Today’s Wonder of the Day was inspired by Jonah. Jonah Wonders, “What makes bones grow?” Thanks for WONDERing with us, Jonah!
Do you love to go to amusement parks in the summer? The warm rays of the Sun on your skin and the taste of the sweet cotton candy make great memories. Of course, the best memories probably come from the thrilling rides that take your breath away.
When you're little, though, you don't always get to ride the most exciting rides. As you step up to the front of the roller coaster entrance, you're usually greeted by a sign indicating you have to be THIS tall to ride. If you're under that mark, you probably yearn for the day when you'll grow tall enough to ride.
Most kids spend time when they're little dreaming about what life will be like when they grow bigger. But have you ever WONDERed exactly what happens inside your body to make you grow? Specifically, have you ever thought about how your bones grow?
When you were born, every part of you was tiny — even your bones! Babies are born with about 300 bones. This is approximately 100 more than the 206 bones you'll have as a full-grown adult. So what happens? Do you lose some bones?
Not at all! Many of the tiny bones you're born with fuse together over time to form bigger, longer bones as you mature. They also go through significant changes as they get bigger and grow into mature adult bones.
When babies are born, many of their bones are made partly or mostly of a soft, flexible substance called cartilage. Pinch the end of your nose and the top of your ear. Feel how they're soft and flexible? That's because those parts of your body are made of cartilage.
As you grow, the cartilage in your bones grows. Over time, it slowly gets replaced by bone with the help of calcium. This process is called ossification. During ossification, layer upon layer of calcium and phosphate salts begin to accumulate on cartilage cells.
Once encased in these minerals, the cartilage cells die, leaving tiny pockets behind. Blood vessels grow into these tiny pockets, delivering specialized cells called osteoblasts. The osteoblasts help to collect additional calcium and also produce a substance full of collagen fibers.
Osteoblasts also produce layers of cortical bone that surround the cartilage. After making the cortical bone, osteoblasts become cells called osteocytes that work to form a sponge-like lattice of marrow and a substance called cancellous bone inside the developing bone.
Eventually, other cells known as osteoclasts make their way into the middle of developing bones. They use hydrolytic enzymes and acids to dissolve the cancellous bone and make room for more marrow. This process continues until all the cartilage has turned to bone.
The process of ossification is usually complete by your mid-twenties. At that point, your bones are as big as they'll ever be. Although they won't continue to grow bigger, they can heal and repair themselves in the case of fractures.