Periods - understanding the menstrual cycle

What are periods? 

Periods are basically the shedding of the lining of the uterus or the womb along with blood. This lining is developed in the womb in anticipation of pregnancy and gets shed in a case when there is no pregnancy. 

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How long do normal periods last?

Periods that last around 2 to 7 days are said to be normal. Any period lasting for more than 7 days is considered a prolonged period.

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How much bleeding during periods is normal?

Different women can have a different ‘normal’ amount of blood loss during their periods. But about 3 to 5 tablespoons of blood and a maximum of 80 ml of blood loss during a period is considered normal. While it may not be possible to practically measure the amount of blood you lose in your periods, anything more than 3 to 4 sanitary pads per day along with the passage of clots is considered heavy. Also, any number of sanitary pads more than what you normally use can be considered as a heavy period.  

Duration of a menstrual cycle

The length of a woman's menstrual cycle may vary from woman to woman, although the typical period lasts 28 days. Any cycle regularly occurring at every 21 to every 35 days is normal. 

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What happens during the menstrual cycle?

The menstrual cycle is more than just the period - It is a sequence of events in the brain, ovaries, and uterus that are related to hormones - chemical messages that travel through the blood from one region of the body to another.

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The cycle has two components- the uterine and the ovarian. Both these components not only work in sync with each other but are also dependent on each other for their flawless functioning. 

The cycle is split into the phases-menstrual phase, the follicular, or proliferative phase, and the luteal, or secretory phase. Ovulation is the major event that occurs between the follicular and the secretory phases, while periods come between the secretory and follicular phases.

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Understanding the menstrual cycle 

In order to understand the menstrual cycle better, let us first look at the reproductive organs in a woman's body.

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• The hypothalamus- an area in the brain that secretes many hormones, out of which the ‘GnRH’, or gonadotropin-releasing hormone is important in the menstrual cycle
• The pituitary- a pea-shaped gland in the brain that produces the hormones FSH (Follicle stimulating hormone) and LH (luteinizing hormone)
• Ovaries- structures on either side of the uterus, where eggs are formed, matured and released
• The womb (uterus) prepares itself every month by preparing a thick layer where a fertilized egg can implant and a baby can grow.
• Fallopian tubes-  two tiny tubes that link the ovaries to the womb through which the egg travels towards the uterus after ovulation, and where fertilization actually takes place. 
• Cervix- or the mouth of the uterus.
• Vagina, or the birth canal- is the organ for copulation, as an exit for the menstrual blood to flow out and for the baby to deliver.

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What drives the whole menstrual cycle are hormones from the HPO- or hypothalamic-pituitary-ovarian axis?

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GnRH (gonadotropin-releasing hormone) from the hypothalamus induces the pituitary gland to first secrete the hormone FSH (follicle stimulating hormone) which, in turn, acts on the ovary, inducing it to start the development of the ovarian eggs/ follicles. 

These developing ovarian follicles produce the hormone Estrogen, which causes the development of the lining of the uterus in anticipation of a pregnancy.

High levels of Estrogen from the ovarian follicles in turn inhibit the production of more FSH and cause the secretion of another hormone called LH (luteinizing hormone) from the pituitary. 

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Ovulation - or the release of a mature egg from the ovary, happens under the influence of LH.  After ovulation, the cells surrounding the mature ovulated follicle form a complex called the ‘Corpus Luteum’, which secretes the hormone Progesterone. Progesterone causes the uterine lining to bind and mature. This corpus luteum has a life of 14 days. So if a pregnancy does not occur, the corpus luteum degenerates, and Progesterone secretion stops and leading to the shedding of the uterine lining resulting in periods. 

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The whole cycle repeats itself month on month for nearly 3 decades of a woman’s life.  

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