What is the Menstrual cycle & Menstruation? Discuss in details about various phases and hormones of the menstrual cycle.

Menstrual cycle & Menstruation

Menstruation is a woman’s once-a-month bleeding, also called a “period.” When women menstruate, the body releases the monthly build-up of the endometrium lining. Blood & tissue flow from the uterus through the slight opening in your cervix & pass out of the body through your vagina. During the monthly menstruation or menstrual cycle, the uterus lining forms to prepare for pregnancy. If women don’t get pregnant, progesterone & estrogen hormone levels start decreasing. When the level of estrogen and progesterone becomes low, they tell your body to begin menstruation.

The menstrual cycle or female reproductive cycle is the regular natural change that occurs in the female reproductive system (definitely in the uterus & ovaries) that makes pregnancy possible. This cycle is essential for the creation of oocytes, and the uterus preparation for pregnancy. The menstrual cycle arises due to the increase and decrease of estrogen.

During the reproductive years, non-pregnant women’s normally show cyclical changes in uterus & ovaries. Every reproductive cycle takes around one month and comprises oogenesis & prepare the uterus to take a fertilizes ovum. These events are controlled by hormones secreted by anterior pituitary, hypothalamus & ovaries. Normally, the female reproductive cycle includes uterine & ovarian cycles, related cyclical changes in cervix & breast and hormonal changes that control them.

Phases of the Menstrual cycle:

Menstrual cycle includes various phases. The exact duration of phases of the reproductive cycle may be different for the individual woman. The duration of the menstrual cycle ranges from about 23 to 33 days. The phases of the menstrual cycle are: -

1.      Follicular or proliferative phase

2.      Ovulation

3.      Luteal phase

Details of all phases are: -

1.      Follicular or proliferative phase

This phase starts with the end of menstruation and it occurs between day 1 to day 14 of the menstrual cycle. Day 1 of this phase is bright red bleeding and day 14 is marked by ovulation. When this phase starts, estrogen & progesterone levels are low that results, the upper layer of the uterus lining (endometrium) breakdown and bleeding occurs. The pituitary gland releases a hormone called Follicle-stimulating hormone (FSH) which stimulate the development of follicles on the surface of ovaries. Each follicle contains an egg. One of these follicles become leading and develop a single mature egg (Graffian follicle). When more than one follicle develops mature egg, this can cause twins. The maturing follicles produce estrogen hormone which peaks in the one or two days before ovulation. In the second part of this phase (after menstruation), the uterus lining becomes thicker & enriched with blood in the response of increased estrogen level. Later in this phase, FSH level starts to decrease, only one follicle continues to develop. This follicle release estrogen. High level of estrogen promotes the secretion of luteinizing hormone (LH) from the pituitary gland. On day 12, a surge of LH cause release of the egg from the follicle. LH surge also causes an increase in testosterone, which increase the sex drive.

This phase also creates an environment that is friendly & helpful to possible incoming sperm.

2.      Ovulation or ovulatory phase

Ovulation is the release of the egg from the matured follicle (Graffian follicle). This phase normally occurs on 14 days of the cycle. This phase begins with the surge of LH hormone levels. LH hormone stimulates the release of the egg (ovulation). After release, egg enters the fallopian tube and toward the uterus. The life span of an egg is approximately 24 hours. If sperm are present, fertilization may take place and if egg not got fertilized and it collapses after 24 hours.

If anyone wants to have a baby, they can improve to getting chance of getting pregnant if they know about fertile window & ovulation in the reproductive cycle.

3.      Luteal phase

During this phase, LH & FSH hormone levels decrease. After releasing the egg, follicle got ruptured and forms a corpus luteum, which start to release progesterone and some amount of estrogen. These hormones maintain the thickened uterus lining and wait for the fertilized egg to implant. If fertilized occurred, corpus luteum keep produce progesterone continuously, which prevents the uterus lining from being shed and when fertilization does not occur, corpus luteum collapses & die and progesterone level drop. Drop-in progesterone level causes the uterus lining to shed. This is known as Menstruation and then the menstrual cycle repeats.

Advantage of Menstruation:

·         Menstruation causes iron loss and losing iron reduces the risk of heart problems and enhances life span which makes women live longer than man.

·         It assures you of normal functioning for a healthy life.

·         It helps to remove the waste from your body.

·         Pain during menstruation makes you resistant for the pain to an extent in life.

·         It increases sexual desires in females during the period.

Hormonal regulation of Menstrual cycle

Hypothalamus part of the brain secretes Gonadotropin-releasing hormone (GnRH), that control the menstrual cycle. GnRH, released by the hypothalamus of the brain stimulates the anterior pituitary gland to release FSH & LH. FSH stimulate the growth of follicles and LH to stimulate the development of ovarian follicles. These hormones (FSH & LH) also stimulate ovarian follicles to secrete estrogen. At the middle cycle, LH triggers ovulation and promotes the formation of corpus luteum. Corpus luteum produces and secretes progesterone, estrogen, relaxin and inhibin hormone.

Estrogen has several important functions: -

·         Development and maintenance of female reproductive structures, breasts & sex characteristics.

·         Lower blood cholesterol level.

·         Increase in protein anabolism.

·         Inhibit the release of FSH & LH from anterior pituitary by the hypothalamus.

Progesterone & estrogen cooperate and maintain the endometrium for a fertilized egg and prepare mammary gland for milk secretion.

The small quantity of relaxin hormone relaxes the uterus by inhibiting contraction of the myometrium. During pregnancy, the placenta produces more relaxin which relaxes the uterine smooth muscle. At the end of pregnancy (during childbirth), relaxin hormone increases the flexibility of the pelvic system & dilate the uterine cervix, that eases the baby delivery.

Inhibin hormone is secreted growing follicles & corpus luteum after ovulation. It inhibits the section of FSH at a lesser extent. When embryo implanted, cells present nearby embryo start to produce a hormone known as Human chorionic gonadotropin (HCG). HCG maintain corpus luteum (which produce progesterone) until the growing embryo can produce their own hormone. Pregnancy is detected by testing the increased level of HCG hormone in female urine.