MENSTRUAL CYCLE

🔴MENSTRUAL CYCLE 🔴

 

♣︎ It occurs in monkeys, apes and human beings. 

♣︎ Cycle consists of 3 phases-menstrual, proliferative and secretory phase. 

♣︎Blood flows in the last few days of the cycle. The broken endometrium is passed out during 

menstruation. 

♣︎Female does not permit copulation during menstrual phase of the cycle. 

🔵OESTROUS CYCLE 🔵 

♣︎It occurs in non primates like cow, sheep, rat, deer, dog, tiger etc. 

♣︎ It consists of a short period of oestrous or heat. it is 12-24 hours in cow followed by anoestrous or passive period.

 

♣︎Blood does not flow in this cycle. The broken endometrium is reabsorbed.

 

♣︎ Female permits copulation only during oestrous period.

 

♣︎Both in plants and animals, hormones are responsible for the transition between different 

phases of life cycle. 

★Interaction between hormones and environmental factors regulate the 

reproductive processes.

Menstrual Cycle

(1) Menstruation occurs in human, 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.

Phases of Menstrual Cycle

The menstrual cycle consists of following four phases:

(1) Menstrual Phase:

(i) In a 28 days menstrual cycle,the menses takes 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 progestrone production is reduced.

(iv) Production of oestrogen is also reduced in this phase.

(v) The endometrium of uterus breaks down & menstruation begins.

(vi) The cells of endometrium secretions, blood & unfertilised ovum constitutes the menstrual flow.

(2) Follicular Phase:

(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 oestrogens.

(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

(3) Ovulatory Phase:

(i) Both LH & FSH attain a peak level in the middle of cycle (about 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 progestrone.

(iii) Endometrium thickens.

(iv) Uterine glands become secretory.

Hormonal Control of MC

(i) FSH stimulates the ovarian follicles to produce oestrogens.

(ii) LH stimulates corpus luteum to secrete progestrone.

(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 progestrone.