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The menstrual cycle is a crucial aspect of female reproductive health, beginning at puberty. The onset of this cycle is known as ‘menarche.’ It involves a series of cyclic changes in the ovaries and uterus, which occur simultaneously.
In the ovaries, an ovum (egg) develops and matures each month. Once mature, the egg is released into the fallopian tube. Concurrently, the uterus prepares for a potential pregnancy by developing a thick, spongy inner lining rich in blood vessels.
If fertilization of the egg occurs, pregnancy begins, and the lining of the uterus supports the developing embryo. If fertilization does not take place, the egg and the thickened uterine lining, along with its blood vessels, are shed from the body. This shedding results in menstruation, which is the bleeding experienced by women.
The menstrual cycle continues throughout a woman's reproductive years until it ceases, typically between the ages of 45 and 52, marking the onset of menopause. The years between menarche and menopause define a woman's reproductive age when she is capable of conceiving and bearing a child.
In humans, sex determination is based on the combination of sex chromosomes present in the cells. Each human cell contains 23 pairs of chromosomes, including one pair of sex chromosomes: X and Y. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).
During reproduction, gametes (egg and sperm) carry only one set of chromosomes. An unfertilized egg always contains one X chromosome. However, male sperm carry either an X or a Y chromosome.
When a sperm with an X chromosome fertilizes an egg, the resulting embryo will develop into a female (XX). Conversely, when a sperm with a Y chromosome fertilizes an egg, the resulting embryo will develop into a male (XY). This combination of sex chromosomes determines the sex of the offspring.
