Biology 30 · Reproduction
Reproductive systems and hormones
This unit is mostly a story about four hormones — FSH, LH, estrogen and progesterone — and the feedback loops that switch them on and off. Get the timing right and the questions follow.
The male reproductive system
The idea: sperm are made in the testes, mature in the epididymis, and leave through the vas deferens and urethra, mixed with fluid from three glands.
| Structure | Job |
|---|---|
| Seminiferous tubules (in the testes) | Make sperm |
| Interstitial cells (in the testes) | Make testosterone |
| Epididymis | Stores sperm while they mature |
| Vas deferens | Carries sperm toward the urethra |
| Seminal vesicles, prostate, Cowper's glands | Add fluids that nourish and protect sperm, forming semen |
The testes sit outside the body because sperm develop best a few degrees below core body temperature.
Male hormones
- The hypothalamus releases GnRH, which tells the pituitary to release FSH and LH.
- FSH stimulates sperm production.
- LH stimulates the interstitial cells to make testosterone.
- High testosterone switches GnRH, FSH and LH back down — negative feedback. That is why taking extra testosterone-like steroids can reduce sperm production.
The female reproductive system
The idea: an egg matures in the ovary, travels down the oviduct where it may be fertilized, and an embryo implants in the lining of the uterus.
| Structure | Job |
|---|---|
| Ovaries | Mature eggs in follicles; make estrogen and progesterone |
| Oviducts (fallopian tubes) | Carry the egg to the uterus; where fertilization usually happens |
| Uterus | Where the embryo implants and develops |
| Endometrium | The blood-rich lining of the uterus, rebuilt each cycle |
| Cervix | The opening between the uterus and the vagina |
Watch out: fertilization happens in the oviduct, not the uterus. The early embryo takes several days to travel down and implant.
The menstrual cycle
The idea: FSH grows a follicle, which makes estrogen; an LH surge triggers ovulation; the leftover follicle becomes the corpus luteum, which makes progesterone to hold the lining in place.
| Phase | What is happening |
|---|---|
| Flow (about days 1–5) | The endometrium is shed as menstruation. |
| Follicular (about days 6–13) | FSH grows a follicle. The follicle releases estrogen, which rebuilds the endometrium. |
| Ovulation (about day 14) | A surge of LH makes the follicle release its egg. |
| Luteal (about days 15–28) | The empty follicle becomes the corpus luteum, releasing progesterone (and some estrogen) to maintain the endometrium. |
If there is no pregnancy
Nothing keeps the corpus luteum going, so it breaks down. Progesterone and estrogen fall, the endometrium can no longer be maintained, and it is shed. Low hormones also release the brake on FSH, and the next cycle begins.
Feedback, in both directions
- Negative feedback: high estrogen and progesterone after ovulation hold FSH and LH down, so no new follicle starts.
- Positive feedback: just before ovulation, rising estrogen triggers the LH surge instead of suppressing it.
- At menopause the ovaries stop responding, estrogen and progesterone stay low, and with no negative feedback, FSH and LH rise.
Reproductive technologies
The idea: almost every technology works on one of three things — hormones, the path sperm or eggs travel, or where fertilization happens.
| Technology | How it works |
|---|---|
| Combined birth control pill | Synthetic estrogen and progesterone hold FSH and LH down by negative feedback, so no follicle matures and no egg is released. |
| Vasectomy | The vas deferens is cut or blocked so sperm cannot leave. Testosterone is unaffected. |
| Tubal ligation | The oviducts are cut or blocked so eggs and sperm cannot meet. |
| Artificial insemination | Sperm are placed directly into the uterus. |
| In vitro fertilization (IVF) | Eggs are fertilized in a lab, and an early embryo is placed in the uterus. |
Watch out: the pill works by preventing ovulation, not by blocking sperm. Link it to negative feedback — that is what exam questions are testing.