||It has been suggested that Lingula of left lung be merged into this article. (Discuss) Proposed since September 2013.|
|Detailed diagram of the lungs|
|Gray's||subject #240 1093-1096|
The human lungs are the organs of respiration in humans. Humans have two lungs, a right lung and a left lung. The right lung consists of three lobes while the left lung is slightly smaller consisting of only two lobes (the left lung has a "cardiac notch" allowing space for the heart within the chest).1 Together, the lungs contain approximately 2,400 kilometres (1,500 mi) of airways and 300 to 500 million alveoli, having a total surface area of about 70 square metres (750 sq ft) to 100 square metres (1076.39 sq ft) (8,4 x 8,4 m) in adults — roughly the same area as one side of a tennis court.2 Furthermore, if all of the capillaries that surround the alveoli were unwound and laid end to end, they would extend for about 992 kilometres (616 mi). The lungs together weigh approximately 2.3 kilograms (5.1 lb), with the right lung weighing more than the left.
The pleural cavity is the potential space between the parietal pleura, lining the inner wall of the thoracic cage, and the visceral pleura lining the lungs.
Although strictly speaking, the lung parenchyma refers only to the functional alveolar tissue, the term is often used to refer to all lung tissue, including the respiratory bronchioles, alveolar ducts, terminal bronchioles, and all connecting tissues.33
The trachea divides into two bronchi (one for each side), usually at the level of the fifth thoracic vertebra. This junction is also known as the carina of trachea. The conducting zone contains the trachea, the bronchi, the bronchioles, and the terminal bronchioles The respiratory zone contains the respiratory bronchioles, the alveolar ducts, and the alveoli. The conducting zone and the respiratory stuffers (but not the alveoli) are made up of airways. The conducting zone has no gas exchange with the blood, and is reinforced with cartilage in order to hold open the airways. The conducting zone warms the air to 37 °C (99 °F) and humidifies the air. It also cleanses the air by removing particles via cilia located on the walls of all the passageways. The lungs are surrounded by the rib cage.
The human right lung is divided into three lobes (as opposed to two lobes on the left), superior, middle, and inferior, by two interlobular fissures:
The right lung has a higher volume, total capacity and weight, than that of the left lung. This is despite being 5cm shorter due to the diaphragm rising higher on the right side to accommodate the liver. The right lung is also broader than the left, owing to the inclination of the heart to the left side.
- One of these, the oblique fissure, separates the inferior from the middle and superior lobes, and corresponds closely with the fissure in the left lung. Its direction is, however, more vertical, and it cuts the lower border about 7.5 cm. behind its anterior extremity.
- The other fissure, the horizontal fissure, separates the superior from the middle lobe. It begins in the previous fissure near the posterior border of the lung, and, running horizontally forward, cuts the anterior border on a level with the sternal end of the fourth costal cartilage; on the mediastinal surface it may be traced backward to the hilum.
The middle lobe, the smallest lobe of the right lung, is wedge-shaped, and includes the part of the anterior border and the anterior part of the base of the lung. (There is no middle lobe on the left lung, though there is a lingula.)
The superior and inferior lobes are similar to their counterparts on the left lung.
On the mediastinal surface, immediately above the hilum, is an arched furrow which accommodates the azygos vein; while running superiorly, and then arching laterally some little distance below the apex, is a wide groove for the superior vena cava and right innominate vein; behind this, and proximal to the apex, is a furrow for the innominate artery.
Behind the hilum and the attachment of the pulmonary ligament is a vertical groove for the esophagus; this groove becomes less distinct below, owing to the inclination of the lower part of the esophagus to the left of the middle line.
In front and to the right of the lower part of the esophageal groove is a deep concavity for the extrapericardiac portion of the thoracic part of the inferior vena cava.
As seen on the surface, this fissure begins on the mediastinal surface of the lung at the upper and posterior part of the hilum, and runs backward and upward to the posterior border, which it crosses at a point about 6 cm. below the apex.
It then extends downward and forward over the costal surface, and reaches the lower border a little behind its anterior extremity, and its further course can be followed upward and backward across the mediastinal surface as far as the lower part of the hilum.
On the mediastinal surface, immediately above the hilum, is a well-marked curved furrow produced by the aortic arch, and running upward from this toward the apex is a groove accommodating the left subclavian artery; a slight impression in front of the latter and close to the margin of the lung lodges the left innominate vein.
Behind the hilum and pulmonary ligament is a vertical furrow produced by the descending aorta, and in front of this, near the base of the lung, the lower part of the esophagus causes a shallow impression.
The respiratory zone is the site of gas exchange with blood.
- The sympathetic nervous system via noradrenaline acting on the beta receptors causes bronchodilation.
- The parasympathetic nervous system via acetylcholine, which acts on the M-3 muscarinic receptors, maintains the resting tone of the bronchiolar smooth muscle. This action is related, although considered distinct from bronchoconstriction.
- Many other non-autonomic nervous and biochemical stimuli, including carbon dioxide and oxygen, are also involved in the regulation process.
Mediastinal surface of left lung.
- Tomco, Rachel. "Lungs and Mechanics of Breathing". AnatomyOne. Amirsys, Inc. Retrieved 2012-09-28.
- Notter, Robert H. (2000). Lung surfactants: basic science and clinical applications. New York, N.Y: Marcel Dekker. p. 120. ISBN 0-8247-0401-0. Retrieved 2008-10-11.
- medilexicon.com > Medical Dictionary - 'Parenchyma Of Lung' In turn citing: Stedman's Medical Dictionary. 2006
- Walter F., PhD. Boron (2004). Medical Physiology: A Cellular And Molecular Approaoch. Elsevier/Saunders. ISBN 1-4160-2328-3. Page 605