a heart is a kind of organ & a kidney is a kind of organ in an animal & a bladder is a kind of organ & the heart, blood vessels, kidneys, and bladder work together & blood vessels are a kind of organ ->  the heart, blood vessels, kidneys, and bladder working together is an example of different parts of body working together  the heart, blood vessels, kidneys, and bladder working together is an example of different parts of body working together & an organ system is made of different parts of the body working together -> the heart, blood vessels, kidneys, and bladder working together makes them an organ system