Menstruation

Menstruation

              Menstruation is the final event in a long series of complex maneuvers executed by the body with split-second timing. The whole process unfolds according to a detailed script prepared by an internal computer. The plan is reviewed constantly, moment by moment, and up-dated monthly. In spite of the advances of science, our knowledge in this area is still rudimentary. Controlling the menstrual cycle is roughly equivalent to launching a space vehicle, the egg, at the same time the launching pad is being built. Simultaneously a gigantic landing facility, the uterus, must be prepared in case the little traveler through inner space should come back in a new form – fertilized. Concurrently, preparations must be made to tear down everything that has been built up in order to start again from scratch each month.

              As the menstrual period finishes, the ovary begins pouring one of the primary female sex hormones, oestrogen, into the blood-stream. The presence of oestrogen is reported to the Central Control Area, the pituitary gland at the base of the brain. In response, Central Control directs the release of a supporting hormone, FSH. FSH restimulates increased production of oestrogen. Oestrogen acts on every reproductive organ but specifically causes rapid growth of the inner lining of the uterus. At the surface of the ovary, the egg scheduled for launch that month is already straining at its moorings. Now secretion of the other female sex hormone, progesterone, begins. When the presence of progesterone is detected by the pituitary, it responds with counter hormone, LH.

              Most of the progesterone is funneled to the uterus where it intensifies the preparations already under way. Central Control is constantly monitoring hormone levels at all areas of the body. When the ratio of FSH to LH reaches the critical point, a rapid count-down begins, and the ovum is hurled into the abdominal cavity.

              Hopefully, it goes into the Fallopian tubes. But it goes into the abdomen first. As the egg bursts from the surface of the ovary it travels freely into the vast emptiness of the pelvis. At the upper end of the Fallopian tubes, two enormous funnels with grasping fingers clutch eagerly at the tiny egg. Most eggs slide willingly into the friendly grasp. Meanwhile, back at the uterus, big things are happening. The lining has enlarged dramatically. Each individual cell is bursting at the seams. The blood vessels have become immense and are pulsating rhythmically. Day after day the build-up continues as the detection systems remain constantly alert for information about the fate of the recently launched egg. If the egg is not fertilized, Central Control reluctantly pushes the button marked DESTRUCT and everything comes crashing down. Ruthlessly the blood supply to the uterine lining is choked off. Cells on the surface are left to starve and die. They will soon slough off by the millions. Menstruation is under way. For the next three to seven days, all that remains of the ambitious undertaking of the past three weeks goes down the drain. Appropriately, menstruation has been called ‘the weeping of a disappointed uterus’. The body is perpetually optimistic; the entire project will begin again next month.

              The menstrual flow consist of the cupful or so of thin red fluid which trickles out of the vagina during each menstrual period is about fifty per cent blood mixed with varying amounts of mucus and ‘clots’. These so-called ‘clots’ are actually pieces of the uterine lining which have broken away. Menstrual blood itself does not clot, because it has already clotted. As blood pours out of the uterine wall, it coagulates quickly. As always, a short time after coagulating blood liquefies and once again flows freely.

Why does menstruation stop during pregnancy?

              It doesn’t always. In a small number of cases monthly bleeding continues throughout pregnancy. Not quite so rare is a menstrual flow during the first month or two. Usually the increase in maternal hormone from the newly formed placenta, are adequate to keep the uterine lining from decomposing. Lactation may further delay the return of the period. Lactation itself is not well understood. At birth both breasts are generally prepared to supply abundant milk. If the child begins to nurse, nervous impulses go from the nipples to Central Control in the pituitary gland. This produces still another hormone, lactogenic hormone, which starts the milk flowing and keeps it available until nursing stops. Almost like magic, when the sucking stops, the milk stops. At the same time menstruation is suppressed.