What Is the Menstrual Cycle?
The menstrual cycle is a monthly process that happens in the bodies of people with uteruses. It takes about 28 days on average, though it can vary from 21 to 35 days. During this cycle, the body prepares for the possibility of pregnancy. If pregnancy doesn't happen, the body sheds the lining of the uterus, which is called a period. This whole process is controlled by hormones—chemical messengers that tell the body what to do.
The Four Key Hormones
Four main hormones control the menstrual cycle: FSH (follicle-stimulating hormone), LH (luteinising hormone), oestrogen, and progesterone. These hormones are made in different parts of the body and send signals to each other like a team working together.
Think of it like a group chat between friends: one person sends a message, which makes someone else reply, which then tells a third person to do something. Each message changes what happens next.
FSH and LH: The Pituitary Messengers
FSH and LH are made by the pituitary gland, a tiny gland at the base of the brain. At the start of the menstrual cycle, FSH tells the ovaries (the female reproductive organs) to start making eggs and produce oestrogen. Around day 14 of the cycle, a surge of LH triggers ovulation—when an egg is released from the ovary.
Oestrogen and Progesterone: The Ovary Hormones
Oestrogen is made by the ovaries during the first half of the cycle. It makes the lining of the uterus thick and spongy, ready to receive a fertilised egg. After ovulation, the ovary produces progesterone, which keeps the uterus lining healthy. If an egg is not fertilised, levels of both oestrogen and progesterone drop sharply. This drop triggers the body to shed the uterus lining, causing a period.
Think of it like decorating a room: oestrogen gets the room ready and nice, then progesterone keeps it tidy. When you decide you don't need the room after all, you clear everything out.
Why This Matters
Understanding these hormones helps explain why people with periods experience different feelings, energy levels, and physical changes each month. It also helps doctors treat problems like irregular periods or painful cramps. The menstrual cycle shows how powerful and clever the human body is at keeping itself balanced.