Caption

Contraceptive pill. Illustration showing the mechanism of the contraceptive pill. Oral contraceptives act on the brain's hypothalamus (purple area) disturbing the natural release of hormones from the pituitary gland (small red area). The pituitary normally produces luteinizing hormone (LH) and follicle-stimulating hormone (FSH), causing ovulation in one of the two ovules (marked by blue arrow). Oral pills contain progesterone and usually also oestrogen so that no egg cell, or ovum, (yellow/red) ripens, preventing fertilisation. The pill is an extremely reliable method of contraception. The female reproductive system may be seen in lower frame.