Spermatogenesis

SPERMATOGENESIS

  • Spermatogenesis refers to the process of formation of spermatozoa (sperm) from primitive germ cells (spermatogonia).
  • Occurs as the result of stimulation by gonadotropins.
  • The seminiferous tubules of the testes are the starting point for the process.
  • Maturation occurs in the epididymis.
  • The location [Testes/Scrotum] is specifically important as the process of spermatogenesis requires a lower temperature to produce viable sperm, specifically 1°-8 °C lower than normal body temperature of 37 °C (98.6 °F)
  • Begins at an average age of 13 years.
  • The two testes of the human adult form up to 120 million sperm each day.

STEPS INVOLVED IN SPERMATOGENESIS

  • Spermatogonia (primitive germ cells) undergo mitosis to form primary spermatocytes. Both spermatogonia and primary spermatocytes have diploid chromosomes (46 chromosomes or diploid of 23 chromosomes).
  • Primary spermatocytes are large cells with large round nuclei in which the nuclear chromatin is condensed into dark, threadlike, coiled chromatids
  • Primary spermatocytes undergo meiosis to form secondary spermatocytes. Secondary spermatocytes have haploid (23) chromosomes.
  • Secondary spermatocytes undergo mitosis to form spermatids.
  • Spermatids do not divide further but undergo morphological changes to form sperms (spermatozoa). This step of formation of spermatozoa from spermatids is called spermiogenesis. The spermiogenesis takes place in the deep folds of cytoplasm of sertoli cells.
  • 1 primary spermatocyte gives rise to 4 spermatids.
  • 1 Spermatogoniurn gives rise to 512 spermatids.
  • It takes 74 days for the spermatogonium to become spermatozoa.

HORMONES INVOLVED IN SPERMATOGENESIS

Hormones required for spermatogenesis are FSH, LH, testosterone, estrogen, growth hormones, inhibin and activin.

  • FSH is responsible for initiation of spermatogenesis. It binds with sertoli cells and spermatogonia and induces the proliferation of spermatogonia. It stimulates certoli cells to secrete endrogen binding protein, inhibin, mullerian inhibing substance and estrogen.
  • LH stimulates leydig cells to secrete testosterone.
  • Testosterone is the principles hormone which directly stimulates spermatogenesis. It is responsible for the sequence of remaining stages of spermatogenesis (after initiatin by FSH). It is also responsible for maintenance of spermatogenesis.
  • Estrogen is formed from testosterone (by aromatase) in sertoli cells. It is essential for spermeogenesis (last step of spermatogenesis, i.e. formation of spermatozoa from spermatids).
  • Growth hormone is essentialy promotes early division of spermatogonia.
  • Inhibin plays an important role in regulation of spermatogenesis by feedback inhibition of FSH secretion.
  • Activin stimulates FSH secretion and stimulates spermatogenesis.

Exam Question

  • Time taken for spermatogenesis is 74 days.
  • Spermatogenesis occurs at temperature lower than core body temperature.
  • Meiosis in spermatogenesis occurs in the step of primary spermatocyte to secondary spermatocyte.
  • Spermatogenesis is maintained by Testosterone, FSH, & LH hormones .
  • Spermatogenesis takes place in Seminiferous tubule.
  • Growth hormone specifically promotes early divisions of spermatogonia themselves.
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