These tubes consist of muscles that allow air to pass deep in to the lungs. Bronchial tubes consistently change width, increasing in girth as an individual inhales and becoming narrower upon exhalation. In a person with a well functioning respiratory system all parts of the airway function synergistically to ensure maximum intake of oxygen and exhalation of carbon dioxide with each breath. .

             Air enters the body through the nose and mouth. It passes through the pharynx, larynx and trachea, all important parts of the airway (Polk, 18). The noses and sinuses act as conditioners adjusting the air temperature as it passes through other structures in the airway. The pharynx or back of the throat allows liquids and solids entering the airway to "drop out before entering the lungs" (Polk, 19). Likewise the larynx helps prevent other unwanted particles in the air from entering the lungs (Polk, 19). It is here that the body's cough reflex lies. If something unwanted is present in the air being inhaled, the larynx will stimulate a cough reflex to help expel the object. While the larynx isn't the only trigger for a cough reflect it is very important to the entire breathing process (Polk, 19). .

             When a person inhales, the chest muscles in the body contract allowing the ribs to separate slightly. Air is then drawn into the lungs. The opposite happens when an individual exhales, allowing air to forcefully come out of the lungs. The abdomen is also involved in breathing. The abdomen attaches to the front and back of the ribs, pushing them up and out when breathing. Breathing thus incorporates the chest and abdomen. The more a person engages all the muscles and organs involved in respiration including the abdomen, the better able they are to take a full breath of air.

             Asthma Physiology and Pathology.

             In times of old doctors ascribed asthma to anyone having difficulty breathing regardless of the cause; during the 20th century however researchers refined asthma to include difficult breathing "Because of a problem that begins in the bronchial tubes of the lungs" (Polk, 15).