4.1 Gamete Formation
The male reproductive system
- Testes produce male gametes (sperms) and male sex hormones
- Scrotum holds the testes and is located outside the main body cavity
- Epididymis - seminiferous tubules join together to form a tightly coiled tube
- The epididymis is connected to the vas deferens (sperm duct) - stores the sperms
- The two sperm ducts are joined to the urethra - connects bladder to the penis
- The sperm pass from the seminiferous tubules through the epididymis and vas deferens into the urethra
- Seminal vesicles - secretes a thick, clear fluid containing nutrients for the sperm
- Prostate gland - secretes a milky white fluid that activates or increases the mobility of the sperm
Structure of the human sperm
- head - large nucleus
- acrosome (specialised lysosome) - contain hydrolytic enzymes - to digest the protective layers surrounding
an ovum, enabling the sperm to penetrate
and fertilise it
- midpiece - large number of mitochondria - provide the energy needed for the movement of the tail
Sperm formation in humans
Spermatogenesis takes place in densly coiled seminiferous tubules1. Germinal epithelial cells of a seminiferous tubules divide by mitosis to produce diploid spermatogonia
2. The spermatogonia grow to become primary spermatocytes which are large diploid cells
3. Each primary spermatocyte undergoes meiosis I to form two haploid secondary spermatocytes
4. Each secondary spermatocyte divides again during meiosis II to produce two spermatids.
5. The spermatids obtain nourishment from nearby nutritive cells (Sertoli cells), develop tails and mature into
sperms through cell differentiation
The female reproductive system
- Ovaries produce the female gametes and secrete female sex hormones (oestrogen and progesterone)
- The Fallopian tubes extend from the ovaries to the uterus.
- The uterus holds the developing embryo and foetus
Ovum formation in humans
Oogenesis takes place in the ovaries
1. Oogenesis - formation of oocytes
2. The germinal epithelial cells near the surface of an ovary multiply by mitosis to form diploid oogonia
3. The oogonia grow to form an primary oocytes
4. Each primary oocyte is surrounded by a layer of follicle cells that nourish the developing oocyte and
secrete female sex hormones
The primary oocyte and these accessory cells make up a primary follicle
5. All primary oocytes undergo meiosis but stop at prophase I of meiosis I
6. Every month during the reproductive years, a few primary oocytes become active and meiosis resumes.
Only one primary follicle mature completely
7. The diploid primary oocyte completes meiosis I to form haploid cells
- first polar body - degenerates and leaves the body (smaller cell)
- secondary oocyte - contains most of the cytoplasm (larger cell)
8. The secondary oocyte starts meiosis II which progresses until metaphase II
The first polar body may also complete meiosis II to form two polar bodies
9. The secondary oocyte with the layers of follicle cells around it - secondary follicle
10. The second follicle increases in size and mature to form Graafian follicle
11. Graafian follicle merges with the wall of the ovary in 28 days then rupture, releasing the secondary
oocyte (egg) into the Fallopian tube
12. Ovulation - the release of secondary oocyte from the ovary
13. If a sperm penetrates the secondary oocyte during fertilisation, meiosis II will be completed and two
haploid cells are formed.
14. Larger cell - ovum
Smaller cell - second polar body
15. The nuclei of the sperm cell and the ovum then fuse to form a diploid zygote
16. Once a Graafian follicle has released a secondary oocyte, it develops into a yellowish mass of cells -
corpus luteum
17 Corpus luteum - begins to degenerate (pregnancy does not take place)
- will not degenerate and continue to secrete oestrogen and progesterone (pregnancy
takes place)
4.2 The Role of Hormones in the Menstrual Cycle
The hormones involved in the menstrual cycle
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