Whether they have an innie or an outie, most people take their bellybutton for granted. After all, what’s it good for except trapping lint, sweat and other icky stuff? Well, that may be true now, but the next time you look at your bellybutton, remember that it once played a very important role in your life.

Before you were born, you spent nine months growing in your mother’s body. Little kids think babies grow in their mom’s stomach, but if that were true, babies would be digested like a piece of cheese! In reality, babies grow inside a special organ that women have called the uterus. (Babies are called fetuses before they are born.)

During the pregnancy, fetuses can’t eat or breathe in the traditional sense. They do need oxygen and nutrients, however, and the uterus is designed to provide them. Soon after the fetus attaches to the inside of its mom’s uterus, something called the placenta begins to grow. A short time later, the fetus begins to develop the umbilical cord that will attach to the placenta.

The umbilical cord is made of a tough, jelly-like material called Wharton’s jelly. Lying within the cord are three blood vessels: two arteries and one vein. At the time of birth, the umbilical cord is about 20 inches long and 3/4-inch thick.

The umbilical cord is a biological highway that allows the fetus to grow. Oxygen-rich blood and nutrients travel from the mother’s body into the fetus. Oxygen-poor blood and waste products travel from the fetus back to the mom’s body. The mom gets rid of the baby’s waste through her lungs and kidneys.

After a baby is born, he is still attached to his mom’s placenta via the umbilical cord. Blood will continue to travel back and forth for a few minutes after birth. In some cultures, the blood is allowed to stop flowing on its own, after which the cord is tied off. In other cultures, the obstetrician or midwife will attach a plastic clamp to the cord to interrupt the blood supply between mom and baby. Once the clamp is applied, the cord is cut.

The umbilical clamp is left in place for about 24 hours, then the nurse removes it. The baby is now left with something referred to as an umbilical stump, a brownish lump made up of dried-out Wharton’s jelly and its contents. In most cases, the stump falls off in a week or so.

The grown-up name for the “defect” that’s left on the baby’s abdomen, after the umbilical stump falls off, is the navel. But to you, it’s known as the bellybutton. And a cute one at that!

Bennett is a Washington pediatrician and author of health-related books for kids.