Also found in: Dictionary, Thesaurus, Medical, Idioms, Wikipedia.


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 classic literature ?
My violent struggles had only accelerated my already dangerously accelerated heart, and increased the need for oxygen in my suffocating lungs.
I can, indeed, hardly doubt that all vertebrate animals having true lungs have descended by ordinary generation from an ancient prototype, of which we know nothing, furnished with a floating apparatus or swimbladder.
Seeing how important an organ of locomotion the tail is in most aquatic animals, its general presence and use for many purposes in so many land animals, which in their lungs or modified swim-bladders betray their aquatic origin, may perhaps be thus accounted for.
Weakly I rose for the last time--my tortured lungs gasped for the breath that would fill them with a strange and numbing element, but instead I felt the revivifying breath of life-giving air surge through my starving nostrils into my dying lungs.
What of her anger and pent feelings, her lungs were irritated into the dry, hacking cough, and with blood-suffused face and one hand clenched against her chest, she waited for the paroxysm to pass.
Still there was no alternative, and, filling his lungs with the close and reeking air of the chamber, Tarzan of the Apes dived into the dark and watery hole which he could not see but had felt out and found with his feet and legs.
He felt his head emerge; his eyes were blinded by the sunlight; his chest expanded convulsively, and with a supreme and crowning agony his lungs engulfed a great draught of air, which instantly he expelled in a shriek!
He gargled his mouth and throat, took a suck at a divided lemon, and all the while the towels worked like mad, driving oxygen into his lungs to purge the pounding blood and send it back revivified for the struggle yet to come.
600,000,000 air cells in one pair of lungs, and 2,000 pores to a square inch of surface; so you see what quantities of air we must have, and what care we should take of our skin so all the little doors will open and shut right.
To be sure the same sound was that very moment perhaps being heard all over the seas, from hundreds of whalemen's look-outs perched as high in the air; but from few of those lungs could that accustomed old cry have derived such a marvellous cadence as from Tashtego the Indian's.
Doctors came to see her singly and in consultation, talked much in French, German, and Latin, blamed one another, and prescribed a great variety of medicines for all the diseases known to them, but the simple idea never occurred to any of them that they could not know the disease Natasha was suffering from, as no disease suffered by a live man can be known, for every living person has his own peculiarities and always has his own peculiar, personal, novel, complicated disease, unknown to medicine- not a disease of the lungs, liver, skin, heart, nerves, and so on mentioned in medical books, but a disease consisting of one of the innumerable combinations of the maladies of those organs.
The lungs absorb the oxygen, which is indispensable for the support of life, and reject the nitrogen.