The Menstrual Cycle

What is menstruation?

Menstruation is a woman’s monthly bleeding, also called a period. When you menstruate, your body is shedding the lining of the uterus (womb). Menstrual blood flows from the uterus through the small opening in the cervix, and passes out of the body through the vagina. Most menstrual periods last from three to five days.


What is the menstrual cycle?

Menstruation is part of the menstrual cycle, which prepares your body for pregnancy each month. A cycle is counted from the first day of one period to the first day of the next period. The average menstrual cycle is 28 days long. Cycles can range anywhere from 21 to 35 days in adults and from 21 to 45 days in young teens. Body chemicals called hormones rise and fall during the month to make the menstrual cycle happen.

What happens during the menstrual cycle?

In the latter part of the first half of the cycle (follicular phase), levels of estrogen (one of the two principal “female” hormones) rise and make the lining of the uterus (womb) grow and thicken. At the same time, an egg (ovum) in one of the ovaries starts to mature. At about day 14 of a typical 28-day cycle, the egg leaves the ovary. This is called ovulation. After the egg has left the ovary (luteal phase) it travels through the fallopian tube to the uterus. Progesterone (the other principal “female” hormone) levels rise and help prepare the uterine lining for pregnancy. A woman is most likely to get pregnant during the three days before ovulation or on the day of ovulation. Keep in mind, women with cycles that are shorter or longer than average may ovulate earlier or later than day 14. If the egg is fertilized by a man’s sperm cell and attaches to the uterine wall, the woman becomes pregnant. If the egg is not fertilized, it will break apart. If pregnancy does not occur, hormone levels drop, and the thickened lining of the uterus is shed during the menstrual period. See figure below for details.

menstrual cycle

What changes in a woman’s body during the menstrual cycle?

As a woman’s cycle progresses many physiological changes occur according to what time in her cycle it is. A follicle (egg) is able to be prepared for fertilization because of signaling from changing hormones in the body, these hormones also prepare the lining in the uterus (endometrium) for potential implantation of a fertilized egg.The term histology refers to the microspcopic appearance of a structure.


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