Human ventilation is also carried out by the respiratory system. It is used to breathe in oxygen for natural processes and then expel gaseous wastes, such as moisture, carbon dioxide and trace amounts of other gases. This system gives oxygen directly to the blood; the blood distributes the oxygen everywhere else.
The human respiratory system consists of a tube leading from the nose and mouth down to two lungs. The lungs have millions of specialized cells called alveoli. These cells filter oxygen from the rest of the gas breathed in for providing directly to the blood. This is possible because of the tiny blood vessels called capillaries that surround the alveoli.
Breathing is controlled by the expansion and contraction of the diaphragm. This dome-shaped muscle is located below the lungs, and it compresses and expands the lungs to make the body perform the subconscious reflex of breathing. The diaphragm does this about 12 to 20 times every minute, changing according to what an individual is doing.
People in a state of panic might hyperventilate, or breathe much faster than normal, in an effort to introduce more oxygen to the blood in an emergency. This biological reflex is one of the few that can be consciously controlled. Anyone hyperventilating can calm themselves down by forcing more measured breathing.