B29: Human Reproduction and Hormones

Question: Explain how FSH, oestrogen, LH, and progesterone interact during the menstrual cycle.

Solution: At the start of the cycle, the pituitary gland releases FSH, which stimulates an egg to mature in the ovary and triggers the ovaries to produce oestrogen. Oestrogen builds up the uterus lining and inhibits FSH (preventing further egg maturation). When oestrogen reaches a high level, it stimulates a surge of LH from the pituitary gland, which triggers ovulation (release of the egg). After ovulation, the remains of the follicle form the corpus luteum, which produces progesterone. Progesterone maintains the uterus lining and inhibits both FSH and LH. If the egg is not fertilised, progesterone levels drop, the uterus lining breaks down (period), and FSH begins to rise again to start a new cycle.

Question: Explain how negative feedback controls the levels of FSH and LH during the menstrual cycle.

Solution: Oestrogen inhibits FSH production – as oestrogen levels rise, FSH levels fall. This is negative feedback because the rising oestrogen acts to reduce the hormone (FSH) that stimulated its production. Similarly, progesterone inhibits both FSH and LH – as progesterone levels rise after ovulation, FSH and LH levels fall. This prevents another egg from maturing and being released during the same cycle. If the egg is not fertilised, the corpus luteum breaks down, progesterone falls, and the inhibition of FSH and LH is removed – allowing the cycle to begin again.

Question: Explain how the combined contraceptive pill prevents pregnancy.

Solution: The combined pill contains oestrogen and progesterone. These hormones inhibit the release of FSH from the pituitary gland. Without FSH, no egg matures in the ovary, so ovulation does not occur. In addition, progesterone makes the cervical mucus thicker, which blocks sperm from entering the uterus. The pill also thins the uterus lining, making it less likely that a fertilised egg could implant. Together, these effects make pregnancy very unlikely.

Question: Describe the stages of IVF treatment and explain why FSH and LH are given at the start.

Solution: In IVF, the woman is first given FSH and LH injections to stimulate the ovaries to produce multiple mature eggs (superovulation). Normally only one egg matures per cycle, but the hormones cause several to mature at once. The eggs are then collected from the ovaries using a fine needle. In the lab, the eggs are fertilised with sperm in a petri dish. The resulting embryos are grown for a few days, and then one or two are implanted into the woman's uterus. If implantation is successful, the pregnancy continues as normal. Extra embryos can be frozen for future use.

Question: Discuss the ethical issues associated with IVF treatment.

Solution: IVF raises several ethical issues. First, the process creates more embryos than are needed, and unused embryos may be destroyed or used for research, which some people believe is morally wrong as they consider embryos to be potential human life. Second, the ability to select which embryos to implant raises concerns about “designer babies.” Third, IVF increases the risk of multiple births, which can lead to premature birth and health problems for the babies. Fourth, IVF is expensive, and not all couples can afford it or access it on the NHS, raising concerns about fairness. Finally, the emotional toll of unsuccessful IVF cycles on couples is significant.