The cyclical change in female primate of Mammal , Menstrual cycle

MENSTRUAL CYCLE 

• In the primate group  of females in Mammals,   After attaining puberty, there are several physical, anatomical and hormonal changes occur in every month of the female body.

• These changes are termed cyclical  changes. The cyclical changes or reproductive cycle in female primate is  called the menstrual cycle which is essential to settle the pregnancy.

• The first menstruation begins at puberty and is called menarche. In human beings, menstrual cycles cases around 50 years of age; that termed as menopause. 

• In human females, the average   time  interval of menstrual cycle is  about 28/29 days.  The cycle of event starting from one menstruation till the next one is called the menstrual cycle.

• Lack of menstruation may be indicatier of pregnancy. However, it may also be caused due to some other underlying causes like stress, poor health etc.

• During each menstrual cycle, an egg is developed in the ovary through oogenesis  and is released from the ovaries by ovulation.

• The lining of the uterus becomes thick to maintain the pregnancy. If fertilization does not occur then  the  lining  of the uterus is broken  and the next menstrual cycle occurs.

• The  menstrual cycle is divided into four phases - menstrual phase, follicular phase, ovulation phase and luteal phase. The Duration and intensity  of each phase may vary from female  to female.

The menstrual phase

• It is the first stage of the menstrual cycle.

• The menstrual flow  occur due to breakdown of endometrial lining of the uterus and its blood vessels which forms liquid that comes out through vagina. Menstruation only occurs if the released ovum is not fertilised. 

• During this phase, the thick  lining of the endometrium of the uterus is broken and passes out from the body through vagina. .

• During this phase , a combination of blood, mucus, and tissue of the endometrium of the uterus are released from vagina in form waste.

• Next phase of the menstrual cycle begins, when an egg is not fertilized that was released during the previous menstrual cycle.

• On average, women are in the menstrual phase of their cycle for 3 to 7 days. Some women have longer periods than others.

The follicular phase

• During this phase, the primary follicles in the ovary grow to become a fully mature Graafian follicle and simultaneously the endometrium of uterus regenerates through proliferation. 

• These changes in the ovary and the uterus are induced by changes in the levels of pituitary and ovarian hormones .

• The secretion of gonadotropins (LH and PSH) increases gradually during the follicular phase, and stimulates follicular development as well as secretion of estrogens by the growing follicles. 

• It starts when the hypothalamus transmits a signal to the pituitary gland to release follicle-stimulating hormone (FSH).

• This hormone stimulates your ovaries to produce around 5 to 20 small sacs called follicles. Each follicle contains an immature egg.

• Only the healthiest egg will eventually mature.  The remaining follicles will be reabsorbed into the body.

• The  follicles are developed in mature follice under the influence of estrogen during the process of oogenesis. 

• This phase also starts to rebuild  the endometrium lining of the uterus for implantation.

• The average follicular phase  takes about 16 days. It can range from 11 to 27 days, depending on your cycle.

Ovulatory phase

• Both LH and FSH attain a peak level in the mid  of menstrual cycle.  

• Rapid secretion of LH about 14 and 15 day of menstrual cycle  called LH surge  whih induces rupturing of Graafian follicle and  release of ovum by the ovulation.

• This phase is marked by the release of eggs  through the  process of ovulation. 

• During this phase , the pituitary gland releases luteinizing hormone (LH) at peak level.

• This stimulates the rupturing of mature follicles. The release of Luteinizing hormone at peak level to rupture the mature follicle is called LH surge.

• During ovulation, the ovary releases a mature egg when mature follicle ruptures. The egg travels down the fallopian tube toward the uterus to be fertilized by sperm.

👌👌Remember - If sperm are released during the ovulatory phase, there are strong chances to settle the pregnancy . 

• Ovulation generally occurs at around day 14 of the menstrual cycle. It lasts about 24 hours. After a day, the egg will die or dissolve if it is not fertilized.

Luteal phase

• At this phase. the remaining parts of the Graafian follicle transform as the corpus luteum. 

• The corpus luteum secretes large amounts of progesterone which is essential for maintenance of the endometrium. 

• Such an endometrium is necessary for implantation of the  ovum and other events of pregnancy. 

• During pregnancy all events of the menstrual cycle stop and there is no menstruation.. 

• In the absence of fertilisation, the corpus luteum degenerates. This causes disintegration of the endometrium leading to menstruation, marking a new cycle.

• It is the last phase of the menstrual cycle. When the egg is released from  the graafian follicle then the graafian follicle is  changed into the yellowish structures called  corpus luteum.

• This structure releases hormones, mainly progesterone and some estrogen. The rise in hormones keeps the endometrium lining of the uterus thick and makes the uterus suitable  for implantation.

• If the egg is fertilised and gets implanted,   the body will produce human chorionic gonadotropin (hCG).

• It also passed out in trace through uriene.This is the hormone pregnancy tests detect. It helps maintain the corpus luteum and keeps the uterine lining thick.

• If the egg is not fertilised  the corpus luteum will shrink away and change into corpus albicans.

• This leads to decreased levels of estrogen and progesterone, which causes the onset of the next menstrual phase of menstrual cycle.