Spermatogenisis and Oogensis

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Spermatogenisis and Oogensis
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Oogenesis

• Begins in the female embryo with production of
  oogonia from primordial germ cells
• Oogonia divide by mitosis to form primary oocytes
• They are developmentally arrested cells (stopped
  at prophase I before birth)
• Reside in a small follicle
• At puberty, FSH periodically stimulates small
  group of follicles to resume growth and
  development

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• Typically only one follicle fully matures each
  month.
• That primary oocyte completes meiosis I
• Second meiotic division begins, but stops at
  metaphase
• The secondary oocyte is arrested in meiosis II
  until released at ovulation.
• Only if a sperm cell penetrates the oocyte does
  meiosis II resume

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• Each of the meiotic division results in unequal
  cytokinesis.
• The smaller cells become polar bodies that
  eventually degenerate (the first polar body may
  or may not divide a second time)
• The ruptured follicle left from ovulation becomes
  the corpus luteum
• If the released oocyte does not complete
  oogenesis (fertilization), that corpus luteum
  degenerates.

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• FSH stimulates follicle development
• Estrogen produced by growing follicles (and
  corpus luteum), high amounts signal ovulation
• LH stimulates corpus luteum growth and
  maintenance
• Progesterone produced by corpus luteum.
  Inhibits further ovulation, maintains uterine
  lining during pregnancy

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Spermatogenesis

• Initial germ cells of the embryonic testes
  divide and differentiate into stem cells which
  divide mitotically into spermatogonia
• Spermatogonia generate spermatocytes (by mitosis)
• Each spermatocyte gives rise to 4
  spermatids meiotic cell division to reduce
  chromosome number from diploid (2n 46) to
  haploid (n 23)
• Spermatids differentiate into sperm

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Spermatogenesis

• Stem cells situated near outter edge of
  seminiferous tubules
• As spermatogenesis proceeds, cells move steadily
  inwards, as they pass through the stages
• In the last step, the mature sperm are released
  into the lumen of the tubule, which they travel
  through to reach the epididymis.

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Spermatogenesis
Sertoli Cells influence/nurture developing sperm
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Video Representation

• Spermatogenesis
• http//highered.mcgraw-hill.com/sites/0072495855/s
  tudent_view0/chapter28/animation__spermatogenesis_
  _quiz_1_.html
• Oogenesis
• http//highered.mcgraw-hill.com/sites/0072495855/s
  tudent_view0/chapter28/animation__maturation_of_th
  e_follicle_and_oocyte.html

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Spermatogenesis vs. Oogenesis
Spermatogenesis Oogenesis
All 4 products of meiosis develop into mature gametes 1 mature gamete (ovum), 3 polar bodies that degenerate
Occurs throughout adolescence and adulthood Mitotic divisions complete before birth, and production of mature gametes ceases around age 50
Produces mature sperm from percursor cells in continuous sequence Had long interruptions during the development of mature gamete