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Menstrual Cycle Part -1
Menstruation occurs in human, apes and old world monkeys.
Menstruation is bleeding from the uterus of adult females at intervals of one lunar month.
Beginning of menstruation or first menstruation is called menarche.
The beginning of menstruation varies. It usually occurs between 12 and 15 years.
The cycle of events starting from one menstruation till the next one is called Menstrual Cycle.
In human females, menstruation is repeated at an average interval of about 28/29 days.
One ovum is released (ovulation) during the middle of each menstrual cycle.
It is regulated by certain hormones, some of which are secreted by the pituitary gland.
The pituitary gland is stimulated by releasing factors produced in the hypothalamus.
The hormones produced by the pituitary gland influence the ovaries. The hormones secreted by the ovaries affect the walls of the uterus.
The menstrual cycle consists of following four phases:
In a 28 days menstrual cycle, the menses takes place on cycle days 3-5.
The production of LH from the anterior lobe of the pituitary gland is reduced.
The withdrawal of this hormone causes degeneration of the corpus luteum and, therefore progestrone production is reduced.
Production of oestrogen is also reduced in this phase.
The endometrium of uterus breaks down & menstruation begins.
The cells of endometrium secretions, blood & unfertilised ovum constitutes the menstrual flow.
This phase usually includes cycle days 6-13 or 14 in a 28 days cycle.
The follicle stimulating hormone (FSH) secreted by the anterior lobe of the pituitary gland stimulates the ovarian follicle to secrete oestrogens.
Oestrogen stimulates the proliferation of the endometrium of the uterine wall.
The endometrium becomes thicker by rapid cell multiplication and this is accompanied by an increase in uterine glands & blood vessels.
Both LH & FSH attain a peak level n the middle of cycle (about 14th day).
Oestrogen concentration in blood increases.
Rapid secretion of LH induces rupturing of graffian follicle and thereby the release of ovum.
In fact LH causes ovulation.
Includes cycle days 15 to 28.
Corpus luteum secretes progestrone.
Uterine glands become secretory.
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