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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


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  1. Spermatogenesis refers to the process of formation of spermatozoa (sperm) from primitive germ cells (spermatogonia). Spermatogenesis begins at puberty and 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 seminiferoustubules.
  2. Steps in spermatogenesis involve:
    1. Spermatogonia (primitive germ cells) undergo mitosis to form primary spermatocytes. Both spermatogoniaand 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 mitosistoformspermatids.
    4. Spermatidsdo not divide further but undergo morphological changes to form sperms (spermatozoa). This step offormation of spermatozoa from spermatids is 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.
  3. A fully formed sperm (spermatozoan)is an intricate motile cells about 55-65 µm in length. Sperm has following parts
    1. Head and neck (5µm),
    2. Middle piece (5µm),
    3. Principal piece (50µm),
    4. End piece (5µm).
Further development of spermatozoa (sperms)
  1. 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 deference, distal end of which also receives the secretions of seminal vesicle, and continues as the ejaculatory duct. The ejaculatory duct joins the prostatic urethra.
  2. Once ejaculated into the female, vaginal secretions improve the motility and fertilizing ability of sperms. Further exposure to secretions of female genital tract (in uterus and/or fallopian tube) further improves the mobility and fertilizing 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 fertilization takes place.
Temperature and spermatogenesis
Spermatogenesis requires a temperature considerably lower than that of the interior of the body (core body temperature).The testes are normally maintained at a temperature of about 32°C (5° less than core temperature). They are kept cool by air circulating around the scrotum and probable by heat exchange in a countercurrent fashion between the spermatic arteries and veins. Failure of testicular descent (cryptorchidism) exposes the testis to a higher temperature (intraabodimal) which results in defective spermatogenesis and infertility.


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  1. Oogenesis refers to the process of formation of ova from the primitive germ cells. Unlike fetal testis (in which spermatogenesis beings at puberty), the fetal ovary begins oogenesis by 10 weeks of gestation.
  2. The sequence of events in oogenesis are:
    1. The primitive germ cells undergo mitotic divisions to form oogonia (diploid cells). Oogonium is unique in that it is the only female cell in which both 'X' chromosomes are active.
    2. The oogoniaproliferate by mitosis to form primary oocytes (diploid cells).
    3. Primary oocytes formed from the oogonia enter a prolonged prophase (diplotene stage) of the first meiotic division and remain in this stage until ovulation occurs after puberty.
    4. Primary oocytes complete the first meiotic division at puberty just before ovulation to form secondary oocyte (haploid cell) and 1st polarbody.
    5. Secondary oocyte immediately begins second meiotic division but this division stops at metaphase and is completed only if the mature ovum (ootid) is fertilized with sperm. At that time second polar body (polocyte) is extruded and the fertilized ovum proceeds to form a new individual. Fertilization normally occurs in the ampulla of fallopian tube -

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