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{{BioPsy}}
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The '''respiratory system''' is an organ system which is used for [[gas exchange]]. Among four-legged animals, the respiratory system generally includes tubes, such as the [[bronchi]], used to carry [[air]] to the [[lungs]], where gas exchange takes place. A [[diaphragm (anatomy)|diaphragm]] pulls air in and pushes it out. Respiratory systems of various types are found in a wide variety of organisms. Even trees have respiratory systems.
  
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{{PsyPerspective}}
   
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==Respiratory system in humans and other animals==
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{{See also|Respiratory tract}}
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[[Image:Respiratory system.svg|thumb| |300px]]
  
   
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{{Infobox Anatomy
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In [[human]]s and other [[mammal]]s, the respiratory system consists of the airways, the lungs, and the respiratory muscles that mediate the movement of air into and out of the body. Within the alveolar system of the lungs, molecules of [[oxygen]] and [[carbon dioxide]] are passively exchanged, by [[diffusion]], between the gaseous environment and the blood. Thus, the respiratory system facilitates oxygenation of the blood with a concomitant removal of carbon dioxide and other gaseous metabolic wastes from the circulation.
  
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|Name = Respiratory system
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The system also helps to maintain the acid-base balance of the body through the efficient removal of carbon dioxide from blood.
  
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|Latin = systema respiratorium
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|Image = Respiratory system complete en.svg
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|Caption = A complete, schematic view of the human respiratory system with their parts and functions. |
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|Precursor =
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The '''respiratory system''' (or '''ventilatory system''') is the biological system of an organism that introduces respiratory gases to the interior and performs [[gas exchange]]. In [[human]]s and other [[mammal]]s, the anatomical features of the respiratory system include airways, [[lung]]s, and the respiratory muscles. [[Molecule]]s of [[oxygen]] and [[carbon dioxide]] are passively exchanged, by [[diffusion]], between the gaseous external environment and the [[blood]]. This exchange process occurs in the alveolar region of the lungs.<ref>{{cite book
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==Anatomy==
  
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| last = Haton
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The respiratory system can be conveniently subdivided into an [[upper respiratory tract]] and [[lower respiratory tract]], trachea and lungs. These sections are also called the ''conducting zone'' and a ''respiratory zone''.
  
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| first = Anthea
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| coauthors = Jean, Hopkins Susan, Johnson Charles William, McLaughlin Maryanna Quon Warner David, LaHart Wright, Jill
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| title = Human Biology and Health
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| publisher = Prentice Hall
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| year = 2010 | location = Englewood Cliffs,
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| pages = 108–118
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| isbn = 0-12-981176-1{{Please check ISBN|reason=Check digit (1) does not correspond to calculated 9.}}}}</ref> Other animals, such as [[insects]], have respiratory systems with very simple anatomical features, and in [[amphibians]] even the [[skin]] plays a vital role in [[gas exchange]].
   
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The conducting zone starts with the [[nares]] (nostrils) of the [[nose]], which open into the [[nasopharynx]] (nasal cavity). The primary functions of the nasal passages are to: 1) filter, 2) warm, 3) moisten, and 4) provide resonance in speech. The nasopharnyx opens into the [[oropharynx]] (behind the oral cavity). The oropharynx leads to the [[laryngopharynx]], and empties into the [[larynx]] (voicebox), which contains the [[vocal cords]], passing through the [[glottis]], connecting to the [[trachea]] (wind pipe) which leads down to the [[thorax|thoracic cavity]] (chest) where it divides into the right and left "main stem" [[bronchus|bronchi]]. The subdivision of the bronchus are: primary, secondary, and tertiary divisions (first, second and third levels). In all, there are up to 16 more times into even smaller [[bronchiole]]s.
 
   
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The bronchioles lead to the respiratory zone of the lungs which consists of [[respiratory bronchiole]]s, [[alveolar duct]]s and the [[alveoli]], the multi-lobulated sacs in which most of the gas exchange occurs.
 
   
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==Comparative anatomy and physiology==
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[[Ventilation]] of the lungs is carried out by the muscles of respiration. [[Inhalation]] is initiated by the [[diaphragm (anatomy)|diaphragm]] and supported by the [[external intercostal muscles]]. Normal resting respirations are 10 to 18 breaths per minute. During vigorous inhalation (at rates exceeding 35 breaths per minute), or in approaching respiratory failure, [[accessory muscles of respiration]] are recruited for support. These consist of [[sternocleidomastoid]], [[platysma]], and the [[strap muscles of the neck]]. [[Exhalation]] is generally a passive process, however active or ''forced'' exhalation is achieved by the [[abdominal muscles|abdominal]] and the [[internal intercostal muscles]].
  
   
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=Humans==
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Air moves through the body in the following order:
  
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In humans the '''respiratory tract''' is the part of the [[anatomy]] involved with the process of [[Respiration (physiology)|respiration]].
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*Nostrils
  
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*Nasal cavity
  
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*Pharynx (naso-, oro-, laryngo-)
  
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*Larynx (voice box)
  
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*Trachea (wind pipe)
  
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*Thoracic cavity (chest)
  
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*Bronchi (right and left)
  
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*Alveoli (site of gas exchange)
  
   
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The respiratory tract is divided into 3 segments:
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[[Ventilation]] occurs under the control of the autonomic nervous system from the part of the [[brain stem]], the [[ medulla oblongata]] and the [[pons]]. This area of the brain forms the respiration regulatory center, a series of interconnected nerons within the lower and middle brain stem which coordinate respiratory movements. The sections are the [[pneumotaxic center]], the [[apneustic center]], and the dorsal and ventral respiratory groups. This section is especially sensative during infancy, and the neurons can be destroyed if the infant is dropped or shaken violently. The result can be death due to "[[shaken baby syndrome]]."
  
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*[[Upper respiratory tract]]: [[human nose|nose]] and nasal passages, [[paranasal sinus]]es, and [[throat]] or [[pharynx]]
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*Respiratory airways: [[voice box]] or [[larynx]], [[Vertebrate trachea|trachea]], [[bronchus|bronchi]], and [[bronchiole]]s
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*[[Lung]]s: [[respiratory bronchiole]]s, [[alveolar duct]]s, [[alveolar sac]]s, and [[alveoli]]
   
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The respiratory tract is a common site for infections. [[Upper respiratory tract infection]]s are probably the most common infections in the world.
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References:
  
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*[http://www.wrongdiagnosis.com/medical/respiration_regulatory_center_printer.htm Medical Dictionary]
  
   
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Most of the respiratory tract exists merely as a piping system for air to travel in the lungs, and [[alveoli]] are the only part of the lung that exchanges [[oxygen]] and [[carbon dioxide]] with the [[blood]].
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*[http://www.usask.ca/medicine/prevent/sbs.html Fact sheet on Shaken Baby Syndrome]
  
   
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Moving down the respiratory tract starting at the trachea, the tubes get smaller and divide into more and more tubes. There are estimated to be about 20 to 23 divisions, ending up at an alveolus.
   
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Even though the cross-sectional area of each bronchus or bronchiole is smaller, because there are so many, the total surface area is larger. This means there is less resistance at the terminal bronchioles. (Most resistance is around the 3-4 division from the trachea due to turbulence.)
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The respiratory system lies dormant in the human fetus during pregnancy. At birth, the respiratory system is drained of fluid and cleaned to assure proper functioning of the system. If an infant is born before forty weeks gestational age, the newborn may expereince respiratory failure due to the under-developed lungs. This is due to the incomplete development of the [[alveoli]] type II cells in the lungs. The infant lungs do not function due to the collapse of the alveoli caused by surface tension of water remaining in the lungs. [[Surfactant]] is lacking from the lungs, leading to the condition. This condition may be avoided if the mother is given a series of steriod shots in the final week prior to delivery. The steriods accelerate the development of the type II cells.
  
   
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==General histology==
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Reference:
  
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The respiratory tract is covered in an [[epithelium]], the type of which varies down the tract. There are [[gland]]s and [[mucus]] produced by [[goblet cell]]s in parts, as well as [[smooth muscle]], [[elastin]] or [[cartilage]].
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*[http://ajpregu.physiology.org/cgi/content/full/281/3/R770 Department of Environmental Biology, University of Adelaide, Adelaide, South Australia]]
  
   
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Most of the epithelium (from the nose to the bronchi) is covered in pseudostratified columnar [[cilia]]ted [[epithelial cell]]s, commonly called [[respiratory epithelium]]. The cilia beat in one direction, moving mucus towards the throat where it is swallowed. Moving down the bronchioles, the cells get more cuboidal in shape but are still ciliated.
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===Circulation===
  
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The right side of the heart pumps blood from the [[right ventricle]] through the [[pulmonary semilunar valve]] into the [[pulmonary trunk]]. The trunk branches into right and left [[pulmonary arteries]] to the [[pulmonary blood vessel]]s. The vessels generally accompany the [[airway]]s and also undergo numerous branchings. Once the gas exchange process is complete in the [[pulmonary capallaries]], blood is returned to the left side of the heart through four [[pulmonary veins]], two from each side. The [[pulmonary circulation]] has a very low resistance, due to the short distance within the lungs, compared to the [[systemic circulation]], and for this reason, all the pressures within the pulmonary blood vessels are normally low as compared to the pressure of the systemic circulation loop.
  
   
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Cartilage is present until the small bronchi. In the trachea they are C-shaped rings, whereas in the bronchi they are interspersed plates.
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==Functions==
  
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The major function of the respiratory system is [[gas exchange]]. Respiration consists of a mechanical cycle of inhalation and exhalation, with gaseous exchange occurring in between. As gas exchange occurs, the acid-base balance of the body is maintained as part of [[homeostasis]]. If proper ventilation is not maintained two opposing conditions could occur: 1) [[respiratory acidosis]], a life threatening condition, and 2) [[respiratory alkalosis]].
  
   
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Glands are abundant in the upper respiratory tract, but there are fewer lower down and they are absent starting at the bronchioles. The same goes for goblet cells, although there are scattered ones in the first bronchioles.
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Inhalation is driven primarily by the [[diaphragm (anatomy)|diaphragm]]. When the diaphragm contracts, the ribcage expands and the contents of the abdomen are moved downward. This results in a larger thoracic volume, which in turn causes a decrease in intrathoracic pressure. As the pressure in the chest falls, air moves into the conducting zone. Here, the air is filtered, warmed, and humidified as it flows to the lungs.
  
   
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Smooth muscle starts in the trachea, where it joins the C-shaped rings of cartilage. It continues down the bronchi and bronchioles, which it completely encircles.
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Exhalation, on the other hand, is typically a passive process. The lungs have a natural elasticity; as they recoil from the stretch of inhalation, air flows back out until the pressures in the chest and the atmosphere reach equilibrium.
  
   
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Instead of hard cartilage, the bronchi and bronchioles are composed of elastic tissue.
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A simple [[:wikibooks:Constructing school science lab equipment/Bell jar model lung|model of how the lungs are inflated]] can be built from a [[bell jar]].
  
   
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===Horses===
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During forced inhalation, as when taking a deep breath, the [[external intercostal muscles]] and accessory muscles further expand the thoracic cavity.
  
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Horses are [[obligate nasal breathing|obligate nasal breathers]] which means that they are different from many other mammals because they do not have the option of breathing through their mouths and must take in oxygen through their noses.
   
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===Elephants===
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During forced exhalation, as when blowing out a candle, expiratory muscles including the [[abdominal muscles]] and [[internal intercostal muscles]], generate abdominal and thoracic pressure, which forces air out of the lungs.
 
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The [[elephant]] is the only animal known to have no [[pleural space]]. Rather, the [[parietal pleura|parietal]] and [[visceral pleura]] are both composed of dense [[connective tissue]] and joined to each other via loose connective tissue.<ref>{{cite journal
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| last = West
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| first = John B.
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| coauthors = Ravichandran
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| title = Snorkel breathing in the elephant explains the unique anatomy of its pleura
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| journal = Respiration Physiology
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| volume = 126
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| issue = 1
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| pages = 1–8
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| year = 1993
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| pmid = 11311306
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| doi = 10.1016/S0034-5687(01)00203-1}}</ref> This lack of a pleural space, along with an unusually thick [[Thoracic diaphragm|diaphragm]], are thought to be [[Evolution#Outcomes|evolutionary adaptations]] allowing the elephant to remain underwater for long periods of time while breathing through its [[Elephant#Trunk|trunk]] which emerges as a snorkel.<ref>{{cite journal
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| last = West
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| first = John B.
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| title = Why doesn't the elephant have a pleural space?
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| journal = News Physiol Sci
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| volume = 17
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| pages = 47–50
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| year = 2002
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| accessdate =
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| pmid = 11909991 }}</ref>
   
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===Birds===
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Upon inhalation, gas exchange occurs at the [[alveoli]], the tiny sacs which are the basic functional component of the lungs. The alveolar walls are extremely thin (approx. 0.2 micrometres), and are permeable to gases. The alveoli are lined with pulmonary capillaries, the walls of which are also thin enough to permit gas exchange. All gases diffuse from the alveolar air to the blood in the pulmonary capillaries, as carbon dioxide diffuses in the opposite direction, from capillary blood to alveolar air. At this point, the pulmonary blood is oxygen-rich, and the lungs are holding carbon dioxide. Exhalation follows, thereby ridding the body of the carbon dioxide and completing the cycle of respiration.
 
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{{main section|Bird anatomy|Respiratory system}}
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The respiratory system of birds differs significantly from that found in mammals, containing unique anatomical features such as [[air sacs]]. The lungs of birds also do not have the capacity to inflate as birds lack a [[Thoracic diaphragm|diaphragm]] and a [[pleural cavity]]. Gas exchange in birds occurs between air capillaries and [[capillary|blood capillaries]], rather than in [[alveoli]].
   
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===Reptiles===
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Other:
  
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The [[anatomy|anatomical structure]] of the [[lungs]] is less complex in [[reptiles]] than in [[mammals]], with reptiles lacking the very extensive airway tree structure found in mammalian lungs. [[Gas exchange]] in reptiles still occurs in [[alveoli]] however, reptiles do not possess a [[thoracic diaphragm|diaphragm]]. Thus, breathing occurs via a change in the volume of the body cavity which is controlled by contraction of [[intercostal muscles]] in all reptiles except [[turtles]]. In turtles, contraction of specific pairs of flank muscles governs [[inhalation|inspiration]] or [[Exhalation|expiration]].<ref>[http://www.britannica.com/EBchecked/topic/498684/reptile/38473/Respiratory-system Britannica On-line Encyclopedia]</ref>
   
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===Amphibians===
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In an average resting adult, the lungs take up about 250ml of oxygen every minute while excreting about 200ml of carbon dioxide. During an average breath, an adult will exchange from 500 ml to 700 ml of air. This average breath capacity is called [[tidal volume]].
  
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Both the lungs and the [[Frog#Morphology and physiology|skin]] serve as respiratory organs in [[amphibians]]. The skin of these animals is highly vascularized and moist, with moisture maintained via secretion of [[mucus]] from specialized cells. While the lungs are of primary importance to breathing control, the skin's unique properties aid rapid gas exchange when amphibians are submerged in oxygen-rich water.<ref>{{cite journal
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| last = Gottlieb
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| first = G
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| coauthors = Jackson DC
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| title = Importance of pulmonary ventilation in respiratory control in the bullfrog
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| journal = Am J Physiol
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| volume = 230
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| pages = 608–13
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| year = 1976
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| accessdate =
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| pmid = 4976
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| issue = 3 }}</ref>
   
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===Fish===
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The movement of gas through the larynx, pharynx and mouth allows us to speak, or ''[[phonation|phonate]]''.
  
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In most fish respiration takes place through [[Gills_(biology)#Vertebrate_gills|gills]]. (See also [[aquatic respiration]].) [[Lungfish]], however, do possess one or two lungs. The [[Anabantoidei|labyrinth fish]] have developed a special organ that allows them to take advantage of the oxygen of the air.
   
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==Anatomy in invertebrates==
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The respiratory tract is constantly exposed to [[microbe]]s due to the extensive surface area, which is why the respiratory system includes many mechanisms to defend itself and prevent [[pathogen]]s from entering the body.
  
   
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===Insects===
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Virtually all the body's blood travels through the lungs every minute. The lungs add and remove many chemical messengers from the blood as it flows through pulmonary capillary bed . The fine capillaries also trap blood clots that have formed in systemic veins.
  
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{{Main|Respiratory system of insects}}
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Air enters the respiratory systems of most [[insects]] through a series of external openings called [[spiracles]]. These external openings, which act as muscular valves in some insects, lead to the internal respiratory system, a densely networked array of tubes called [[invertebrate trachea|tracheae]]. The scientific tracheal system within an individual is composed of interconnecting transverse and longitudinal tracheae which maintain equivalent pressure throughout the system. These tracheae branch repeatedly, eventually forming tracheoles, which are blind-ended, water-filled compartments only one micrometer in diameter.<ref>[http://www.earthlife.net/insects/anatomy.html Introduction to Insect Anatomy]</ref> It is at this level of the tracheoles that oxygen is delivered to the cells for respiration. The trachea are water-filled due to the [[cell membrane|permeable membrane]] of the surrounding [[tissue (biology)|tissue]]s. During exercise, the water level retracts due to the increase in concentration of [[lactic acid]] in the [[muscle cell]]s. This lowers the [[water potential]] and the water is drawn back into the cells via [[osmosis]] and air is brought closer to the muscle cells. The [[diffusion pathway]] is then reduced and gases can be transferred more easily.
   
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Insects were once believed to exchange gases with the environment continuously by the [[simple diffusion]] of gases into the tracheal system. More recently, however, large variation in insect ventilatory patterns have been documented and insect respiration appears to be highly variable. Some small insects do demonstrate continuous respiration and may lack muscular control of the spiracles. Others, however, utilize [[muscle contraction|muscular contraction]] of the [[abdomen]] along with coordinated spiracle contraction and relaxation to generate cyclical gas exchange patterns and to reduce water loss into the atmosphere. The most extreme form of these patterns is termed [[discontinuous gas exchange]] cycles (DGC).<ref>{{cite journal
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==Diseases of the respiratory system==
  
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| last = Lighton
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[[Respiratory disease|Diseases of the respiratory system]] can be classified into four general areas:
  
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| first = JRB
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| title = Discontinuous gas exchange in insects
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| journal = Annu Rev Entomology
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| volume = 41
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| pages = 309–324
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| date = January 1996
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| accessdate = }}</ref>
   
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===Molluscs===
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*Obstructive Diseases (e.g., [[Emphysema]], [[Bronchitis]], [[Asthma]])
  
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[[Molluscs]] generally possess gills that allow exchange of oxygen from an aqueous environment into the circulatory system. These animals also possess a heart that pumps blood which contains [[hemocyaninine]] as its oxygen-capturing molecule. Hence, this respiratory system is similar to that of vertebrate fish. The [[respiratory system of gastropods]] can include either gills or a lung.
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*Restrictive Diseases (e.g., [[Fibrosis]], [[Sarcoidosis]], Alveolar Damage, Pleural Effusion)
  
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*Vascular Diseases (e.g., [[Pulmonary Edema]], [[Pulmonary Embolism]], [[Pulmonary Hypertension]])
  
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*Infectious, Environmental and Other Diseases (e.g., [[Pneumonia]], [[Tuberculosis]], [[Asbestosis]], Particulate Pollutants)
  
   
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==Respiratory system in plants==
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==Physiology in mammals==
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{{See also|Respiratory physiology|Respiration (physiology)}}
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Plant respiration is limited by the process of [[diffusion]]. As well as using photosynthesis, plants take in oxygen (although very little of it) through their stomata (pl. stoma), holes on the undersides of their leaves. However, even a [[baobab]] tree is mostly dead because [[air]] can penetrate only skin deep. However, most plants are not involved in highly metabolic activities like [[hunting]], i.e. they do not need the energy necessary for [[predator]]s, and thus their breathing is limited.
  
   
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===Ventilation===
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==Tissue engineering==
  
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In respiratory physiology, ventilation (or ventilation rate) is the rate at which gas enters or leaves the lung. It is categorized under the following definitions:
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In [[tissue engineering]], respiration is an essential problem. The small depth of diffusion respiration sufficient to support the metabolism of an average human cell is less than a millimeter (0.04 in). However, various substances can be used to enhance this depth.
  
   
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{| class="wikitable"
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==Sources==
  
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|-
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*Perkins, M. 2003. Respiration Power Point Presentation. Biology 182 Course Handout. Orange Coast College, Costa Mesa, CA.
  
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! Measurement !! Equation !! Description
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|-
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| Minute ventilation || tidal volume * respiratory rate[1][2]|| the total volume of gas entering the lungs per minute.
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|-
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| Alveolar ventilation || (tidal volume - dead space) * respiratory rate [1] || the volume of gas per unit time that reaches the alveoli, the respiratory portions of the lungs where gas exchange occurs.
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|-
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| Dead space ventilation || dead space * respiratory rate[3] || the volume of gas per unit time that does not reach these respiratory portions, but instead remains in the airways (trachea, bronchi, etc.).
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|}
   
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====Control====
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''See also'':
  
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Ventilation occurs under the control of the autonomic [[nervous system]] from parts of the [[brain stem]], the [[medulla oblongata]] and the [[pons]]. This area of the brain forms the respiration regulatory center, a series of interconnected [[brain cell]]s within the lower and middle brain stem which coordinate respiratory movements. The sections are the [[pneumotaxic center]], the [[apneustic center]], and the [[dorsal respiratory group|dorsal]] and [[ventral respiratory group]]s. This section is especially sensitive during infancy, and the neurons can be destroyed if the infant is dropped and/or shaken violently. The result can be death due to "[[shaken baby syndrome]]".<ref>*[http://www.usask.ca/medicine/prevent/sbs.html Fact sheet on Shaken Baby Syndrome]</ref>
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*[[Liquid breathing]]
  
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*[[aquatic respiration]]
  
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The breathing rate increases with the concentration of carbon dioxide in the blood, which is detected by peripheral [[chemoreceptor]]s in the [[aorta]] and [[common carotid artery|carotid artery]] and central chemoreceptors in the medulla. Exercise also increases respiratory rate, due to the action of [[proprioception|proprioceptors]], the increase in body temperature, the release of [[epinephrine]], and motor impulses originating from the brain.<ref>{{cite web|title=Respiration|url=http://people.eku.edu/ritchisong/301notes6.htm|publisher=Harvey Project|accessdate=27 July 2012}}</ref> In addition, it can increase due to increased inflation in the lungs, which is detected by stretch receptors.
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*[[Involuntary control of respiration]]
  
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====Inhalation====
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[[Inhalation]] is initiated by the [[diaphragm (anatomy)|diaphragm]] and supported by the [[external intercostal muscles]]. Normal resting respirations are 10 to 18 breaths per minute, with a time period of 2 seconds. During vigorous inhalation (at rates exceeding 35 breaths per minute), or in approaching respiratory failure, [[accessory muscles of respiration]] are recruited for support. These consist of [[sternocleidomastoid]], [[platysma]], and the [[scalene muscles]] of the neck. [[Pectoral muscles]] and [[latissimus dorsi]] are also accessory muscles.
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Under normal conditions, the diaphragm is the primary driver of inhalation. When the diaphragm contracts, the [[rib]]cage expands and the contents of the abdomen are moved downward. This results in a larger [[thorax|thoracic]] volume and negative pressure (with respect to atmospheric pressure) inside the thorax. As the pressure in the chest falls, air moves into the conducting zone. Here, the air is filtered, warmed, and humidified as it flows to the lungs.
  +
  +
During forced inhalation, as when taking a deep breath, the [[external intercostal muscles]] and accessory muscles aid in further expanding the [[thoracic cavity]].
  +
During inhalation the diaphragm contracts.
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  +
====Exhalation====
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  +
[[Exhalation]] is generally a passive process; however, active or ''forced'' exhalation is achieved by the [[abdominal muscles|abdominal]] and the [[internal intercostal muscles]]. During this process air is forced or ''exhaled'' out.
  +
  +
The lungs have a natural elasticity: as they recoil from the stretch of inhalation, air flows back out until the pressures in the chest and the atmosphere reach equilibrium.<ref>A simple [[:wikibooks:Constructing school science lab equipment/Bell jar model lung|model of how the lungs are inflated]] can be built from a [[bell jar]]</ref>
  +
  +
During forced exhalation, as when blowing out a candle, expiratory muscles including the abdominal muscles and internal intercostal muscles, generate abdominal and thoracic pressure, which forces air out of the lungs.
  +
  +
===Gas exchange===
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The major function of the respiratory system is [[gas exchange]] between the external environment and an organism's [[circulatory system]]. In humans and other mammals, this exchange facilitates [[Oxygenation (medical)|oxygenation]] of the blood with a concomitant removal of carbon dioxide and other gaseous [[metabolic waste]]s from the [[circulatory system|circulation]].<ref>{{cite web|title=Respiratory Physiology|url=http://www.nda.ox.ac.uk/wfsa/html/u12/u1211_01.htm}}</ref> As gas exchange occurs, the acid-base balance of the body is maintained as part of [[homeostasis]]. If proper ventilation is not maintained, two opposing conditions could occur: [[respiratory acidosis]], a life threatening condition, and [[respiratory alkalosis]].
  +
  +
Upon inhalation, gas exchange occurs at the [[pulmonary alveolus|alveoli]], the tiny sacs which are the basic functional component of the lungs. The alveolar walls are extremely thin (approx. 0.2 micrometres). These walls are composed of a single layer of [[epithelium|epithelial cells]] (type I and type II epithelial cells) close to the [[capillaries|pulmonary capillaries]] which are composed of a single layer of [[endothelium|endothelial cells]]. The close proximity of these two cell types allows permeability to gases and, hence, gas exchange.
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This whole mechanism of gas exchange is carried by the simple phenomenon of pressure difference. When the air pressure is high inside the lungs, the air from lungs flow out. When the air pressure is low inside, then air flows into the lungs.
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===Immune functions===
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Airway epithelial cells can secrete a variety of molecules that aid in the defense of lungs. Secretory immunoglobulins (IgA), collectins (including Surfactant A and D), defensins and other peptides and proteases, reactive oxygen species, and reactive nitrogen species are all generated by airway epithelial cells. These secretions can act directly as antimicrobials to help keep the airway free of infection. Airway epithelial cells also secrete a variety of chemokines and cytokines that recruit the traditional immune cells and others to site of infections.
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Most of the respiratory system is lined with mucous membranes that contain mucosal-associated [[lymphoid system#lymphoid tissue|lymphoid tissue]], which produces [[white blood cell]]s such as [[lymphocyte]]s.
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===Metabolic and endocrine functions of the lungs===
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In addition to their functions in gas exchange, the lungs have a number of metabolic functions. They manufacture surfactant for local use, as noted above. They also contain a fibrinolytic system that lyses clots in the pulmonary vessels. They release a variety of substances that enter the systemic arterial blood and they remove other substances from the systemic venous blood that reach them via the pulmonary artery. Prostaglandins are removed from the circulation, but they are also synthesized in the lungs and released into the blood when lung tissue is stretched.
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The lungs also activate one hormone; the physiologically inactive decapeptide angiotensin I is converted to the pressor, aldosterone-stimulating octapeptide angiotensin II in the pulmonary circulation. The reaction occurs in other tissues as well, but it is particularly prominent in the lungs. Large amounts of the angiotensin-converting enzyme responsible for this activation are located on the surface of the endothelial cells of the pulmonary capillaries. The converting enzyme also inactivates bradykinin. Circulation time through the pulmonary capillaries is less than one second, yet 70% of the angiotensin I reaching the lungs is converted to angiotensin II in a single trip through the capillaries. Four other peptidases have been identified on the surface of the pulmonary endothelial cells.
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====Vocalization====
  +
The movement of gas through the [[larynx]], [[pharynx]] and [[mouth]] allows humans to [[speech|speak]], or ''[[phonation|phonate]]''. Vocalization, or singing, in birds occurs via the [[Bird anatomy#Respiratory system|syrinx]], an organ located at the base of the trachea. The vibration of air flowing across the larynx ([[vocal cords]]), in humans, and the syrinx, in birds, results in sound. Because of this, gas movement is extremely vital for [[communication]] purposes.
  +
  +
====Temperature control====
  +
[[Panting]] in dogs,cats and some other animals provides a means of controlling body temperature. This physiological response is used as a cooling mechanism.''
  +
  +
====Coughing and sneezing====
  +
Irritation of nerves within the [[nasal cavity|nasal passages]] or [[airways]], can induce [[coughing]] and [[sneezing]]. These responses cause air to be expelled forcefully from the [[Vertebrate trachea|trachea]] or [[nose]], respectively. In this manner, irritants caught in the [[mucus]] which lines the respiratory tract are expelled or moved to the [[mouth]] where they can be [[swallowed]]. During coughing, contraction of the smooth muscle narrows the trachea by pulling the ends of the cartilage plates together and by pushing soft tissue out into the lumen. This increases the expired airflow rate to dislodge and remove any irritant particle or mucus.
  +
  +
==Development==
  +
  +
===Humans and mammals===
  +
{{Further|Development of human lung}}
  +
The respiratory system lies dormant in the human [[fetus]] during [[pregnancy]]. At birth, the respiratory system becomes fully functional upon exposure to air, although some lung development and growth continues throughout childhood.<ref>{{cite web|last=Michelle|first=Julia|title=How Do Babies Breathe in the Womb?|url=http://www.livestrong.com/article/27084-babies-breathe-womb/|accessdate=7 March 2011}}</ref> [[premature birth|Pre-term birth]] can lead to infants with under-developed lungs. These lungs show incomplete development of the [[pulmonary alveolus#Anatomy|alveolar type II cells]], cells that produce [[surfactant]]. The lungs of pre-term infants may not function well because the lack of surfactant leads to increased surface tension within the alveoli. Thus, many alveoli collapse such that no gas exchange can occur within some or most regions of an infant's lungs, a condition termed [[infant respiratory distress syndrome|respiratory distress syndrome]]. Basic scientific experiments, carried out using cells from chicken lungs, support the potential for using [[steroids]] as a means of furthering development of type II alveolar cells.<ref>[http://ajpregu.physiology.org/cgi/content/full/281/3/R770 Department of Environmental Biology, University of Adelaide, Adelaide, South Australia]</ref> In fact, once a pre-mature birth is threatened, every effort is made to delay the birth, and a series of [[steroid]] shots is frequently administered to the mother during this delay in an effort to promote lung growth.<ref>[http://www.pregnancy-facts.com/articles/childbirth/premature-babies.php Pregnancy-facts.com]</ref>
  +
  +
==Disease==
  +
[[Respiratory disease|Disorders of the respiratory system]] can be classified into four general areas:
  +
* Obstructive conditions (e.g., [[emphysema]], [[bronchitis]], [[Allergic asthma|asthma]])
  +
* Restrictive conditions (e.g., [[fibrosis]], [[sarcoidosis]], alveolar damage, [[pleural effusion]])
  +
* Vascular diseases (e.g., [[pulmonary edema]], [[pulmonary embolism]], [[pulmonary hypertension]])
  +
* Infectious, environmental and other "diseases" (e.g., [[pneumonia]], [[tuberculosis]], [[asbestosis]], [[air pollution#Pollutants|particulate pollutants]]):
  +
  +
[[Cough]]ing is of major importance, as it is the body's main method to remove dust, [[mucus]], [[saliva]], and other debris from the lungs. Inability to cough can lead to [[infection]]. Deep breathing exercises may help keep finer structures of the lungs clear from particulate matter, etc.
  +
  +
The respiratory tract is constantly exposed to [[microbe]]s due to the extensive surface area, which is why the respiratory system includes many mechanisms to defend itself and prevent [[pathogen]]s from entering the body.
  +
  +
Disorders of the respiratory system are usually treated internally by a [[pulmonology|pulmonologist]] and [[Respiratory therapy|Respiratory Therapist]].
  +
  +
==See also==
  +
*[[Aquatic respiration]]
  +
*[[Artificial respiration]]
 
*[[Gill]]
  
*[[Gill]]
  +
*[[Involuntary control of respiration]]
  +
*[[Liquid breathing]]
  +
*[[Respiration stimulating drugs]]
  +
*[[Respiratory distress]]
  +
*[[Respiratory tract disorders]]
  +
*[[Thorax]]
  +
  +
==References==
  +
{{reflist}}
   
 
==External links==
  
==External links==
  +
*[http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookRespsys.html#Diseases%20of%20the%20Respiratory%20Sys A high school level description of the respiratory system]
−
*[http://www.scienceaid.co.uk/biology/humans/respiratorysystem.html Science aid: Respiratory System] A simple guide for high school students
  
 
*[http://www.leeds.ac.uk/chb/lectures/anatomy7.html Introduction to Respiratory System]
  
*[http://www.leeds.ac.uk/chb/lectures/anatomy7.html Introduction to Respiratory System]
  +
*[http://www.scienceaid.co.uk/biology/humans/lungs.html Science aid: Respiratory System] A simple guide for high school students
  +
*[http://www.bio.umass.edu/biology/bemis/FAOV4/Ch18.doc The Respiratory System] University level (Microsoft Word document)
  +
*[http://meded.ucsd.edu/ifp/jwest/resp_phys/index.html Lectures in respiratory physiology] by noted respiratory physiologist [[John B. West]] (also at [http://www.youtube.com/playlist?list=PLE69608EC343F5691&hl=en YouTube])
   
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{{Organ systems}}
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{{Respiratory_system}}
  
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{{organ_systems}}
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{{Nose anatomy}}
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{{Parynx anatomy}}
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{{Lower respiratory system anatomy}}
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{{Thoracic cavity}}
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{{Respiratory physiology}}
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{{Respiratory pathology}}
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{{Development of respiratory system}}
   
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{{DEFAULTSORT:Respiratory System}}
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[[Category:Anatomical systems]]
 
[[Category:Respiratory system]]
  
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{{EnWP|Respiratory system}}

Latest revision as of 00:56, 11 February 2014

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See also: Respiratory tract
Respiratory system
File:Respiratory system complete en.svg
A complete, schematic view of the human respiratory system with their parts and functions.
Latin systema respiratorium
[[List of subjects in Gray's Anatomy:{{{GraySubject}}}#Gray.27s_page_.23|Gray's]] subject #{{{GraySubject}}}
System
MeSH [1]
[[Image:|190px|center|]]

The respiratory system (or ventilatory system) is the biological system of an organism that introduces respiratory gases to the interior and performs gas exchange. In humans and other mammals, the anatomical features of the respiratory system include airways, lungs, and the respiratory muscles. Molecules of oxygen and carbon dioxide are passively exchanged, by diffusion, between the gaseous external environment and the blood. This exchange process occurs in the alveolar region of the lungs.[1] Other animals, such as insects, have respiratory systems with very simple anatomical features, and in amphibians even the skin plays a vital role in gas exchange.


Comparative anatomy and physiology

Humans=

In humans the respiratory tract is the part of the anatomy involved with the process of respiration.

The respiratory tract is divided into 3 segments:

The respiratory tract is a common site for infections. Upper respiratory tract infections are probably the most common infections in the world.

Most of the respiratory tract exists merely as a piping system for air to travel in the lungs, and alveoli are the only part of the lung that exchanges oxygen and carbon dioxide with the blood.

Moving down the respiratory tract starting at the trachea, the tubes get smaller and divide into more and more tubes. There are estimated to be about 20 to 23 divisions, ending up at an alveolus.

Even though the cross-sectional area of each bronchus or bronchiole is smaller, because there are so many, the total surface area is larger. This means there is less resistance at the terminal bronchioles. (Most resistance is around the 3-4 division from the trachea due to turbulence.)

General histology

The respiratory tract is covered in an epithelium, the type of which varies down the tract. There are glands and mucus produced by goblet cells in parts, as well as smooth muscle, elastin or cartilage.

Most of the epithelium (from the nose to the bronchi) is covered in pseudostratified columnar ciliated epithelial cells, commonly called respiratory epithelium. The cilia beat in one direction, moving mucus towards the throat where it is swallowed. Moving down the bronchioles, the cells get more cuboidal in shape but are still ciliated.

Cartilage is present until the small bronchi. In the trachea they are C-shaped rings, whereas in the bronchi they are interspersed plates.

Glands are abundant in the upper respiratory tract, but there are fewer lower down and they are absent starting at the bronchioles. The same goes for goblet cells, although there are scattered ones in the first bronchioles.

Smooth muscle starts in the trachea, where it joins the C-shaped rings of cartilage. It continues down the bronchi and bronchioles, which it completely encircles.

Instead of hard cartilage, the bronchi and bronchioles are composed of elastic tissue.

Horses

Horses are obligate nasal breathers which means that they are different from many other mammals because they do not have the option of breathing through their mouths and must take in oxygen through their noses.

Elephants

The elephant is the only animal known to have no pleural space. Rather, the parietal and visceral pleura are both composed of dense connective tissue and joined to each other via loose connective tissue.[2] This lack of a pleural space, along with an unusually thick diaphragm, are thought to be evolutionary adaptations allowing the elephant to remain underwater for long periods of time while breathing through its trunk which emerges as a snorkel.[3]

Birds

Template:Main section The respiratory system of birds differs significantly from that found in mammals, containing unique anatomical features such as air sacs. The lungs of birds also do not have the capacity to inflate as birds lack a diaphragm and a pleural cavity. Gas exchange in birds occurs between air capillaries and blood capillaries, rather than in alveoli.

Reptiles

The anatomical structure of the lungs is less complex in reptiles than in mammals, with reptiles lacking the very extensive airway tree structure found in mammalian lungs. Gas exchange in reptiles still occurs in alveoli however, reptiles do not possess a diaphragm. Thus, breathing occurs via a change in the volume of the body cavity which is controlled by contraction of intercostal muscles in all reptiles except turtles. In turtles, contraction of specific pairs of flank muscles governs inspiration or expiration.[4]

Amphibians

Both the lungs and the skin serve as respiratory organs in amphibians. The skin of these animals is highly vascularized and moist, with moisture maintained via secretion of mucus from specialized cells. While the lungs are of primary importance to breathing control, the skin's unique properties aid rapid gas exchange when amphibians are submerged in oxygen-rich water.[5]

Fish

In most fish respiration takes place through gills. (See also aquatic respiration.) Lungfish, however, do possess one or two lungs. The labyrinth fish have developed a special organ that allows them to take advantage of the oxygen of the air.

Anatomy in invertebrates

Insects

Main article: Respiratory system of insects

Air enters the respiratory systems of most insects through a series of external openings called spiracles. These external openings, which act as muscular valves in some insects, lead to the internal respiratory system, a densely networked array of tubes called tracheae. The scientific tracheal system within an individual is composed of interconnecting transverse and longitudinal tracheae which maintain equivalent pressure throughout the system. These tracheae branch repeatedly, eventually forming tracheoles, which are blind-ended, water-filled compartments only one micrometer in diameter.[6] It is at this level of the tracheoles that oxygen is delivered to the cells for respiration. The trachea are water-filled due to the permeable membrane of the surrounding tissues. During exercise, the water level retracts due to the increase in concentration of lactic acid in the muscle cells. This lowers the water potential and the water is drawn back into the cells via osmosis and air is brought closer to the muscle cells. The diffusion pathway is then reduced and gases can be transferred more easily.

Insects were once believed to exchange gases with the environment continuously by the simple diffusion of gases into the tracheal system. More recently, however, large variation in insect ventilatory patterns have been documented and insect respiration appears to be highly variable. Some small insects do demonstrate continuous respiration and may lack muscular control of the spiracles. Others, however, utilize muscular contraction of the abdomen along with coordinated spiracle contraction and relaxation to generate cyclical gas exchange patterns and to reduce water loss into the atmosphere. The most extreme form of these patterns is termed discontinuous gas exchange cycles (DGC).[7]

Molluscs

Molluscs generally possess gills that allow exchange of oxygen from an aqueous environment into the circulatory system. These animals also possess a heart that pumps blood which contains hemocyaninine as its oxygen-capturing molecule. Hence, this respiratory system is similar to that of vertebrate fish. The respiratory system of gastropods can include either gills or a lung.

Physiology in mammals

See also: Respiratory physiology and Respiration (physiology)

Ventilation

In respiratory physiology, ventilation (or ventilation rate) is the rate at which gas enters or leaves the lung. It is categorized under the following definitions:

Measurement Equation Description
Minute ventilation tidal volume * respiratory rate[1][2] the total volume of gas entering the lungs per minute.
Alveolar ventilation (tidal volume - dead space) * respiratory rate [1] the volume of gas per unit time that reaches the alveoli, the respiratory portions of the lungs where gas exchange occurs.
Dead space ventilation dead space * respiratory rate[3] the volume of gas per unit time that does not reach these respiratory portions, but instead remains in the airways (trachea, bronchi, etc.).

Control

Ventilation occurs under the control of the autonomic nervous system from parts of the brain stem, the medulla oblongata and the pons. This area of the brain forms the respiration regulatory center, a series of interconnected brain cells within the lower and middle brain stem which coordinate respiratory movements. The sections are the pneumotaxic center, the apneustic center, and the dorsal and ventral respiratory groups. This section is especially sensitive during infancy, and the neurons can be destroyed if the infant is dropped and/or shaken violently. The result can be death due to "shaken baby syndrome".[8]

The breathing rate increases with the concentration of carbon dioxide in the blood, which is detected by peripheral chemoreceptors in the aorta and carotid artery and central chemoreceptors in the medulla. Exercise also increases respiratory rate, due to the action of proprioceptors, the increase in body temperature, the release of epinephrine, and motor impulses originating from the brain.[9] In addition, it can increase due to increased inflation in the lungs, which is detected by stretch receptors.

Inhalation

Inhalation is initiated by the diaphragm and supported by the external intercostal muscles. Normal resting respirations are 10 to 18 breaths per minute, with a time period of 2 seconds. During vigorous inhalation (at rates exceeding 35 breaths per minute), or in approaching respiratory failure, accessory muscles of respiration are recruited for support. These consist of sternocleidomastoid, platysma, and the scalene muscles of the neck. Pectoral muscles and latissimus dorsi are also accessory muscles.

Under normal conditions, the diaphragm is the primary driver of inhalation. When the diaphragm contracts, the ribcage expands and the contents of the abdomen are moved downward. This results in a larger thoracic volume and negative pressure (with respect to atmospheric pressure) inside the thorax. As the pressure in the chest falls, air moves into the conducting zone. Here, the air is filtered, warmed, and humidified as it flows to the lungs.

During forced inhalation, as when taking a deep breath, the external intercostal muscles and accessory muscles aid in further expanding the thoracic cavity. During inhalation the diaphragm contracts.

Exhalation

Exhalation is generally a passive process; however, active or forced exhalation is achieved by the abdominal and the internal intercostal muscles. During this process air is forced or exhaled out.

The lungs have a natural elasticity: as they recoil from the stretch of inhalation, air flows back out until the pressures in the chest and the atmosphere reach equilibrium.[10]

During forced exhalation, as when blowing out a candle, expiratory muscles including the abdominal muscles and internal intercostal muscles, generate abdominal and thoracic pressure, which forces air out of the lungs.

Gas exchange

The major function of the respiratory system is gas exchange between the external environment and an organism's circulatory system. In humans and other mammals, this exchange facilitates oxygenation of the blood with a concomitant removal of carbon dioxide and other gaseous metabolic wastes from the circulation.[11] As gas exchange occurs, the acid-base balance of the body is maintained as part of homeostasis. If proper ventilation is not maintained, two opposing conditions could occur: respiratory acidosis, a life threatening condition, and respiratory alkalosis.

Upon inhalation, gas exchange occurs at the alveoli, the tiny sacs which are the basic functional component of the lungs. The alveolar walls are extremely thin (approx. 0.2 micrometres). These walls are composed of a single layer of epithelial cells (type I and type II epithelial cells) close to the pulmonary capillaries which are composed of a single layer of endothelial cells. The close proximity of these two cell types allows permeability to gases and, hence, gas exchange. This whole mechanism of gas exchange is carried by the simple phenomenon of pressure difference. When the air pressure is high inside the lungs, the air from lungs flow out. When the air pressure is low inside, then air flows into the lungs.

Immune functions

Airway epithelial cells can secrete a variety of molecules that aid in the defense of lungs. Secretory immunoglobulins (IgA), collectins (including Surfactant A and D), defensins and other peptides and proteases, reactive oxygen species, and reactive nitrogen species are all generated by airway epithelial cells. These secretions can act directly as antimicrobials to help keep the airway free of infection. Airway epithelial cells also secrete a variety of chemokines and cytokines that recruit the traditional immune cells and others to site of infections.

Most of the respiratory system is lined with mucous membranes that contain mucosal-associated lymphoid tissue, which produces white blood cells such as lymphocytes.

Metabolic and endocrine functions of the lungs

In addition to their functions in gas exchange, the lungs have a number of metabolic functions. They manufacture surfactant for local use, as noted above. They also contain a fibrinolytic system that lyses clots in the pulmonary vessels. They release a variety of substances that enter the systemic arterial blood and they remove other substances from the systemic venous blood that reach them via the pulmonary artery. Prostaglandins are removed from the circulation, but they are also synthesized in the lungs and released into the blood when lung tissue is stretched. The lungs also activate one hormone; the physiologically inactive decapeptide angiotensin I is converted to the pressor, aldosterone-stimulating octapeptide angiotensin II in the pulmonary circulation. The reaction occurs in other tissues as well, but it is particularly prominent in the lungs. Large amounts of the angiotensin-converting enzyme responsible for this activation are located on the surface of the endothelial cells of the pulmonary capillaries. The converting enzyme also inactivates bradykinin. Circulation time through the pulmonary capillaries is less than one second, yet 70% of the angiotensin I reaching the lungs is converted to angiotensin II in a single trip through the capillaries. Four other peptidases have been identified on the surface of the pulmonary endothelial cells.

Vocalization

The movement of gas through the larynx, pharynx and mouth allows humans to speak, or phonate. Vocalization, or singing, in birds occurs via the syrinx, an organ located at the base of the trachea. The vibration of air flowing across the larynx (vocal cords), in humans, and the syrinx, in birds, results in sound. Because of this, gas movement is extremely vital for communication purposes.

Temperature control

Panting in dogs,cats and some other animals provides a means of controlling body temperature. This physiological response is used as a cooling mechanism.

Coughing and sneezing

Irritation of nerves within the nasal passages or airways, can induce coughing and sneezing. These responses cause air to be expelled forcefully from the trachea or nose, respectively. In this manner, irritants caught in the mucus which lines the respiratory tract are expelled or moved to the mouth where they can be swallowed. During coughing, contraction of the smooth muscle narrows the trachea by pulling the ends of the cartilage plates together and by pushing soft tissue out into the lumen. This increases the expired airflow rate to dislodge and remove any irritant particle or mucus.

Development

Humans and mammals

Further information: Development of human lung

The respiratory system lies dormant in the human fetus during pregnancy. At birth, the respiratory system becomes fully functional upon exposure to air, although some lung development and growth continues throughout childhood.[12] Pre-term birth can lead to infants with under-developed lungs. These lungs show incomplete development of the alveolar type II cells, cells that produce surfactant. The lungs of pre-term infants may not function well because the lack of surfactant leads to increased surface tension within the alveoli. Thus, many alveoli collapse such that no gas exchange can occur within some or most regions of an infant's lungs, a condition termed respiratory distress syndrome. Basic scientific experiments, carried out using cells from chicken lungs, support the potential for using steroids as a means of furthering development of type II alveolar cells.[13] In fact, once a pre-mature birth is threatened, every effort is made to delay the birth, and a series of steroid shots is frequently administered to the mother during this delay in an effort to promote lung growth.[14]

Disease

Disorders of the respiratory system can be classified into four general areas:

Coughing is of major importance, as it is the body's main method to remove dust, mucus, saliva, and other debris from the lungs. Inability to cough can lead to infection. Deep breathing exercises may help keep finer structures of the lungs clear from particulate matter, etc.

The respiratory tract is constantly exposed to microbes due to the extensive surface area, which is why the respiratory system includes many mechanisms to defend itself and prevent pathogens from entering the body.

Disorders of the respiratory system are usually treated internally by a pulmonologist and Respiratory Therapist.

See also

References

  1. ↑ Haton, Anthea; Jean, Hopkins Susan, Johnson Charles William, McLaughlin Maryanna Quon Warner David, LaHart Wright, Jill (2010). Human Biology and Health, 108–118, Englewood Cliffs,: Prentice Hall.
  2. ↑ West, John B., Ravichandran (1993). Snorkel breathing in the elephant explains the unique anatomy of its pleura. Respiration Physiology 126 (1): 1–8.
  3. ↑ West, John B. (2002). Why doesn't the elephant have a pleural space?. News Physiol Sci 17: 47–50.
  4. ↑ Britannica On-line Encyclopedia
  5. ↑ Gottlieb, G, Jackson DC (1976). Importance of pulmonary ventilation in respiratory control in the bullfrog. Am J Physiol 230 (3): 608–13.
  6. ↑ Introduction to Insect Anatomy
  7. ↑ Lighton, JRB (January 1996). Discontinuous gas exchange in insects. Annu Rev Entomology 41: 309–324.
  8. ↑ *Fact sheet on Shaken Baby Syndrome
  9. ↑ Respiration. Harvey Project. URL accessed on 27 July 2012.
  10. ↑ A simple model of how the lungs are inflated can be built from a bell jar
  11. ↑ Respiratory Physiology.
  12. ↑ Michelle, Julia How Do Babies Breathe in the Womb?. URL accessed on 7 March 2011.
  13. ↑ Department of Environmental Biology, University of Adelaide, Adelaide, South Australia
  14. ↑ Pregnancy-facts.com

External links


Human organ systems
Cardiovascular system - Digestive system - Endocrine system - Immune system - Integumentary system - Lymphatic system - Muscular system - Nervous system - Skeletal system - Reproductive system - Respiratory system - Urinary system

Template:Nose anatomy Template:Parynx anatomy Template:Lower respiratory system anatomy Template:Thoracic cavity

v·d·e
Respiratory system, physiology: respiratory physiology
Volumes

lung volumes - vital capacity - functional residual capacity - respiratory minute volume - closing capacity - dead space - spirometry - body plethysmography - peak flow meter - thoracic independent volume - bronchial challenge test

Airways

ventilation (V) (positive pressure) - breath (inhalation, exhalation) -respiratory rate - respirometer - pulmonary surfactant - compliance - hysteresivity - airway resistance

Blood

pulmonary circulation - perfusion (Q) - hypoxic pulmonary vasoconstriction - pulmonary shunt

Interactions

ventilation/perfusion ratio (V/Q) and scan - zones of the lung - gas exchange - pulmonary gas pressures - alveolar gas equation - hemoglobin - oxygen-haemoglobin dissociation curve (2,3-DPG, Bohr effect, Haldane effect) - carbonic anhydrase (chloride shift) - oxyhemoglobin - respiratory quotient - arterial blood gas - diffusion capacity - Dlco

Control of respiration

pons (pneumotaxic center, apneustic center) - medulla (dorsal respiratory group, ventral respiratory group) - chemoreceptors (central, peripheral) - pulmonary stretch receptors - Hering-Breuer reflex

Insufficiency

high altitude - oxygen toxicity - hypoxia

v·d·e
Pathology of respiratory system (J, 460-519)
Acute upper respiratory infections

Upper respiratory tract infection · Common cold · Rhinitis · Sinusitis · Pharyngitis (Strep throat)  · Tonsillitis · Laryngitis · Tracheitis · Croup · Epiglottitis

Influenza and Pneumonia

Influenza · Pneumonia (Viral, Bacterial, Bronchopneumonia) · Severe acute respiratory syndrome

Other acute lower respiratory infections

Bronchitis (Acute, Chronic)  · Bronchiolitis

Other diseases of upper respiratory tract

Vasomotor rhinitis · Hay fever · Atrophic rhinitis · Nasal polyp · Deviated septum · Adenoid hypertrophy · Peritonsillar abscess · Vocal fold nodule · Laryngospasm

Chronic lower respiratory diseases

Emphysema · COPD · Asthma · Status asthmaticus · Bronchiectasis

Lung diseases due to external agents

Pneumoconiosis (Coalworker's pneumoconiosis, Asbestosis, Silicosis, Bauxite fibrosis, Berylliosis, Siderosis) · Byssinosis · Hypersensitivity pneumonitis (Farmer's lung, Bird fancier's lung)

Other, principally affecting
the interstitium

Acute respiratory distress syndrome · Pulmonary edema · Hamman-Rich syndrome · Interstitial lung disease

Suppurative and necrotic conditions
of lower respiratory tract

Lung abscess · Pleural effusion · Empyema

Other

Pneumothorax · Hemothorax · Hemopneumothorax · Mendelson's syndrome · Respiratory failure · Atelectasis · Mediastinal emphysema  · Mediastinitis

see also congenital (Q30-Q34, 748)

Template:Development of respiratory system

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