The breathing process is controlled by the respiratory center of the brain. The purpose of respiration is to obtain oxygen, which is then transported around the body in the blood. It ends up in body cells, where it combines with glucose to produce energy. Carbon dioxide is a by-product of this process, and is expelled on breathing out. Breathing is an automatic process: it cannot be stopped voluntarily, although its rate and depth can be controlled. An adult human takes between 13 and 80 breaths a minute, depending on the degree of exertion.
Air flows in and out of the lungs because the pressure of air in the chest is constantly changing in relation to the pressure of air outside the body. During inhalation, the diaphragm contracts and descends while the rib cage rises and expands. The decrease in pressure in the lungs draws air in. The opposite occurs during exhalation as the diaphragm rises and the ribs fall. This increases the pressure in the lungs and air flows out.


No comments: