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If you have had the misfortune of
observing a live human, than you notice one constant. Well actually two,
one they are annoying, and two their chest moves. Why they act this should
be adequately explained in the nervous sysetem.
Their chest contains ribs. These ribs protect the heart and lungs. The heart pumps blood. The diaphragm can contract and expand. It is located beneath the lungs on top of the liver. When the diaphragm contracts then the space in the chest cavity increases. The lungs expand to fill this space. When the lungs expand, the pressure inside is dropped. This decrease in pressure draws the atmosphere in. Atmosphere passes through the nose into the nasal cavity. Then it enters the pharynx where it can pass into the larynx. Because atmosphere can also enter throught the mouth, as well as food, a flap (epiglottis) closes the entrance to the larynx. when swallowing. But when just atmosphere is passing into the larynx, the epiglottis opens and allows the atmosphere to enter. From the larynx, which contains the chords of vocality (allows them to make noise), air enters the trachea. It then branches into two bronchia. These two bronchia divide into bronchioles. The smallest bronchioles end in atmosphere sacs called collectively acinus. The acinus is made of several individual alveoli. The walls of the alveoli are extremely thin to allow oxygen to pass through to the red blood cells flowing through the capillaries and carbon dioxide to go from the blood to the atmosphere. |