The skeletal system functions to provide structure and protect internal organs. It works with the muscular and nervous systems to allow movement. The main organs are bones, bone marrow, joints, and teeth. If the skeletal system stops functioning properly, bones can break easily and posture may be affected. Joints provide flexible connections between bones and come in three types: movable, immovable, and freely movable. Diseases of the skeletal system include leukemia, which affects blood cell production, bursitis which causes joint pain, and osteoporosis which weakens bones. Prevention includes a healthy diet, proper nutrition, and exercise.