Question

Menstruation is triggered by an abrupt decline in the amount of a hormone :

Answer 1

Luteinizing hormone is a hormone produced by gonadotropic cells in the anterior pituitary gland. The production of LH is regulated by gonadotropin-releasing hormone from the hypothalamus. In females, an acute rise of LH triggers ovulation and development of the corpus luteum. Sudden decline in LH causes menstruation.

Follicle stimulating hormone (FSH) is secreted from the anterior part of pituitary gland. It stimulates the growth of ovarian follicles in females.

Oestrogen is the female sex hormone secreted from ovarian follicles and stimulate the development of female secondary sex organs.

The corpus luteum secretes large amounts of progesterone which is essential for maintenance of the endometrium (wall of the uterus) . Such an endometrium is necessary for implantation of the fertilized ovum. In the absence of fertilization, the corpus luteum degenerates resulting in decline of progesterone level. This causes disintegration of the endometrium leading to menstruation, making a new cycle.