Lung, disorders of

The most common lung disorders are infections. These diseases include pneumonia, tracheitis, and croup. Bronchitis and bronchiolitis, which are inflammatory disorders affecting the airways within the lungs, can be complications of colds or influenza. The disorder bronchiectasis may occur as a complication of severe bacterial pneumonia or cystic fibrosis. The lungs can also be affected by allergic disorders. The most important of these is asthma. Another such disorder is allergic alveolitis, which is usually a reaction to dust of plant or animal origin. Irritation of the airways, usually by tobacco- smoking, can cause diseases characterized by damage to lung tissue and narrowing of the airways (see pulmonary disease, chronic obstructive). The lungs can also be affected by cancerous tumours; lung cancer is one of the most common cancers. Noncancerous lung tumours are uncommon. Injury to a lung, usually resulting from penetration of the chest wall, can cause the lung to collapse (see pneumothorax; haemothorax). Damage to the interior of the lungs can be caused by inhalation of toxic substances (see asbestosis; silicosis). Blood supply to the lungs may be reduced by pulmonary embolism. Lung disorders can be investigated in various ways, such as chest X-ray, bronchoscopy, and pulmonary function tests.