The Menstrual Cycle for Dummies
Menarche, which is the onset of menses or menstruation, is often considered to be the hallmark of puberty among females. It occurs at the age of around 12 years on an average; however, the first menses can occur anywhere between the ages of 9 and 17 years.
Menstruation is the bleeding from the uterus of an adult female at intervals of one lunar month (28 days) on an average. It occurs from puberty to menopause. Menstrual periods are missed (amenorrhea) during pregnancy and lactation periods and also in abnormal states. The menstrual cycle is divided into three phases. From the day of onset of the bleeding to the fourth day is the bleeding phase.
The proliferative phase starts from the fifth day and ends on the fourteenth day, around the time when the egg is released. The fifteenth day onwards to the twenty-eighth day is the secretary phase.
In the bleeding phase, blood, endometrium, the unfertilized egg, mucus, and white blood cells in plenty are cast off. The blood loss is more on the second and third day. Due to the breakdown of the clot forming tissues, blood is not allowed to clot in the uterus.
The basal one-third of the endometrium remains intact and is concerned with the process of regeneration, which is initiated by the third day of the bleeding phase and continues into the proliferating phase.
The proliferative phase is so named as the endometrium continues to proliferate (to multiply/to regenerate) till it becomes about 5 mm thick. This is controlled by a hormone called estrogen that is secreted by the ovaries. Meanwhile, the Graffian follicles mature in the ovaries under the influence of the Follicle Stimulating Hormone (FSH) of the anterior pituitary and are maintained by the Luteinizing Hormone (LH).
The ovulation period is around the twelfth to fourteenth day of the cycle; however it is varies from person to person.
The secretary phase covers the last 14 days of the menstrual cycle and is influenced by the hormone progesterone secreted by the corpus luteum. In the first week of this stage, the new blood vessels form in the endometrium, the endometrial glands get filled with glycogen and mucin secretions, there is infiltration with white blood cells, and the stroma cells enlarge. In the second week, secretion activity is at its maximum. The endometrium at this stage is 7-8 mm in thickness and appears to be soft, edematous, and velvety.
If the ovum fails to fertilize, the corpus luteum starts degenerating by the twenty-second day of the cycle, resulting in a sudden fall in progesterone levels. The lower one-third of the endometrial lining has straight arteries that remain unaffected. However, the upper two-thirds of the endometrium have tortuous arteries that get constricted due to a fall in progesterone levels.
This results in the destruction and shedding of the upper two-thirds of the endometrium, which also gets discarded along with the blood, causing the onset of the bleeding phase.
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