The human skeleton contains 206 bones, all held in place by connective tissues such as ligaments and tendons. Several types of bone make up the skeletal system, each classified according to its shape: long, short, irregular, and flat. Together, they perform several different functions.

The skeleton is a mechanical framework that muscles pull on to create movement. It gives structure to the body, protects the internal organs, and determines body size and shape. The skeleton also works as a factory, because various blood cells are manufactured in the marrow of the bones. Bones also act as storage depots, holding minerals such as calcium and phosphorus for the body to use later.

Bone is a living tissue and its structure is continuously changing. For example, the skeleton of the fetus in the womb is mostly cartilage. As pregnancy continues, bone develops. After the child is born, certain areas are still a combination of bone and cartilage. These areas are called growth plates. In the long bones, such as the arms and legs, there are growth plates at each end. Growth plates are what allow bones to lengthen as a child ages. By the time a child reaches age 20, the 270 softer bones she was born with have fused to form the 206-bone structure of the skeleton.