-Bone, although strong, is a constantly changing tissue that has several functions. Bones serve as rigid structures to the body and as shields to protect delicate internal organs. They provide housing for the bone marrow, where the blood cells are formed. Bones also maintain the body's reservoir of calcium. In children, some bones have areas called growth plates. Bones lengthen in these areas until the child reaches full height, at which time the growth plates close. Thereafter, bones grow in thickness rather than in length, based on the body's need for additional bone strength in certain areas.

-Cartilage is a type of connective tissue that surrounds the ends of bones to facilitate smooth movement. Tough yet flexible, both the cellular components and the surrounding matrix of cartilage are designed to hold water to help support and cushion the joints. Everyday wear and tear can eventually take its toll on cartilage, causing it to degenerate. joint pain and stiffness caused by this degeneration is referred to as osteoarthritis.

-Joints are the junctions between two or more bones. Some joints do not normally move, such as those located between the plates of the skull. Other joints allow a large and complex range of motion. The configuration of a joint determines the degree and direction of possible motion. For example, the shoulder joints, which have a ball-and-socket design, allow inward and outward rotation as well as forward, backward, and sideways motion of the arms. Hinge joints of the knees, fingers, and toes allow only bending (flexion) and straightening (extension).

-Muscle is a soft tissue found in most animals. Muscle cells contain protein filaments of actin and myosin that slide past one another, producing a contraction that changes both the length and the shape of the cell. Muscles function to produce force and motion.