The Science Behind Your Monthly Cycle
The process of an egg leaving the ovary and traveling into the fallopian tube — occurs at about day 14 of an average 28-day cycle.
Here’s how it works:
- When the body’s level of estrogen (a hormone) drops, the hypothalamus in the brain alerts its neighbor, the pituitary gland.
- The pituitary gland sends out follicle-stimulating hormone (FSH), which helps follicles in the ovary to mature. Each ovarian follicle contains an egg. Mature follicles and eggs make estrogen.
- When the body’s estrogen level is restored, the pituitary gland sends out luteinizing hormone (LH) to open the mature follicle.
- A day or so later, the follicle then releases its egg into the fallopian tube.
- The empty follicle makes the hormone progesterone. Progesterone helps the uterus prepare for pregnancy by thickening its lining.
- If no pregnancy occurs, the follicle stops making progesterone. The thickened lining and other tissues 6 pass out of the uterus as a menstrual period.
Like blood pressure and heart rate, a woman’s menstrual cycle is a sign of her overall health. Menstrual irregularities — such as missing a period or having a heavier-than-usual period — could signal a health problem.