The human skeletal system has three main functions: to provide strength, support and shape to the body; to protect delicate organs; and to provide leverage for movement. It is composed of bones, cartilages, and joints. The skeletal system is divided into the axial skeleton, which forms the body's central axis, and the appendicular skeleton, which includes the limbs. Key parts of the axial skeleton are the skull, vertebral column, rib cage, and sternum, while the appendicular skeleton comprises the upper and lower limbs. Important processes involved with the skeletal system are hematopoiesis, where red blood cells are produced, and ossification, which is the formation of bone tissue.