MECHANISMS OF MENSTRUATION

Although regression of the endometrium is initiated by withdrawal of the sustaining influences of oestrogen and progestrone, the subsequent complex chain of events in the endometrium that cause it to break down is still incompletely understood and is due to interplay of multiple factors.

HORMONAL REGULATION

Regulation of the menstrual cycle begins in the hypothalamus. It integrates information from the external and the internal environment relayed to by other parts of the central nervous system. It is through the hypothalamus that factors such as stress or starvation affect menstrual patterns. Hypothalamus cells also respond to a variety of circulating hormone levels. The same area of hypothalamus is also involved in regulating sexual behavior, body temperature and food and water intake. Click to see slides

GnRH, the hypothalamic messenger to the pituitary gland, after release travels directly to the anterior pituitary. Subtle changes in the GnRH pulses determine what response (if any) occurs in the pituitary. GnRH, However, is not responsible for the mid cycle rise in FSH and LH. These rises occur because of oestrogen and progesterone that occurs within pituitary and alters pituitary responsiveness to GnRH.

Menstrual disturbance may also occur because of a functional ovarian cyst. Most commonly, functional cysts involve as especially exuberant corpus luteum that fails to degenerate on schedule. A cyst may continue to produce estrogen and progesterone for several weeks or even months.