Basic to the entire menstrual cycle are the female sex hormones. They are--

• Pituitary hormones--Follicle stimulating hormone (FSH),Leutinising hormone(LH)
• Ovarian hormones--Estrogen, Progesterone.

The menstrual cycle actually has 2 components. The ovarian cycle & the uterine cycle. Let's look at them one by one.

Ovarian cycle--

Let's start with the end of each cycle. Slowly the FSH from the pituitary stimulates the growth of a few primordial follicles. With their development they start secreting estrogen. The primordial follicles grow into graffian follicles(the mature form). Though multiple follicles start growing, only one dominant follicle ripens to full maturity while the others degenerate. This fully mature follicle then ovulates.

What is ovulation?--
It is a process by which the ovarian follicle discharges its ovum into the peritoneal cavity (cavity of the abdomen) It is seen at puberty & is restricted to the reproductive period.

How does ovulation occur?--
In a 28 day cycle ovulation generally occurs on the 14th day. It is caused by LH surge.

What is LH surge?--
There is a rapid increase in the level of LH 24--36 hours before ovulation.T his in turn is responsible for ovulation.
After ovulation the follicular cells covering the ovum form the corpus leuteum. In absence of pregnancy it degenerates after 7-8 post ovulatory days. In case of pregnancy the corpus luteum keeps on growing to support the pregnancy until development of placenta.

Uterine (Endometrial) Cycle--

• Proliferative phase-- It is under control of estrogen secreted by the follicles in the ovary. It causes rapid proliferation of the cells of the endometrial cells. glands develop during this phase & the entire tissue is highly vascular.
• Secretory phase-- Coincides with the post ovulatory phase of the ovarian cycle. Under control of progesterone. The glands develop fully & the uterus prepares itself to receive the fertilized ovum.
• Menstrual phase-- In absence of pregnancy the corpus luteum degenerates & this leads to a sudden fall in the levels of estrogen & progesterone. Sudden withdrawl of the hormonal support of the uterus causes shedding of the proliferated endometrium & hence bleeding.this manifests as menstruation. In case of pregnancy, the hormonal support continues & the endometrium receives the fertilized ovum; there being no ovulation.

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