The respiratory system is responsible for oxygen intake so that cells throughout the systems of the body can receive the oxygen they need for cellular respiration. The digestive system is essential for breaking down food into usable chemical units, providing the glucose used in the same process of cellular respiration (as well as other nutrients necessary for our body systems) to flourish. The circulatory system collects oxygen from the alveoli in the lungs and glucose and other nutrients from the digestive system and distributes them to where they are needed in the body. Simultaneously, it also provides these systems with the chemicals they require and takes many waste chemicals that these cells produce away to be processed out by the kidneys or liver.