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n. one of the pair of organs of respiration, situated in the chest cavity on either side of the heart and enclosed by a serous membrane (see pleura). The lungs are fibrous elastic sacs that are expanded and compressed by movements of the rib cage and diaphragm during breathing. They communicate with the atmosphere through the trachea, which opens into the pharynx. The trachea divides into two bronchi (see bronchus), which enter the lungs and branch into bronchioles. These divide further and terminate in minute air sacs (see alveolus), the sites of gaseous exchange. (See illustration.) Atmospheric oxygen is absorbed and carbon dioxide from the blood of the pulmonary capillaries is released into the lungs; in each case down a concentration gradient (see pulmonary circulation). The total capacity of the lungs in an adult male is about 5.5 litres, but during normal breathing only about 500 ml of air is exchanged (see also residual volume). Other functions of the lung include water evaporation: an important factor in the fluid balance and heat regulation of the body.

http://www.lunguk.org/ British Lung Foundation: basic information on the lungs and some common lung conditions

The lungs. Showing the lobes and main air passages (left) with details of the alveoli (right).

Subjects: Medicine and Health.

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