It is the respiration and cardiac systems that ensure that adequate oxygen is delivered to the human brain. The process of breathing brings oxygen into the lungs. The cardiac system pumps blood past the lungs, enabling this oxygen to be picked up by the red blood cells, and transported on to the brain.
The other essential requirement for cerebral cellular function is glucose/ sugar. This, too, needs to be transported to the cells of the brain via the blood supply.
Respiration within the cells of the brain produces the essential energy needed for brain function and results in the production of CO2 and water, which must then be removed, again via the blood supply. These by-products are excreted from the body through the lungs, or in the form of HCO3 via the kidneys.
The respiratory system that allows air to be drawn into the lungs, oxygen extracted and carbon dioxide removed is essential for human life. The circulatory or cardiac system (the system that pumps blood around the body and allows these essential items to be transported to and from the cells of the brain) is also critical.
Any interference with either the respiratory or cardiac systems quickly leads to death.