Oxygen Bar<\/h1>\r\n<\/div>\r\nBelly up to the bar and get your favorite... oxygen? That\u2019s right \u2014 in some cities, you can get a shot of pure oxygen, with or without your choice of added flavors. Bar patrons inhale oxygen through a plastic tube inserted into their nostrils, paying up to a dollar per minute to inhale the pure gas. Proponents of the practice claim that breathing in extra oxygen will remove toxins from the body, strengthen the immune system, enhance concentration and alertness, increase energy, and even cure cancer!\u00a0These claims, however, have not been substantiated by controlled scientific studies. Normally, blood leaving the lungs is almost completely saturated with oxygen, even without the use of extra oxygen, so it\u2019s unlikely that a higher concentration of oxygen in air inside the lungs would lead to significantly greater oxygenation of the blood. Oxygen enters the blood in the lungs as part of the process of gas exchange.\r\n\r\nWhat is Gas Exchange?<\/h1>\r\n<\/div>\r\n[pb_glossary id=\"4288\"]Gas exchange[\/pb_glossary]<\/strong>\u00a0is the biological process through which gases are transferred across cell membranes to either enter or leave the blood. Oxygen is constantly needed by cells for aerobic cellular respiration, and the same process continually produces carbon dioxide as a waste product. Gas exchange takes place between the blood and cells throughout the body, with oxygen leaving the blood and entering the cells, and carbon dioxide leaving the cells and entering the blood. Gas exchange also takes place between the blood and the air in the lungs, with oxygen entering the blood from the inhaled air inside the lungs, and carbon dioxide leaving the blood and entering the air to be exhaled from the lungs.\r\n\r\nGas Exchange in the Lungs<\/h1>\r\n<\/div>\r\nAlveoli are the basic functional units of the lungs where gas exchange takes place between the air and the blood.[pb_glossary id=\"4311\"]\u00a0Alveoli (singular, alveolus)<\/strong>[\/pb_glossary] are tiny air sacs that consist of connective and epithelial tissues. The connective tissue includes elastic fibres that allow alveoli to stretch and expand as they fill with air during inhalation. During exhalation, the fibres allow the alveoli to spring back and expel the air. Special cells in the walls of the alveoli secrete a film of fatty substances called [pb_glossary id=\"4339\"]surfactant<\/strong>[\/pb_glossary]. This substance prevents the alveolar walls from collapsing and sticking together when air is expelled. Other cells in alveoli include [pb_glossary id=\"4340\"]macrophages<\/span>[\/pb_glossary]<\/span>, which are mobile scavengers that engulf and destroy foreign particles that manage to reach the lungs in inhaled air.<\/span>\r\n\r\nAs shown in Figure 13.4.2, alveoli are arranged in groups like clusters of grapes. Each alveolus is covered with epithelium that is just one cell thick. It is surrounded by a bed of [pb_glossary id=\"4341\"]pulmonary[\/pb_glossary] capillaries, each of which has a wall of epithelium just one cell thick. As a result, gases must cross through only two cells to pass between an alveolus and its surrounding capillaries.\r\n\r\n[caption id=\"attachment_4343\" align=\"aligncenter\" width=\"519\"]![\"13.4.2](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Alveolus_diagram.svg_-2.png\")
Figure 13.4.2 Clusters of alveolar sacs make up most of the functional tissue of the lungs. Note that in this and subsequent illustrations, arteries, which carry oxygenated blood, are colored red; and veins, which carry deoxygenated blood, are colored blue.<\/em>[\/caption]\r\n\r\nThe pulmonary artery (also shown in Figure 13.4.2) carries deoxygenated blood from the heart to the lungs. Then, the blood travels through the pulmonary capillary beds, where it picks up oxygen and releases carbon dioxide. The oxygenated blood then leaves the lungs and travels back to the heart through pulmonary veins. There are four pulmonary veins (two for each lung), and all four carry oxygenated blood to the heart. From the heart, the oxygenated blood is then pumped to cells throughout the body.\r\n\r\nMechanism of Gas Exchange<\/h1>\r\n<\/div>\r\nGas exchange occurs by [pb_glossary id=\"1655\"]diffusion[\/pb_glossary] across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a [pb_glossary id=\"5705\"]passive[\/pb_glossary] process that requires no energy. To diffuse across cell membranes, gases must first be dissolved in a liquid. Oxygen and carbon dioxide are transported around the body dissolved in blood. Both gases bind to the protein hemoglobin in red blood cells, although oxygen does so more effectively than carbon dioxide. Some carbon dioxide also dissolves in blood plasma.\r\n\r\nAs shown in Figure 13.4.3, oxygen in inhaled air diffuses into a pulmonary capillary from the alveolus. Carbon dioxide in the blood diffuses in the opposite direction. The carbon dioxide can then be exhaled from the body.\r\n\r\n[caption id=\"attachment_4344\" align=\"aligncenter\" width=\"695\"]![\"13.4.3](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Gas_exchange_in_the_aveolus.svg_-2.png\")
Figure 13.4.3 A single alveolus is a tiny structure that is specialized for gas exchange between inhaled air and the blood in pulmonary capillaries.<\/em>[\/caption]\r\n\r\nGas exchange by diffusion depends on having a large surface area through which gases can pass. Although each alveolus is tiny, there are hundreds of millions of them in the lungs of a healthy adult, so the total surface area for gas exchange is huge. It is estimated that this surface area may be as great as 100 m2<\/sup> (or approximately 1,076 ft\u00b2). Often we think of lungs as balloons, but this type of structure would have very limited surface area and there wouldn't be enough space for blood to interface with the air in the alveoli.\u00a0 The structure alveoli take in the lungs is more like a giant mass of soap bubbles \u2014\u00a0 millions of tiny little chambers making up one large mass \u2014 this is what increases surface area giving blood lots of space to come into close enough contact to exchange gases by diffusion.\r\n\r\nGas exchange by diffusion also depends on maintaining a steep concentration gradient for oxygen and carbon dioxide. Continuous blood flow in the capillaries and constant breathing maintain this gradient.\r\n\r\n \t- Each time you inhale, there is a greater concentration of oxygen in the air in the alveoli than there is in the blood in the pulmonary capillaries. As a result, oxygen diffuses from the air inside the alveoli into the blood in the capillaries. Carbon dioxide, in contrast, is more concentrated in the blood in the pulmonary capillaries than it is in the air inside the alveoli.\u00a0As a result, carbon dioxide diffuses in the opposite direction.<\/li>\r\n \t
- The cells of the body have a much lower concentration of oxygen than does the oxygenated blood that reaches them in peripheral capillaries, which are the capillaries that supply tissues throughout the body. As a result, oxygen diffuses from the peripheral capillaries into body cells. The opposite is true of carbon dioxide. It has a much higher concentration in body cells than it does in the blood of the peripheral capillaries. Thus, carbon dioxide diffuses from body cells into the peripheral capillaries.<\/li>\r\n<\/ul>\r\n\r\n
\r\n13.4 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [pb_glossary id=\"4288\"]Gas exchange[\/pb_glossary] is the biological process through which gases are transferred across cell membranes to either enter or leave the blood. Gas exchange takes place continuously between the blood and cells throughout the body, and also between the blood and the air inside the lungs.<\/li>\r\n \t
- Gas exchange in the lungs takes place in [pb_glossary id=\"4311\"]alveoli[\/pb_glossary], which are tiny air sacs surrounded by networks of [pb_glossary id=\"5923\"]capillaries[\/pb_glossary]. The pulmonary artery carries deoxygenated blood from the heart to the lungs, where it travels through pulmonary capillaries, picking up oxygen and releasing carbon dioxide. The oxygenated blood then leaves the lungs through pulmonary veins.<\/li>\r\n \t
- Gas exchange occurs by diffusion across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a passive process that requires no energy.<\/li>\r\n \t
- Gas exchange by diffusion depends on the large surface area provided by the hundreds of millions of alveoli in the lungs. It also depends on a steep concentration gradient for oxygen and carbon dioxide. This gradient is maintained by continuous blood flow and constant breathing.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n13.4 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- What is gas exchange?<\/li>\r\n \t
- Summarize the flow of blood into and out of the lungs for gas exchange.<\/li>\r\n \t
- [h5p id=\"609\"]<\/li>\r\n \t
- Describe the mechanism by which gas exchange takes place.<\/li>\r\n \t
- Identify the two main factors upon which gas exchange by diffusion depends.<\/li>\r\n \t
- If the concentration of oxygen were higher inside of a cell than outside of it, which way would the oxygen flow? Explain your answer.<\/li>\r\n \t
- Why is it important that the walls of the alveoli are only one cell thick?<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n13.4 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=nRpwdwm06Ic&feature=emb_logo\r\nOxygen movement from alveoli to capillaries | NCLEX-RN | Khan Academy, khanacademymedicine, 2013.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=KmgIqVwytwA&feature=emb_logo\r\n
About Carbon Monoxide and Carbon Monoxide Poisoning, EMDPrepare, 2009.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=GVU_zANtroE\r\n
Oxygen\u2019s surprisingly complex journey through your body - Enda Butler, TED-Ed, 2017.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 13.4.1<\/strong>\r\n\r\nOxygen Bar<\/a> by\u00a0Farrukh<\/a> on Flickr<\/a> is used under a CC BY-NC 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/2.0\/) license.\r\n\r\nFigure 13.4.2<\/strong>\r\n\r\nAlveolus_diagram.svg<\/a>\u00a0by Mariana Ruiz Villarreal [LadyofHats<\/a>] on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 13.4.3<\/strong>\r\n\r\nGas_exchange_in_the_aveolus.svg<\/a> by domdomegg<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\nReferences<\/h2>\r\n
EMDPrepare. (2009, December 21). About carbon monoxide and carbon monoxide poisoning. YouTube. https:\/\/www.youtube.com\/watch?v=KmgIqVwytwA&feature=youtu.be<\/p>\r\n
khanacademymedicine. (2013, February 25). Oxygen movement from alveoli to capillaries | NCLEX-RN | Khan Academy. YouTube. https:\/\/www.youtube.com\/watch?v=nRpwdwm06Ic&feature=youtu.be<\/p>\r\n
TED-Ed. (2017, April 13). Oxygen\u2019s surprisingly complex journey through your body - Enda Butler. YouTube. https:\/\/www.youtube.com\/watch?v=GVU_zANtroE&feature=youtu.be<\/p>","rendered":"
<\/p>\n![\"13.4.1](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/Oxygen-Bar-by-Farrukh-on-flickr-2.jpg\")
Figure 13.4.1 Would you pay for air?<\/em><\/figcaption><\/figure>\n\nOxygen Bar<\/h1>\n<\/div>\n
Belly up to the bar and get your favorite… oxygen? That\u2019s right \u2014 in some cities, you can get a shot of pure oxygen, with or without your choice of added flavors. Bar patrons inhale oxygen through a plastic tube inserted into their nostrils, paying up to a dollar per minute to inhale the pure gas. Proponents of the practice claim that breathing in extra oxygen will remove toxins from the body, strengthen the immune system, enhance concentration and alertness, increase energy, and even cure cancer!\u00a0These claims, however, have not been substantiated by controlled scientific studies. Normally, blood leaving the lungs is almost completely saturated with oxygen, even without the use of extra oxygen, so it\u2019s unlikely that a higher concentration of oxygen in air inside the lungs would lead to significantly greater oxygenation of the blood. Oxygen enters the blood in the lungs as part of the process of gas exchange.<\/p>\n
\nWhat is Gas Exchange?<\/h1>\n<\/div>\n
Gas exchange<\/a><\/strong>\u00a0is the biological process through which gases are transferred across cell membranes to either enter or leave the blood. Oxygen is constantly needed by cells for aerobic cellular respiration, and the same process continually produces carbon dioxide as a waste product. Gas exchange takes place between the blood and cells throughout the body, with oxygen leaving the blood and entering the cells, and carbon dioxide leaving the cells and entering the blood. Gas exchange also takes place between the blood and the air in the lungs, with oxygen entering the blood from the inhaled air inside the lungs, and carbon dioxide leaving the blood and entering the air to be exhaled from the lungs.<\/p>\n\nGas Exchange in the Lungs<\/h1>\n<\/div>\n
Alveoli are the basic functional units of the lungs where gas exchange takes place between the air and the blood.\u00a0Alveoli (singular, alveolus)<\/strong><\/a> are tiny air sacs that consist of connective and epithelial tissues. The connective tissue includes elastic fibres that allow alveoli to stretch and expand as they fill with air during inhalation. During exhalation, the fibres allow the alveoli to spring back and expel the air. Special cells in the walls of the alveoli secrete a film of fatty substances called surfactant<\/strong><\/a>. This substance prevents the alveolar walls from collapsing and sticking together when air is expelled. Other cells in alveoli include macrophages<\/span><\/a><\/span>, which are mobile scavengers that engulf and destroy foreign particles that manage to reach the lungs in inhaled air.<\/span><\/p>\nAs shown in Figure 13.4.2, alveoli are arranged in groups like clusters of grapes. Each alveolus is covered with epithelium that is just one cell thick. It is surrounded by a bed of pulmonary<\/a> capillaries, each of which has a wall of epithelium just one cell thick. As a result, gases must cross through only two cells to pass between an alveolus and its surrounding capillaries.<\/p>\nFigure 13.4.2 Clusters of alveolar sacs make up most of the functional tissue of the lungs. Note that in this and subsequent illustrations, arteries, which carry oxygenated blood, are colored red; and veins, which carry deoxygenated blood, are colored blue.<\/em><\/figcaption><\/figure>\nThe pulmonary artery (also shown in Figure 13.4.2) carries deoxygenated blood from the heart to the lungs. Then, the blood travels through the pulmonary capillary beds, where it picks up oxygen and releases carbon dioxide. The oxygenated blood then leaves the lungs and travels back to the heart through pulmonary veins. There are four pulmonary veins (two for each lung), and all four carry oxygenated blood to the heart. From the heart, the oxygenated blood is then pumped to cells throughout the body.<\/p>\n
\nMechanism of Gas Exchange<\/h1>\n<\/div>\n
Gas exchange occurs by diffusion<\/a> across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a passive<\/a> process that requires no energy. To diffuse across cell membranes, gases must first be dissolved in a liquid. Oxygen and carbon dioxide are transported around the body dissolved in blood. Both gases bind to the protein hemoglobin in red blood cells, although oxygen does so more effectively than carbon dioxide. Some carbon dioxide also dissolves in blood plasma.<\/p>\nAs shown in Figure 13.4.3, oxygen in inhaled air diffuses into a pulmonary capillary from the alveolus. Carbon dioxide in the blood diffuses in the opposite direction. The carbon dioxide can then be exhaled from the body.<\/p>\nFigure 13.4.3 A single alveolus is a tiny structure that is specialized for gas exchange between inhaled air and the blood in pulmonary capillaries.<\/em><\/figcaption><\/figure>\nGas exchange by diffusion depends on having a large surface area through which gases can pass. Although each alveolus is tiny, there are hundreds of millions of them in the lungs of a healthy adult, so the total surface area for gas exchange is huge. It is estimated that this surface area may be as great as 100 m2<\/sup> (or approximately 1,076 ft\u00b2). Often we think of lungs as balloons, but this type of structure would have very limited surface area and there wouldn’t be enough space for blood to interface with the air in the alveoli.\u00a0 The structure alveoli take in the lungs is more like a giant mass of soap bubbles \u2014\u00a0 millions of tiny little chambers making up one large mass \u2014 this is what increases surface area giving blood lots of space to come into close enough contact to exchange gases by diffusion.<\/p>\nGas exchange by diffusion also depends on maintaining a steep concentration gradient for oxygen and carbon dioxide. Continuous blood flow in the capillaries and constant breathing maintain this gradient.<\/p>\n
\n- Each time you inhale, there is a greater concentration of oxygen in the air in the alveoli than there is in the blood in the pulmonary capillaries. As a result, oxygen diffuses from the air inside the alveoli into the blood in the capillaries. Carbon dioxide, in contrast, is more concentrated in the blood in the pulmonary capillaries than it is in the air inside the alveoli.\u00a0As a result, carbon dioxide diffuses in the opposite direction.<\/li>\n
- The cells of the body have a much lower concentration of oxygen than does the oxygenated blood that reaches them in peripheral capillaries, which are the capillaries that supply tissues throughout the body. As a result, oxygen diffuses from the peripheral capillaries into body cells. The opposite is true of carbon dioxide. It has a much higher concentration in body cells than it does in the blood of the peripheral capillaries. Thus, carbon dioxide diffuses from body cells into the peripheral capillaries.<\/li>\n<\/ul>\n\n\n
\n13.4 Summary<\/span><\/h1>\n<\/header>\n\n\n- Gas exchange<\/a> is the biological process through which gases are transferred across cell membranes to either enter or leave the blood. Gas exchange takes place continuously between the blood and cells throughout the body, and also between the blood and the air inside the lungs.<\/li>\n
- Gas exchange in the lungs takes place in alveoli<\/a>, which are tiny air sacs surrounded by networks of capillaries<\/a>. The pulmonary artery carries deoxygenated blood from the heart to the lungs, where it travels through pulmonary capillaries, picking up oxygen and releasing carbon dioxide. The oxygenated blood then leaves the lungs through pulmonary veins.<\/li>\n
- Gas exchange occurs by diffusion across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a passive process that requires no energy.<\/li>\n
- Gas exchange by diffusion depends on the large surface area provided by the hundreds of millions of alveoli in the lungs. It also depends on a steep concentration gradient for oxygen and carbon dioxide. This gradient is maintained by continuous blood flow and constant breathing.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n\n
\n13.4 Review Questions<\/span><\/h1>\n<\/header>\n\n\n- What is gas exchange?<\/li>\n
- Summarize the flow of blood into and out of the lungs for gas exchange.<\/li>\n
- \n\n
What is Gas Exchange?<\/h1>\r\n<\/div>\r\n[pb_glossary id=\"4288\"]Gas exchange[\/pb_glossary]<\/strong>\u00a0is the biological process through which gases are transferred across cell membranes to either enter or leave the blood. Oxygen is constantly needed by cells for aerobic cellular respiration, and the same process continually produces carbon dioxide as a waste product. Gas exchange takes place between the blood and cells throughout the body, with oxygen leaving the blood and entering the cells, and carbon dioxide leaving the cells and entering the blood. Gas exchange also takes place between the blood and the air in the lungs, with oxygen entering the blood from the inhaled air inside the lungs, and carbon dioxide leaving the blood and entering the air to be exhaled from the lungs.\r\n\r\nGas Exchange in the Lungs<\/h1>\r\n<\/div>\r\nAlveoli are the basic functional units of the lungs where gas exchange takes place between the air and the blood.[pb_glossary id=\"4311\"]\u00a0Alveoli (singular, alveolus)<\/strong>[\/pb_glossary] are tiny air sacs that consist of connective and epithelial tissues. The connective tissue includes elastic fibres that allow alveoli to stretch and expand as they fill with air during inhalation. During exhalation, the fibres allow the alveoli to spring back and expel the air. Special cells in the walls of the alveoli secrete a film of fatty substances called [pb_glossary id=\"4339\"]surfactant<\/strong>[\/pb_glossary]. This substance prevents the alveolar walls from collapsing and sticking together when air is expelled. Other cells in alveoli include [pb_glossary id=\"4340\"]macrophages<\/span>[\/pb_glossary]<\/span>, which are mobile scavengers that engulf and destroy foreign particles that manage to reach the lungs in inhaled air.<\/span>\r\n\r\nAs shown in Figure 13.4.2, alveoli are arranged in groups like clusters of grapes. Each alveolus is covered with epithelium that is just one cell thick. It is surrounded by a bed of [pb_glossary id=\"4341\"]pulmonary[\/pb_glossary] capillaries, each of which has a wall of epithelium just one cell thick. As a result, gases must cross through only two cells to pass between an alveolus and its surrounding capillaries.\r\n\r\n[caption id=\"attachment_4343\" align=\"aligncenter\" width=\"519\"] Figure 13.4.2 Clusters of alveolar sacs make up most of the functional tissue of the lungs. Note that in this and subsequent illustrations, arteries, which carry oxygenated blood, are colored red; and veins, which carry deoxygenated blood, are colored blue.<\/em>[\/caption]\r\n\r\nThe pulmonary artery (also shown in Figure 13.4.2) carries deoxygenated blood from the heart to the lungs. Then, the blood travels through the pulmonary capillary beds, where it picks up oxygen and releases carbon dioxide. The oxygenated blood then leaves the lungs and travels back to the heart through pulmonary veins. There are four pulmonary veins (two for each lung), and all four carry oxygenated blood to the heart. From the heart, the oxygenated blood is then pumped to cells throughout the body.\r\n\r\nMechanism of Gas Exchange<\/h1>\r\n<\/div>\r\nGas exchange occurs by [pb_glossary id=\"1655\"]diffusion[\/pb_glossary] across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a [pb_glossary id=\"5705\"]passive[\/pb_glossary] process that requires no energy. To diffuse across cell membranes, gases must first be dissolved in a liquid. Oxygen and carbon dioxide are transported around the body dissolved in blood. Both gases bind to the protein hemoglobin in red blood cells, although oxygen does so more effectively than carbon dioxide. Some carbon dioxide also dissolves in blood plasma.\r\n\r\nAs shown in Figure 13.4.3, oxygen in inhaled air diffuses into a pulmonary capillary from the alveolus. Carbon dioxide in the blood diffuses in the opposite direction. The carbon dioxide can then be exhaled from the body.\r\n\r\n[caption id=\"attachment_4344\" align=\"aligncenter\" width=\"695\"] Figure 13.4.3 A single alveolus is a tiny structure that is specialized for gas exchange between inhaled air and the blood in pulmonary capillaries.<\/em>[\/caption]\r\n\r\nGas exchange by diffusion depends on having a large surface area through which gases can pass. Although each alveolus is tiny, there are hundreds of millions of them in the lungs of a healthy adult, so the total surface area for gas exchange is huge. It is estimated that this surface area may be as great as 100 m2<\/sup> (or approximately 1,076 ft\u00b2). Often we think of lungs as balloons, but this type of structure would have very limited surface area and there wouldn't be enough space for blood to interface with the air in the alveoli.\u00a0 The structure alveoli take in the lungs is more like a giant mass of soap bubbles \u2014\u00a0 millions of tiny little chambers making up one large mass \u2014 this is what increases surface area giving blood lots of space to come into close enough contact to exchange gases by diffusion.\r\n\r\nGas exchange by diffusion also depends on maintaining a steep concentration gradient for oxygen and carbon dioxide. Continuous blood flow in the capillaries and constant breathing maintain this gradient.\r\n\r\n \t- Each time you inhale, there is a greater concentration of oxygen in the air in the alveoli than there is in the blood in the pulmonary capillaries. As a result, oxygen diffuses from the air inside the alveoli into the blood in the capillaries. Carbon dioxide, in contrast, is more concentrated in the blood in the pulmonary capillaries than it is in the air inside the alveoli.\u00a0As a result, carbon dioxide diffuses in the opposite direction.<\/li>\r\n \t
- The cells of the body have a much lower concentration of oxygen than does the oxygenated blood that reaches them in peripheral capillaries, which are the capillaries that supply tissues throughout the body. As a result, oxygen diffuses from the peripheral capillaries into body cells. The opposite is true of carbon dioxide. It has a much higher concentration in body cells than it does in the blood of the peripheral capillaries. Thus, carbon dioxide diffuses from body cells into the peripheral capillaries.<\/li>\r\n<\/ul>\r\n\r\n
\r\n13.4 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [pb_glossary id=\"4288\"]Gas exchange[\/pb_glossary] is the biological process through which gases are transferred across cell membranes to either enter or leave the blood. Gas exchange takes place continuously between the blood and cells throughout the body, and also between the blood and the air inside the lungs.<\/li>\r\n \t
- Gas exchange in the lungs takes place in [pb_glossary id=\"4311\"]alveoli[\/pb_glossary], which are tiny air sacs surrounded by networks of [pb_glossary id=\"5923\"]capillaries[\/pb_glossary]. The pulmonary artery carries deoxygenated blood from the heart to the lungs, where it travels through pulmonary capillaries, picking up oxygen and releasing carbon dioxide. The oxygenated blood then leaves the lungs through pulmonary veins.<\/li>\r\n \t
- Gas exchange occurs by diffusion across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a passive process that requires no energy.<\/li>\r\n \t
- Gas exchange by diffusion depends on the large surface area provided by the hundreds of millions of alveoli in the lungs. It also depends on a steep concentration gradient for oxygen and carbon dioxide. This gradient is maintained by continuous blood flow and constant breathing.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n13.4 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- What is gas exchange?<\/li>\r\n \t
- Summarize the flow of blood into and out of the lungs for gas exchange.<\/li>\r\n \t
- [h5p id=\"609\"]<\/li>\r\n \t
- Describe the mechanism by which gas exchange takes place.<\/li>\r\n \t
- Identify the two main factors upon which gas exchange by diffusion depends.<\/li>\r\n \t
- If the concentration of oxygen were higher inside of a cell than outside of it, which way would the oxygen flow? Explain your answer.<\/li>\r\n \t
- Why is it important that the walls of the alveoli are only one cell thick?<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n13.4 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=nRpwdwm06Ic&feature=emb_logo\r\nOxygen movement from alveoli to capillaries | NCLEX-RN | Khan Academy, khanacademymedicine, 2013.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=KmgIqVwytwA&feature=emb_logo\r\n
About Carbon Monoxide and Carbon Monoxide Poisoning, EMDPrepare, 2009.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=GVU_zANtroE\r\n
Oxygen\u2019s surprisingly complex journey through your body - Enda Butler, TED-Ed, 2017.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 13.4.1<\/strong>\r\n\r\nOxygen Bar<\/a> by\u00a0Farrukh<\/a> on Flickr<\/a> is used under a CC BY-NC 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/2.0\/) license.\r\n\r\nFigure 13.4.2<\/strong>\r\n\r\nAlveolus_diagram.svg<\/a>\u00a0by Mariana Ruiz Villarreal [LadyofHats<\/a>] on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 13.4.3<\/strong>\r\n\r\nGas_exchange_in_the_aveolus.svg<\/a> by domdomegg<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\nReferences<\/h2>\r\n
EMDPrepare. (2009, December 21). About carbon monoxide and carbon monoxide poisoning. YouTube. https:\/\/www.youtube.com\/watch?v=KmgIqVwytwA&feature=youtu.be<\/p>\r\n
khanacademymedicine. (2013, February 25). Oxygen movement from alveoli to capillaries | NCLEX-RN | Khan Academy. YouTube. https:\/\/www.youtube.com\/watch?v=nRpwdwm06Ic&feature=youtu.be<\/p>\r\n
TED-Ed. (2017, April 13). Oxygen\u2019s surprisingly complex journey through your body - Enda Butler. YouTube. https:\/\/www.youtube.com\/watch?v=GVU_zANtroE&feature=youtu.be<\/p>","rendered":"
<\/p>\nFigure 13.4.1 Would you pay for air?<\/em><\/figcaption><\/figure>\n\nOxygen Bar<\/h1>\n<\/div>\n
Belly up to the bar and get your favorite… oxygen? That\u2019s right \u2014 in some cities, you can get a shot of pure oxygen, with or without your choice of added flavors. Bar patrons inhale oxygen through a plastic tube inserted into their nostrils, paying up to a dollar per minute to inhale the pure gas. Proponents of the practice claim that breathing in extra oxygen will remove toxins from the body, strengthen the immune system, enhance concentration and alertness, increase energy, and even cure cancer!\u00a0These claims, however, have not been substantiated by controlled scientific studies. Normally, blood leaving the lungs is almost completely saturated with oxygen, even without the use of extra oxygen, so it\u2019s unlikely that a higher concentration of oxygen in air inside the lungs would lead to significantly greater oxygenation of the blood. Oxygen enters the blood in the lungs as part of the process of gas exchange.<\/p>\n
\nWhat is Gas Exchange?<\/h1>\n<\/div>\n
Gas exchange<\/a><\/strong>\u00a0is the biological process through which gases are transferred across cell membranes to either enter or leave the blood. Oxygen is constantly needed by cells for aerobic cellular respiration, and the same process continually produces carbon dioxide as a waste product. Gas exchange takes place between the blood and cells throughout the body, with oxygen leaving the blood and entering the cells, and carbon dioxide leaving the cells and entering the blood. Gas exchange also takes place between the blood and the air in the lungs, with oxygen entering the blood from the inhaled air inside the lungs, and carbon dioxide leaving the blood and entering the air to be exhaled from the lungs.<\/p>\n\nGas Exchange in the Lungs<\/h1>\n<\/div>\n
Alveoli are the basic functional units of the lungs where gas exchange takes place between the air and the blood.\u00a0Alveoli (singular, alveolus)<\/strong><\/a> are tiny air sacs that consist of connective and epithelial tissues. The connective tissue includes elastic fibres that allow alveoli to stretch and expand as they fill with air during inhalation. During exhalation, the fibres allow the alveoli to spring back and expel the air. Special cells in the walls of the alveoli secrete a film of fatty substances called surfactant<\/strong><\/a>. This substance prevents the alveolar walls from collapsing and sticking together when air is expelled. Other cells in alveoli include macrophages<\/span><\/a><\/span>, which are mobile scavengers that engulf and destroy foreign particles that manage to reach the lungs in inhaled air.<\/span><\/p>\nAs shown in Figure 13.4.2, alveoli are arranged in groups like clusters of grapes. Each alveolus is covered with epithelium that is just one cell thick. It is surrounded by a bed of pulmonary<\/a> capillaries, each of which has a wall of epithelium just one cell thick. As a result, gases must cross through only two cells to pass between an alveolus and its surrounding capillaries.<\/p>\nFigure 13.4.2 Clusters of alveolar sacs make up most of the functional tissue of the lungs. Note that in this and subsequent illustrations, arteries, which carry oxygenated blood, are colored red; and veins, which carry deoxygenated blood, are colored blue.<\/em><\/figcaption><\/figure>\nThe pulmonary artery (also shown in Figure 13.4.2) carries deoxygenated blood from the heart to the lungs. Then, the blood travels through the pulmonary capillary beds, where it picks up oxygen and releases carbon dioxide. The oxygenated blood then leaves the lungs and travels back to the heart through pulmonary veins. There are four pulmonary veins (two for each lung), and all four carry oxygenated blood to the heart. From the heart, the oxygenated blood is then pumped to cells throughout the body.<\/p>\n
\nMechanism of Gas Exchange<\/h1>\n<\/div>\n
Gas exchange occurs by diffusion<\/a> across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a passive<\/a> process that requires no energy. To diffuse across cell membranes, gases must first be dissolved in a liquid. Oxygen and carbon dioxide are transported around the body dissolved in blood. Both gases bind to the protein hemoglobin in red blood cells, although oxygen does so more effectively than carbon dioxide. Some carbon dioxide also dissolves in blood plasma.<\/p>\nAs shown in Figure 13.4.3, oxygen in inhaled air diffuses into a pulmonary capillary from the alveolus. Carbon dioxide in the blood diffuses in the opposite direction. The carbon dioxide can then be exhaled from the body.<\/p>\nFigure 13.4.3 A single alveolus is a tiny structure that is specialized for gas exchange between inhaled air and the blood in pulmonary capillaries.<\/em><\/figcaption><\/figure>\nGas exchange by diffusion depends on having a large surface area through which gases can pass. Although each alveolus is tiny, there are hundreds of millions of them in the lungs of a healthy adult, so the total surface area for gas exchange is huge. It is estimated that this surface area may be as great as 100 m2<\/sup> (or approximately 1,076 ft\u00b2). Often we think of lungs as balloons, but this type of structure would have very limited surface area and there wouldn’t be enough space for blood to interface with the air in the alveoli.\u00a0 The structure alveoli take in the lungs is more like a giant mass of soap bubbles \u2014\u00a0 millions of tiny little chambers making up one large mass \u2014 this is what increases surface area giving blood lots of space to come into close enough contact to exchange gases by diffusion.<\/p>\nGas exchange by diffusion also depends on maintaining a steep concentration gradient for oxygen and carbon dioxide. Continuous blood flow in the capillaries and constant breathing maintain this gradient.<\/p>\n
\n- Each time you inhale, there is a greater concentration of oxygen in the air in the alveoli than there is in the blood in the pulmonary capillaries. As a result, oxygen diffuses from the air inside the alveoli into the blood in the capillaries. Carbon dioxide, in contrast, is more concentrated in the blood in the pulmonary capillaries than it is in the air inside the alveoli.\u00a0As a result, carbon dioxide diffuses in the opposite direction.<\/li>\n
- The cells of the body have a much lower concentration of oxygen than does the oxygenated blood that reaches them in peripheral capillaries, which are the capillaries that supply tissues throughout the body. As a result, oxygen diffuses from the peripheral capillaries into body cells. The opposite is true of carbon dioxide. It has a much higher concentration in body cells than it does in the blood of the peripheral capillaries. Thus, carbon dioxide diffuses from body cells into the peripheral capillaries.<\/li>\n<\/ul>\n\n\n
\n13.4 Summary<\/span><\/h1>\n<\/header>\n\n\n- Gas exchange<\/a> is the biological process through which gases are transferred across cell membranes to either enter or leave the blood. Gas exchange takes place continuously between the blood and cells throughout the body, and also between the blood and the air inside the lungs.<\/li>\n
- Gas exchange in the lungs takes place in alveoli<\/a>, which are tiny air sacs surrounded by networks of capillaries<\/a>. The pulmonary artery carries deoxygenated blood from the heart to the lungs, where it travels through pulmonary capillaries, picking up oxygen and releasing carbon dioxide. The oxygenated blood then leaves the lungs through pulmonary veins.<\/li>\n
- Gas exchange occurs by diffusion across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a passive process that requires no energy.<\/li>\n
- Gas exchange by diffusion depends on the large surface area provided by the hundreds of millions of alveoli in the lungs. It also depends on a steep concentration gradient for oxygen and carbon dioxide. This gradient is maintained by continuous blood flow and constant breathing.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n\n
\n13.4 Review Questions<\/span><\/h1>\n<\/header>\n\n\n- What is gas exchange?<\/li>\n
- Summarize the flow of blood into and out of the lungs for gas exchange.<\/li>\n
- \n\n
Gas Exchange in the Lungs<\/h1>\r\n<\/div>\r\nAlveoli are the basic functional units of the lungs where gas exchange takes place between the air and the blood.[pb_glossary id=\"4311\"]\u00a0Alveoli (singular, alveolus)<\/strong>[\/pb_glossary] are tiny air sacs that consist of connective and epithelial tissues. The connective tissue includes elastic fibres that allow alveoli to stretch and expand as they fill with air during inhalation. During exhalation, the fibres allow the alveoli to spring back and expel the air. Special cells in the walls of the alveoli secrete a film of fatty substances called [pb_glossary id=\"4339\"]surfactant<\/strong>[\/pb_glossary]. This substance prevents the alveolar walls from collapsing and sticking together when air is expelled. Other cells in alveoli include [pb_glossary id=\"4340\"]macrophages<\/span>[\/pb_glossary]<\/span>, which are mobile scavengers that engulf and destroy foreign particles that manage to reach the lungs in inhaled air.<\/span>\r\n\r\nAs shown in Figure 13.4.2, alveoli are arranged in groups like clusters of grapes. Each alveolus is covered with epithelium that is just one cell thick. It is surrounded by a bed of [pb_glossary id=\"4341\"]pulmonary[\/pb_glossary] capillaries, each of which has a wall of epithelium just one cell thick. As a result, gases must cross through only two cells to pass between an alveolus and its surrounding capillaries.\r\n\r\n[caption id=\"attachment_4343\" align=\"aligncenter\" width=\"519\"] Figure 13.4.2 Clusters of alveolar sacs make up most of the functional tissue of the lungs. Note that in this and subsequent illustrations, arteries, which carry oxygenated blood, are colored red; and veins, which carry deoxygenated blood, are colored blue.<\/em>[\/caption]\r\n\r\nThe pulmonary artery (also shown in Figure 13.4.2) carries deoxygenated blood from the heart to the lungs. Then, the blood travels through the pulmonary capillary beds, where it picks up oxygen and releases carbon dioxide. The oxygenated blood then leaves the lungs and travels back to the heart through pulmonary veins. There are four pulmonary veins (two for each lung), and all four carry oxygenated blood to the heart. From the heart, the oxygenated blood is then pumped to cells throughout the body.\r\n\r\nMechanism of Gas Exchange<\/h1>\r\n<\/div>\r\nGas exchange occurs by [pb_glossary id=\"1655\"]diffusion[\/pb_glossary] across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a [pb_glossary id=\"5705\"]passive[\/pb_glossary] process that requires no energy. To diffuse across cell membranes, gases must first be dissolved in a liquid. Oxygen and carbon dioxide are transported around the body dissolved in blood. Both gases bind to the protein hemoglobin in red blood cells, although oxygen does so more effectively than carbon dioxide. Some carbon dioxide also dissolves in blood plasma.\r\n\r\nAs shown in Figure 13.4.3, oxygen in inhaled air diffuses into a pulmonary capillary from the alveolus. Carbon dioxide in the blood diffuses in the opposite direction. The carbon dioxide can then be exhaled from the body.\r\n\r\n[caption id=\"attachment_4344\" align=\"aligncenter\" width=\"695\"] Figure 13.4.3 A single alveolus is a tiny structure that is specialized for gas exchange between inhaled air and the blood in pulmonary capillaries.<\/em>[\/caption]\r\n\r\nGas exchange by diffusion depends on having a large surface area through which gases can pass. Although each alveolus is tiny, there are hundreds of millions of them in the lungs of a healthy adult, so the total surface area for gas exchange is huge. It is estimated that this surface area may be as great as 100 m2<\/sup> (or approximately 1,076 ft\u00b2). Often we think of lungs as balloons, but this type of structure would have very limited surface area and there wouldn't be enough space for blood to interface with the air in the alveoli.\u00a0 The structure alveoli take in the lungs is more like a giant mass of soap bubbles \u2014\u00a0 millions of tiny little chambers making up one large mass \u2014 this is what increases surface area giving blood lots of space to come into close enough contact to exchange gases by diffusion.\r\n\r\nGas exchange by diffusion also depends on maintaining a steep concentration gradient for oxygen and carbon dioxide. Continuous blood flow in the capillaries and constant breathing maintain this gradient.\r\n\r\n \t- Each time you inhale, there is a greater concentration of oxygen in the air in the alveoli than there is in the blood in the pulmonary capillaries. As a result, oxygen diffuses from the air inside the alveoli into the blood in the capillaries. Carbon dioxide, in contrast, is more concentrated in the blood in the pulmonary capillaries than it is in the air inside the alveoli.\u00a0As a result, carbon dioxide diffuses in the opposite direction.<\/li>\r\n \t
- The cells of the body have a much lower concentration of oxygen than does the oxygenated blood that reaches them in peripheral capillaries, which are the capillaries that supply tissues throughout the body. As a result, oxygen diffuses from the peripheral capillaries into body cells. The opposite is true of carbon dioxide. It has a much higher concentration in body cells than it does in the blood of the peripheral capillaries. Thus, carbon dioxide diffuses from body cells into the peripheral capillaries.<\/li>\r\n<\/ul>\r\n\r\n
\r\n13.4 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [pb_glossary id=\"4288\"]Gas exchange[\/pb_glossary] is the biological process through which gases are transferred across cell membranes to either enter or leave the blood. Gas exchange takes place continuously between the blood and cells throughout the body, and also between the blood and the air inside the lungs.<\/li>\r\n \t
- Gas exchange in the lungs takes place in [pb_glossary id=\"4311\"]alveoli[\/pb_glossary], which are tiny air sacs surrounded by networks of [pb_glossary id=\"5923\"]capillaries[\/pb_glossary]. The pulmonary artery carries deoxygenated blood from the heart to the lungs, where it travels through pulmonary capillaries, picking up oxygen and releasing carbon dioxide. The oxygenated blood then leaves the lungs through pulmonary veins.<\/li>\r\n \t
- Gas exchange occurs by diffusion across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a passive process that requires no energy.<\/li>\r\n \t
- Gas exchange by diffusion depends on the large surface area provided by the hundreds of millions of alveoli in the lungs. It also depends on a steep concentration gradient for oxygen and carbon dioxide. This gradient is maintained by continuous blood flow and constant breathing.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n13.4 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- What is gas exchange?<\/li>\r\n \t
- Summarize the flow of blood into and out of the lungs for gas exchange.<\/li>\r\n \t
- [h5p id=\"609\"]<\/li>\r\n \t
- Describe the mechanism by which gas exchange takes place.<\/li>\r\n \t
- Identify the two main factors upon which gas exchange by diffusion depends.<\/li>\r\n \t
- If the concentration of oxygen were higher inside of a cell than outside of it, which way would the oxygen flow? Explain your answer.<\/li>\r\n \t
- Why is it important that the walls of the alveoli are only one cell thick?<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n13.4 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=nRpwdwm06Ic&feature=emb_logo\r\nOxygen movement from alveoli to capillaries | NCLEX-RN | Khan Academy, khanacademymedicine, 2013.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=KmgIqVwytwA&feature=emb_logo\r\n
About Carbon Monoxide and Carbon Monoxide Poisoning, EMDPrepare, 2009.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=GVU_zANtroE\r\n
Oxygen\u2019s surprisingly complex journey through your body - Enda Butler, TED-Ed, 2017.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 13.4.1<\/strong>\r\n\r\nOxygen Bar<\/a> by\u00a0Farrukh<\/a> on Flickr<\/a> is used under a CC BY-NC 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/2.0\/) license.\r\n\r\nFigure 13.4.2<\/strong>\r\n\r\nAlveolus_diagram.svg<\/a>\u00a0by Mariana Ruiz Villarreal [LadyofHats<\/a>] on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 13.4.3<\/strong>\r\n\r\nGas_exchange_in_the_aveolus.svg<\/a> by domdomegg<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\nReferences<\/h2>\r\n
EMDPrepare. (2009, December 21). About carbon monoxide and carbon monoxide poisoning. YouTube. https:\/\/www.youtube.com\/watch?v=KmgIqVwytwA&feature=youtu.be<\/p>\r\n
khanacademymedicine. (2013, February 25). Oxygen movement from alveoli to capillaries | NCLEX-RN | Khan Academy. YouTube. https:\/\/www.youtube.com\/watch?v=nRpwdwm06Ic&feature=youtu.be<\/p>\r\n
TED-Ed. (2017, April 13). Oxygen\u2019s surprisingly complex journey through your body - Enda Butler. YouTube. https:\/\/www.youtube.com\/watch?v=GVU_zANtroE&feature=youtu.be<\/p>","rendered":"
<\/p>\nFigure 13.4.1 Would you pay for air?<\/em><\/figcaption><\/figure>\n\nOxygen Bar<\/h1>\n<\/div>\n
Belly up to the bar and get your favorite… oxygen? That\u2019s right \u2014 in some cities, you can get a shot of pure oxygen, with or without your choice of added flavors. Bar patrons inhale oxygen through a plastic tube inserted into their nostrils, paying up to a dollar per minute to inhale the pure gas. Proponents of the practice claim that breathing in extra oxygen will remove toxins from the body, strengthen the immune system, enhance concentration and alertness, increase energy, and even cure cancer!\u00a0These claims, however, have not been substantiated by controlled scientific studies. Normally, blood leaving the lungs is almost completely saturated with oxygen, even without the use of extra oxygen, so it\u2019s unlikely that a higher concentration of oxygen in air inside the lungs would lead to significantly greater oxygenation of the blood. Oxygen enters the blood in the lungs as part of the process of gas exchange.<\/p>\n
\nWhat is Gas Exchange?<\/h1>\n<\/div>\n
Gas exchange<\/a><\/strong>\u00a0is the biological process through which gases are transferred across cell membranes to either enter or leave the blood. Oxygen is constantly needed by cells for aerobic cellular respiration, and the same process continually produces carbon dioxide as a waste product. Gas exchange takes place between the blood and cells throughout the body, with oxygen leaving the blood and entering the cells, and carbon dioxide leaving the cells and entering the blood. Gas exchange also takes place between the blood and the air in the lungs, with oxygen entering the blood from the inhaled air inside the lungs, and carbon dioxide leaving the blood and entering the air to be exhaled from the lungs.<\/p>\n\nGas Exchange in the Lungs<\/h1>\n<\/div>\n
Alveoli are the basic functional units of the lungs where gas exchange takes place between the air and the blood.\u00a0Alveoli (singular, alveolus)<\/strong><\/a> are tiny air sacs that consist of connective and epithelial tissues. The connective tissue includes elastic fibres that allow alveoli to stretch and expand as they fill with air during inhalation. During exhalation, the fibres allow the alveoli to spring back and expel the air. Special cells in the walls of the alveoli secrete a film of fatty substances called surfactant<\/strong><\/a>. This substance prevents the alveolar walls from collapsing and sticking together when air is expelled. Other cells in alveoli include macrophages<\/span><\/a><\/span>, which are mobile scavengers that engulf and destroy foreign particles that manage to reach the lungs in inhaled air.<\/span><\/p>\nAs shown in Figure 13.4.2, alveoli are arranged in groups like clusters of grapes. Each alveolus is covered with epithelium that is just one cell thick. It is surrounded by a bed of pulmonary<\/a> capillaries, each of which has a wall of epithelium just one cell thick. As a result, gases must cross through only two cells to pass between an alveolus and its surrounding capillaries.<\/p>\nFigure 13.4.2 Clusters of alveolar sacs make up most of the functional tissue of the lungs. Note that in this and subsequent illustrations, arteries, which carry oxygenated blood, are colored red; and veins, which carry deoxygenated blood, are colored blue.<\/em><\/figcaption><\/figure>\nThe pulmonary artery (also shown in Figure 13.4.2) carries deoxygenated blood from the heart to the lungs. Then, the blood travels through the pulmonary capillary beds, where it picks up oxygen and releases carbon dioxide. The oxygenated blood then leaves the lungs and travels back to the heart through pulmonary veins. There are four pulmonary veins (two for each lung), and all four carry oxygenated blood to the heart. From the heart, the oxygenated blood is then pumped to cells throughout the body.<\/p>\n
\nMechanism of Gas Exchange<\/h1>\n<\/div>\n
Gas exchange occurs by diffusion<\/a> across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a passive<\/a> process that requires no energy. To diffuse across cell membranes, gases must first be dissolved in a liquid. Oxygen and carbon dioxide are transported around the body dissolved in blood. Both gases bind to the protein hemoglobin in red blood cells, although oxygen does so more effectively than carbon dioxide. Some carbon dioxide also dissolves in blood plasma.<\/p>\nAs shown in Figure 13.4.3, oxygen in inhaled air diffuses into a pulmonary capillary from the alveolus. Carbon dioxide in the blood diffuses in the opposite direction. The carbon dioxide can then be exhaled from the body.<\/p>\nFigure 13.4.3 A single alveolus is a tiny structure that is specialized for gas exchange between inhaled air and the blood in pulmonary capillaries.<\/em><\/figcaption><\/figure>\nGas exchange by diffusion depends on having a large surface area through which gases can pass. Although each alveolus is tiny, there are hundreds of millions of them in the lungs of a healthy adult, so the total surface area for gas exchange is huge. It is estimated that this surface area may be as great as 100 m2<\/sup> (or approximately 1,076 ft\u00b2). Often we think of lungs as balloons, but this type of structure would have very limited surface area and there wouldn’t be enough space for blood to interface with the air in the alveoli.\u00a0 The structure alveoli take in the lungs is more like a giant mass of soap bubbles \u2014\u00a0 millions of tiny little chambers making up one large mass \u2014 this is what increases surface area giving blood lots of space to come into close enough contact to exchange gases by diffusion.<\/p>\nGas exchange by diffusion also depends on maintaining a steep concentration gradient for oxygen and carbon dioxide. Continuous blood flow in the capillaries and constant breathing maintain this gradient.<\/p>\n
\n- Each time you inhale, there is a greater concentration of oxygen in the air in the alveoli than there is in the blood in the pulmonary capillaries. As a result, oxygen diffuses from the air inside the alveoli into the blood in the capillaries. Carbon dioxide, in contrast, is more concentrated in the blood in the pulmonary capillaries than it is in the air inside the alveoli.\u00a0As a result, carbon dioxide diffuses in the opposite direction.<\/li>\n
- The cells of the body have a much lower concentration of oxygen than does the oxygenated blood that reaches them in peripheral capillaries, which are the capillaries that supply tissues throughout the body. As a result, oxygen diffuses from the peripheral capillaries into body cells. The opposite is true of carbon dioxide. It has a much higher concentration in body cells than it does in the blood of the peripheral capillaries. Thus, carbon dioxide diffuses from body cells into the peripheral capillaries.<\/li>\n<\/ul>\n\n\n
\n13.4 Summary<\/span><\/h1>\n<\/header>\n\n\n- Gas exchange<\/a> is the biological process through which gases are transferred across cell membranes to either enter or leave the blood. Gas exchange takes place continuously between the blood and cells throughout the body, and also between the blood and the air inside the lungs.<\/li>\n
- Gas exchange in the lungs takes place in alveoli<\/a>, which are tiny air sacs surrounded by networks of capillaries<\/a>. The pulmonary artery carries deoxygenated blood from the heart to the lungs, where it travels through pulmonary capillaries, picking up oxygen and releasing carbon dioxide. The oxygenated blood then leaves the lungs through pulmonary veins.<\/li>\n
- Gas exchange occurs by diffusion across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a passive process that requires no energy.<\/li>\n
- Gas exchange by diffusion depends on the large surface area provided by the hundreds of millions of alveoli in the lungs. It also depends on a steep concentration gradient for oxygen and carbon dioxide. This gradient is maintained by continuous blood flow and constant breathing.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n\n
\n13.4 Review Questions<\/span><\/h1>\n<\/header>\n\n\n- What is gas exchange?<\/li>\n
- Summarize the flow of blood into and out of the lungs for gas exchange.<\/li>\n
- \n\n
Mechanism of Gas Exchange<\/h1>\r\n<\/div>\r\nGas exchange occurs by [pb_glossary id=\"1655\"]diffusion[\/pb_glossary] across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a [pb_glossary id=\"5705\"]passive[\/pb_glossary] process that requires no energy. To diffuse across cell membranes, gases must first be dissolved in a liquid. Oxygen and carbon dioxide are transported around the body dissolved in blood. Both gases bind to the protein hemoglobin in red blood cells, although oxygen does so more effectively than carbon dioxide. Some carbon dioxide also dissolves in blood plasma.\r\n\r\nAs shown in Figure 13.4.3, oxygen in inhaled air diffuses into a pulmonary capillary from the alveolus. Carbon dioxide in the blood diffuses in the opposite direction. The carbon dioxide can then be exhaled from the body.\r\n\r\n[caption id=\"attachment_4344\" align=\"aligncenter\" width=\"695\"] Figure 13.4.3 A single alveolus is a tiny structure that is specialized for gas exchange between inhaled air and the blood in pulmonary capillaries.<\/em>[\/caption]\r\n\r\nGas exchange by diffusion depends on having a large surface area through which gases can pass. Although each alveolus is tiny, there are hundreds of millions of them in the lungs of a healthy adult, so the total surface area for gas exchange is huge. It is estimated that this surface area may be as great as 100 m2<\/sup> (or approximately 1,076 ft\u00b2). Often we think of lungs as balloons, but this type of structure would have very limited surface area and there wouldn't be enough space for blood to interface with the air in the alveoli.\u00a0 The structure alveoli take in the lungs is more like a giant mass of soap bubbles \u2014\u00a0 millions of tiny little chambers making up one large mass \u2014 this is what increases surface area giving blood lots of space to come into close enough contact to exchange gases by diffusion.\r\n\r\nGas exchange by diffusion also depends on maintaining a steep concentration gradient for oxygen and carbon dioxide. Continuous blood flow in the capillaries and constant breathing maintain this gradient.\r\n\r\n \t- Each time you inhale, there is a greater concentration of oxygen in the air in the alveoli than there is in the blood in the pulmonary capillaries. As a result, oxygen diffuses from the air inside the alveoli into the blood in the capillaries. Carbon dioxide, in contrast, is more concentrated in the blood in the pulmonary capillaries than it is in the air inside the alveoli.\u00a0As a result, carbon dioxide diffuses in the opposite direction.<\/li>\r\n \t
- The cells of the body have a much lower concentration of oxygen than does the oxygenated blood that reaches them in peripheral capillaries, which are the capillaries that supply tissues throughout the body. As a result, oxygen diffuses from the peripheral capillaries into body cells. The opposite is true of carbon dioxide. It has a much higher concentration in body cells than it does in the blood of the peripheral capillaries. Thus, carbon dioxide diffuses from body cells into the peripheral capillaries.<\/li>\r\n<\/ul>\r\n\r\n
\r\n13.4 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [pb_glossary id=\"4288\"]Gas exchange[\/pb_glossary] is the biological process through which gases are transferred across cell membranes to either enter or leave the blood. Gas exchange takes place continuously between the blood and cells throughout the body, and also between the blood and the air inside the lungs.<\/li>\r\n \t
- Gas exchange in the lungs takes place in [pb_glossary id=\"4311\"]alveoli[\/pb_glossary], which are tiny air sacs surrounded by networks of [pb_glossary id=\"5923\"]capillaries[\/pb_glossary]. The pulmonary artery carries deoxygenated blood from the heart to the lungs, where it travels through pulmonary capillaries, picking up oxygen and releasing carbon dioxide. The oxygenated blood then leaves the lungs through pulmonary veins.<\/li>\r\n \t
- Gas exchange occurs by diffusion across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a passive process that requires no energy.<\/li>\r\n \t
- Gas exchange by diffusion depends on the large surface area provided by the hundreds of millions of alveoli in the lungs. It also depends on a steep concentration gradient for oxygen and carbon dioxide. This gradient is maintained by continuous blood flow and constant breathing.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n13.4 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- What is gas exchange?<\/li>\r\n \t
- Summarize the flow of blood into and out of the lungs for gas exchange.<\/li>\r\n \t
- [h5p id=\"609\"]<\/li>\r\n \t
- Describe the mechanism by which gas exchange takes place.<\/li>\r\n \t
- Identify the two main factors upon which gas exchange by diffusion depends.<\/li>\r\n \t
- If the concentration of oxygen were higher inside of a cell than outside of it, which way would the oxygen flow? Explain your answer.<\/li>\r\n \t
- Why is it important that the walls of the alveoli are only one cell thick?<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n13.4 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=nRpwdwm06Ic&feature=emb_logo\r\nOxygen movement from alveoli to capillaries | NCLEX-RN | Khan Academy, khanacademymedicine, 2013.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=KmgIqVwytwA&feature=emb_logo\r\n
About Carbon Monoxide and Carbon Monoxide Poisoning, EMDPrepare, 2009.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=GVU_zANtroE\r\n
Oxygen\u2019s surprisingly complex journey through your body - Enda Butler, TED-Ed, 2017.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 13.4.1<\/strong>\r\n\r\nOxygen Bar<\/a> by\u00a0Farrukh<\/a> on Flickr<\/a> is used under a CC BY-NC 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/2.0\/) license.\r\n\r\nFigure 13.4.2<\/strong>\r\n\r\nAlveolus_diagram.svg<\/a>\u00a0by Mariana Ruiz Villarreal [LadyofHats<\/a>] on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 13.4.3<\/strong>\r\n\r\nGas_exchange_in_the_aveolus.svg<\/a> by domdomegg<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\nReferences<\/h2>\r\n
EMDPrepare. (2009, December 21). About carbon monoxide and carbon monoxide poisoning. YouTube. https:\/\/www.youtube.com\/watch?v=KmgIqVwytwA&feature=youtu.be<\/p>\r\n
khanacademymedicine. (2013, February 25). Oxygen movement from alveoli to capillaries | NCLEX-RN | Khan Academy. YouTube. https:\/\/www.youtube.com\/watch?v=nRpwdwm06Ic&feature=youtu.be<\/p>\r\n
TED-Ed. (2017, April 13). Oxygen\u2019s surprisingly complex journey through your body - Enda Butler. YouTube. https:\/\/www.youtube.com\/watch?v=GVU_zANtroE&feature=youtu.be<\/p>","rendered":"
<\/p>\nFigure 13.4.1 Would you pay for air?<\/em><\/figcaption><\/figure>\n\nOxygen Bar<\/h1>\n<\/div>\n
Belly up to the bar and get your favorite… oxygen? That\u2019s right \u2014 in some cities, you can get a shot of pure oxygen, with or without your choice of added flavors. Bar patrons inhale oxygen through a plastic tube inserted into their nostrils, paying up to a dollar per minute to inhale the pure gas. Proponents of the practice claim that breathing in extra oxygen will remove toxins from the body, strengthen the immune system, enhance concentration and alertness, increase energy, and even cure cancer!\u00a0These claims, however, have not been substantiated by controlled scientific studies. Normally, blood leaving the lungs is almost completely saturated with oxygen, even without the use of extra oxygen, so it\u2019s unlikely that a higher concentration of oxygen in air inside the lungs would lead to significantly greater oxygenation of the blood. Oxygen enters the blood in the lungs as part of the process of gas exchange.<\/p>\n
\nWhat is Gas Exchange?<\/h1>\n<\/div>\n
Gas exchange<\/a><\/strong>\u00a0is the biological process through which gases are transferred across cell membranes to either enter or leave the blood. Oxygen is constantly needed by cells for aerobic cellular respiration, and the same process continually produces carbon dioxide as a waste product. Gas exchange takes place between the blood and cells throughout the body, with oxygen leaving the blood and entering the cells, and carbon dioxide leaving the cells and entering the blood. Gas exchange also takes place between the blood and the air in the lungs, with oxygen entering the blood from the inhaled air inside the lungs, and carbon dioxide leaving the blood and entering the air to be exhaled from the lungs.<\/p>\n\nGas Exchange in the Lungs<\/h1>\n<\/div>\n
Alveoli are the basic functional units of the lungs where gas exchange takes place between the air and the blood.\u00a0Alveoli (singular, alveolus)<\/strong><\/a> are tiny air sacs that consist of connective and epithelial tissues. The connective tissue includes elastic fibres that allow alveoli to stretch and expand as they fill with air during inhalation. During exhalation, the fibres allow the alveoli to spring back and expel the air. Special cells in the walls of the alveoli secrete a film of fatty substances called surfactant<\/strong><\/a>. This substance prevents the alveolar walls from collapsing and sticking together when air is expelled. Other cells in alveoli include macrophages<\/span><\/a><\/span>, which are mobile scavengers that engulf and destroy foreign particles that manage to reach the lungs in inhaled air.<\/span><\/p>\nAs shown in Figure 13.4.2, alveoli are arranged in groups like clusters of grapes. Each alveolus is covered with epithelium that is just one cell thick. It is surrounded by a bed of pulmonary<\/a> capillaries, each of which has a wall of epithelium just one cell thick. As a result, gases must cross through only two cells to pass between an alveolus and its surrounding capillaries.<\/p>\nFigure 13.4.2 Clusters of alveolar sacs make up most of the functional tissue of the lungs. Note that in this and subsequent illustrations, arteries, which carry oxygenated blood, are colored red; and veins, which carry deoxygenated blood, are colored blue.<\/em><\/figcaption><\/figure>\nThe pulmonary artery (also shown in Figure 13.4.2) carries deoxygenated blood from the heart to the lungs. Then, the blood travels through the pulmonary capillary beds, where it picks up oxygen and releases carbon dioxide. The oxygenated blood then leaves the lungs and travels back to the heart through pulmonary veins. There are four pulmonary veins (two for each lung), and all four carry oxygenated blood to the heart. From the heart, the oxygenated blood is then pumped to cells throughout the body.<\/p>\n
\nMechanism of Gas Exchange<\/h1>\n<\/div>\n
Gas exchange occurs by diffusion<\/a> across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a passive<\/a> process that requires no energy. To diffuse across cell membranes, gases must first be dissolved in a liquid. Oxygen and carbon dioxide are transported around the body dissolved in blood. Both gases bind to the protein hemoglobin in red blood cells, although oxygen does so more effectively than carbon dioxide. Some carbon dioxide also dissolves in blood plasma.<\/p>\nAs shown in Figure 13.4.3, oxygen in inhaled air diffuses into a pulmonary capillary from the alveolus. Carbon dioxide in the blood diffuses in the opposite direction. The carbon dioxide can then be exhaled from the body.<\/p>\nFigure 13.4.3 A single alveolus is a tiny structure that is specialized for gas exchange between inhaled air and the blood in pulmonary capillaries.<\/em><\/figcaption><\/figure>\nGas exchange by diffusion depends on having a large surface area through which gases can pass. Although each alveolus is tiny, there are hundreds of millions of them in the lungs of a healthy adult, so the total surface area for gas exchange is huge. It is estimated that this surface area may be as great as 100 m2<\/sup> (or approximately 1,076 ft\u00b2). Often we think of lungs as balloons, but this type of structure would have very limited surface area and there wouldn’t be enough space for blood to interface with the air in the alveoli.\u00a0 The structure alveoli take in the lungs is more like a giant mass of soap bubbles \u2014\u00a0 millions of tiny little chambers making up one large mass \u2014 this is what increases surface area giving blood lots of space to come into close enough contact to exchange gases by diffusion.<\/p>\nGas exchange by diffusion also depends on maintaining a steep concentration gradient for oxygen and carbon dioxide. Continuous blood flow in the capillaries and constant breathing maintain this gradient.<\/p>\n
\n- Each time you inhale, there is a greater concentration of oxygen in the air in the alveoli than there is in the blood in the pulmonary capillaries. As a result, oxygen diffuses from the air inside the alveoli into the blood in the capillaries. Carbon dioxide, in contrast, is more concentrated in the blood in the pulmonary capillaries than it is in the air inside the alveoli.\u00a0As a result, carbon dioxide diffuses in the opposite direction.<\/li>\n
- The cells of the body have a much lower concentration of oxygen than does the oxygenated blood that reaches them in peripheral capillaries, which are the capillaries that supply tissues throughout the body. As a result, oxygen diffuses from the peripheral capillaries into body cells. The opposite is true of carbon dioxide. It has a much higher concentration in body cells than it does in the blood of the peripheral capillaries. Thus, carbon dioxide diffuses from body cells into the peripheral capillaries.<\/li>\n<\/ul>\n\n\n
\n13.4 Summary<\/span><\/h1>\n<\/header>\n\n\n- Gas exchange<\/a> is the biological process through which gases are transferred across cell membranes to either enter or leave the blood. Gas exchange takes place continuously between the blood and cells throughout the body, and also between the blood and the air inside the lungs.<\/li>\n
- Gas exchange in the lungs takes place in alveoli<\/a>, which are tiny air sacs surrounded by networks of capillaries<\/a>. The pulmonary artery carries deoxygenated blood from the heart to the lungs, where it travels through pulmonary capillaries, picking up oxygen and releasing carbon dioxide. The oxygenated blood then leaves the lungs through pulmonary veins.<\/li>\n
- Gas exchange occurs by diffusion across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a passive process that requires no energy.<\/li>\n
- Gas exchange by diffusion depends on the large surface area provided by the hundreds of millions of alveoli in the lungs. It also depends on a steep concentration gradient for oxygen and carbon dioxide. This gradient is maintained by continuous blood flow and constant breathing.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n\n
\n13.4 Review Questions<\/span><\/h1>\n<\/header>\n\n\n- What is gas exchange?<\/li>\n
- Summarize the flow of blood into and out of the lungs for gas exchange.<\/li>\n
- \n\n
13.4 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- [pb_glossary id=\"4288\"]Gas exchange[\/pb_glossary] is the biological process through which gases are transferred across cell membranes to either enter or leave the blood. Gas exchange takes place continuously between the blood and cells throughout the body, and also between the blood and the air inside the lungs.<\/li>\r\n \t
- Gas exchange in the lungs takes place in [pb_glossary id=\"4311\"]alveoli[\/pb_glossary], which are tiny air sacs surrounded by networks of [pb_glossary id=\"5923\"]capillaries[\/pb_glossary]. The pulmonary artery carries deoxygenated blood from the heart to the lungs, where it travels through pulmonary capillaries, picking up oxygen and releasing carbon dioxide. The oxygenated blood then leaves the lungs through pulmonary veins.<\/li>\r\n \t
- Gas exchange occurs by diffusion across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a passive process that requires no energy.<\/li>\r\n \t
- Gas exchange by diffusion depends on the large surface area provided by the hundreds of millions of alveoli in the lungs. It also depends on a steep concentration gradient for oxygen and carbon dioxide. This gradient is maintained by continuous blood flow and constant breathing.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n13.4 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- What is gas exchange?<\/li>\r\n \t
- Summarize the flow of blood into and out of the lungs for gas exchange.<\/li>\r\n \t
- [h5p id=\"609\"]<\/li>\r\n \t
- Describe the mechanism by which gas exchange takes place.<\/li>\r\n \t
- Identify the two main factors upon which gas exchange by diffusion depends.<\/li>\r\n \t
- If the concentration of oxygen were higher inside of a cell than outside of it, which way would the oxygen flow? Explain your answer.<\/li>\r\n \t
- Why is it important that the walls of the alveoli are only one cell thick?<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n13.4 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=nRpwdwm06Ic&feature=emb_logo\r\nOxygen movement from alveoli to capillaries | NCLEX-RN | Khan Academy, khanacademymedicine, 2013.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=KmgIqVwytwA&feature=emb_logo\r\n
About Carbon Monoxide and Carbon Monoxide Poisoning, EMDPrepare, 2009.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=GVU_zANtroE\r\n
Oxygen\u2019s surprisingly complex journey through your body - Enda Butler, TED-Ed, 2017.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 13.4.1<\/strong>\r\n\r\nOxygen Bar<\/a> by\u00a0Farrukh<\/a> on Flickr<\/a> is used under a CC BY-NC 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/2.0\/) license.\r\n\r\nFigure 13.4.2<\/strong>\r\n\r\nAlveolus_diagram.svg<\/a>\u00a0by Mariana Ruiz Villarreal [LadyofHats<\/a>] on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 13.4.3<\/strong>\r\n\r\nGas_exchange_in_the_aveolus.svg<\/a> by domdomegg<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\nReferences<\/h2>\r\n
EMDPrepare. (2009, December 21). About carbon monoxide and carbon monoxide poisoning. YouTube. https:\/\/www.youtube.com\/watch?v=KmgIqVwytwA&feature=youtu.be<\/p>\r\n
khanacademymedicine. (2013, February 25). Oxygen movement from alveoli to capillaries | NCLEX-RN | Khan Academy. YouTube. https:\/\/www.youtube.com\/watch?v=nRpwdwm06Ic&feature=youtu.be<\/p>\r\n
TED-Ed. (2017, April 13). Oxygen\u2019s surprisingly complex journey through your body - Enda Butler. YouTube. https:\/\/www.youtube.com\/watch?v=GVU_zANtroE&feature=youtu.be<\/p>","rendered":"
<\/p>\nFigure 13.4.1 Would you pay for air?<\/em><\/figcaption><\/figure>\n\nOxygen Bar<\/h1>\n<\/div>\n
Belly up to the bar and get your favorite… oxygen? That\u2019s right \u2014 in some cities, you can get a shot of pure oxygen, with or without your choice of added flavors. Bar patrons inhale oxygen through a plastic tube inserted into their nostrils, paying up to a dollar per minute to inhale the pure gas. Proponents of the practice claim that breathing in extra oxygen will remove toxins from the body, strengthen the immune system, enhance concentration and alertness, increase energy, and even cure cancer!\u00a0These claims, however, have not been substantiated by controlled scientific studies. Normally, blood leaving the lungs is almost completely saturated with oxygen, even without the use of extra oxygen, so it\u2019s unlikely that a higher concentration of oxygen in air inside the lungs would lead to significantly greater oxygenation of the blood. Oxygen enters the blood in the lungs as part of the process of gas exchange.<\/p>\n
\nWhat is Gas Exchange?<\/h1>\n<\/div>\n
Gas exchange<\/a><\/strong>\u00a0is the biological process through which gases are transferred across cell membranes to either enter or leave the blood. Oxygen is constantly needed by cells for aerobic cellular respiration, and the same process continually produces carbon dioxide as a waste product. Gas exchange takes place between the blood and cells throughout the body, with oxygen leaving the blood and entering the cells, and carbon dioxide leaving the cells and entering the blood. Gas exchange also takes place between the blood and the air in the lungs, with oxygen entering the blood from the inhaled air inside the lungs, and carbon dioxide leaving the blood and entering the air to be exhaled from the lungs.<\/p>\n\nGas Exchange in the Lungs<\/h1>\n<\/div>\n
Alveoli are the basic functional units of the lungs where gas exchange takes place between the air and the blood.\u00a0Alveoli (singular, alveolus)<\/strong><\/a> are tiny air sacs that consist of connective and epithelial tissues. The connective tissue includes elastic fibres that allow alveoli to stretch and expand as they fill with air during inhalation. During exhalation, the fibres allow the alveoli to spring back and expel the air. Special cells in the walls of the alveoli secrete a film of fatty substances called surfactant<\/strong><\/a>. This substance prevents the alveolar walls from collapsing and sticking together when air is expelled. Other cells in alveoli include macrophages<\/span><\/a><\/span>, which are mobile scavengers that engulf and destroy foreign particles that manage to reach the lungs in inhaled air.<\/span><\/p>\nAs shown in Figure 13.4.2, alveoli are arranged in groups like clusters of grapes. Each alveolus is covered with epithelium that is just one cell thick. It is surrounded by a bed of pulmonary<\/a> capillaries, each of which has a wall of epithelium just one cell thick. As a result, gases must cross through only two cells to pass between an alveolus and its surrounding capillaries.<\/p>\nFigure 13.4.2 Clusters of alveolar sacs make up most of the functional tissue of the lungs. Note that in this and subsequent illustrations, arteries, which carry oxygenated blood, are colored red; and veins, which carry deoxygenated blood, are colored blue.<\/em><\/figcaption><\/figure>\nThe pulmonary artery (also shown in Figure 13.4.2) carries deoxygenated blood from the heart to the lungs. Then, the blood travels through the pulmonary capillary beds, where it picks up oxygen and releases carbon dioxide. The oxygenated blood then leaves the lungs and travels back to the heart through pulmonary veins. There are four pulmonary veins (two for each lung), and all four carry oxygenated blood to the heart. From the heart, the oxygenated blood is then pumped to cells throughout the body.<\/p>\n
\nMechanism of Gas Exchange<\/h1>\n<\/div>\n
Gas exchange occurs by diffusion<\/a> across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a passive<\/a> process that requires no energy. To diffuse across cell membranes, gases must first be dissolved in a liquid. Oxygen and carbon dioxide are transported around the body dissolved in blood. Both gases bind to the protein hemoglobin in red blood cells, although oxygen does so more effectively than carbon dioxide. Some carbon dioxide also dissolves in blood plasma.<\/p>\nAs shown in Figure 13.4.3, oxygen in inhaled air diffuses into a pulmonary capillary from the alveolus. Carbon dioxide in the blood diffuses in the opposite direction. The carbon dioxide can then be exhaled from the body.<\/p>\nFigure 13.4.3 A single alveolus is a tiny structure that is specialized for gas exchange between inhaled air and the blood in pulmonary capillaries.<\/em><\/figcaption><\/figure>\nGas exchange by diffusion depends on having a large surface area through which gases can pass. Although each alveolus is tiny, there are hundreds of millions of them in the lungs of a healthy adult, so the total surface area for gas exchange is huge. It is estimated that this surface area may be as great as 100 m2<\/sup> (or approximately 1,076 ft\u00b2). Often we think of lungs as balloons, but this type of structure would have very limited surface area and there wouldn’t be enough space for blood to interface with the air in the alveoli.\u00a0 The structure alveoli take in the lungs is more like a giant mass of soap bubbles \u2014\u00a0 millions of tiny little chambers making up one large mass \u2014 this is what increases surface area giving blood lots of space to come into close enough contact to exchange gases by diffusion.<\/p>\nGas exchange by diffusion also depends on maintaining a steep concentration gradient for oxygen and carbon dioxide. Continuous blood flow in the capillaries and constant breathing maintain this gradient.<\/p>\n
\n- Each time you inhale, there is a greater concentration of oxygen in the air in the alveoli than there is in the blood in the pulmonary capillaries. As a result, oxygen diffuses from the air inside the alveoli into the blood in the capillaries. Carbon dioxide, in contrast, is more concentrated in the blood in the pulmonary capillaries than it is in the air inside the alveoli.\u00a0As a result, carbon dioxide diffuses in the opposite direction.<\/li>\n
- The cells of the body have a much lower concentration of oxygen than does the oxygenated blood that reaches them in peripheral capillaries, which are the capillaries that supply tissues throughout the body. As a result, oxygen diffuses from the peripheral capillaries into body cells. The opposite is true of carbon dioxide. It has a much higher concentration in body cells than it does in the blood of the peripheral capillaries. Thus, carbon dioxide diffuses from body cells into the peripheral capillaries.<\/li>\n<\/ul>\n\n\n
\n13.4 Summary<\/span><\/h1>\n<\/header>\n\n\n- Gas exchange<\/a> is the biological process through which gases are transferred across cell membranes to either enter or leave the blood. Gas exchange takes place continuously between the blood and cells throughout the body, and also between the blood and the air inside the lungs.<\/li>\n
- Gas exchange in the lungs takes place in alveoli<\/a>, which are tiny air sacs surrounded by networks of capillaries<\/a>. The pulmonary artery carries deoxygenated blood from the heart to the lungs, where it travels through pulmonary capillaries, picking up oxygen and releasing carbon dioxide. The oxygenated blood then leaves the lungs through pulmonary veins.<\/li>\n
- Gas exchange occurs by diffusion across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a passive process that requires no energy.<\/li>\n
- Gas exchange by diffusion depends on the large surface area provided by the hundreds of millions of alveoli in the lungs. It also depends on a steep concentration gradient for oxygen and carbon dioxide. This gradient is maintained by continuous blood flow and constant breathing.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n\n
\n13.4 Review Questions<\/span><\/h1>\n<\/header>\n\n\n- What is gas exchange?<\/li>\n
- Summarize the flow of blood into and out of the lungs for gas exchange.<\/li>\n
- \n\n
- \r\n \t
- [pb_glossary id=\"4288\"]Gas exchange[\/pb_glossary] is the biological process through which gases are transferred across cell membranes to either enter or leave the blood. Gas exchange takes place continuously between the blood and cells throughout the body, and also between the blood and the air inside the lungs.<\/li>\r\n \t
- Gas exchange in the lungs takes place in [pb_glossary id=\"4311\"]alveoli[\/pb_glossary], which are tiny air sacs surrounded by networks of [pb_glossary id=\"5923\"]capillaries[\/pb_glossary]. The pulmonary artery carries deoxygenated blood from the heart to the lungs, where it travels through pulmonary capillaries, picking up oxygen and releasing carbon dioxide. The oxygenated blood then leaves the lungs through pulmonary veins.<\/li>\r\n \t
- Gas exchange occurs by diffusion across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a passive process that requires no energy.<\/li>\r\n \t
- Gas exchange by diffusion depends on the large surface area provided by the hundreds of millions of alveoli in the lungs. It also depends on a steep concentration gradient for oxygen and carbon dioxide. This gradient is maintained by continuous blood flow and constant breathing.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n 13.4 Review Questions<\/span><\/h1>\r\n<\/header>\r\n
\r\n- \r\n \t
- What is gas exchange?<\/li>\r\n \t
- Summarize the flow of blood into and out of the lungs for gas exchange.<\/li>\r\n \t
- [h5p id=\"609\"]<\/li>\r\n \t
- Describe the mechanism by which gas exchange takes place.<\/li>\r\n \t
- Identify the two main factors upon which gas exchange by diffusion depends.<\/li>\r\n \t
- If the concentration of oxygen were higher inside of a cell than outside of it, which way would the oxygen flow? Explain your answer.<\/li>\r\n \t
- Why is it important that the walls of the alveoli are only one cell thick?<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n 13.4 Explore More<\/span><\/h1>\r\n<\/header>\r\n
\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=nRpwdwm06Ic&feature=emb_logo\r\nOxygen movement from alveoli to capillaries | NCLEX-RN | Khan Academy, khanacademymedicine, 2013.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=KmgIqVwytwA&feature=emb_logo\r\n
About Carbon Monoxide and Carbon Monoxide Poisoning, EMDPrepare, 2009.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=GVU_zANtroE\r\n
Oxygen\u2019s surprisingly complex journey through your body - Enda Butler, TED-Ed, 2017.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 13.4.1<\/strong>\r\n\r\nOxygen Bar<\/a> by\u00a0Farrukh<\/a> on Flickr<\/a> is used under a CC BY-NC 2.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-nc\/2.0\/) license.\r\n\r\nFigure 13.4.2<\/strong>\r\n\r\nAlveolus_diagram.svg<\/a>\u00a0by Mariana Ruiz Villarreal [LadyofHats<\/a>] on Wikimedia Commons is released into the public domain<\/a> (https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 13.4.3<\/strong>\r\n\r\nGas_exchange_in_the_aveolus.svg<\/a> by domdomegg<\/a> on Wikimedia Commons is used under a CC BY 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/4.0) license.\r\n
References<\/h2>\r\n
EMDPrepare. (2009, December 21). About carbon monoxide and carbon monoxide poisoning. YouTube. https:\/\/www.youtube.com\/watch?v=KmgIqVwytwA&feature=youtu.be<\/p>\r\n
khanacademymedicine. (2013, February 25). Oxygen movement from alveoli to capillaries | NCLEX-RN | Khan Academy. YouTube. https:\/\/www.youtube.com\/watch?v=nRpwdwm06Ic&feature=youtu.be<\/p>\r\n
TED-Ed. (2017, April 13). Oxygen\u2019s surprisingly complex journey through your body - Enda Butler. YouTube. https:\/\/www.youtube.com\/watch?v=GVU_zANtroE&feature=youtu.be<\/p>","rendered":"
<\/p>\n
Figure 13.4.1 Would you pay for air?<\/em><\/figcaption><\/figure>\n \nOxygen Bar<\/h1>\n<\/div>\n
Belly up to the bar and get your favorite… oxygen? That\u2019s right \u2014 in some cities, you can get a shot of pure oxygen, with or without your choice of added flavors. Bar patrons inhale oxygen through a plastic tube inserted into their nostrils, paying up to a dollar per minute to inhale the pure gas. Proponents of the practice claim that breathing in extra oxygen will remove toxins from the body, strengthen the immune system, enhance concentration and alertness, increase energy, and even cure cancer!\u00a0These claims, however, have not been substantiated by controlled scientific studies. Normally, blood leaving the lungs is almost completely saturated with oxygen, even without the use of extra oxygen, so it\u2019s unlikely that a higher concentration of oxygen in air inside the lungs would lead to significantly greater oxygenation of the blood. Oxygen enters the blood in the lungs as part of the process of gas exchange.<\/p>\n
\nWhat is Gas Exchange?<\/h1>\n<\/div>\n
Gas exchange<\/a><\/strong>\u00a0is the biological process through which gases are transferred across cell membranes to either enter or leave the blood. Oxygen is constantly needed by cells for aerobic cellular respiration, and the same process continually produces carbon dioxide as a waste product. Gas exchange takes place between the blood and cells throughout the body, with oxygen leaving the blood and entering the cells, and carbon dioxide leaving the cells and entering the blood. Gas exchange also takes place between the blood and the air in the lungs, with oxygen entering the blood from the inhaled air inside the lungs, and carbon dioxide leaving the blood and entering the air to be exhaled from the lungs.<\/p>\n
\nGas Exchange in the Lungs<\/h1>\n<\/div>\n
Alveoli are the basic functional units of the lungs where gas exchange takes place between the air and the blood.\u00a0Alveoli (singular, alveolus)<\/strong><\/a> are tiny air sacs that consist of connective and epithelial tissues. The connective tissue includes elastic fibres that allow alveoli to stretch and expand as they fill with air during inhalation. During exhalation, the fibres allow the alveoli to spring back and expel the air. Special cells in the walls of the alveoli secrete a film of fatty substances called surfactant<\/strong><\/a>. This substance prevents the alveolar walls from collapsing and sticking together when air is expelled. Other cells in alveoli include macrophages<\/span><\/a><\/span>, which are mobile scavengers that engulf and destroy foreign particles that manage to reach the lungs in inhaled air.<\/span><\/p>\n
As shown in Figure 13.4.2, alveoli are arranged in groups like clusters of grapes. Each alveolus is covered with epithelium that is just one cell thick. It is surrounded by a bed of pulmonary<\/a> capillaries, each of which has a wall of epithelium just one cell thick. As a result, gases must cross through only two cells to pass between an alveolus and its surrounding capillaries.<\/p>\n
Figure 13.4.2 Clusters of alveolar sacs make up most of the functional tissue of the lungs. Note that in this and subsequent illustrations, arteries, which carry oxygenated blood, are colored red; and veins, which carry deoxygenated blood, are colored blue.<\/em><\/figcaption><\/figure>\n The pulmonary artery (also shown in Figure 13.4.2) carries deoxygenated blood from the heart to the lungs. Then, the blood travels through the pulmonary capillary beds, where it picks up oxygen and releases carbon dioxide. The oxygenated blood then leaves the lungs and travels back to the heart through pulmonary veins. There are four pulmonary veins (two for each lung), and all four carry oxygenated blood to the heart. From the heart, the oxygenated blood is then pumped to cells throughout the body.<\/p>\n
\nMechanism of Gas Exchange<\/h1>\n<\/div>\n
Gas exchange occurs by diffusion<\/a> across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a passive<\/a> process that requires no energy. To diffuse across cell membranes, gases must first be dissolved in a liquid. Oxygen and carbon dioxide are transported around the body dissolved in blood. Both gases bind to the protein hemoglobin in red blood cells, although oxygen does so more effectively than carbon dioxide. Some carbon dioxide also dissolves in blood plasma.<\/p>\n
As shown in Figure 13.4.3, oxygen in inhaled air diffuses into a pulmonary capillary from the alveolus. Carbon dioxide in the blood diffuses in the opposite direction. The carbon dioxide can then be exhaled from the body.<\/p>\n
Figure 13.4.3 A single alveolus is a tiny structure that is specialized for gas exchange between inhaled air and the blood in pulmonary capillaries.<\/em><\/figcaption><\/figure>\n Gas exchange by diffusion depends on having a large surface area through which gases can pass. Although each alveolus is tiny, there are hundreds of millions of them in the lungs of a healthy adult, so the total surface area for gas exchange is huge. It is estimated that this surface area may be as great as 100 m2<\/sup> (or approximately 1,076 ft\u00b2). Often we think of lungs as balloons, but this type of structure would have very limited surface area and there wouldn’t be enough space for blood to interface with the air in the alveoli.\u00a0 The structure alveoli take in the lungs is more like a giant mass of soap bubbles \u2014\u00a0 millions of tiny little chambers making up one large mass \u2014 this is what increases surface area giving blood lots of space to come into close enough contact to exchange gases by diffusion.<\/p>\n
Gas exchange by diffusion also depends on maintaining a steep concentration gradient for oxygen and carbon dioxide. Continuous blood flow in the capillaries and constant breathing maintain this gradient.<\/p>\n
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- Each time you inhale, there is a greater concentration of oxygen in the air in the alveoli than there is in the blood in the pulmonary capillaries. As a result, oxygen diffuses from the air inside the alveoli into the blood in the capillaries. Carbon dioxide, in contrast, is more concentrated in the blood in the pulmonary capillaries than it is in the air inside the alveoli.\u00a0As a result, carbon dioxide diffuses in the opposite direction.<\/li>\n
- The cells of the body have a much lower concentration of oxygen than does the oxygenated blood that reaches them in peripheral capillaries, which are the capillaries that supply tissues throughout the body. As a result, oxygen diffuses from the peripheral capillaries into body cells. The opposite is true of carbon dioxide. It has a much higher concentration in body cells than it does in the blood of the peripheral capillaries. Thus, carbon dioxide diffuses from body cells into the peripheral capillaries.<\/li>\n<\/ul>\n\n\n
\n 13.4 Summary<\/span><\/h1>\n<\/header>\n
\n- \n
- Gas exchange<\/a> is the biological process through which gases are transferred across cell membranes to either enter or leave the blood. Gas exchange takes place continuously between the blood and cells throughout the body, and also between the blood and the air inside the lungs.<\/li>\n
- Gas exchange in the lungs takes place in alveoli<\/a>, which are tiny air sacs surrounded by networks of capillaries<\/a>. The pulmonary artery carries deoxygenated blood from the heart to the lungs, where it travels through pulmonary capillaries, picking up oxygen and releasing carbon dioxide. The oxygenated blood then leaves the lungs through pulmonary veins.<\/li>\n
- Gas exchange occurs by diffusion across cell membranes. Gas molecules naturally move down a concentration gradient from an area of higher concentration to an area of lower concentration. This is a passive process that requires no energy.<\/li>\n
- Gas exchange by diffusion depends on the large surface area provided by the hundreds of millions of alveoli in the lungs. It also depends on a steep concentration gradient for oxygen and carbon dioxide. This gradient is maintained by continuous blood flow and constant breathing.<\/li>\n<\/ul>\n<\/div>\n<\/div>\n
\n\n 13.4 Review Questions<\/span><\/h1>\n<\/header>\n
\n- \n
- What is gas exchange?<\/li>\n
- Summarize the flow of blood into and out of the lungs for gas exchange.<\/li>\n
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- Gas exchange in the lungs takes place in alveoli<\/a>, which are tiny air sacs surrounded by networks of capillaries<\/a>. The pulmonary artery carries deoxygenated blood from the heart to the lungs, where it travels through pulmonary capillaries, picking up oxygen and releasing carbon dioxide. The oxygenated blood then leaves the lungs through pulmonary veins.<\/li>\n
- Gas exchange<\/a> is the biological process through which gases are transferred across cell membranes to either enter or leave the blood. Gas exchange takes place continuously between the blood and cells throughout the body, and also between the blood and the air inside the lungs.<\/li>\n
![Alveolus_diagram.svg<\/a>\u00a0by Mariana Ruiz Villarreal [](\"https:\/\/commons.wikimedia.org\/wiki\/File:Alveolus_diagram.svg\"){kind=link}
![Gas_exchange_in_the_aveolus.svg<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Gas_exchange_in_the_aveolus.svg\"){kind=link}