SECTION 3: THE REGULATION OF THE MEN-STRUAL CYCLE

1. Hypothalamo-pituitary-ovarian axis

1.1 Hypothalamus under the influence of cerebral cortex -GnRh

GnRh acts on pituitary （anterior）- FSH, LH

Under the effect of FSH and LH ovary produces - estrogen and progesterone from maturing follicle and corpus luteum.

The effect of estrogen and progesterone in the endometrium leads to menstruation.

Uterine cycle

1.2 Proliferative phase （preovulatory phase or follicular）phase:

At the end of menstruation all except the deep layers of the endometrium have sloughed.

A new endometrium regrows under the influence of estrogens from the developing follicle.

The endometrium increases rapidly in thickness from the 5thday to the 14th day of the menstrual cycle.

1.3 Secretory phase or luteal phase

After ovulation, the endometrium becomes more highly vascularized and slightly edematous under the influence of estrogen and progesterone from the corpus luteum.

The gland becomes coiled and tortuous and they begin to secrete a clear fluid.

Bleeding Phase:

When the corpus luteum regresses, hormonal support for the endometrium is withdrawn.

The endometrium becomes thinner.

Foci of necrosis appear in the endometrium.

Spasm and degeneration of the walls of the spiral arteries take place leading to spotty hemorrhage that become confluent and produces the menstrual flow.

Regulation of secretion of estrogen & progesterone

In general both estrogen & progesterone shows negative feedback inhibition.

Through positive feedback action estrogen produces LH surge （rapid rise & fall）just before ovulation.

Inhibin inhibits secretion of FSH

Menstrual cycle

Regulation of menstrual cycle

The regulatory system functions through the hormones of the hypothalamo -pituitary-ovarian axis.

2. Hormones involved in regulation of the menstrual cycle are:

2.1 Hypothalamic hormone- GnRH: it triggers the cyclic changes during the menstrual cycle by stimulating secretion of FSH and LH from anterior pituitary.

2.2 Anterior pituitary hormones - FSH and LH: FSH stimulates the growth of immature ovarian follicles. LH triggers ovulation and sustains corpus luteum.

2.3 Ovarian hormones- Estrogen and Progesterone:ovaarian follicles secrete a large quantity of estrogen. The corpus luteum secretes a large quantity of progesterone. Estrogen is responsible for the growth of follicles. Both the steroids act together to produce the changes in uterus, cervix and vagina.

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