Bones have five main functions: providing structure and support, protecting organs, allowing muscle attachment and movement, housing marrow that produces blood cells, and storing minerals. Bones are made of compact and spongy bone tissues and bone marrow. Cartilage covers bone ends and acts as a shock absorber in joints. There are several types of joints that allow different ranges of motion, from immovable to movable joints like ball-and-socket joints, which allow the most movement. Joints are lubricated and protected by cartilage and fluid to allow for smooth movement.