Adults are held up by a skeleton composed of 206 bones that protect the body's vital organs. Though it's a sturdy frame, it's vulnerable to problems—think issues like like osteoporosis and stress fractures, says Chad Deal, MD, director of the Center for Osteoporosis and Metabolic Health at the Cleveland Clinic.

RELATED: 7 Things You Didn't Know About Your Bones

Bones are flexible enough to give a bit when physical force is applied, but if that force is too great, they'll snap like a plastic ruler bent too far. Luckily, they also repair themselves naturally (even better with a cast). Here's how bones heal.

1. Immediately after a fracture occurs, a blood clot and callus form around it.

2. New "threads" of bone cells start to grow on both sides of the fracture line toward one another.

3. Eventually, the fracture closes up and the callus is absorbed by the new cells. This process may take from six weeks to a year.

RELATED: 14 Non-Dairy Foods That Are High in Calcium