What are the roles of LH and FSH in the menstrual cycle?

LH and FSH are hormones that regulate the menstrual cycle by controlling ovulation and the preparation of the uterus for pregnancy.

Luteinising hormone (LH) and follicle-stimulating hormone (FSH) are both produced by the pituitary gland and play crucial roles in the menstrual cycle. Their primary function is to regulate the growth and development of the ovarian follicles, the release of the egg (ovulation), and the preparation of the uterus for possible pregnancy.

At the beginning of the menstrual cycle, the pituitary gland releases FSH. This hormone stimulates the growth of several ovarian follicles in the ovaries. Each follicle contains an immature egg. As these follicles grow, they start to produce the hormone oestrogen. The rising levels of oestrogen in the body signal the pituitary gland to reduce the production of FSH and increase the production of LH.

The surge in LH levels triggers ovulation, which is the release of the mature egg from the dominant follicle into the fallopian tube. This usually occurs around the middle of the menstrual cycle. After ovulation, the remnants of the dominant follicle in the ovary transform into a structure known as the corpus luteum. The corpus luteum produces progesterone, which prepares the uterus for a potential pregnancy by thickening its lining to receive a fertilised egg.

If fertilisation does not occur, the corpus luteum degenerates, leading to a drop in progesterone levels. This drop triggers the shedding of the uterine lining, known as menstruation, and the start of a new menstrual cycle. The low levels of progesterone and oestrogen signal the pituitary gland to start producing FSH again, and the cycle repeats.

In summary, LH and FSH are key hormones that control the menstrual cycle. FSH initiates the growth of ovarian follicles and the production of oestrogen, while LH triggers ovulation and the formation of the corpus luteum, which produces progesterone to prepare the uterus for pregnancy.