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| {{See also|Respiratory tract}} | |||
| {{Infobox Anatomy | |||
| |Name = Respiratory system | |||
| |Latin = systema respiratorium | |||
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| |Image = Respiratory system complete en.svg | |||
| |Caption = A complete, schematic view of the human respiratory system with their parts and functions. | | |||
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| |Precursor = | |||
| |System = | |||
| |Artery = | |||
| |Vein = | |||
| |Nerve = | |||
| |Lymph = | |||
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| }} | |||
| The '''respiratory system''' (or '''ventilatory system''') is the ] that introduces respiratory gases to the interior and performs ]. In humans and other ]s, the anatomical features of the respiratory system include airways, ]s, and the respiratory muscles. ]s of ] and ] are passively exchanged, by ], between the gaseous external environment and the ]. This exchange process occurs in the alveolar region of the lungs.<ref>{{cite book|last=Maton|first=Anthea|coauthors=Jean, Hopkins Susan, Johnson Charles William, McLaughlin Maryanna Quon Warner David, LaHart Wright, Jill|title=Human Biology and Health|publisher=Prentice Hall|year=2010 |location=Englewood Cliffs|pages= 108–118|isbn=0134234359}}</ref> Other animals, such as ], have respiratory systems with very simple anatomical features, and in ] even the ] plays a vital role in ]. ] also have respiratory systems but the directionality of gas exchange can be opposite to that in animals. The respiratory system in plants also includes anatomical features such as holes on the undersides of ] known as ].<ref>{{cite book|last=West|first=John B.|title=Respiratory physiology-- the essentials|publisher=Williams & Wilkins|location=Baltimore|pages=1–10|isbn=0-683-08937-4}}</ref> | |||
| ==Comparative anatomy and physiology== | |||
| ===Horses=== | |||
| Horses are ] 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 ] is the only animal known to have no ]. Rather, the ] and ] are both composed of dense ] and joined to each other via loose connective tissue.<ref>{{cite journal|last=West|first=John B.|coauthors=Ravichandran|title=Snorkel breathing in the elephant explains the unique anatomy of its pleura|journal=Respiration Physiology|volume=126|issue=1|pages=1–8|year=1993|pmid=11311306|doi=10.1016/S0034-5687(01)00203-1}}</ref> This lack of a pleural space, along with an unusually thick ], are thought to be ] allowing the elephant to remain underwater for long periods of time while breathing through its ] which emerges as a snorkel.<ref>{{cite journal | |||
| | last = West | |||
| | first = John B. | |||
| | title = Why doesn't the elephant have a pleural space? | |||
| | journal = News Physiol Sci | |||
| | volume = 17 | |||
| | pages = 47–50 | |||
| | year = 2002 | |||
| | accessdate = | |||
| | pmid = 11909991 }}</ref> | |||
| ===Birds=== | |||
| {{main section|Bird anatomy|Respiratory system}} | |||
| The respiratory system of birds differs significantly from that found in mammals, containing unique anatomical features such as ]. The lungs of birds also do not have the capacity to inflate as birds lack a ] and a ]. Gas exchange in birds occurs between air capillaries and ], rather than in ]. | |||
| ===Reptiles=== | |||
| ] while breathing.]] | |||
| The ] of the ] is less complex in ] than in ], with reptiles lacking the very extensive airway tree structure found in mammalian lungs. ] in reptiles still occurs in ] however, reptiles do not possess a ]. Thus, breathing occurs via a change in the volume of the body cavity which is controlled by contraction of ] in all reptiles except ]. In turtles, contraction of specific pairs of flank muscles governs ] or ].<ref></ref> | |||
| ===Amphibians=== | |||
| Both the lungs and the ] serve as respiratory organs in ]. The skin of these animals is highly vascularized and moist, with moisture maintained via secretion of ] 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 | |||
| | last = Gottlieb | |||
| | first = G | |||
| | coauthors = Jackson DC | |||
| | title = Importance of pulmonary ventilation in respiratory control in the bullfrog | |||
| | journal = Am J Physiol | |||
| | volume = 230 | |||
| | pages = 608–13 | |||
| | year = 1976 | |||
| | accessdate = | |||
| | pmid = 4976 | |||
| | issue = 3 }}</ref> | |||
| ===Fish=== | |||
| In most fish, respiration takes place through ]. (See also ].) ], however, do possess one or two lungs. The ] have developed a special organ that allows them to take advantage of the oxygen of the air. | |||
| ==Anatomy in invertebrates== | |||
| ===Insects=== | |||
| {{Main|Respiratory system of insects}} | |||
| Most insects breath passively through their 'Spiracles' (special openings in the ]) and the air reaches the body by means of a series of smaller and smaller pipes called 'trachaea' when their diameter is relatively large and 'tracheoles' when their diameter is very small. Diffusion of gases is effective over small distances but not over larger ones, this is one of the reasons insects are all relatively small. Insects which do not have spiracles and trachaea, such as some Collembola, breathe directly through their skins, also by diffusion of gases.<ref></ref> | |||
| The number of spiracles an insect has is variable between species, however they always come in pairs, one on each side of the body, and usually one per segment. Some of the Diplura have eleven, with four pairs on the thorax, but in most of the ancient forms of insects, such as Dragonflies and Grasshoppers there are two thoracic and eight abdominal spiracles. However in most of the remaining insects there are less. | |||
| 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 ] of the surrounding ]s. During exercise, the water level retracts due to the increase in concentration of ] in the ]s. This lowers the ] and the water is drawn back into the cells via ] and air is brought closer to the muscle cells. The ] is then reduced and gases can be transferred more easily. | |||
| Insects were once believed to exchange gases with the environment continuously by the ] 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 ] of the ] 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 ] cycles (DGC).<ref>{{cite journal | |||
| | last = Lighton | |||
| | first = JRB | |||
| | title = Discontinuous gas exchange in insects | |||
| | journal = Annu Rev Entomology | |||
| | volume = 41 | |||
| | pages = 309–324 | |||
| | date = January 1996 | |||
| | accessdate = }}</ref> | |||
| ===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 ] as its oxygen-capturing molecule. Hence, this respiratory system is similar to that of vertebrate fish. The ] can include either gills or a lung. | |||
| ==Physiology in mammals== | |||
| {{See also|Respiratory physiology|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: | |||
| {| class="wikitable" | |||
| |- | |||
| ! Measurement !! Equation !! Description | |||
| |- | |||
| | Minute ventilation || tidal volume * respiratory rate|| the total volume of gas entering the lungs per minute. | |||
| |- | |||
| | Alveolar ventilation || (tidal volume - dead space) * respiratory rate || 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 || 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 ] from parts of the ], the ] and the ]. This area of the brain forms the respiration regulatory center, a series of interconnected ]s within the lower and middle brain stem which coordinate respiratory movements. The sections are the ], the ], and the ] and ]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 "]".<ref>*</ref> | |||
| The breathing rate increases with the concentration of carbon dioxide in the blood, which is detected by peripheral ]s in the ] and ] and central chemoreceptors in the medulla. Exercise also increases respiratory rate, due to the action of ], the increase in body temperature, the release of ], 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. | |||
| ====Inhalation==== | |||
| ] is initiated by the ] and supported by the ]. 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, ] are recruited for support. These consist of ], ], and the ] of the neck. ] and ] are also accessory muscles. | |||
| Under normal conditions, the diaphragm is the primary driver of inhalation. When the diaphragm contracts, the ]cage expands and the contents of the abdomen are moved downward. This results in a larger ] 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 ] and accessory muscles aid in further expanding the ]. | |||
| During inhalation the diaphragm contracts. | |||
| ====Exhalation==== | |||
| ] is generally a passive process; however, active or ''forced'' exhalation is achieved by the ] and the ]. 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 ] can be built from a ]</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=== | |||
| The major function of the respiratory system is ] between the external environment and an organism's ]. In humans and other mammals, this exchange facilitates ] of the blood with a concomitant removal of carbon dioxide and other gaseous ]s from the ].<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 ]. If proper ventilation is not maintained, two opposing conditions could occur: ], a life threatening condition, and ]. | |||
| Upon inhalation, gas exchange occurs at the ], 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 ] (type I and type II epithelial cells) close to the ] which are composed of a single layer of ]. 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 ], which produces ]s such as ]s. | |||
| ===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 ], ] and ] allows humans to ], or '']''. Vocalization, or singing, in birds occurs via the ], an organ located at the base of the trachea. The vibration of air flowing across the larynx (]), in humans, and the syrinx, in birds, results in sound. Because of this, gas movement is extremely vital for ] purposes. | |||
| ====Temperature control==== | |||
| ] 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 ] or ], can induce ] and ]. These responses cause air to be expelled forcefully from the ] or ], respectively. In this manner, irritants caught in the ] which lines the respiratory tract are expelled or moved to the ] where they can be ]. 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 ] during ]. 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> ] can lead to infants with under-developed lungs. These lungs show incomplete development of the ], cells that produce ]. 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 ]. Basic scientific experiments, carried out using cells from chicken lungs, support the potential for using ] as a means of furthering development of type II alveolar cells.<ref></ref> In fact, once a pre-mature birth is threatened, every effort is made to delay the birth, and a series of ] shots is frequently administered to the mother during this delay in an effort to promote lung growth.<ref></ref> | |||
| ==Disease== | |||
| ] can be classified into four general areas: | |||
| * Obstructive conditions (e.g., ], ], ]) | |||
| * Restrictive conditions (e.g., ], ], alveolar damage, ]) | |||
| * Vascular diseases (e.g., ], ], ]) | |||
| * Infectious, environmental and other "diseases" (e.g., ], ], ], ]): | |||
| ]ing is of major importance, as it is the body's main method to remove dust, ], ], and other debris from the lungs. Inability to cough can lead to ]. Deep breathing exercises may help keep finer structures of the lungs clear from particulate matter, etc. | |||
| The respiratory tract is constantly exposed to ]s due to the extensive surface area, which is why the respiratory system includes many mechanisms to defend itself and prevent ]s from entering the body. | |||
| Disorders of the respiratory system are usually treated internally by a ] and ]. | |||
| ==Plants== | |||
| ]s use ] gas in the process of ], and exhale ] gas as waste. The chemical equation of photosynthesis is 6 CO<sub>2</sub> (carbon dioxide) and 6 H<sub>2</sub>O (water) and that makes 6 O<sub>2</sub> (oxygen) and C<sub>6</sub>H<sub>12</sub>O<sub>6</sub> (glucose). What is not expressed in the chemical equation is the capture of energy from sunlight which occurs. Photosynthesis uses electrons on the carbon atoms as the repository for that energy. Respiration is the opposite of photosynthesis. It reclaims the energy to power chemical reactions in cells. In so doing the carbon atoms and their electrons are combined with oxygen forming a gas which is easily removed from both the cells and the organism. Plants use both processes, photosynthesis to capture the energy and respiration to use it. | |||
| Plant respiration is limited by the process of ]. Plants take in carbon dioxide through holes on the undersides of their ] known as ] or pores. However, most plants require little air.{{Citation needed|date=February 2007}} Most plants have relatively few living cells outside of their surface because air (which is required for metabolic content) can penetrate only skin deep. However, most plants are not involved in highly ] activities, and thus have no need of these living cells. | |||
| ==References== | |||
| {{reflist}} | |||
| ==External links== | |||
| * | |||
| * | |||
| * A simple guide for high school students | |||
| * University level (Microsoft Word document) | |||
| * by noted respiratory physiologist ] (also at ) | |||
| {{Organ systems}} | |||
| {{Nose anatomy}} | |||
| {{Lower respiratory system anatomy}} | |||
| {{Thoracic cavity}} | |||
| {{Respiratory physiology}} | |||
| {{Respiratory pathology}} | |||
| {{Development of respiratory system}} | |||
| {{DEFAULTSORT:Respiratory System}} | |||
| ] | |||
Revision as of 12:14, 11 April 2013
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