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1. either one of a pair of spongy saclike respiratory organs within the thorax of higher vertebrates, which oxygenate the blood and remove its carbon dioxide
2. any similar or analogous organ in other vertebrates or in invertebrates


Paired, air-filled respiratory sacs, usually in the anterior or anteroventral part of the trunk of most tetrapods. They lie within the coelom and are covered by peritoneum. In mammals they are within special chambers of the coelom known as pleural cavities and the peritoneum is termed pleura.

Amphibian lungs are often simple sacs, with only small ridges on the internal walls. In higher forms the lungs become more and more subdivided internally, thus increasing greatly the surface areas across which the respiratory exchange takes place. However, even in many reptiles the lungs may be quite simple. Birds have especially complex lungs with a highly differentiated system of tubes leading into and through them to the air sacs which are contained in many parts of the bird's body. Mammalian lungs are simpler, but in them the internal subdivision into tiny sacs or alveoli is extreme; there may be over 350,000,000 of them in one human lung.

In humans the two lungs lie within the chest, separated by the heart and mediastinum. The right lung has three lobes and the left lung two. A bronchus, an artery, and a vein enter each lung medially at the hilum; each branches again and again as it enters the lobules and smaller divisions of the lungs (see illustration). The terminal airways or bronchioles expand into small clusters of grapelike air cells, the alveoli. The alveolar walls consist of a single layer of epithelium and collectively present a huge surface. A small network of blood capillaries in the walls of the alveoli affords surfaces for the actual exchange of gases. See Respiration, Respiratory system

The human lungenlarge picture
The human lung


Either of the paired air-filled sacs, usually in the anterior or anteroventral part of the trunk of most tetrapods, which function as organs of respiration.
References in periodicals archive ?
The SmCCs, both pulmonary and extrapulmonary entities, may share the same origin.
P-B-, PPD (-) subjects without BCG vaccination; P+B-, PPD (+) subjects without BCG vaccination; PTB, Patients with pulmonary tuberculosis; EPTB, Patients with extrapulmonary tuberculosis Table II.
1,4) Like their pulmonary counterparts, extrapulmonary inflammatory pseudotumors (except for head and neck masses) are more common in children than adults (mean age at diagnosis: 9 yr), and they have a general predilection for females.
Extrapulmonary pneumocystosis is, however, a rare complication and represents less than 1% of all cases of infection.
The BODE index reflects the impact of both pulmonary and extrapulmonary factors on prognosis and survival in COPD (Celli et al 2008).
Excision of a solitary extrapulmonary lesion is recommended when possible.
Extrapulmonary thoracic disease such as flail chest or severe kyphoscoliosis.
We initiated a study to investigate the influence of chronic hypoxic pulmonary hypertension on the mechanical properties of the extrapulmonary arteries of rats.
37]Ra in stick penicillinase ELISA for the detection of seroreactivity in pulmonary and extrapulmonary TB, ES-31 showed good potential in detecting IgG antibody in TB Lymphnode, Tubercular meningitis and pulmonary TB.
Respiratory failure can be caused by both intrapulmonary and extrapulmonary conditions.
Hypercapnia: mental changes and extrapulmonary complications.