{"id":4061,"date":"2017-03-27T19:53:55","date_gmt":"2017-03-27T19:53:55","guid":{"rendered":"https:\/\/courses.lumenlearning.com\/wm-biology2\/?post_type=chapter&#038;p=4061"},"modified":"2024-04-26T02:28:18","modified_gmt":"2024-04-26T02:28:18","slug":"the-mechanics-of-human-breathing","status":"publish","type":"chapter","link":"https:\/\/courses.lumenlearning.com\/wm-biology2\/chapter\/the-mechanics-of-human-breathing\/","title":{"raw":"The Mechanics of Human Breathing","rendered":"The Mechanics of Human Breathing"},"content":{"raw":"<div class=\"textbox learning-objectives\">\r\n<h3>Learning Outcomes<\/h3>\r\n<ul>\r\n \t<li>Describe how the structures of the lungs and thoracic cavity control the mechanics of breathing<\/li>\r\n<\/ul>\r\n<\/div>\r\n\r\n[caption id=\"attachment_2902\" align=\"alignright\" width=\"450\"]<img class=\"wp-image-2902\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/08195159\/Figure_39_03_02ab-1024x652.jpg\" alt=\"In this graph, pressure is plotted against volume. The line curves downward steeply at first, then more gradually.\" width=\"450\" height=\"287\" \/> Figure 1. This graph shows data from Boyle\u2019s original 1662 experiment, which shows that pressure and volume are inversely related. No units are given as Boyle used arbitrary units in his experiments.[\/caption]\r\n\r\nBoyle\u2019s Law is the gas law that states that in a closed space, pressure and volume are inversely related. As volume decreases, pressure increases and vice versa (Figure 1). The relationship between gas pressure and volume helps to explain the mechanics of breathing.\r\n\r\nThere is always a slightly negative pressure within the thoracic cavity, which aids in keeping the airways of the lungs open. During inhalation, volume increases as a result of contraction of the diaphragm, and pressure decreases (according to Boyle\u2019s Law). This decrease of pressure in the thoracic cavity relative to the environment makes the cavity less than the atmosphere (Figure 2a). Because of this drop in pressure, air rushes into the respiratory passages. To increase the volume of the lungs, the chest wall expands. This results from the contraction of the <b>intercostal muscles<\/b>, the muscles that are connected to the rib cage. Lung volume expands because the diaphragm contracts and the intercostals muscles contract, thus expanding the thoracic cavity. This increase in the volume of the thoracic cavity lowers pressure compared to the atmosphere, so air rushes into the lungs, thus increasing its volume. The resulting increase in volume is largely attributed to an increase in alveolar space, because the bronchioles and bronchi are stiff structures that do not change in size.\r\n\r\n[caption id=\"attachment_2903\" align=\"aligncenter\" width=\"1024\"]<img class=\"size-large wp-image-2903\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/08195241\/Figure_39_03_03-1024x428.jpg\" alt=\"Part a shows expanded lungs with alveoli filled with air during inhalation. The diaphragm is pulled downward, and the muscles of the chest wall are bulled outward. Part b shows collapsed lungs during expiration. The diaphragm is pushed upward, and the chest cavity muscles are pushed inward.\" width=\"1024\" height=\"428\" \/> Figure 2. The lungs, chest wall, and diaphragm are all involved in respiration, both (a) inhalation and (b) expiration. (credit: modification of work by Mariana Ruiz Villareal)[\/caption]\r\n\r\n[caption id=\"\" align=\"alignright\" width=\"301\"]<img id=\"7\" src=\"https:\/\/openstax.org\/resources\/f893b5984dfb5b78f735965bbc8654586e60cc52\" alt=\"The illustration shows human lungs. Each lung is covered by an inner visceral pleura and an outer parietal pleura. The intrapleural space is the space between the two membranes.\" width=\"301\" height=\"376\" data-media-type=\"image\/png\" \/> Figure 3. A tissue layer called pleura surrounds the lung and interior of the thoracic cavity. (credit: modification of work by NCI)[\/caption]\r\n\r\nThe chest wall expands out and away from the lungs. The lungs are elastic; therefore, when air fills the lungs, the <b>elastic recoil\u00a0<\/b>within the tissues of the lung exerts pressure back toward the interior of the lungs and pushes air back out of the lungs. These outward and inward forces compete to inflate and deflate the lung with every breath. Upon exhalation, the lungs recoil to force the air out of the lungs, and the intercostal muscles relax, returning the chest wall back to its original position (Figure 2b).\r\n\r\nThe diaphragm also relaxes and moves higher into the thoracic cavity. This increases the pressure within the thoracic cavity relative to the environment, and air rushes out of the lungs. The movement of air out of the lungs is a passive event; no muscles are contracting to expel the air.\r\n\r\nEach lung is surrounded by an invaginated sac. The layer of tissue that covers the lung and dips into spaces is called the visceral\u00a0<b>pleura<\/b>. A second layer of parietal pleura lines the interior of the thorax (Figure 3). The space between these layers, the <b>intrapleural space<\/b>, contains a small amount of fluid that protects the tissue and reduces the friction generated from rubbing the tissue layers together as the lungs contract and relax. <b>Pleurisy<\/b> results when these layers of tissue become inflamed; it is painful because the inflammation increases the pressure within the thoracic cavity and reduces the volume of the lung.\r\n<div class=\"textbox\">\r\n\r\nView how Boyle\u2019s Law is related to breathing and watch this\u00a0video:\r\n\r\n<iframe src=\"\/\/plugin.3playmedia.com\/show?mf=1611011&amp;p3sdk_version=1.10.1&amp;p=20361&amp;pt=375&amp;video_id=NB1aCBId6qA&amp;video_target=tpm-plugin-zixixw79-NB1aCBId6qA\" width=\"800px\" height=\"450px\" frameborder=\"0\" marginwidth=\"0px\" marginheight=\"0px\"><\/iframe>\r\n\r\n<\/div>\r\n<div class=\"textbox tryit\">\r\n<h3>Try It<\/h3>\r\nhttps:\/\/assess.lumenlearning.com\/practice\/9fafbcb1-0456-498e-93b1-a0cef60c4182\r\n<\/div>","rendered":"<div class=\"textbox learning-objectives\">\n<h3>Learning Outcomes<\/h3>\n<ul>\n<li>Describe how the structures of the lungs and thoracic cavity control the mechanics of breathing<\/li>\n<\/ul>\n<\/div>\n<div id=\"attachment_2902\" style=\"width: 460px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2902\" class=\"wp-image-2902\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/08195159\/Figure_39_03_02ab-1024x652.jpg\" alt=\"In this graph, pressure is plotted against volume. The line curves downward steeply at first, then more gradually.\" width=\"450\" height=\"287\" \/><\/p>\n<p id=\"caption-attachment-2902\" class=\"wp-caption-text\">Figure 1. This graph shows data from Boyle\u2019s original 1662 experiment, which shows that pressure and volume are inversely related. No units are given as Boyle used arbitrary units in his experiments.<\/p>\n<\/div>\n<p>Boyle\u2019s Law is the gas law that states that in a closed space, pressure and volume are inversely related. As volume decreases, pressure increases and vice versa (Figure 1). The relationship between gas pressure and volume helps to explain the mechanics of breathing.<\/p>\n<p>There is always a slightly negative pressure within the thoracic cavity, which aids in keeping the airways of the lungs open. During inhalation, volume increases as a result of contraction of the diaphragm, and pressure decreases (according to Boyle\u2019s Law). This decrease of pressure in the thoracic cavity relative to the environment makes the cavity less than the atmosphere (Figure 2a). Because of this drop in pressure, air rushes into the respiratory passages. To increase the volume of the lungs, the chest wall expands. This results from the contraction of the <b>intercostal muscles<\/b>, the muscles that are connected to the rib cage. Lung volume expands because the diaphragm contracts and the intercostals muscles contract, thus expanding the thoracic cavity. This increase in the volume of the thoracic cavity lowers pressure compared to the atmosphere, so air rushes into the lungs, thus increasing its volume. The resulting increase in volume is largely attributed to an increase in alveolar space, because the bronchioles and bronchi are stiff structures that do not change in size.<\/p>\n<div id=\"attachment_2903\" style=\"width: 1034px\" class=\"wp-caption aligncenter\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-2903\" class=\"size-large wp-image-2903\" src=\"https:\/\/s3-us-west-2.amazonaws.com\/courses-images\/wp-content\/uploads\/sites\/1223\/2017\/02\/08195241\/Figure_39_03_03-1024x428.jpg\" alt=\"Part a shows expanded lungs with alveoli filled with air during inhalation. The diaphragm is pulled downward, and the muscles of the chest wall are bulled outward. Part b shows collapsed lungs during expiration. The diaphragm is pushed upward, and the chest cavity muscles are pushed inward.\" width=\"1024\" height=\"428\" \/><\/p>\n<p id=\"caption-attachment-2903\" class=\"wp-caption-text\">Figure 2. The lungs, chest wall, and diaphragm are all involved in respiration, both (a) inhalation and (b) expiration. (credit: modification of work by Mariana Ruiz Villareal)<\/p>\n<\/div>\n<div style=\"width: 311px\" class=\"wp-caption alignright\"><img loading=\"lazy\" decoding=\"async\" id=\"7\" src=\"https:\/\/openstax.org\/resources\/f893b5984dfb5b78f735965bbc8654586e60cc52\" alt=\"The illustration shows human lungs. Each lung is covered by an inner visceral pleura and an outer parietal pleura. The intrapleural space is the space between the two membranes.\" width=\"301\" height=\"376\" data-media-type=\"image\/png\" \/><\/p>\n<p class=\"wp-caption-text\">Figure 3. A tissue layer called pleura surrounds the lung and interior of the thoracic cavity. (credit: modification of work by NCI)<\/p>\n<\/div>\n<p>The chest wall expands out and away from the lungs. The lungs are elastic; therefore, when air fills the lungs, the <b>elastic recoil\u00a0<\/b>within the tissues of the lung exerts pressure back toward the interior of the lungs and pushes air back out of the lungs. These outward and inward forces compete to inflate and deflate the lung with every breath. Upon exhalation, the lungs recoil to force the air out of the lungs, and the intercostal muscles relax, returning the chest wall back to its original position (Figure 2b).<\/p>\n<p>The diaphragm also relaxes and moves higher into the thoracic cavity. This increases the pressure within the thoracic cavity relative to the environment, and air rushes out of the lungs. The movement of air out of the lungs is a passive event; no muscles are contracting to expel the air.<\/p>\n<p>Each lung is surrounded by an invaginated sac. The layer of tissue that covers the lung and dips into spaces is called the visceral\u00a0<b>pleura<\/b>. A second layer of parietal pleura lines the interior of the thorax (Figure 3). The space between these layers, the <b>intrapleural space<\/b>, contains a small amount of fluid that protects the tissue and reduces the friction generated from rubbing the tissue layers together as the lungs contract and relax. <b>Pleurisy<\/b> results when these layers of tissue become inflamed; it is painful because the inflammation increases the pressure within the thoracic cavity and reduces the volume of the lung.<\/p>\n<div class=\"textbox\">\n<p>View how Boyle\u2019s Law is related to breathing and watch this\u00a0video:<\/p>\n<p><iframe loading=\"lazy\" src=\"\/\/plugin.3playmedia.com\/show?mf=1611011&amp;p3sdk_version=1.10.1&amp;p=20361&amp;pt=375&amp;video_id=NB1aCBId6qA&amp;video_target=tpm-plugin-zixixw79-NB1aCBId6qA\" width=\"800px\" height=\"450px\" frameborder=\"0\" marginwidth=\"0px\" marginheight=\"0px\"><\/iframe><\/p>\n<\/div>\n<div class=\"textbox tryit\">\n<h3>Try It<\/h3>\n<p>\t<iframe id=\"assessment_practice_9fafbcb1-0456-498e-93b1-a0cef60c4182\" class=\"resizable\" src=\"https:\/\/assess.lumenlearning.com\/practice\/9fafbcb1-0456-498e-93b1-a0cef60c4182?iframe_resize_id=assessment_practice_id_9fafbcb1-0456-498e-93b1-a0cef60c4182\" frameborder=\"0\" style=\"border:none;width:100%;height:100%;min-height:300px;\"><br \/>\n\t<\/iframe>\n<\/div>\n\n\t\t\t <section class=\"citations-section\" role=\"contentinfo\">\n\t\t\t <h3>Candela Citations<\/h3>\n\t\t\t\t\t <div>\n\t\t\t\t\t\t <div id=\"citation-list-4061\">\n\t\t\t\t\t\t\t <div class=\"licensing\"><div class=\"license-attribution-dropdown-subheading\">CC licensed content, Shared previously<\/div><ul class=\"citation-list\"><li>Biology 2e. <strong>Provided by<\/strong>: OpenStax. <strong>Located at<\/strong>: <a target=\"_blank\" href=\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\">http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8<\/a>. <strong>License<\/strong>: <em><a target=\"_blank\" rel=\"license\" href=\"https:\/\/creativecommons.org\/licenses\/by\/4.0\/\">CC BY: Attribution<\/a><\/em>. <strong>License Terms<\/strong>: Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction<\/li><\/ul><\/div>\n\t\t\t\t\t\t <\/div>\n\t\t\t\t\t <\/div>\n\t\t\t <\/section>","protected":false},"author":17,"menu_order":12,"template":"","meta":{"_candela_citation":"[{\"type\":\"cc\",\"description\":\"Biology 2e\",\"author\":\"\",\"organization\":\"OpenStax\",\"url\":\"http:\/\/cnx.org\/contents\/185cbf87-c72e-48f5-b51e-f14f21b5eabd@10.8\",\"project\":\"\",\"license\":\"cc-by\",\"license_terms\":\"Access for free at https:\/\/openstax.org\/books\/biology-2e\/pages\/1-introduction\"}]","CANDELA_OUTCOMES_GUID":"f8a29524-61b2-4741-a858-742d50c3cbff, 17707dc1-0538-437f-8e5a-4bfe755b8adb","pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[],"contributor":[],"license":[],"class_list":["post-4061","chapter","type-chapter","status-publish","hentry"],"part":3792,"_links":{"self":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/4061","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/users\/17"}],"version-history":[{"count":17,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/4061\/revisions"}],"predecessor-version":[{"id":8626,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/4061\/revisions\/8626"}],"part":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/parts\/3792"}],"metadata":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapters\/4061\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/media?parent=4061"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/pressbooks\/v2\/chapter-type?post=4061"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/contributor?post=4061"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/courses.lumenlearning.com\/wm-biology2\/wp-json\/wp\/v2\/license?post=4061"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}