Respiratory disease, any of the diseases and disorders that affect human respiration. Diseases of the respiratory system may affect any of the structures and organs that have to do with breathing, including the nasal cavities, the pharynx (or throat), the larynx, the trachea (or windpipe), the bronchi and bronchioles, the tissues of the lungs, and the respiratory muscles of the chest cage. The respiratory tract is the site of an exceptionally large range of disorders for three main reasons: 1) it is exposed to the environment and therefore may be affected by inhaled organisms, dusts, or gases; 2) it possesses a large network of capillaries through which the entire output of the heart has to pass, which means that diseases that affect the small blood vessels are likely to affect the lung; and 3) it may be the site of “sensitivity” or allergic phenomena that may profoundly affect function. - Britannica, 2015.
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