Hormones can be used for controlling human reproduction. Explain the use of hormones in:

• contraception
• the treatment of infertility.

**Hormonal Contraception:** The aim of hormonal contraception is to prevent pregnancy by disrupting the normal menstrual cycle. The most common form is the combined oral contraceptive pill, which contains synthetic versions of oestrogen and progesterone. - **Oestrogen:** A consistently high level of oestrogen inhibits the pituitary gland from releasing FSH. Without FSH, no egg follicle will mature in the ovary. - **Progesterone:** This hormone inhibits the release of LH from the pituitary gland, preventing ovulation (the release of a mature egg). It also causes the mucus in the cervix to become thick and sticky, forming a plug that makes it difficult for sperm to swim through to the uterus. **Hormonal Treatment of Infertility:** Some women are infertile because they do not produce enough FSH to stimulate their eggs to mature. This can be treated with fertility drugs. - **FSH and LH Injections:** The woman is given injections of drugs containing FSH and LH. These hormones stimulate the ovaries to mature one or more egg follicles. This process is carefully monitored. - **IVF (In Vitro Fertilisation):** This hormonal stimulation is a key first step in IVF. Once the eggs are mature, they are surgically collected from the ovary. They are then fertilised with sperm in a petri dish in a laboratory. The fertilised eggs develop into embryos. After a few days, one or two of the healthiest embryos are selected and transferred into the woman's uterus to continue development.