But instead of wood, the body's framework is made of all the bones in our skeletal system. Some bones, like the ribs, permit respiration and protect vital organs such as the heart from harm. Others, like the spinal vertebrae, form the framework to keep us upright as well as surround and protect the spinal cord. Unlike a house's framework, however, the body's framework is alive - bones are living tissue. They reshape themselves throughout our lives.
Bones grow at special areas called growth plates .
These tunnels keep bones lightweight, yet provide the strength necessary to support the body. The tunnels also allow for the exchange of nutrients and waste products. Collagen, a protein, gives bones their elasticity while calcium salts make them hard. Bone marrow, located in the center of our long bones, makes blood cells. To develop properly and grow strong, our bones need calcium , vitamin D , and regular exercise.