Menopause depends on a complex network of hormonal communications between the ovary, hypothalamus, and pituitary gland in the brain. The hypothalamus secretes gondadotropin releasing hormone (GnRH) which triggers the production of follicle-stimulating hormone (FSH) by the pituitary gland. The FSH then stimulates the growth of the egg follicles in the ovaries to trigger ovulation. As the egg follicles grow, Oestrogen is manufactured and released into the blood.
This chain reaction is not just one-way. Oestrogen, one of the ovarian oestrogens in the bloodstream, also acts on the hypothalamus, causing a change in GnRH. Next, this altered hormone stimulates the pituitary gland to produce luteinising hormone (LH) which causes the egg follicles to burst and the ovum to be released. After the egg is expelled, progesterone is also manufactured by the collapsed egg follicle which develops into the corpus luteum.