1. defends the body after it has been invaded by a microscopic organism. immune system 2. regulates the body's metabolism, growth, and functions of the sexual organs. circulatory system 3. protects the internal tissues of the body from potential harm. endocrine system 4. responsible for conception. muscular system 5. provides the body with a framework that is strong and mobile skeletal system 6. consists of 600 skeletal muscles that allow the body to move. reproductive system 7. carries life-giving blood to the cells. integumentary system. for a !