Gas exchange or respiration in humans is the means by which getting oxygen from air into the blood and carbon dioxide out of the blood into the air. Humans must exchange these gases with the environment because oxygen is essential for cells, which use this vital substance to release the energy needed for cellular activities. In addition to supplying oxygen, carbon dioxide needs to be removed in order to prevent the buildup of this waste product in the body tissues. As breathing is the act or process of respiration, it consists of two phases, inspiration and expiration. During inspiration, the diaphragm moves downward increasing the volume of the thoracic cavity, and the intercostal muscles contract, which makes the rib cage move upward and forward increasing the volume of the lungs. The increase in pressure inside the lungs makes the air from the atmosphere move into the lungs because air always moves from an area of high pressure to a low pressure area. During expiration, the intercostal muscles that lift the rib cage and the diaphragm relax. As a result, the rib cage and the diaphragm return to their original positions and the lungs contract with them. With each contraction of the lungs, the air inside them is forced out.
Inhaled air consists of 79.02% nitrogen and other trace gases, 20.94% oxygen and 0.04% carbon dioxide. Humans breathe in by increasing the volume in the chest cavity, thereby reducing the pressure in the lungs below atmospheric pressure. The higher pressure of the external air forces air to get in through the nose and mouth and down a tube called the trachea. The trachea forks to form two tubes called the bronchi, each of which branches into numerous bronchioles. From there, the bronchioles eventually lead to tiny air sacs called alveoli. Gas exchange occurs at the level of the alveoli. The purpose of gas exchange is to get the oxygen to every cell of the body where the oxygen is used to produce ATP energy in the mitochondria of the cells....
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