Jun 26, 2011

Spermatogenesis and Oogenesis

- takes place in seminiferous tubules
- 2 types of cells : Germinal epithelial cells & Sertoli cells

1. Germinal epithelial cells divide by mitosis - produce diploid(2n) spermatogonia
2. Spermatogonium grows - primary spermatocyte(2n)
3. Primary spermatocyte undergoes meiosis I - form 2 secondary spermatocytes(n)
4. Secondary spermatocytes divide through meiosis II - form 2 spermatids
5. Spermatids obtain nutrients from Sertoli cells - mature into sperms/spermatozoa

- takes place in the ovaries
- form oocytes in the ovary of foetus (begins before birth)


1. Germinal epithilial cells multiply by mitosis - form oogonia/oogonium(2n)
2. Oogonium grows - form primary oocyte(2n)
3. Oocyte surrounded by follicle cells (follicle cell - nourishing the oocyte & secrete oestrogen)
4. Primary oocyte + follicle - Primary follicle
5. Feotus grows, primary oocytes undergo meiosis I but stops at Prophase 1.
6. During birth - 2 millions primary oocytes
7. At puberty - 400 000 primary oocytes
8. Every month, primary oocytes become active (meiosis) - only 1 primary follicle matures
9. Meiosis I forms 2 cells
i. First polar body - degenerates (Meiosis II may/may not occur)
ii. Secondary oocyte starts Meiosis II - until Metaphase II
10. Secondary oocyte + follicle = Secondary follicle
11. Secondary follicle matures into Graafian follicle
12. Ovarian wall ruptures - releases Secondary oocyte/Egg (ovulation process)
13. If a sperm penetrates the secondary oocyte, Meiosis II completes and form 2 haploid cells.
i. Ovum (n)
ii. Second polar body (smaller cell)
15. Nucles of sperm + nucles of ovum - zygote (2n/diploid)
16. Graafian follicle (left over in ovary) - forms corpus luteum
17. No pregnancy - corpus luteum degenerates (after 10 days)
18. Pregnancy occurs - corpus luteum secretes progesterone and oestrogen until placenta takes over the tasks (3 months)


minning said...

can i know, what is fertilization actually?? when sperm diffuse with SECONDARY OOCYTE or OVUM to form zygote..? in the notes above, it states that when the sperm penetrate the secondary oocyte, it will complete the meiosis 2 to form ovum and second polar body. Thus, what is the function of ovum here?

rozaini said...

Actually sperm fuses with the secondary oocyte (after ovulation). Meiosis II completed. Then a larger ovum and a smaller polar body formed. The fertilised ovum is now called zygote......This is the correct one.
But at F5 level, we accept sperm fuses with ovum....even at SPM level..