IB Biology, SL and HL content for cardiology, menstrual hormones, pregnancy and sexual reproduction. Includes: description of stages of oogenesis and spermatogenesis | description and explanation of hormones and feedback loops | stages of the menstrual cycle | pregnancy and the role of hCG and oxy...
Oogenesis: The production of egg cells in the ovaries
Spermatogenesis: The production of sperm in the testes
Oogenesis Stages: Fetal development Puberty Fertilisationàpregnancy
1. 400,000 primordial cells are formed by mitosis (baby is born with 400,000 eggs in
ovaries)
2. These germ cells (oogonia) undergo cell growth until they are big enough to undergo
meiosis (when they reach this size, they are called primary oocytes)
3. Primary oocytes begin meiosis but are paused in prophase I, when granulosa cells
surround them to form follicles
4. At puberty when menstrual cycle begins, FSH triggers continued meiosis of some
primary oocytes
5. These oocytes complete meiosis I and form 2 cells of unequal sizes
6. One cell retains the cytoplasmà is the secondary oocyte, and the other cell is the
polar body
7. Polar body is trapped in follicle and degenerates
8. Secondary oocyte begins meiosis II but is paused in metaphase II
9. Secondary oocyte is released from ovary (ovulation) and enters oviduct
10. Follicle cells surrounding oocyte form corona radiata to nourish secondary oocyte
11. Oocyte fertilised by spermà meiosis II is completed, another polar body and the
ootid (if not fertilised, ovulation occurs and follicle is released into uterus)
12. Ootid differentiates into ovum
13. Ovum nucleus fuses with sperm nucleus to form zygote
,Spermatogenesis Stages: (only occurs at puberty)
1. Germinal epithelial cells divide by mitosis to form spermatogonia
2. Spermatogonia grow larger and become primary spermatocytes
3. Each spermatocyte undergoes meiosis I to produce 2 (haploid) secondary
spermatocytes
4. Each secondary spermatocyte undergoes meiosis II to produce 2 (haploid)
spermatids
5. Spermatids attach to Sertoli cells and differentiate into spermatozoa (sperm- have
developed tails now)
6. Sperm detach from Sertoli cells and are carried out of testes by seminiferous tubule
fluid in centre of seminiferous tubule
*Testosterone causes elongated spermatids to attach to Sertoli cells, and then causes
spermatozoa to detach from them
, Differences between Oogenesis and Spermatogenesis:
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