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17. What is menstrual cycle? Which hormones regulate menstrual cycle?

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Menstrual cycle: The reproductive cycles in female primates is called the menstrual cycle. In a 28 days menstrual cycle, the menses takes place on cycle days 3-5. The menstrual cycle consists of phases like menstrual phase, follicular phase, ovulatory phase and luteal phase.

Menstrual phase

1. The production of LH from the anterior lobe of the pituitary gland is reduced.

2. The withdrawal of this hormone causes degeneration of the corpus luteum and, therefore progesterone production is reduced.

3. Production of oestrogen is also reduced in this phase.

4. The endometrium of the uterus breaks down & menstruation begins.

5. The cells of endometrium secretions, blood & unfertilised ovum constitute the menstrual flow.

Follicular phase-

1. This phase usually includes cycle days 6-13 or 14 in a 28 days cycle.

2. The follicle stimulating hormone (FSH) secreted by the anterior lobe of the pituitary gland stimulates the ovarian follicle to secrete oestrogens.

3. Oestrogen stimulates the proliferation of the endometrium of the uterine wall.

4. The endometrium becomes thicker by rapid cell multiplication and this is accompanied by an increase in uterine glands & blood vessels.

Ovulatory phase

1. Both LH & FSH attain a peak level in the middle of the cycle (about 14th day).

2. Oestrogen concentration in blood increases.

3.  Rapid secretion of LH induces rupturing of the graffian follicle and thereby the release of the ovum. In fact, LH causes ovulation.

Luteal Phase:

1. Includes cycle days 15 to 28.

2. Corpus luteum secretes progesterone.

3. Endometrium thickens.

4. Uterine glands become secretory. 

Hormonal control of the menstrual cycle. 

1. FSH stimulates the ovarian follicles to produce oestrogens.

2. LH stimulates corpus luteum to secrete progesterone.

3. Menstrual phase is caused by the increased production of oestrogens.

4. LH causes ovulation

5. The proliferative phase is caused by the increased production of oestrogens.

6. The secretory phase is caused by increased production of progesterone.

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Sonika

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