Dr. Universe explains belly buttons

Ask Dr. Universe is a science-education column from Washington State University.

  • Thursday, January 17, 2019 3:00pm
  • Life
Illustrations by Rob McClurkan

Illustrations by Rob McClurkan

Dr. Universe: Why do we have a belly button? – Jane, 9, Kennewick, WA

Dear Jane,

Whether you have an innie or an outie, pretty much all us mammals have a belly button. But before you had a belly button, there was actually a different bit of anatomy in its place.

While you were still growing inside of your mother, a small, bendy tube on your tummy connected the two of you. This tube is how you got pretty much everything you needed to grow before you were born into the world.

When a mother eats something—maybe it’s salad or ice cream—she gets different nutrients like proteins, fats, and vitamins from the food. The tube, or umbilical cord, helps her pass along the different nutrients so the baby can grow.

That’s what I found out from my friend Gina Cronrath, a nursing instructor at Washington State University. She also told me the umbilical cord helps remove waste from the baby, as well.

“After the baby is born, it can drink on its own and go to the bathroom into a diaper,” she said. “So the umbilical cord isn’t needed.”

It actually isn’t until about five weeks into a mother’s pregnancy that the umbilical cord starts to grow—and it will keep growing until the cord is about two feet long. A pregnant mother’s belly can really stretch out. Sometimes a mother will even get a temporary outie belly button. Then it will return to an innie.

After a baby is born, a doctor, midwife or birth partner will help cut the umbilical cord. Don’t worry, though—it doesn’t hurt the mother or the baby. Unlike, say, your skin, the cord doesn’t have nerves that would help you sense pain. It actually has a kind of jelly-like texture and this substance helps protect the blood vessels inside of the cord.

A small part of the cord will stay attached to the baby’s belly for a couple of days before it falls off. What’s left is a brand new belly button. Or if you want to use the more scientific name, it’s a brand new navel.

It turns out that a lot more humans have innies than outies. It all depends on how the muscles and skin heal up after the cord is cut. In a way, the belly button is the body’s first scar.

From big blue whales bellies to furry cat bellies to human bellies, mammals share a connection to their mothers through the umbilical cord. After you are born, what was once a big part of your survival doesn’t serve much purpose anymore—except for maybe collecting a bit of lint.

One thing is for sure, your question really got me contemplating my navel in a whole new way. And as Cronrath put it, our belly buttons are a kind of reminder that our mothers took care of us right from the beginning.

Sincerely,

Dr. Universe


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