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Bone Facts: Lesson for Kids

Instructor: Lindsy Frazer

Dr. Frazer has taught several college level Science courses and has a master's degree in Human Biology and a PhD in Library and Information Science.

Did you know that babies have more bones than adults? Learn about how bones grow and change as you age, what your bones do, and what they're made of in this lesson.

Your Bones Are Alive!

Think about dinosaur bones you might have seen in a museum, or maybe even animal bones you have seen in your backyard. Did they remind you of rocks? We sometimes think of bones as non-living things, but the bones that make up your skeleton are alive, and just like other parts of your body, they grow and change as you age.

Bones Grow

Babies are born with 300 different bones. As you grow up, many of the 300 small bones fuse, or grow together. So by the time you are an adult, your skeleton will have only 206 bones.

Human adults have 206 bones.
Skeleton

When we are about 25 years old our bones stop growing larger, but they keep on building new bone cells to replace old cells. So even though your skeleton stops getting bigger, your bones are constantly changing.

What Do Bones Do?

Bones have three main jobs: they give your body its shape, they work with your muscles to help you move, and they protect your organs and other soft parts.

Bones Give You Shape

Think about the worms you see in your yard. Worms' bodies are squishy and soft like jelly because worms don't have bones. Without our bones, humans would be squishy blobs of skin!

Bones Help You Move

Your bones can't move on their own, but your muscles and bones work together like a team to help you move. Your muscles are attached to your bones, so when you move your muscles, your bones move as well.

When this girl decides to kick the ball, she will contract her leg muscles, causing her whole leg, bones and all, to move.
girl playing soccer

Bones Protect Other Body Parts

Your bones also act like a shield that protects the softer parts of your body. The bones in your skull protect your brain like a built-in helmet. Your rib cage - the bones around your chest and back - protect important organs like your heart and lungs.

What Are Bones Made Of?

Bones have to be very strong to protect your organs, but also very light so you can move around. Bones can be both strong and light because they are made of two different types of material. The outer layer of your bones is made of a material called compact bone. Compact bone is dense, smooth and very hard.

Under the compact bone is a lighter, less dense material called cancellous bone, pronounced 'KAN-sell-us'. Cancellous bone is sometimes called 'spongy bone' because like the sponge in your kitchen it has many little holes and air pockets. These holes make cancellous bone very light and are passageways for blood vessels that supply your bones with nutrients so they can live and grow.

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