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Although bones appear very hard, under the surface they are more like sponges, with lots of air. This makes bones very strong, but very light.
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The adult human body has 206 bones in the skeleton. These bones are grown together from about 300 bones at birth!
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The spine, which runs down the center of the back, allows the body to bend forward, backward, side to side, and rotate to each side. It provides support for the entire upper body (everything above the hips), and also protects the spinal cord.
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The ribs, which are in your chest, give support for your lungs, heart, and upper body muscles. One of the biggest jobs the ribs have is to protect the heart and lungs, and also the kidneys.
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The skull, which contains the brain and protects it, is made up of different bones which grow together during childhood. It has places for the eyes, and the ears, and only has one moving part - the lower jaw bone, called the mandible.
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The hands are made up of many different bones which allow a huge variety of movement. In fact, between the hands, wrists, and fingers, there are 54 bones!
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The pelvis, which is the bowl-shaped structure that makes up the hips, attaches the legs to the spine. The pelvis supports the spine, which supports the entire upper body. The back of the pelvis is the sacrum, one of the strongest bones in the body. During pregnancy, the ligaments soften and get a little longer, allowing the bones of the pelvis to relax to fit a baby through. The special hormone that causes this to happen is called relaxin!
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The longest bone in the body is called the femur, which connects the pelvis to the knee.
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The smallest bone in the body is in the middle ear, and is called the stapes, which is latin for stirrup (this bone is shaped like a stirrup). It is only 0.1 to 0.13 inches long!
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Bones are broken down and remade constantly, just like skin. In fact, all of the bones are slowly replaced until they are new bone once every 7 years!
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The insides of some bones contain special material called bone marrow. Bone marrow has lots of cells which make red blood cells. Red blood cells carry oxygen all over the body. Every second, bone marrow produces two million red blood cells!
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The best way to look at bones is with a special photo called an X-ray. X-rays help tell doctors where a fracture is located, so they know where to put a cast.
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