The menstrual cycle is complex and controlled by many different glands and the hormones they produce. A brain structure called the hypothalamus causes the nearby pituitary gland to produce certain chemicals, which prompt the ovaries to produce the sex hormones estrogen and progesterone. Learn more about menstrual cycle side effects and more.
The menstrual cycle is a biofeedback system, which means each structure and gland is affected by the activity of the others. The four main phases of the menstrual cycle are menstruation, the follicular phase, ovulation and the luteal phase.
The average length of the menstrual cycle is 28 days, but this can vary between women and from one cycle to the next in individuals. The length of the menstrual cycle is calculated from the first day of the period to the day before the next period starts.
Girls get their first period (menarche), on average, between the ages of 11 and 14. By this stage, other sexual characteristics have usually developed, such as pubic hair and budding breasts.
Menstruation is the elimination of the thickened lining of the uterus (endometrium) from the body through the vagina. The 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 one week, depending on the individual.
Sanitary pads or tampons are used to absorb the menstrual flow. Both pads and tampons need to be changed regularly (at least every four hours). Using tampons has been associated with an increased risk of a rare illness called toxic shock syndrome.
Menstrual Cycle Side Effects
- Premenstrual syndrome (PMS) – hormonal events before a period can trigger a range of side effects in women at risk, including fluid retention, headaches, fatigue, and irritability. Treatment options include exercise and dietary changes.
- Dysmenorrhoea – or painful periods. It is thought that the uterus is prompted by certain hormones to squeeze harder than necessary to dislodge its lining. Treatment options include painkillers and the oral contraceptive pill.
- Menorrhagia – or heavy menstrual flow. If left untreated, this can cause anemia. Treatment options include oral contraceptives to regulate the flow.
- Amenorrhoea – or absence of menstrual periods. This is considered abnormal, apart from during pre-puberty, pregnancy, lactation and menopause. Possible causes include low or high body weight and excessive exercise.