1. brain is the main organ of this system respiratory system 2. produces hormones endocrine system 3. breaks food down for body's use excretory system 4. sends nutrients to all the body's cells circulatory system 5. provides structure for the body nervous system 6. provides support and movement digestive system 7. kidneys are the main organs of this system muscular system 8. lungs are the primary organs of this system skeletal system