The skeletal system provides structure, protection, movement, mineral storage, and blood cell formation. There are various bone types including long bones, short bones, flat bones, and irregular bones. Bones are composed of compact bone and spongy bone. The skeletal system is divided into the axial skeleton which includes the skull, vertebral column, rib cage, and the appendicular skeleton which connects to the axial skeleton and includes the upper and lower limbs. Diseases that can affect the skeletal system include osteoporosis, rickets, osteomalacia, and rheumatoid arthritis.