Hormones in Human Reproduction, Menstrual Cycle & IVF

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FSH (Follicle Stimulating Hormone)

Secreted by the pituitary gland. It has two roles: it causes an egg to mature inside a follicle in the ovaries, and it stimulates the ovaries to produce and secrete the hormone oestrogen.

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Oestrogen

Secreted by the ovaries. It has three roles: it causes the lining of the uterus (endometrium) to grow and thicken after menstruation, it inhibits the release of FSH (so only one egg matures per cycle), and it stimulates the release of LH from the pituitary gland.

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LH (Luteinising Hormone)

Secreted by the pituitary gland in a sharp surge around Day 14 of the cycle when oestrogen peaks. LH stimulates the release of the mature egg from the ovary (ovulation). The empty follicle then develops into the corpus luteum.

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Progesterone

Secreted by the empty follicle (corpus luteum) in the ovary after ovulation. It maintains the thick, spongy lining of the uterus ready for an embryo to implant, and inhibits the release of both FSH and LH. If the egg is not fertilised, progesterone drops and the lining breaks down (menstruation).

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Hormonal vs Non-Hormonal Contraception

Hormonal methods (oral contraceptive pill, skin patch, subdermal implant, hormone injection, hormonal IUS) use oestrogen and/or progesterone to inhibit FSH/maturation and thicken cervical mucus. Non-hormonal methods (male/female condoms, diaphragms, copper IUD, spermicides, surgical sterilisation, abstinence) physically block sperm or kill sperm/prevent implantation without hormonal side effects.

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In Vitro Fertilisation (IVF) Steps (Higher Tier)

1. Give the mother synthetic FSH and LH to stimulate the maturation of several eggs. 2. Collect the mature eggs from the mother's ovaries and fertilise them with the father's sperm in a laboratory dish. 3. The fertilised eggs develop into microscopic balls of cells (embryos) in an incubator. 4. Insert one or two healthy embryos into the mother's uterus.

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1. Q1

   Explain how the hormones FSH, oestrogen, LH, and progesterone interact to control the first 21 days of the human menstrual cycle. [6 marks]

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   Click “Check Mark Scheme” to compare your answer, 1. At the start of the cycle, the pituitary gland secretes FSH, which causes an egg to mature in the ovary and stimulates the ovaries to produce oestrogen [1 mark]. 2. Rising oestrogen levels cause the lining of the uterus to thicken and repair after menstruation [1 mark]. 3. High oestrogen levels inhibit further FSH secretion from the pituitary gland (so no more eggs mature) and stimulate a surge in LH secretion [1 mark]. 4. Around Day 14, the surge in LH stimulates ovulation (the release of the mature egg from the ovary) [1 mark]. 5. The empty egg follicle in the ovary then secretes progesterone [1 mark]. 6. Progesterone maintains the thick uterus lining ready for embryo implantation and inhibits both FSH and LH release [1 mark].

2. Q2

   A woman takes the combined oral contraceptive pill, which contains oestrogen and progesterone. Explain how this prevents her from becoming pregnant, and evaluate the use of the oral pill compared to male condoms. [5 marks]

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   Click “Check Mark Scheme” to compare your answer, 1. High levels of oestrogen and progesterone in the pill continuously inhibit the pituitary gland from producing FSH and LH [1 mark]. 2. Without FSH and LH, no eggs mature in the ovaries and ovulation cannot occur (progesterone also thickens cervical mucus to block sperm) [1 mark]. 3. Advantage of the pill: It is over 99% effective when taken correctly and does not interrupt intercourse [1 mark]. 4. Disadvantage of the pill: A woman may forget to take it daily, it can cause hormonal side effects (headaches, nausea, raised blood pressure), and it offers zero protection against STIs [1 mark]. 5. Advantage of condoms: Male condoms have no hormonal side effects and are the only method that protects against sexually transmitted infections such as HIV and gonorrhoea (though they can occasionally split/slip) [1 mark].

3. Q3

   Describe the stages of In Vitro Fertilisation (IVF) for a couple where the woman has blocked fallopian tubes (oviducts). [4 marks]

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   Click “Check Mark Scheme” to compare your answer, 1. The mother is given injections of FSH and LH to stimulate the maturation of several eggs in her ovaries [1 mark]. 2. The mature eggs are surgically collected from the mother's ovaries and mixed with the father's sperm in a laboratory dish to allow fertilisation [1 mark]. 3. The fertilised eggs are incubated in the lab for a few days while they divide by mitosis to form small embryos (balls of cells) [1 mark]. 4. One or two healthy embryos are then transferred via a thin tube through the cervix directly into the mother's uterus to implant in the lining, bypassing the blocked oviducts [1 mark].

4. Q4

   Give three disadvantages or ethical concerns associated with IVF fertility treatments. [3 marks]

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   Click “Check Mark Scheme” to compare your answer, 1. The treatment is very emotionally and physically stressful for the patients (with hormonal side effects), and the success rate is relatively low (Especially in older women) [1 mark]. 2. Transferring more than one embryo can lead to multiple births (twins or triplets), which increases the risk of premature birth, miscarriage, or stillbirth [1 mark]. 3. Unused embryos produced during IVF are often frozen or destroyed, which some people consider unethical because each embryo is a potential human life [1 mark].

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