what is the central idea of this paragraph ?
Blood has many functions, but its single most critical job is to move oxygen around the body. Blood picks up inhaled oxygen in the lungs and takes it through the circulatory system. Blood drops off oxygen at the body’s various organs and tissues. The importance of blood’s oxygen delivery service cannot be overstated. If organs and tissues don’t get enough oxygen, they cannot work properly. If organs and tissues are deprived of oxygen for too long, they cease to function and die.