2. Pharynx Nasal and Oral
During breathing air enters through the nostrils, nasopharynx, and oral pharynx then through the glottis in to the trachea and further right and left bronchi and Lung alveoli. Only in the alveoli actual exchange of oxygen and carbon dioxide takes place.
During inspiration (inhaling),
◦ The external intercostal muscles contract, lifting the ribs up and out. ◦ The diaphragm contracts, drawing it down .
During expiration (exhaling), these processes are reversed and the natural elasticity of the lungs returns them to their normal volume. At rest, we breathe 15-18 times a minute exchanging about 500 ml of air. In more vigorous expiration, ◦ The internal intercostal muscles draw the ribs down and inward ◦ The wall of the abdomen contracts pushing the stomach and liver upward. Under these conditions, an average adult male can flush his lungs with about 4 liters of air at each breath. The below table shows what happens to the composition of air when it reaches the alveoli. Some of the oxygen dissolves in the...