Dear Biologists,
My entire high school has become obsessed with the question of whether or not your belly button is definatively a hole. A general yes or no answer with an explanation would be greatly appreciated as our entire class awaits to announce the truth.
Hayley Siegel ( perplexed AP biology student)

Hi There,

Your belly button is definitely not a hole! The belly button is basically a scar from where your unbilical vessels once entered your body in utero. The umbilical vessels travel between the placenta and the growing embryo.  Before birth, a baby receives all nutrition via these vessels, and one end interfaces directly with major vessels close to your heart. At birth, when the baby takes it's first breath, this vessel closes off via a sudden pressure change as the lungs work for the first time. After this point the umbilical vessels are no longer needed, so the bit outside the baby's tummy is tied and cut, forming your belly button. Once the internal vessels are no longer in use, they drain of blood and are allowed to atrophie into remnants by the new born's body and are no longer used for blood circulation.