Spermatogenesis and Oogenesis

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

Stages
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

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

Stages

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)