The menstrual cycle is complex and controlled by many different glands and the hormones produced by these glands.
The four phases of the menstrual cycle are:
- the follicular phase
- the luteal phase.
Common menstrual problems include heavy or painful periods and premenstrual syndrome (PMS). Knowing when in the menstrual cycle a woman is most likely to conceive can increase the chances of pregnancy.
The average duration of the menstrual cycle is 28 to 29 days, these cycles can vary from one woman to another also from one cycle to another. The duration of the menstrual cycle is calculated from the first day of menstruation until the day before the start of the next menstrual period.
Girls have their first period (menarche), on average, between the ages of 11 and 14. At this point, other sexual characteristics have developed, such as pubic hair and breasts.
Hormones and menstrual cycle: The menstrual cycle is complex and is controlled by many different glands and the hormones these glands produce. A brain structure called the hypothalamus causes the nearby pituitary gland to produce certain chemicals, prompting the ovaries to produce the sex hormones estrogen and progesterone. The menstrual cycle is a biofeedback system, meaning that each structure and gland is affected by the activity of others.
Menstruation - Menstruation is the removal of the thickened lining of the uterus (endometrium) from the body through the vagina. Menstrual fluid contains blood, cells from the lining of the uterus (endometrial cells) and mucus. The average length of a period is between three days and a week.
Sanitary pads or tampons are used to absorb menstrual flow. Pads and tampons should be changed regularly (at least every four hours). Tampon use has been associated with an increased risk of a rare condition called toxic shock syndrome (TSS).
Follicular phase - The follicular phase begins on the first day of menstruation and ends with ovulation. Prompted by the hypothalamus, the pituitary gland releases follicle-stimulating hormone (FSH). This hormone stimulates the ovary to produce about five to 20 follicles (tiny nodules or cysts), which bead on the surface.
Each follicle houses an immature egg. Usually, only one follicle becomes an egg, while the others die. This can happen around the 10th day of a 28-day cycle. The growth of follicles stimulates the thickening of the lining of the uterus in preparation for possible pregnancy.
Ovulation - Ovulation is the release of a mature egg from the surface of the ovary. This usually happens in the middle of the cycle, about two weeks before the onset of menstruation.
During the follicular phase, the developing follicle causes an increase in estrogen levels. The hypothalamus in the brain recognizes these increasing levels and releases a chemical called gonadotropin-releasing hormone (GnRH). This hormone causes the pituitary gland to produce high levels of luteinizing hormone (LH) and FSH.
Within two days, ovulation is triggered by high LH levels. The egg is channeled into the fallopian tube and into the uterus by waves of small hair-like projections. The shelf life of a typical egg is only about 24 hours. Unless he encounters a sperm during this time, he will die.
When you want to have a baby, you can improve your chances of getting pregnant if you know ovulation and the "fertile window" of the menstrual cycle. Learn more about ovulation and the fertility window.
Luteal phase - During ovulation, the egg bursts from its follicle, but the ruptured follicle remains on the surface of the ovary. For the next two weeks or so, the follicle turns into a structure known as the corpus luteum. This structure begins to release progesterone, as well as small amounts of estrogen. This combination of hormones keeps the thickened lining of the uterus, waiting for a fertilized egg to stick (implant).
If a fertilized egg implants in the lining of the uterus, it produces the hormones necessary to maintain the corpus luteum. This includes human chorionic gonadotropin (HCG), the hormone that is detected in a urine test for pregnancy. The corpus luteum continues to produce the high levels of progesterone necessary to maintain the thickened lining of the uterus.
If pregnancy does not occur, the corpus luteum withers and dies, usually around the 22nd day of a 28-day cycle. The drop in progesterone levels causes the lining of the uterus to fall. This is called menstruation. The cycle then repeats.
Common menstrual problems – Some of the most common menstrual problems include:
premenstrual syndrome (PMS) – hormonal events before menstruation can trigger a range of side effects in women at risk, including water retention, headaches, fatigue and irritability. Treatment options include exercise and dietary changes
dysmenorrhea – or painful periods. It is believed that the uterus is prompted by certain hormones to squeeze harder than necessary to dislodge its mucosa. Treatment options include painkillers and the oral contraceptive pill
Heavy menstrual bleeding (formerly known as menorrhagia) - if left untreated, it can cause anemia. Treatment options include oral contraceptives and a hormonal intrauterine device (IUD) to regulate flow
amenorrhea - or absence of menstruation. This is considered abnormal, except during pre-puberty, pregnancy, lactation and post-menopause. Possible causes include low or high body weight and excessive exercise.