Pulmonary Ventilation or breathing has two phases. Inspiration or inhalation moves air into the lungs, and expiration or exhalation moves are out of the lungs. The lungs are enclosed within the thoracic cavity. Thus changes in the shape and size of the thoracic cavity result in changes in the air pressure within that cavity & in the lungs. This difference in air pressure causes the movement of air into and out of the lungs. Air …showed first 75 words of 395 total…

…showed last 75 words of 395 total…muscles depress the rib cage and decrease the front to back size of the thorax. Contraction of the abdominal muscles pushes the abdominal organs against the underside of the diaphragm, thus elevating it and making more dome shaped. The result is to further shorten or decrease the top to bottom size of the thoracic cavity. As the thoracic cavity decreases in size, the air pressure within it increases and air flows out of the lungs.