Spermatogenesis

 The process of spermatogenesis takes place in male gonads called Testes. Each testis has seminiferous tubules which are lined by cuboidal epithelium called germinal epithelium. The cells of germinal epithelium undergo spermatogenesis to produce sperms. In between germinal cells are present Sertoil  cells or Nurse cells. Sertoil cells provide nourishment to the sperms.

Germinal cells in testes are known as primary germinal cells or primordial germ cells. Primordial cell passes through three phases namely. 

1) Multiplication phase

2) Growth phase

3) Maturation phase

1) Multiplication phase :

Primordial cells undergo repeated mitosis divisions to produce large number of spermatogonia. Each spermatogonium is diploid ( 2n ).

2) The growth phase :

Spermatogonium cell accumulates food and grows in size. Now it is called primary spermatocyte.

3) The maturation phase : 

The primary spermatocyte undergoes first meiotic or maturation division. The homologous chromosomes start pairing. Each homologous chromosome splits longitudinally. Chiasma formation results in exchange of genetic material.

At the end of I meiotic division, two haploid, secondary spermatocytes are formed. Each secondary spermatocyte undergoes II meiotic division and produces spermatids. So at the end of maturation phase each spermatogonium produces four haploid spermatids. Spermatid is non motile so it has to undergo spermiogenesis to become functional, motile male gamete i.e. spermatozoan.

Many changes occur in spermatid like, sperm increases in length, centrioles are distinguished into proximal and distal centrioles, distal centriole gives rise to axial filament, mitochondria become spirally coiled, Golgi complex forms Acrosome.