The word menstruation, from which the term “menstrual cycle” derives, comes from the Latin word “mensis,” meaning month. The menstrual cycle is defined as the time span from the first day of one menstrual period to the first day of the next one.
Every moment, from puberty to menopause, this intricate and finely tuned pattern of actively prepares your body to nourish a new life by lining the womb, akin it ready to accept a fertilized egg, unless it is suppressed by contraceptive pills, breastfeeding, or pregnancy, for example. If an egg is not fertilized that month, the lining of the uterus, falls away in the form of a period or menstruation. Although, for convenience sake, a normal menstrual cycle is usually calculated as 28 days, in fact a 28 day cycle is relatively rare and many women have a shorter or longer cycles; Anything from 24-40 days.
During each cycle, the reproductive organs undergo a series of changes under the influence of hormones that cause a follicle, a sac containing an egg or ovum, to mature in the ovary. At ovulation, the egg is released from the follicle into the abdominal cavity from where it finds its way the fallopian tubes and travels down the uterus. If fertilization does not occur, the egg, together with the lining of the womb the (endometrium) is shed in the menstrual flow, allowing a new lining to grow, ready to nurture another pregnancy.
Menstruation lasts on average for four to five days, but again the length of time varies greatly from woman to woman, and bleeding can last anything from three to ten days.
1. The menstrual phase of menstruation
Generally this phase runs from the first to the fifth day of your cycle. During this phase, the lining of the uterus, or endometrium, is ejected. Tissues and bleeding from the vagina pass in the form of a period. By the fifth day, the follicles of the ovaries are beginning to produce a higher level of estrogen.
Follicular phase, or proliferative phase
Between days 6 and 14 of the menstrual cycle, the follicle develops, these are eggs in the ovaries. During this phase the endometrium is regenerated by the influence of increasing estrogen levels. The inside layer of the uterus becomes thick and velvety, rich in blood capillaries. The rising level of estrogen can also cause the lining of the cervix to become elastic and thin, like egg-white, so that the sperm can easily pass into the uterus. Ovulation marks the end of the follicular phase, and this occurs 13 to 14 days before the start of menstrual bleeding. So, on a 28-day menstrual cycle, ovulation should occur near day 14, and menstrual bleeding around day 26.
From day 15 to 28 of your menstrual cycle is the stage when the symptoms of premenstrual syndrome (PMS) will develop, even though we do not know exactly what triggers it. During the secretory phase, progesterone levels increase the blood supply to the uterus, creating an environment rich in blood and nutrients preparing the uterus for a potential embryo. Rising levels of progesterone cause a thickening of the lining of the cervix and become sticky, clogging the outlet of the uterus, preventing sperm entry. Towards the end of this phase, if fertilization does not occur, progesterone levels fall, depriving oxygen and nutrients to the endometrium in preparation for being expelled in the form of a menstruation.
Hormones and the Menstrual Cycle
The menstrual cycle is regulated by hormonal activity secreted by the endocrine glands of the body, or hormonal system. From the first day of our conception until we die, our body is under the influence of a cocktail of hormones produced in our glands. The ovaries have two functions: The organs of the reproductive system, storing and producing eggs, and are also glands of the endocrine system, producing the female sex hormones estrogen and progesterone.
Hormones are chemical messengers that travel through the bloodstream,
activating cells and tissues throughout the body. Each hormone has a specific function for a particular type of tissue. To ensure that a hormone will not connect with other cells at random, the cells have specific receptors, either inside, or on its surface. The hormones that travel through the blood connect with these receptors, thus avoiding detours and mistakes.
The glands of the endocrine system work together to ensure that our body
is maintained at a balanced level of homeostasis. This is possible through some feedback mechanisms that inhibit, or slow the production by specific glands once levels are sufficient, and can be activated once again when needed, like an air conditioning thermostat. The system is finely calibrated in such a way that if something goes amiss, it can affect the entire body. This is one reason why PMS can have widespread effects as throughout the body, by is its interaction with other parts of the endocrine system.
Hormones Gone Wild
On the first day of your menstrual cycle, your hypothalamus will produce a hormone called GnRH (Gonadotrophin Releasing Hormone). This will activate the pituitary to produce a chemical messenger called FSH (Follicle Stimulant Hormone), and a leuteinizing hormone, LH. The FSH will travel through the bloodstream until it reaches the ovaries, where it stimulates development of the follicles. It also triggers the secretion of estrogen in the ovaries.
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