Hormones in reproduction and negative feedback

Biology · Homeostasis and response. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.

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The idea

The menstrual cycle lasts about 28 days and is controlled by four hormones. FSH and LH come from the pituitary gland. Oestrogen and progesterone come from the ovaries. An egg matures, the uterus lining builds up, the egg is released at about day 14 and the lining is then maintained. In males, testosterone from the testes stimulates sperm production.

Contraception can use hormones: the pill, or an implant, injection or skin patch. Non-hormonal methods include barriers (condoms, diaphragms), spermicides, intrauterine devices, abstinence and sterilisation.

The same hormones can treat infertility. FSH and LH are given as a fertility drug, and they are the first step in IVF.

Rules to remember

FSH (pituitary): makes an egg mature in the ovary.
Oestrogen (ovaries): builds up the uterus lining and inhibits FSH.
LH (pituitary): triggers ovulation, the release of the egg.
Progesterone (ovaries): maintains the uterus lining after ovulation and during pregnancy.
The pill contains hormones that inhibit FSH, so no eggs mature. Implants, injections and patches release progesterone slowly, which stops eggs maturing and being released for months or years.
IVF: FSH and LH given → eggs collected → fertilised by sperm in the laboratory → embryos develop → one or two inserted into the uterus. It is stressful, success rates are low and multiple births are possible.
Thyroxine (thyroid) stimulates the basal metabolic rate and is kept steady by negative feedback. Adrenaline (adrenal glands) raises the heart rate and sends more oxygen and glucose to the brain and muscles: 'fight or flight'.

Common mistake

Mixing up FSH and LH. FSH makes the egg mature; LH makes the ovary release it.

Worked example

Tests show that eggs mature normally in a woman's ovaries but are not being released. Which hormone is most likely to be too low?

Eggs are maturing, so FSH is doing its job.
The step that fails is the release of the egg (ovulation).
Ovulation is triggered by LH from the pituitary gland.

Answer: LH is most likely too low. Giving LH in a fertility drug could help.

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