Nov 19 2009

The Normal Menstrual Cycle

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(Author:Lyrl License: Creative Commons Attribution ShareAlike 3.0)

The normal menstrual cycle is very seldom the way it was described to you in biology class. Cycles can differ from month to month, and it is definitely different from woman to woman. Both what happens and how you feel will differ.

You were born with all the eggs that you will ever have. This is unlike a man where sperm is constantly manufactured in his testicles.

These eggs are stored in your ovaries, each one inside its own sac called a follicle. As you matured into puberty, your body started producing various hormones that cause the eggs to mature, one at a time.

Every cycle, the Hypothalamus gland at the base of your brain will release a chemical messenger called Follicle Stimulating Hormone Releasing Factor (FSH-RF) to tell the pituitary (another gland in the brain), to do its job. The pituitary gland then secretes Follicle Stimulating Hormone (FSH) and a little Luteinizing Hormone (LH) into the bloodstream which will cause the follicles to begin to mature. The hypothalamus gland is also responsible for regulating the body’s thirst, hunger, sleep patterns, libido and endocrine functions.

The maturing follicles in the ovaries will then release another hormone, estrogen. As the follicles ripen over a period of about seven days, they secrete more and more estrogen into your bloodstream. Estrogen causes the lining of your uterus to thicken. It causes your cervical mucus to change. When the estrogen level reaches a certain point it causes the hypothalamus to release Luteinizing Hormone Releasing Factor (LH-RF) causing the pituitary gland to release a large amount of Luteinizing Hormone (LH). This surge of LH triggers the most mature follicle to burst open and release an egg. This is called ovulation.

As ovulation approaches, the blood supply to your ovary increases and your ligaments contract, pulling your ovary closer to your Fallopian tube. This will help the egg to find its way to the fallopian tube, once it is released at ovulation. Just before ovulation, your cervix secretes an abundance of wet clear raw egg-white like "fertile mucous", which is normally very stretchy. Fertile mucous helps facilitate any sperm’s movement toward the egg. It will also protect and nourish the sperm on its way into the uterus; your basal body temperature rises right after ovulation and stays higher by about .4 degrees F until a few days before your next period.

Natural Family Planning (NFP) and Fertility Awareness Methods (FAM) are dependent on these changes in cervical mucus (CM) to predict your fertile time. You can use this as a form of birth control (by avoiding sex when you are fertile) or as an aid to getting pregnant (knowing when you are fertile and should have sex). These methods of birth control are approved by the Catholic Church. If applied correctly, these methods are surprisingly accurate.

Inside the Fallopian tube, the egg is carried along by tiny, hair-like projections, called "cilia" and it is slowly moved toward the uterus. If there are live healthy sperm present in the fallopian tube while the egg is there, the egg may get fertilized.

Between ovulation and menstruation, the follicle from which the egg burst becomes what is known as the corpus luteum. As it heals, it produces the hormones estrogen and, in larger amounts, progesterone which is necessary for the maintenance of a pregnancy. In the later stages of healing, if the uterus is not pregnant, the follicle turns white and is called the corpus albicans.

Progesterone causes the surface of the uterine lining (the endometrium) to become covered with mucus, secreted from glands within the lining itself. If fertilization and implantation does not occur, the ovaries stop producing progesterone and estrogen. Blood starts to leak from the spiral arteries, it pools into "venous lakes" which, once full, burst and, with the endometrial lining, form the menstrual flow.  The outer two thirds of the endometrium start to shed. Once the spiral arteries are exposed in the inner third of the endometrium, it bleeds freely. The ovaries starts to produce estrogen and this will cause a new endometrial cover to form. The bleeding from the spiral arteries stop when it is covered with the new endometrial cover. A new cycle begins.

The endometrium contains an anti-clotting agent that will prevent the menstrual debris and blood from clotting.

Estrogen and progesterone are sometimes called "female" hormones, but both men and women have them, just in different concentrations.


Interesting Menstrual Facts:

  • The start of the menstrual cycle is on day 1 of menstrual bleeding. The next cycle starts on the first day of the next flow.
  • The average cycle is 28 days long
  • Between 21 and 35 days are considered normal
  • Average flow is 35 ml.
  • Between 10 and 80 ml is considered normal.
  • The average length of flow is 3 to 5 days.
  • Between 2 and 7 days of flow is considered normal.
  • Blood: Bright red to dark brown/almost black

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