Menstrual Cycle:

What Really Happens in those 28 Days?!

Basic Biology: the cycle begins

Did you know that when a baby girl is born, she has all the eggs her body will ever use,

and many more, perhaps as many as 450,000? They are stored in her ovaries,

each inside its own sac called a follicle. As she matures into puberty, her body begins

producing various hormones that cause the eggs to mature. This is the beginning of her

first cycle; it's a cycle that will repeat throughout her life until the end of

menopause.

The maturing follicle's!

It all starts with the hypothalamus! The hypothalamus is a gland in the brain that

sends a chemical message to the pituitary gland, another gland in the brain, to release

two hormones into the bloodstream that cause the follicles in the ovaries to begin to mature.

The maturing follicles release the hormone estrogen, which causes the uterine lining to thicken and the cervical mucous to change.

The one most mature follicle will burst and an egg will be released into the fallopian tube.

This is called ovulation.

OvulationInside the Fallopian tube, the egg is carried

along by tiny, hair like projections, called "cilia" toward the uterus. Fertilization occurs if sperm are present as the live egg reaches the uterus. [A tubal pregnancy (ectopic pregnancy) is the

rare situation where the egg is fertilized inside the tube. It is a dangerous life-threatening

situation. If an fertilized egg begins to develop into an embryo inside the tube it will rupture

the tube causing internal bleeding. Surgery is required if the tube ruptures. If the pregnancy

is discovered before the tube ruptures, medication can be used to stop the

development of the embryo.]

HormonesEstrogen and progesterone are sometimes called

"female" hormones, but both men and women have them, just in different concentrations. (Both

men and women also have testosterone.)

Progesterone causes the surface of the uterine lining, the endometrium, to become covered with

mucous. If fertilization and implantation do not occur, the lining and a small amount of blood are

released from the body. This is called the the menstrual flow. Most periods last 4 to 8 days but

this length varies over the course of a lifetime.

Let’s try that again & go through each cycle by itself.

The Menstrual Phase

The cycle starts on the first day of a girl’s menstrual period. During the period, blood and tissue that have built up on the inner lining of the uterus flow out of the vagina. This is menstruation – and it can last anywhere from 2 to 7 days. This phase is from days 1-7 approximately.

Pre – Ovulatory Phase

After menstruation, a girl’s body begins releasing hormones that signal the uterus to get ready to receive a new egg. About the same time, hormones prepare an egg to be released from the ovary. The lining of the uterus thickens and becomes rich in blood and nutrients. This happens in case a sperm fertilizes the egg. The fertilized egg would then attach to this lining, which provides a nurturing environment for the developing embryo and fetus. This phase is approximately from days 6 – 11.

Ovulation Phase

At about the middle of the cycle, or 14 days before the onset of the next period, ovulation occurs. Ovulation is when an egg is released from one of the ovaries. Over the next few days, the egg will travel down the fallopian tube. If the egg is not fertilized by a sperm cell during this time, it will begin to dissolve. Days 14-21

Post-Ovulatory Phase

Most of the time, the egg isn’t fertilized. This means that the uterus no longer needs the extra blood and tissue lining. A change in hormone levels signals the blood vessels that nourish the lining to constrict and temporarily cut off the blood supply. Days 21-28 The cycle then starts over.

That concludes the story of menstruation!