Question

how does FSH and LH regulate in ovulation cycle?

Answer 1

The menstrual cycle consists of four phases: menstrual phase, proliferative phase, ovulatory phase and secretory phase.
1. Menstrual phase: In a 28 day menstrual cycle, the menses takes place on cycle days 3-5. The production of LH from the anterior lobe of the pituitary gland is considerably reduced. The withdrawal of this hormone causes degeneration of the corpus luteum and therefore progesterone production is reduced. Production of oestrogens is also reduced in this phase. The endometrium of uterus breaks down and menstruation begins.
2. Proliferative phase: This phase usually includes cycle day 6-13 or 14 in a 28 day cycle. The FSH secreted by the anterior lobe of the pituitary gland stimulates the ovarian follicle to secrete oestrogens. Oestrogens stimulate the proliferation of endometrium of the uterine wall. The endometrium becomes thicker by rapid cell multiplication and this is accompanied by an increase of uterine glands and blood vessels.
3. Ovulatory phase: Both LH and FSH attain a peak level in the middle of cycle. Rapid secretion of LH induces rupturing of Graafian follicle and thereby the release of ovum. This is called ovulation. In fact, LH causes ovulation.
4. Luteal phase: This phase usually includes cycle days 15-28 in a 28 day cycle. The LH causes ovulation. The remaining cells of the ovarian follicles are stimulated by the LH to develop corpus luteum. The corpus luteum secretes large amount of progesterone. Progesterone stimulates the uterine glands to produce increased amount of watery mucus. During this phase, there is also similar increase in the secretion of watery mucus by the vaginal glands and by the glands of the fallopian tubes. Progesterone is also essential for maintenance of the endothelium. Such an endothelium is required for the implantation of the fertilized ovum and other events of pregnancy. In the absence of fertilization, the corpus luteum degenerates. This causes disintegration of the endothelium leading to menstruation marking a new cycle.