Your Paw-some Question | What determines the size and shape of someone's belly button?

Cosmo and I investigated belly buttons—thanks to WSU nursing professor Cindy Brigham-Althoff.

• Learn more about the placenta with Operation Ouch and Scientific American
• Check out all the belly buttons with Nat Geo
• Find out about placental mammals
• See what's living inside your navel with Nat Geo

Sound effects courtesy Pixabay

 As always, submit burning questions at askdruniverse.wsu.edu.  Who knows where your questions will take us next.

Transcript

Cosmo: Hey, Dr. Universe.

Dr. U: Hey, Cosmo.

Cosmo: What do you call a lazy baby kangaroo?

Dr. U: Tell me.

Cosmo: A pouch potato

Dr. U: Hey friends, I’m Dr. Universe.

Cosmo: And I’m Cosmo.

Dr. U: And if you’re anything like us, you’ve got lots of big questions about our world. Today we’re answering a question sent in by a kid just like you.

Cosmo: Isana wants to know: What determines the size and shape of someone’s belly button?

Dr. U: Nearly all mammals have belly buttons—unless they’re born from eggs or develop in pouches. Like platypuses or kangaroos.

Cosmo: My belly button is a subtle scar on my tummy. It’s covered by fluffy cat fur—and it’s not easy to see. 

But humans have obvious belly buttons. They come in different sizes and shapes.

Dr. U: The scientific name for a belly button is umbilicus. It’s what’s left of your umbilical cord.

Before you were born, a temporary organ called the placenta grew next to you. A cord connected the placenta to a spot in the center of your developing tummy. Oxygen and nutrients traveled in blood from the placenta and down the umbilical cord to your body. Waste left your body and flowed the other direction.

After you—and your placenta—were born, a midwife or doctor placed two clamps on your umbilical cord. They used special scissors to snip the cord between the clamps. That separated you from your placenta.

Cosmo: Oh, man. I was really attached to that thing.

Dr. U: What’s left is a small, meaty stump.

Cosmo: gross

Dr. U: But also super helpful. Some newborn babies need medicine or fluids delivered by an IV. Sometimes they can receive that through their stump, so they don’t feel a needle poke at all.

Within a few weeks, your stump dried up and fell off. It left behind a scar—your belly button!

But that process has nothing to do with the size or shape of your navel. How it looks at the start is a total wild card.

Cosmo: I love surprises.

Dr. U: That’s good because your belly button probably won’t look the same for your whole life.

As people grow and get older, they may add fat tissue to their abdomens. That makes the belly button appear bigger or deeper. It can even change its shape. That’s why an outie belly button—where some of the umbilical scar tissue pokes out instead of dipping in—is super uncommon among adult humans.

Dr. Universe: That’s all for this episode, friends.

Cosmo: Big thanks to Cindy Brigham-Althoff. She’s a nurse midwife and professor at Washington State University.

Dr. Universe: As always, if you’ve got a science question for me, you can submit it at askdruniverse.wsu.edu. That’s A S K D R U N I V E R S E dot W S U dot E D U.