Continually balancing one another in a state known as homeostasis, an inborn balance in humans controlled by an innate intelligence, the sympathetic and parasympathetic nerves monitor our blood supply, regulate our pressure, and mediate our temperature. Together, their coordinated actions from the innate intelligence adjust heart rate and blood flow when we stand suddenly, bend over, or even perform acrobatics upside down.
If we were to climb from sea level to the thin atmosphere of the Himalayas, the innate intelligence would stimulate the sympathetic nerves which in turn would quicken heart pace to send the oxygen we need to our cells. Breathless and dizzy first, we would adjust quickly; our bone marrow would step up red cell production, churning out 50% more of the oxygen-carrying cells than at sea level.
Conversely, if we dive underwater, the innate intelligence uses the parasympathetic system to slow the heart, conserving our limited oxygen supply. The sympathetic system constricts blood vessels. This shuts off blood to almost all tissues and changes the cardiovascular system into a shortened circuit that cycles mainly form heart to brain. Arterioles sensors register the rising level of carbon dioxide waste in the blood and flash the brain a signal to surface from the water.
Amazing isn’t it?