The respiratory system
Respiratory diseases often lead to hospital admission, and patients with chronic obstructive pulmonary disease may require repeated admissions for infective exacerbations. Smoking remains the single most important cause of respiratory disease despite greater awareness of the dangers of cigarette smoking and health warnings placed in advertisements and on cigarette packets. The nasal cavities form the first part of the respiratory passage and extend from the anterior nares or nostrils to the nasopharynx. The nares are lined with respiratory epithelium, with some olfactory epithelium. The respiratory tract includes the nose, nasopharynx and larynx, extending down into the alveoli to include the blood supply. A history of childhood asthma, pneumonia or whooping cough is sometimes relevant to the later development of chest symptoms in an adult. Chest injuries and previous pneumonia may explain changes seen on a chest X-ray.