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.
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.
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.
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.
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.
Even though cancellous bone is lighter than compact bone, it is still very strong, because both types of bone are made of a hard mineral called calcium.
In the very center of your bones is a soft, thick substance that looks like jelly called bone marrow. Bone marrow produces all of your blood cells.
All Shapes and Sizes
The smallest bone in your body, the stirrup, is in your ear, and is about the size of the eraser of a pencil. Your femur, or thigh bone, is the strongest, longest bone in your body. By the time you are an adult it will be over a foot long.
Your bones are alive, and they grow and change as you get older. An adult skeleton has 206 different bones. The three main jobs of your bones are to give your body shape, help your body move, and protect your other body parts.
Bones are made of two types of material: compact bone and cancellous bone. Both compact bone and cancellous bone are made of a hard mineral called calcium. Bone marrow, located inside your bones, makes blood cells.
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