Human lung
Encyclopedia
The human lungs are the organs of respiration
in humans. Humans have two lung
s, with the left being divided into two lobes and the right into three lobes. Together, the lungs contain approximately 2400 kilometres (1,491.3 mi) of airways and 300 to 500 million alveoli, having a total surface area of about 70 sqm in adults — roughly the same area as one side of a tennis
court. Furthermore, if all of the capillaries that surround the alveoli were unwound and laid end to end, they would extend for about 992 kilometres (616.4 mi). Each lung weighs 1.1 kilogram, therefore making the entire organ about 2.3 kilogram.
The conducting zone contains the trachea
, the bronchi, the bronchiole
s, and the terminal bronchioles
The respiratory zone contains the respiratory bronchiole
s, the alveolar duct
s, and the alveoli.
The conducting zone and the respiratory stuffers (but not the alveoli) are made up of airway
s.
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 (98.6 °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 respiratory zone is the site of gas exchange
with blood.
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.
The lung parenchyma
is strictly used to refer solely to alveolar tissue with respiratory bronchiole
s, alveolar duct
s and terminal bronchiole
s. However, it often includes any form of lung tissue, also including bronchioles, bronchi, blood vessel
s and lung interstitium.
-borne substances, e.g. PGE1
, PGE2, PGF2α, leukotrienes, serotonin
, bradykinin
.
Respiration (physiology)
'In physiology, respiration is defined as the transport of oxygen from the outside air to the cells within tissues, and the transport of carbon dioxide in the opposite direction...
in humans. Humans have two lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
s, with the left being divided into two lobes and the right into three lobes. Together, the lungs contain approximately 2400 kilometres (1,491.3 mi) of airways and 300 to 500 million alveoli, having a total surface area of about 70 sqm in adults — roughly the same area as one side of a tennis
Tennis
Tennis is a sport usually played between two players or between two teams of two players each . Each player uses a racket that is strung to strike a hollow rubber ball covered with felt over a net into the opponent's court. Tennis is an Olympic sport and is played at all levels of society at all...
court. Furthermore, if all of the capillaries that surround the alveoli were unwound and laid end to end, they would extend for about 992 kilometres (616.4 mi). Each lung weighs 1.1 kilogram, therefore making the entire organ about 2.3 kilogram.
The conducting zone contains the trachea
Vertebrate trachea
In tetrapod anatomy the trachea, or windpipe, is a tube that connects the pharynx or larynx to the lungs, allowing the passage of air. It is lined with pseudostratified ciliated columnar epithelium cells with goblet cells that produce mucus...
, the bronchi, the bronchiole
Bronchiole
The bronchioles or bronchioli are the first airway branches that no longer contain cartilage or glands in their submucosa. They are branches of the bronchi.The bronchioles terminate by entering the circular sacs called alveoli.- Structure :...
s, and the terminal bronchioles
The respiratory zone contains the respiratory bronchiole
Respiratory bronchiole
The respiratory bronchioles are interrupted by alveoli which are thin walled evaginations. Alveolar ducts are distal continuations of the respiratory bronchioles.-External links:*...
s, the alveolar duct
Alveolar duct
Alveolar ducts are the tiny end ducts of the branching airways that fill the lungs. Each lung holds approximately 1.5 to 2 million of them. The tubules divide into two or three alveolar sacs at the distal end. They are formed from the confluence openings of several alveoli...
s, and the alveoli.
The conducting zone and the respiratory stuffers (but not the alveoli) are made up of airway
Airway
The pulmonary airway comprises those parts of the respiratory system through which air flows, conceptually beginning at the nose and mouth, and terminating in the alveoli...
s.
The conducting zone has no gas exchange
Gas exchange
Gas exchange is a process in biology where gases contained in an organism and atmosphere transfer or exchange. In human gas-exchange, gases contained in the blood of human bodies exchange with gases contained in the atmosphere. Human gas-exchange occurs in the lungs...
with the blood, and is reinforced with cartilage in order to hold open the airways. The conducting zone warms the air to 37 °C (98.6 °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
Human rib cage
-See also:*Terms for bones*Terms for anatomical location*Articulation of head of rib-References:* Clinically Oriented Anatomy, 4th ed. Keith L. Moore and Robert F. Dalley. pp. 62–64...
.
The respiratory zone is the site of gas exchange
Gas exchange
Gas exchange is a process in biology where gases contained in an organism and atmosphere transfer or exchange. In human gas-exchange, gases contained in the blood of human bodies exchange with gases contained in the atmosphere. Human gas-exchange occurs in the lungs...
with blood.
- The sympathetic nervous systemSympathetic nervous systemThe sympathetic nervous system is one of the three parts of the autonomic nervous system, along with the enteric and parasympathetic systems. Its general action is to mobilize the body's nervous system fight-or-flight response...
via noradrenaline acting on the beta receptors causes bronchodilation. - The parasympathetic nervous systemParasympathetic nervous systemThe parasympathetic nervous system is one of the two main divisions of the autonomic nervous system . The ANS is responsible for regulation of internal organs and glands, which occurs unconsciously...
via acetylcholineAcetylcholineThe chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...
, which acts on the M-1 muscarinic receptors, maintains the resting tone of the bronchiolar smooth muscle. This action is related, although considered distinct from bronchoconstrictionBronchoconstrictionBronchoconstriction is the constriction of the airways in the lungs due to the tightening of surrounding smooth muscle, with consequent coughing, wheezing, and shortness of breath. Bronchoconstriction can also be due to an accumulation of thick mucus....
. - Many other non-autonomic nervous and biochemical stimuli, including carbon dioxideCarbon dioxideCarbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
and oxygenOxygenOxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
, are also involved in the regulation process.
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.
The lung parenchyma
Parenchyma
Parenchyma is a term used to describe a bulk of a substance. It is used in different ways in animals and in plants.The term is New Latin, f. Greek παρέγχυμα - parenkhuma, "visceral flesh", f. παρεγχεῖν - parenkhein, "to pour in" f. para-, "beside" + en-, "in" + khein, "to pour"...
is strictly used to refer solely to alveolar tissue with respiratory bronchiole
Respiratory bronchiole
The respiratory bronchioles are interrupted by alveoli which are thin walled evaginations. Alveolar ducts are distal continuations of the respiratory bronchioles.-External links:*...
s, alveolar duct
Alveolar duct
Alveolar ducts are the tiny end ducts of the branching airways that fill the lungs. Each lung holds approximately 1.5 to 2 million of them. The tubules divide into two or three alveolar sacs at the distal end. They are formed from the confluence openings of several alveoli...
s and terminal bronchiole
Terminal bronchiole
A terminal bronchiole is a bronchiole at the end of the conducting zone. At the transition into the respiratory zone, alveoli become present.The terminal bronchiole is the most distal segment of the conducting zone. Each of the terminal bronchioles divides to form respiratory bronchioles which...
s. However, it often includes any form of lung tissue, also including bronchioles, bronchi, blood vessel
Blood vessel
The blood vessels are the part of the circulatory system that transports blood throughout the body. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the capillaries, which enable the actual exchange of water and chemicals between the blood and...
s and lung interstitium.
Modification of substances
The lungs convert angiotensin I to angiotensin II. In addition, they remove several bloodBlood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
-borne substances, e.g. PGE1
Prostaglandin E1
Prostaglandin E1 , known pharmaceutically as alprostadil, is a prostaglandin. It is a drug used in the treatment of erectile dysfunction and has vasodilatory properties.-Sexual dysfunction:...
, PGE2, PGF2α, leukotrienes, serotonin
Serotonin
Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...
, bradykinin
Bradykinin
Bradykinin is a peptide that causes blood vessels to dilate , and therefore causes blood pressure to lower. A class of drugs called ACE inhibitors, which are used to lower blood pressure, increase bradykinin further lowering blood pressure...
.