IntroductionIn this chapter, we will explore three systems that have a close physical connection, and are related in that none of them could function properly without the help of the others. While this is true of all body systems in the widest sense, the integumentary, muscular, and skeletal systems share a particularly intimate connection. The integumentary system, whose major organ is the skin, is responsible for a wide variety of functions, including protection from infection; absorption and excretion (in the sense that organs of the system line all exchange surfaces); temperature regulation; and sensory contact with the environment (in the sense that many sensory receptors, discussed earlier, are located in the skin). Skin is often directly connected to muscles, the major organs of the muscular system. Muscles have but one function: to contract, causing movement. While there are many types of movements, major movements of the body entail the connection of muscles to bones (often via tendons). In fact, it is bones that voluntary muscles cause to move when we raise our arms or lift our legs. In addition, bones, the major organs of the skeletal system, provide the major structural framework of the body. Without bones, there would be no means of supporting the rest of the organism.