed of several coiled seminiferous tubules and their wall is formed by a multi-layered epithelium called germinal epithelium. The germinal epithelium is formed by two types-spermatogonia, primary spermatocyte, secondary spermatocyte and spermatids. When the male animal becomes sexually mature, these spermatogonia begin to produce sperms. This process includes three phases – Multiplication/Mitotic Phase, Growth Phase and Spermatogenesis/Maturation Phase.
Multiplication phase
Mitosis of spermatogonia occurs throughout the life and they are situated near the outer wall of the seminiferous tubules. The spermatogonia are the rounded cells and they are the mother cells from which primary spermatocyte are produced. These are also rounded cells situated near to the spermatogonia.
Growth phase
During this Growth phase, limited growth occurs. This growth phase is insignificant.
Maturation phase
Each primary spermatocyte is divided into two secondary spermatocyte by I meiotic division. From each of the secondary spermatocytes, two spermatids are produced by II meiotic division. Thus from one primary spermatocyte four spermatids are produced.
The spermatids do not divide any more. Each spermatid is gradually transformed into a fully formed, potentially functional male gamete, the spermatozoa. This final phase of spermatogenesis where spermatogenesis does not begin until puberty but is then continues throughout life.
The transformation of the spermatid into mature spermatozoa is known as spermiogenesis.
- During the spermatogenesis the following changes occur;
- The nucleus becomes the sperm head and the cytoplasm appears to be arranged in tail side leaving a thin layer covering the nucleus.
- The centrioles become more conspicuous and form the flagellum.
- The mitochondria become the middle part of the spermatozoan.
- The part of the cytoplasm with golgi apparatus in the apical end forms the acrosomal cap. The remaining part of the cytoplasm disintegrates and leaving the mature spermatozoan stripped off all non-essential parts and consisting only concentrated nuclear material bearing the genes and the tail for the motility.
