Blood must flow to body organs within a relatively narrow range of pressures. the nervous system is able to detect changes in pressure within the circulatory system and respond to these changes by increasing or decreasing the heart rate and contracting or expanding blood vessels to control blood flow, as needed. this example shows how a. blood is an organ in the nervous system. b. the circulatory system is the most important system in the human body. c. organ systems interact to maintain homeostasis within organisms. d. each organ system is responsible for only one task.