The skeletal system consists of 206 bones that are divided into the axial skeleton (skull, vertebral column, ribs, sternum) and appendicular skeleton (limbs and their attaching girdles). Bones provide structure, protection, movement, mineral storage, blood cell formation, and are living tissues that undergo remodeling. The skeletal system includes various bone cell types and bone is composed of inorganic minerals and organic matrix. Common diseases include osteoporosis, rickets, osteomalacia, and Paget's disease.