All the systems are interrelated by hormones. The sensory system's main organ is hormones, without hormones there would be no use for the reproductive system because the hormones is what gets us attracted to a mate. Sometimes hormones get us in trouble, so something may infect us from a mate and then that puts the immune system to work. Hormones are also the cause of adrenaline, which gets the heart pumping, which affects the circulatory and muscular systems. Adrenaline gets you going so you are using your muscles more, and your body's need for oxygen increases so you are using your respiratory system.

The skeletal and nervous systems are related because the bones provide calcium needed to function. The skull also acts as protection for the brain, and the vertebra protects the spinal cord. Between bones and joints there are sensory receptor, which tells the brain the pose...