Gametogenesis- Spermatogenesis

Gametogenesis- Spermatogenesis


GAMETOGENESIS

  • Gametogenesis refers to formation of male gametes (sperms) and female gametes (ova) form the primitive germ cells. 
  • The gametogenesis thus includes:

1) Spermatogenesis

2) Oogenesis

SPERMATOGENESIS

  • Spermatogenesis refers to the process of formation of spermatozoa (sperm) from primitive germ cells (spermatogonia).
  • Spermatogenesis begins at puberty & continues throughout adult life to decline in old age.
  • In humans, it takes an average of 74 days to form a mature sperm from primitive germ cells.
  • Spermatogenesis occurs in seminiferous tubules.
  • Steps in spermatogenesis involve:

1. 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).

2. Primary spermatocytes undergo meiosis to form secondary spermatocytes. Secondary spermatocytes have haploid (23) chromosomes.

3) Secondary spermatocytes undergo mitosis to form spermatids.

4) Spermatids do not divide further but undergo morphological chang4es to form sperms (spermatozoa). This step of formation of spermatozoa from spermatidsis called spermiogenesis. The spermiogenesis takes place in the deep folds of cytoplasm of sertoli cells.

  1. Spermatogenesis Formation of spermatozoa from spermatogonia.
  2. Spermiogenesis- Formation of spermatozoa from spermatids.
  3. Thus, spermiogenesis is the last step of spermatogenesis.
  • A fully formed sperm (spermatozoan) is an intricate motile cells about 55-65 um in lenght.
Further development of spermatozoa (Sperms)
 
  • Spermatozoa leaving the testis (seminiferous tubules) are not fully mobile.They continue their maturation and acquire their mobility during their passage through epididymis.
  • From epididymis they come to vas deferens, distal end of which also receives the secretions of seminal vesicle, and continues as the ejaculatory duct.
  • The ejaculatory duct joins the prostatic urethra.
  • Once ejaculated into the female, vaginal secretions improve the motility & fertilising ability of sperms.
  • Further exposure to secretions of female genital tract (in uterus and/or fallopian tube) further improves the mobility and fertilising ability of the sperms.
  • The beneficial effects of stay in the female genital tract are collectively called capacitation.
  • From the isthmus, capacitated sperms move rapidly to the ampullas, where fertilisation takes place.
Temperature and spermatogenesis
 
  • Spermatogenesis requires a temperature considerably lower than that of the interior of the body (core body temperature).
  • The testis are normally maintained at a temperature of about 32 degree C (5 degree less than core temperature).
SPERM ( Mature spermatozoan)
 
  • A full formed spermatozon is an actively motile cell about 60-65 um in length.
  • It has following part:-
1) Head (4-5 um in length)
  • It is derived from nucleus and contains chromosomal material. it is covered by a cap like structure called acrosomic cap or acrosome or galea capitis.
  • It is formed by golgi apparatus and it contains lysosome like organelle rich in enzymes that help in penetration of spermatozoon into the ovum during fertilisation.
2) The Neck
  • It is very small and connects the head with middle piece.
3) Tail (60 um)
  • Axial filament (axoneme) forms the central skeleton of tail. Axial filament is surrounded by fibrous sheath.
  • Tail is divided into following parts:
i) Middle piece (5 um): It is the proximal part of tail. 
  • In this part fibrous sheath is surrounded by spirally arranged mitochondria in abundance.
ii) Principal piece (50 um)
iii) End piece (5 um)
Exam Question
 
  • Spermatogenesis takes place in Seminiferous tubule.
  • Spermatogenesis is maintained by Testosterone, FSH, & LH.
  • Spermatogenesis occurs at Temperature lower than core body temperature.
  • Time taken for spermatogenesis is 61 days.
  • Sperms acquire motility in Epididymis.
  • Length of a mature human spermatozoon is  50- 60 microns.
  • Capacitance of sperms takes place in Uterus.
  • Sperm capacitation takes about 4-6 hrs.
  • Mitochondria of a sperm is seen in Body of the sperm.
  • Daily sperm production is 120 million per day.
  • Velocity of sperms in female genital tract is 1- 3mm/day.
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