Menstrual Cycle notes for class 12 and NEET Exam
Menstrual Cycle notes for class 12 and NEET Exam
General information:-
(1) Menstruation occurs in humans, apes, and old-world monkeys.
(2) Menstruation is bleeding from the uterus of adult females at intervals of one lunar month.
(3) Beginning of menstruation or first menstruation is called menarche.
(4) The beginning of menstruation varies. It usually occurs between 12 and 15 years.
(5) The cycle of events starting from one menstruation till the next one is called Menstrual Cycle.
(6) In human females, menstruation is repeated at an average interval of about 28/29 days.
(7) One ovum is released (ovulation) during the middle of each menstrual cycle.
(8) It is regulated by certain hormones, some of which are secreted by the pituitary gland.
(9) The pituitary gland is stimulated by releasing factors produced in the hypothalamus.
(10) The hormones produced by the pituitary gland influence the ovaries. The hormones secreted by the ovaries affect the walls of the uterus.
NEET Exam Notes
Phases of Menstrual Cycle:- NEET Exam Notes
The menstrual cycle consists of the following four phases:
(1) Menstrual Phase: Class 12 exam notes
(i) In a 28 days menstrual cycle, the menses take place on cycle days 3-5.
(ii) The production of LH from the anterior lobe of the pituitary gland is reduced.
(iii) The withdrawal of this hormone causes degeneration of the corpus luteum and, therefore progesterone production is reduced.
(iv) Production of estrogens is also reduced in this phase.
(v) The endometrium of the uterus breaks down & menstruation begins.
(vi) The cells of endometrium secretions, blood & unfertilized ovum constitute the menstrual flow.
(2) Follicular Phase: Class 12 exam notes
(i) This phase usually includes cycle days 6-13 or 14 in a 28 days cycle.
(ii) The follicle-stimulating hormone (FSH) secreted by the anterior lobe of the pituitary gland stimulates the ovarian follicle to secrete estrogens.
(iii) Oestrogen stimulates the proliferation of the endometrium of the uterine wall.
(iv) The endometrium becomes thicker by rapid cell multiplication and this is accompanied by an increase in uterine glands & blood vessels.
Various Events during a Menstrual Cycle:- NEET Exam Notes
(3) Ovulatory Phase:
(i) Both LH & FSH attain a peak level in the middle of the cycle (about the 14th day).
(ii) Oestrogen concentration in blood increases.
(iii) Rapid secretion of LH induces rupturing of graffian follicle and thereby the release of ovum.
(iv) In fact LH causes ovulation.
(4) Luteal Phase:
(i) Includes cycle days 15 to 28.
(ii) Corpus luteum secretes progesterone.
(iii) Endometrium thickens.
(iv) Uterine glands become secretory.
Hormonal Control of MC: – Class 12 exam notes
(i) FSH stimulates the ovarian follicles to produce oestrogens.
(ii) LH stimulates corpus luteum to secrete progesterone.
(iii) Menstrual phase is caused by the increased production of oestrogens.
(iv) LH causes ovulation
(v) Proliferative phase is caused by the increased production of oestrogens.
(vi) Secretory phase is caused by increased production of progesterone.
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