Humans have skeletons to protect their internal organs, support the body and make coordinated movements. Some skeletal components also produce blood cells and store minerals.
Bones protect vital organs from damage. The brain and eyes are encased in the skull, while the heart and lungs are behind the ribs. The skeleton also provides a framework for the human body. Without bones, the body would not be able to maintain its shape. Instead, skin, organs and blood vessels would all be in a pile on the ground. Because tendons attach the muscles to the bones, humans are also able to walk, jump, talk and perform hundreds of other movements.
The bone marrow found inside bones is responsible for producing blood cells. In adults, blood cell production is limited to the marrow of certain bones, such as the pelvis and the spine. Bone marrow produces red blood cells, platelets and most of the white blood cells.
The skeleton also stores phosphorus and calcium. In fact, 99 percent of the body's calcium is found in the bones. Bones also store 85 percent of the body's phosphorus supply. The endocrine system regulates the storage of these minerals with vitamin D, calcitonin and parathyroid hormone.