Every month, the womb prepares itself to receive and hold a baby. This preparation involves the thickening of the inner lining of the womb, which also becomes well supplied with blood vessels.
If no conception or pregnancy occurs for that month, this thickened womb-lining breaks down along with the blood and blood vessels in it and passes out through the vagina as the period or menses.
The womb then starts the whole process all over again. The first menstruation in a girl's life is termed menarche while menopause refers to when menstruation ceases.
This elaborate mechanism of menstruation is controlled by several hormones that are released into the blood at varied quantities at different times of the month.
To help expel the menstrual products, the body, under the influence of these hormones, produces substances known as prostaglandins. These substances enable the womb to contract to expel its contents.
During a normal period, the contraction of the womb causes little pain that is not disturbing. The pain of dysmenorrhoea is however disabling.
These are primary dysmenorrhoea and secondary dysmenorrhoea.
In primary dysmenorrhoea, there is no organic or psychological abnormality in the woman.
It is primarily due to the over production of a particular type of prostaglandin which causes excessive contraction of the womb.
When the womb contracts excessively blood supply to the ceIls of the waIl of the womb is cut off for a longer period. This injures the cells, which respond with pain to indicate that something is wrong.
Primary dysmenorrhoea normally affects adolescent women; that is after menarche when the ovulatory cycle becomes established.
The pain of primary dysmenorrhoea can be intermittent, or continuous, lasting for 1-3 days.
It usually starts at the onset of bleeding and then subsiding over the next one or two days. The cramps and pain can be accompanied by headaches, dizziness, nausea and vomiting.
The release of prostaglandins can also cause constipation and/or diarrhoea because of their effect on the smooth muscles of the intestines.
Apart from severe stomach cramps, the pain can also extend into the lower back or into the thighs and legs.
In secondary dysmenorrhoea, there is an abnormality or pathology in the pelvis of the woman.
The pain of secondary dysmenorrhoea is similar to that of primary dysmenorrhoea, but it tends to affect older women.
The pathologies whose presence cause secondary dysmenorrhoea include endometriosis; a disease in which some of the tissue lining the womb happens to be found else where in the body cavity.
Pelvic inflammatory disease (PID), ovarian cysts, fibroids and sexual frustration are also well known causes.