Female sex hormones

1. Oestrogen (oestradiol): secreted from the Graafian follicle, the corpus luteum and the placenta. It causes the female secondary sexual characters (e.g. breast development, wider pelvis), regulates the menstrual cycle and rebuilds the uterine lining (endometrium) after menstruation.
2. Progesterone: from the corpus luteum and the placenta. Important in pregnancy: it regulates the blood supply of the uterine wall and prepares it to receive the embryo, and it brings about the changes of the mammary glands during pregnancy. It also inhibits ovulation (basis of the contraceptive pill).
3. Relaxin: secreted by the placenta and uterus; at the end of pregnancy it relaxes the pubic symphysis and the ligaments of the pelvis, easing delivery.

(The full hormonal control of the menstrual cycle is explained in Chapter 3.)