cts, it moves downward, increasing the volume of the thoracic cavity. Expiration occurs when the diaphragm and rib muscles relax. The respiratory system delivers oxygen to the air sacs but the vital link between air sac and body cell is the circulatory system. Each air sac serves as a tiny depot from which oxygen is loaded into blood brought to the alveolar air by capillaries. Oxygen molecules diffuse from the air sacs into the blood because the air sacs contain a greater concentration of oxygen than does blood entering the pulmonary capillaries. Carbon dioxide moves from the blood where is is more concentrated to the air sacs, where it is less concentrated. Each gas diffuses through the cells lining the alveoli, and the cells lining the capillaries. The factor that determines the direction and rate of diffusion is the pressure or tension of the particular gas. Cellular respiration results in the continuous production of carbon dioxide and utilization of oxygen.Because the larynx contains the vocal cords during swallowing, a flap of tissue, the epiglottis automatically closes off the larynx from the esophagus so that neither food nor liquid can enter the lower air way. Should the defense mechanism fail, chocking will occur. Anyone who begins to choke and gasp should be asked if he or she can speak. If not, the Heimlich Maneuver must be performed. If the person is unconscious, it may be necessary to start cardiopulmonary resuscitation (CPR). CPR is a method for aiding victims of accidents or heart attacks who have suffered cardiac arrest. CPR should not be used if the victim has a pulse or is able to breath. The heart must be started immediately because of irreversible brain damage will occur within four minutes of respiratory arrest. ...
