How do hormones regulate the menstrual cycle?

Hormones regulate the menstrual cycle by controlling the maturation and release of eggs and preparing the uterus for pregnancy.

The menstrual cycle is a complex process that is regulated by a series of hormones. The hypothalamus, a part of the brain, releases gonadotropin-releasing hormone (GnRH). This hormone signals the pituitary gland to produce and release two other hormones: follicle-stimulating hormone (FSH) and luteinising hormone (LH).

FSH stimulates the growth and maturation of follicles in the ovaries. Each follicle contains an egg. As the follicles mature, they start to produce oestrogen. This hormone prepares the lining of the uterus (the endometrium) for a potential pregnancy by causing it to thicken. The rising levels of oestrogen also trigger a surge in LH, which causes the most mature follicle to burst and release its egg in a process known as ovulation.

After ovulation, the ruptured follicle transforms into a structure called the corpus luteum. This structure produces progesterone, another hormone that further prepares the uterus for pregnancy by making the endometrium more glandular and vascular. If the egg is not fertilised, the corpus luteum breaks down, leading to a drop in progesterone levels. This drop triggers the shedding of the endometrium in a process known as menstruation.

The menstrual cycle then starts again, driven by the same sequence of hormonal changes. This intricate interplay of hormones ensures that an egg is released each month and that the uterus is prepared to receive a fertilised egg, should conception occur. Understanding these hormonal changes can also help in the management of menstrual disorders and in the development of contraceptive methods.