Oestrogen causes puberty in female bodies.

• During puberty, a child's body starts developing into an adult's body. 
• The hormone oestrogen is responsible for the female secondary sexual characteristic changes during puberty.
• One of the most important changes during puberty for females is the beginning of the menstrual cycle.

Menstrual Cycle

• Every month, a woman's body undergoes change to prepare for the possibility of pregnancy. 

• An egg is released from one of the ovaries every month. This is called ovulation.
• To prepare for pregnancy, the lining of the uterus becomes thicker and richer in blood vessels. 
• If pregnancy does not happen, the uterus lining is shed. This is called menstruation.

There are 4 different hormones that control the menstrual cycle. 

👇 For IGCSE Biology, it is important to understand how different hormones control the menstrual cycle. 👇

1. FSH (follicle-stimulating hormone)

• During the early days of the menstrual cycle, FSH is released by the pituitary gland.
• The release of FSH is responsible for maturing of the egg in the ovary.
• The maturing egg produces the hormone oestrogen.

2. Oestrogen

• The uterus lining becomes thicker and richer in blood vessels as oestrogen level rises.
• High levels of oestrogen stimulates the pituitary gland to release LH (luteinising hormone).
• The level of oestrogen peaks one or two days before ovulation.

• A sharp increase in the level of FSH and LH triggers the ovary to release the egg (ovulation). Ovulation happens at approximately day 14 of the menstrual cycle.

• After the release of the egg, progesteron is produced.
• Progesteron is responsible for maintaining the thick lining of the uterus.
• If fertilization has occurred, progesteron will keep being released to maintain the uterus lining.
• If fertilization has not occurred, progesteron levels will drop, which results in the shedding of uterus lining (menstruation).

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