How do hormones regulate the menstrual cycle's different phases?

Hormones regulate the menstrual cycle's phases by controlling the growth and release of eggs and the preparation of the uterus.

The menstrual cycle, which lasts approximately 28 days, is regulated by a complex interplay of hormones. The cycle begins with the follicular phase, which is dominated by the hormone oestrogen. The pituitary gland releases follicle-stimulating hormone (FSH), which stimulates the growth of follicles in the ovaries. These follicles produce oestrogen, which causes the lining of the uterus to thicken in preparation for a potential pregnancy.

Around the middle of the cycle, a surge in luteinising hormone (LH), also produced by the pituitary gland, triggers ovulation - the release of a mature egg from the ovary. This is the ovulatory phase. The egg travels down the fallopian tube towards the uterus. If sperm is present and fertilises the egg, it can implant into the thickened uterine lining and pregnancy begins.

If fertilisation does not occur, the cycle moves into the luteal phase. The follicle that released the egg transforms into the corpus luteum, which produces progesterone. This hormone maintains the thickened lining of the uterus. If no fertilised egg implants, the corpus luteum breaks down, progesterone levels drop, and the lining of the uterus is shed in the menstrual phase, commonly known as a period.

In summary, the menstrual cycle is a carefully coordinated process regulated by hormones. FSH and LH from the pituitary gland control the growth and release of eggs from the ovaries, while oestrogen and progesterone prepare and maintain the uterus for potential pregnancy. If no pregnancy occurs, hormone levels drop and the cycle begins again.