Human lung

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Human lung
Lungs open.jpg
Frontal view of lungs cut open
Trachea branches into bronchi
Latin pulmo
Gray's subject #240 1093
MeSH Lung

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

The human lungs are the human organs of respiration.

Humans have two lungs, with the left being divided into two lobes and the right into three lobes. Together, the lungs contain approximately 1500 miles (2,400 km) of airways and 300 to 500 million alveoli, having a total surface area of about 75 m2 in adults — roughly the same area as a tennis court.[1] Furthermore, if all of the capillaries that surround the alveoli were unwound and laid end to end, they would extend for about 620 miles.


The conducting zone and the respiratory zone (but not the alveoli) are made up of airways.

The conducting zone has no gas exchange with the blood, and is reinforced with cartilage and smooth muscle, which are very strong. Smooth muscle has variable resistance to air flow. The conducting zone warms the air to 37 degrees Celsius and humidifies the air. It also cleanses the air by removing particles.

The respiratory zone is the site of gas exchange with blood.

The smooth muscle tone in bronchioles, and therefore bronchiolar diameter, is controlled by:

The intrapleural space is the potential space between the pleura lining the inner wall of the thoracic cage and the pleura lining the lungs.


Total lung capacity (TLC) includes inspiratory reserve volume, tidal volume, expiratory reserve volume, and residual volume.[2] The total lung capacity depends on the person's age, height, weight, sex, and normally ranges between 4,000 and 6,000 cm3 (4 to 6 L). For example, females tend to have a 20–25% lower capacity than males. Tall people tend to have a larger total lung capacity than shorter people. Smokers have a lower capacity than nonsmokers. Lung capacity is also affected by altitude. People who are born and live at sea level will have a smaller lung capacity than people who spend their lives at a high altitude. In addition to the total lung capacity, one also measures the tidal volume, the volume breathed in with an average breath, about 500 cm3. For a detailed discussion of the various lung volumes, see the article on lung volumes.

Typical resting adult respiratory rates are 10–20 breaths per minute with 1/3 of the breath time in inspiration.

Human lungs are to a certain extent 'overbuilt' and have a tremendous reserve volume as compared to the oxygen exchange requirements when at rest. This is the reason that individuals can smoke for years without having a noticeable decrease in lung function while still or moving slowly; in situations like these only a small portion of the lungs are actually perfused with blood for gas exchange. As oxygen requirements increase due to exercise, a greater volume of the lungs is perfused, allowing the body to reach its CO2/O2 exchange requirements.


The following is a list of important medical conditions involving the lung. Many of these are caused or worsened by smoking.

Transplantation now allows for a person to have a single lung transplant, a double-lung transplant, or a transplant of both the heart and lungs.

Modification of substances

The lungs convert angiotensin I to angiotensin II. In addition, they remove several blood-bourne substances, e.g. PGE1, PGE2, PGF, leukotrienes, serotonin, bradykinin. [3]

See also


  1. Rhoades RA, Tanner GA (editors) (2003). Medical Physiology (2nd ed. ed.). Lippincott Williams & Wilkins. ISBN 0-7817-1936-4. 
  2. Weinberger SE (2004). Principles of Pulmonary Medicine (4th ed. ed.). Saunders. ISBN 0-7216-9548-5. 
  3. Walter F., PhD. Boron. Medical Physiology: A Cellular And Molecular Approaoch. Elsevier/Saunders. ISBN 1-4160-2328-3.  Page 605

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