Lub, Dub<\/h1>\r\n<\/div>\r\nLub dub, lub dub, lub dub... That\u2019s how the sound of a beating heart is typically described. Those are also the only two sounds that should be audible when listening to a normal, healthy heart through a stethoscope, as in Figure 14.3.1. \u00a0If a doctor hears something different from the normal lub dub sounds, it\u2019s a sign of a possible heart abnormality. What causes the heart to produce the characteristic lub dub sounds? Read on to find out.\r\n\r\nIntroduction to the Heart<\/h1>\r\n<\/div>\r\nThe\u00a0[pb_glossary id=\"2987\"]heart[\/pb_glossary]<\/strong>\u00a0is a muscular organ behind the sternum (breastbone), slightly to the left of the center of the chest. A normal adult heart is about the size of a fist. The function of the heart is to pump\u00a0blood\u00a0through\u00a0blood vessels\u00a0of the\u00a0[pb_glossary id=\"5927\"]cardiovascular system[\/pb_glossary]. The continuous flow of [pb_glossary id=\"2702\"]blood[\/pb_glossary] through the system is necessary to provide all the\u00a0cells\u00a0of the body with oxygen and\u00a0nutrients, and to remove their metabolic wastes.\r\n\r\nStructure of the Heart<\/h1>\r\n<\/div>\r\nThe heart has a thick muscular wall that consists of several layers of tissue. Internally, the heart is divided into four chambers through which\u00a0blood\u00a0flows. Because of heart valves, blood flows in just one direction through the chambers.\r\nHeart Wall<\/h2>\r\n[caption id=\"attachment_4407\" align=\"alignright\" width=\"424\"]![\"14.3.2](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Blausen_0470_HeartWall-2.png\")
Figure 14.3.2 The wall of the heart is made up mainly of myocardium, which consists largely of cardiac muscle.<\/em>[\/caption]\r\n\r\nAs shown in Figure 14.3.2, the wall of the heart is made up of three layers, called the endocardium, myocardium, and pericardium.\r\n\r\n \t- The\u00a0[pb_glossary id=\"4193\"]endocardium[\/pb_glossary]<\/strong>\u00a0is the innermost layer of the heart wall. It is made up primarily of simple epithelial\u00a0cells. It covers the heart chambers and valves. A thin layer of connective tissue joins the endocardium to the myocardium.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"4191\"]myocardium[\/pb_glossary]<\/strong> is the middle and thickest layer of the heart wall. It consists of [pb_glossary id=\"5925\"]cardiac muscle[\/pb_glossary] surrounded by a framework of collagen. There are two types of cardiac muscle cells in the myocardium: cardiomyocytes \u2014 which have the ability to contract easily \u2014 and pacemaker cells, which conduct electrical impulses that cause the cardiomyocytes to contract. About 99 per cent of cardiac muscle cells are cardiomyocytes, and the remaining one per cent is pacemaker cells. The myocardium is supplied with blood vessels and nerve fibres via the pericardium.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"4194\"]pericardium[\/pb_glossary]<\/strong>\u00a0is a protective sac that encloses and protects the heart. The pericardium consists of two membranes (visceral pericardium and parietal pericardium), between which there is a fluid-filled cavity. The fluid helps to cushion the heart, and also lubricates its outer surface.<\/li>\r\n<\/ul>\r\n
Heart Chambers<\/h2>\r\nAs shown in Figure 14.3.3 the four chambers of the heart include two upper chambers called atria (singular, [pb_glossary id=\"4408\"]atrium[\/pb_glossary])<\/strong>, and two lower chambers called\u00a0[pb_glossary id=\"4409\"]ventricles[\/pb_glossary].<\/strong> The atria are also referred to as receiving chambers, because blood coming into the heart first enters these two chambers. The right atrium receives deoxygenated blood from the upper and lower body through the superior [pb_glossary id=\"4410\"]vena cava[\/pb_glossary] and inferior vena cava, respectively. The left atrium receives oxygenated blood from the lungs through the [pb_glossary id=\"4411\"]pulmonary veins[\/pb_glossary]. The ventricles are also referred to as discharging chambers, because blood leaving the heart passes out through these two chambers. The right ventricle discharges blood to the lungs through the [pb_glossary id=\"4412\"]pulmonary artery[\/pb_glossary], and the left ventricle discharges blood to the rest of the body through the [pb_glossary id=\"4413\"]aorta[\/pb_glossary]. The four chambers are separated from each other by dense connective tissue consisting mainly of [pb_glossary id=\"3970\"]collagen[\/pb_glossary].\r\n\r\n[caption id=\"attachment_4414\" align=\"aligncenter\" width=\"663\"]![\"Figure](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Diagram_of_the_human_heart_cropped.svg_-2.png\")
Figure 14.3.3 This cross-sectional diagram of the heart shows its four chambers and four valves. The white arrows indicate the direction of blood flow through the heart chambers.<\/em>[\/caption]\r\nHeart Valves<\/h2>\r\n[caption id=\"attachment_4423\" align=\"alignleft\" width=\"370\"]![\"14.3.4](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Heart_Valves-2.jpg\")
Figure 14.3.4 If the veins and arteries of the heart were removed, a top-down view of the heart would reveal the four valves that are critical in preventing backflow of blood. Note the three cusps of the tricuspid AV valve and the 2 cusps of the bicuspid AV valve. Also note the size difference between the AV valves and the semilunar valves.<\/em>[\/caption]\r\n\r\nFigure 14.3.4 shows the location of the heart's four valves in a top-down view, looking down at the heart as if the arteries and veins feeding into and out of the heart were removed. The heart valves allow blood to flow from the atria to the ventricles, and from the ventricles to the pulmonary artery and aorta. The valves are constructed in such a way that blood can flow through them in only one direction, thus preventing the backflow of blood. Figure 14.3.5 shows how valves open to let blood into the appropriate chamber, and then close to prevent blood from moving in the wrong direction and the next chamber contracts.\u00a0 The four valves are the:\r\n\r\n \t- [pb_glossary id=\"4415\"]Tricuspid atrioventricular valve[\/pb_glossary]<\/strong>, (can be shortened to tricuspid AV valve) which allows blood to flow from the right atrium to the right ventricle.<\/li>\r\n \t
- [pb_glossary id=\"4416\"]Bicuspid atrioventricular valve[\/pb_glossary] <\/strong>(also know as the mitral valve), which allows blood to flow from the left atrium to the left ventricle.<\/li>\r\n \t
- [pb_glossary id=\"4417\"]Pulmonary semilunar valve[\/pb_glossary]<\/strong>, which allows blood to flow from the right ventricle to the pulmonary artery.<\/li>\r\n \t
- [pb_glossary id=\"4418\"]Aortic semilunar valve[\/pb_glossary]<\/strong>, which allows blood to flow from the left ventricle to the aorta.<\/li>\r\n<\/ol>\r\n[caption id=\"attachment_4419\" align=\"aligncenter\" width=\"411\"]
![\"14.3.4](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/CG_Heart-2.gif\")
Figure 14.3.5 The valves of the heart prevent backflow of blood. The open when the chamber before them contracts (systole) and then close when that chamber relaxes (diastole).<\/em>[\/caption]\r\n\r\n\r\n\r\n[caption id=\"attachment_4426\" align=\"alignright\" width=\"384\"]![\"14.3.6](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Heart_tee_four_chamber_view-2.jpg\")
Figure 14.3.6 The chordae tendoneae, shown in this diagram in white, play a critical role in reinforcing the AV valves of the heart.<\/em>[\/caption]\r\n\r\nThe two atrioventricular (AV) valves prevent backflow when the ventricles are contracting, while the semilunar valves prevent backflow from vessels.\u00a0 This means that the AV valves must withstand much more pressure than do the semilunar valves.\u00a0 In order to withstand the force of the ventricles contracting (to prevent blood from backflowing into the atria), the AV valves are reinforced with structures called [pb_glossary id=\"4424\"]chordae tendineae[\/pb_glossary] \u2014 tendon-like cords of connective tissue which anchor the valve and prevent it from [pb_glossary id=\"4425\"]prolapse[\/pb_glossary].\u00a0 Figure 14.3.6 shows the structure and location of the chordae tendoneae.\r\n\r\nThe chordae tendoneae are under such force that they need special attachments to the interior of the ventricles where they anchor.\u00a0 [pb_glossary id=\"4430\"]Papillary muscles[\/pb_glossary] are specialized muscles in the interior of the ventricle that provide a strong anchor point for the chordae tendineae.\r\nCoronary\u00a0Circulation<\/h1>\r\n<\/div>\r\nThe [pb_glossary id=\"5631\"]cardiomyocyte<\/strong>[\/pb_glossary]s of the muscular walls of the heart are very active cells, because they are responsible for the constant beating of the heart. These cells need a continuous supply of oxygen and\u00a0nutrients. The carbon dioxide and waste products they produce also must be continuously removed. The\u00a0blood vessels\u00a0that carry blood to and from the heart muscle cells make up the [pb_glossary id=\"4421\"]coronary\u00a0circulation[\/pb_glossary]. Note that the blood vessels of the coronary circulation supply heart tissues with blood, and are different from the blood vessels that carry blood to and from the chambers of the heart as part of the general circulation.\u00a0[pb_glossary id=\"4422\"]Coronary arteries[\/pb_glossary] <\/strong>supply oxygen-rich blood to the heart muscle cells. Coronary veins remove deoxygenated blood from the heart\u00a0muscles\u00a0cells.\r\n\r\n \t- There are two [pb_glossary id=\"4422\"]coronary arteries[\/pb_glossary] \u2014 a right coronary artery that supplies the right side of the heart, and a left coronary artery that supplies the left side of the heart. These arteries branch repeatedly into smaller and smaller arteries and finally into capillaries, which exchange gases,\u00a0nutrients, and waste products with cardiomyocytes.<\/li>\r\n \t
- At the back of the heart, small cardiac veins drain into larger veins, and finally into the great cardiac vein, which empties into the right atrium. At the front of the heart, small cardiac veins drain directly into the right atrium.<\/li>\r\n<\/ul>\r\n\r\n
Blood Circulation Through the Heart<\/h1>\r\n<\/div>\r\nFigure 14.3.7 shows how blood circulates through the chambers of the heart. The right atrium collects blood from two large veins, the superior vena cava (from the upper body) and the inferior vena cava (from the lower body). The blood that collects in the right atrium is pumped through the tricuspid valve into the right ventricle. From the right ventricle, the blood is pumped through the pulmonary valve into the pulmonary artery. The pulmonary artery carries the blood to the lungs, where it enters the pulmonary circulation, gives up carbon dioxide, and picks up oxygen. The oxygenated blood travels back from the lungs through the pulmonary veins (of which there are four), and enters the left atrium of the heart. From the left atrium, the blood is pumped through the mitral valve into the left ventricle. From the left ventricle, the blood is pumped through the aortic valve into the aorta, which subsequently branches into smaller arteries that carry the blood throughout the rest of the body. After passing through capillaries and exchanging substances with cells, the blood returns to the right atrium via the superior vena cava and inferior vena cava, and the process begins anew.\r\n\r\n[caption id=\"attachment_4431\" align=\"alignnone\" width=\"3000\"]![\"Figure](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Circulation-of-blood-through-the-heart-2.png\")
Figure 14.3.7 The flow chart in this diagram summarizes the pathway blood takes as it flows into, through, and out of the heart. Trace the path of blood flow in the diagram of the heart as you follow it through the flow chart.<\/em>[\/caption]\r\n\r\n\r\nCardiac Cycle<\/h1>\r\n<\/div>\r\nThe cardiac cycle refers to a single complete heartbeat, which includes one iteration of the lub and dub sounds heard through a stethoscope. During the cardiac cycle, the atria and ventricles work in a coordinated fashion so that blood is pumped efficiently through and out of the heart. The cardiac cycle includes two parts, called diastole and systole, which are illustrated in the diagrams in Figure 14.3.8.\r\n\r\n \t- During\u00a0[pb_glossary id=\"4442\"]diastole[\/pb_glossary],<\/strong>\u00a0the atria contract and pump blood into the ventricles, while the ventricles relax and fill with blood from the atria.<\/li>\r\n \t
- During\u00a0[pb_glossary id=\"4443\"]systole[\/pb_glossary],<\/strong>\u00a0the atria relax and collect blood from the lungs and body, while the ventricles contract and pump blood out of the heart.<\/li>\r\n<\/ul>\r\n[caption id=\"attachment_4444\" align=\"aligncenter\" width=\"495\"]
![\"14.3.8](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Human_healthy_pumping_heart_en.svg_-2.png\")
Figure 14.3.8 Diastole is referred to the filling stage, because this is when the ventricles fill with blood. Systole is referred to the pumping stage because this is when the ventricles pump blood out of the heart.<\/em>[\/caption]\r\n\r\nElectrical Stimulation of the Heart<\/span>\r\n\r\nThe normal, rhythmical beating of the heart is called\u00a0[pb_glossary id=\"4445\"]sinus rhythm[\/pb_glossary].<\/strong>\u00a0It is established by the heart\u2019s\u00a0[pb_glossary id=\"4446\"]pacemaker[\/pb_glossary]<\/strong> cells, which are located in an area of the heart called the [pb_glossary id=\"4195\"]sinoatrial node[\/pb_glossary] (shown in Figure 14.3.9). The pacemaker cells create electrical signals with the movement of electrolytes (sodium, potassium, and calcium ions) into and out of the cells. For each [pb_glossary id=\"4447\"]cardiac cycle[\/pb_glossary], an electrical signal rapidly travels first from the sinoatrial node, to the right and left atria so they contract together. Then, the signal travels to another node, called the [pb_glossary id=\"4448\"]atrioventricular node[\/pb_glossary] (Figure 14.3.9), and from there to the right and left ventricles (which also contract together), just a split second after the atria contract.\r\n\r\n[caption id=\"attachment_4449\" align=\"aligncenter\" width=\"416\"]![\"14.3.9](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Cardiac_Conduction_System-2.jpg\")
Figure 14.3.9 The sinoatrial (SA) node causes the atria to contract and then signals the atrioventricular (AV) nodes to initiate the contraction of the ventricles.<\/em>[\/caption]\r\n\r\nThe normal [pb_glossary id=\"4445\"]sinus rhythm[\/pb_glossary] of the heart is influenced by the [pb_glossary id=\"2935\"]autonomic\u00a0nervous system[\/pb_glossary]\u00a0through sympathetic and parasympathetic nerves. These nerves arise from two paired cardiovascular centers in the [pb_glossary id=\"3075\"]medulla[\/pb_glossary] of the brainstem. The parasympathetic nerves act to decrease the heart rate, and the sympathetic nerves act to increase the heart rate. Parasympathetic input normally predominates. Without it, the pacemaker cells of the heart would generate a resting heart rate of about 100 beats per minute, instead of a normal resting heart rate of about 72 beats per minute. The cardiovascular centers receive input from receptors throughout the body, and act through the sympathetic nerves to increase the heart rate, as needed.\u00a0Increased physical activity, for example, is detected by receptors in\u00a0muscles,\u00a0joints, and tendons. These receptors send\u00a0nerve impulses\u00a0to the cardiovascular centers, causing sympathetic nerves to increase the heart rate, and allowing more blood to flow to the muscles.\r\n\r\nBesides the autonomic\u00a0nervous system, other factors can also affect the heart rate. For example, [pb_glossary id=\"2958\"]thyroid[\/pb_glossary] hormones and [pb_glossary id=\"5869\"]adrenal[\/pb_glossary] hormones (such as epinephrine) can stimulate the heart to beat faster. The heart rate also increases when\u00a0blood pressure\u00a0drops or the body is dehydrated or overheated. On the other hand, cooling of the body and relaxation \u2014 among other factors \u2014 can contribute to a decrease in the heart rate.\r\n\r\nFeature: Human Biology in the News<\/h1>\r\n<\/div>\r\nWhen a patient\u2019s heart is too diseased or damaged to sustain life, a heart transplant is likely to be the only long-term solution. The first successful heart transplant was undertaken in South Africa in 1967. There are over 2,200 Canadians walking around today because of life-saving heart transplant surgery.\u00a0 Approximately 180 heart transplant surgeries are performed each year, but there are still so many Canadians on the transplant list that some die while waiting for a heart. The problem is that far too few hearts are available for transplant \u2014 there is more demand (people waiting for a heart transplant) than supply (organ donors). Sometimes, recipient hopefuls will receive a device called a Total Artificial Heart (see Figure 14.3.10), which can buy them some time until a donor heart becomes available.\r\n\r\n[caption id=\"attachment_7737\" align=\"alignnone\" width=\"1023\"]![\"14.3.10](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2023\/10\/Graphic_of_the_SynCardia_temporary_Total_Artificial_Heart_beside_a_human_heart-e1597182868278-2.jpg\")
Figure 14.3.10 A Total Artificial Heart, shown here, can be used for short periods of time in order to maintain a patient until a donor heart becomes available.<\/em>[\/caption]\r\n\r\nWatch the video below \"Total artificial heart option...\" from Stanford Health Care to see how it works:\r\n\r\nhttps:\/\/youtu.be\/1PtxaxcPnGc\r\nTotal artificial heart option at Stanford (Includes surgical graphic footage), Stanford Health Care, 2014.<\/p>\r\n\r\n
\r\n\r\n14.3 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- The [pb_glossary id=\"2987\"]heart[\/pb_glossary] is a muscular organ behind the sternum and slightly to the left of the center of the chest. Its function is to pump blood through the blood vessels of the\u00a0[pb_glossary id=\"5927\"]cardiovascular system[\/pb_glossary].<\/li>\r\n \t
- The wall of the heart consists of three layers. The middle layer, the [pb_glossary id=\"4191\"]myocardium[\/pb_glossary], is the thickest layer and consists mainly of [pb_glossary id=\"5925\"]cardiac muscle[\/pb_glossary]. The interior of the heart consists of four chambers, with an upper [pb_glossary id=\"4408\"]atrium[\/pb_glossary] and lower [pb_glossary id=\"4409\"]ventricle[\/pb_glossary] on each side of the heart. Blood enters the heart through the atria, which pump it to the ventricles. Then the ventricles pump blood out of the heart. Four valves in the heart keep blood flowing in the correct direction and prevent backflow.<\/li>\r\n \t
- The coronary circulation consists of blood vessels that carry blood to and from the heart muscle cells, and is different from the general circulation of blood through the heart chambers. There are two coronary arteries that supply the two sides of the heart with oxygenated blood. Cardiac veins drain deoxygenated blood back into the heart.<\/li>\r\n \t
- Deoxygenated blood flows into the right atrium through veins from the upper and lower body (superior and inferior [pb_glossary id=\"4410\"]vena cava[\/pb_glossary], respectively), and oxygenated blood flows into the left atrium through four pulmonary veins from the lungs. Each atrium pumps the blood to the ventricle below it. From the right ventricle, deoxygenated blood is pumped to the lungs through the two pulmonary arteries. From the left ventricle, oxygenated blood is pumped to the rest of the body through the aorta.<\/li>\r\n \t
- The [pb_glossary id=\"4447\"]cardiac cycle[\/pb_glossary] refers to a single complete heartbeat. It includes [pb_glossary id=\"4442\"]diastole[\/pb_glossary] \u2014 when the atria contract \u2014 and [pb_glossary id=\"4443\"]systole[\/pb_glossary], when the ventricles contract.<\/li>\r\n \t
- The normal, rhythmic beating of the heart is called [pb_glossary id=\"4445\"]sinus rhythm[\/pb_glossary]. It is established by the heart\u2019s [pb_glossary id=\"4446\"]pacemaker cells[\/pb_glossary] in the [pb_glossary id=\"4195\"]sinoatrial node[\/pb_glossary]. Electrical signals from the pacemaker cells travel to the atria, and cause them to contract. Then, the signals travel to the [pb_glossary id=\"4448\"]atrioventricular node[\/pb_glossary] and from there to the ventricles, causing them to contract. Electrical stimulation from the [pb_glossary id=\"2935\"]autonomic\u00a0nervous system[\/pb_glossary]\u00a0and hormones from the\u00a0[pb_glossary id=\"5985\"]endocrine system[\/pb_glossary]\u00a0can also influence heartbeat.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n14.3 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- What is the heart, where is located, and what is its function?<\/li>\r\n \t
- [h5p id=\"613\"]<\/li>\r\n \t
- Describe the coronary circulation.<\/li>\r\n \t
- Summarize how blood flows into, through, and out of the heart.<\/li>\r\n \t
- Explain what controls the beating of the heart.<\/li>\r\n \t
- What are the two types of cardiac muscle cells in the myocardium?\u00a0What are the differences between these two types of cells?<\/li>\r\n \t
- Explain why the blood from the cardiac veins empties into the right atrium of the heart. Focus on function (rather than anatomy) in your answer.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n14.3 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=1bnzVjOJ6NM\r\nNoel Bairey Merz: The single biggest health threat women face, TED, 2012.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=jJm7zBcN6-M\r\n
Watch a Transcatheter Aortic Valve Replacement (TAVR) Procedure at St. Luke's in Cedar Rapids, Iowa, UnityPoint Health - Cedar Rapids, 2018.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=zU6mmix04PI\r\n
A Change of Heart: My Transplant Experience | Thomas Volk | TEDxUWLaCrosse, TEDx Talks, 2018.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=biGuwQhuAsk\r\n
Heart Transplant Recipient Meets Donor Family For The First Time, WMC Health, 2018.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 14.3.1<\/strong>\r\n\r\n \t- Female clinician dressed in scrubs using a stethoscope<\/a> by Amanda Mills, USCDCP, on Pixnio<\/a> is used under a CC0<\/a> public domain certification license (https:\/\/creativecommons.org\/licenses\/publicdomain\/).<\/li>\r\n \t
- Human heart beating loud and strong<\/a> (audio) by Daniel Simion on Soundbible.com is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.<\/span><\/li>\r\n<\/ul>\r\nFigure 14.3.2<\/strong>\r\n\r\nBlausen_0470_HeartWall<\/a> by BruceBlaus<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\nFigure 14.3.3<\/strong>\r\n\r\nDiagram_of_the_human_heart_(cropped).svg<\/a> by Wapcaplet<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0 <\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license.\r\n\r\nFigure 14.3.4<\/strong>\r\n\r\nHeart_Valves<\/a>\u00a0by OpenStax College<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\nFigure 14.3.5<\/strong>\r\n\r\nCG_Heart Valve Animation<\/a> by DrJanaOfficial<\/a> on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n\r\nFigure 14.3.6<\/strong>\r\n\r\nHeart_tee_four_chamber_view<\/a> by Patrick J. Lynch, medical illustrator from Yale University School of Medicine, on Wikimedia Commons is used under a CC BY 2.5<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.5) license.\r\n\r\nFigure 14.3.7<\/strong>\r\n\r\nCirculation of blood through the heart<\/a> by Christinelmiller<\/a> on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license. [Original image<\/a> in the bottom right is by Wapcaplet<\/a> \/ CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/)]\r\n\r\nFigure 14.3.8<\/strong>\r\n\r\nHuman_healthy_pumping_heart_en.svg<\/a>\u00a0by Mariana Ruiz Villarreal [LadyofHats<\/a>] on Wikimedia Common is released into the public domain<\/a>\u00a0(https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 14.3.9<\/strong>\r\n\r\nCardiac_Conduction_System<\/a> by Cypressvine<\/a> on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n \r\n\r\nReferences<\/span>\r\n
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, June 19). Figure <\/span><\/span>19.12<\/span><\/span>\u00a0<\/span>Heart valves <\/span><\/span>with the atria and major vessels removed [digital image].\u00a0 In Anatomy and Physiology<\/em> (Section 19.1). OpenStax. https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/19-1-heart-anatomy#fig-ch20_01_04<\/span><\/span><\/p>\r\nBlausen.com Staff. (2014). Medical gallery of Blausen Medical 2014. WikiJournal of Medicine 1<\/em> (2). DOI:10.15347\/wjm\/2014.010. ISSN 2002-4436.<\/p>\r\nHeart and Stroke Foundation of Canada. (n.d.). https:\/\/www.heartandstroke.ca\/\r\nSliwa, K., Zilla, P. (2017, December 7). 50th anniversary of the first human heart transplant\u2014How is it seen today? European Heart Journal, 38<\/em>(46):<\/em>3402\u20133404. https:\/\/doi.org\/10.1093\/eurheartj\/ehx695<\/p>\r\nStanford Health Care. (2014, December 3). Total artificial heart option at Stanford (Includes surgical graphic footage). YouTube. https:\/\/www.youtube.com\/watch?v=1PtxaxcPnGc&feature=youtu.be<\/p>\r\n
TED. (2012, March 21). Noel Bairey Merz: The single biggest health threat women face. YouTube. https:\/\/www.youtube.com\/watch?v=1bnzVjOJ6NM&feature=youtu.be<\/p>\r\n
TEDx Talks. (2018, April 18). A change of heart: My transplant experience | Thomas Volk | TEDxUWLaCrosse. YouTube. https:\/\/www.youtube.com\/watch?v=zU6mmix04PI&feature=youtu.be<\/p>\r\n
UMagazine. (2015, Fall). The cutting edge: Patient first to bridge from experimental total artificial heart to transplant. UCLA Health. https:\/\/www.uclahealth.org\/u-magazine\/patient-first-to-bridge-from-experimental-total-artificial-heart-to-transplant<\/p>\r\n
UnityPoint Health - Cedar Rapids. (2018, February 7). Watch a transcatheter aortic valve replacement (TAVR) Procedure at St. Luke's in Cedar Rapids, Iowa. YouTube.\u00a0 https:\/\/www.youtube.com\/watch?v=jJm7zBcN6-M&feature=youtu.be<\/p>\r\n
WMC Health. (2018, September 13). Heart transplant recipient meets donor family for the first time. YouTube. https:\/\/www.youtube.com\/watch?v=biGuwQhuAsk&feature=youtu.be<\/p>\r\n \r\n\r\n \r\n\r\n ","rendered":"
<\/p>\n![\"14.3.1](\"https:\/\/pressbooks.ccconline.org\/acchumanbio\/wp-content\/uploads\/sites\/152\/2019\/06\/Dr.-with-Stethoscope-from-PIXNIO-47572-3006x4500-1-scaled-3.jpg\")
Figure 14.3.1 Healthy hearts are happy hearts. What do you hear?<\/figcaption><\/figure>\n\u00a0<\/em><\/em><\/p>\n\n
Introduction to the Heart<\/h1>\r\n<\/div>\r\nThe\u00a0[pb_glossary id=\"2987\"]heart[\/pb_glossary]<\/strong>\u00a0is a muscular organ behind the sternum (breastbone), slightly to the left of the center of the chest. A normal adult heart is about the size of a fist. The function of the heart is to pump\u00a0blood\u00a0through\u00a0blood vessels\u00a0of the\u00a0[pb_glossary id=\"5927\"]cardiovascular system[\/pb_glossary]. The continuous flow of [pb_glossary id=\"2702\"]blood[\/pb_glossary] through the system is necessary to provide all the\u00a0cells\u00a0of the body with oxygen and\u00a0nutrients, and to remove their metabolic wastes.\r\n\r\nStructure of the Heart<\/h1>\r\n<\/div>\r\nThe heart has a thick muscular wall that consists of several layers of tissue. Internally, the heart is divided into four chambers through which\u00a0blood\u00a0flows. Because of heart valves, blood flows in just one direction through the chambers.\r\nHeart Wall<\/h2>\r\n[caption id=\"attachment_4407\" align=\"alignright\" width=\"424\"] Figure 14.3.2 The wall of the heart is made up mainly of myocardium, which consists largely of cardiac muscle.<\/em>[\/caption]\r\n\r\nAs shown in Figure 14.3.2, the wall of the heart is made up of three layers, called the endocardium, myocardium, and pericardium.\r\n\r\n \t- The\u00a0[pb_glossary id=\"4193\"]endocardium[\/pb_glossary]<\/strong>\u00a0is the innermost layer of the heart wall. It is made up primarily of simple epithelial\u00a0cells. It covers the heart chambers and valves. A thin layer of connective tissue joins the endocardium to the myocardium.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"4191\"]myocardium[\/pb_glossary]<\/strong> is the middle and thickest layer of the heart wall. It consists of [pb_glossary id=\"5925\"]cardiac muscle[\/pb_glossary] surrounded by a framework of collagen. There are two types of cardiac muscle cells in the myocardium: cardiomyocytes \u2014 which have the ability to contract easily \u2014 and pacemaker cells, which conduct electrical impulses that cause the cardiomyocytes to contract. About 99 per cent of cardiac muscle cells are cardiomyocytes, and the remaining one per cent is pacemaker cells. The myocardium is supplied with blood vessels and nerve fibres via the pericardium.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"4194\"]pericardium[\/pb_glossary]<\/strong>\u00a0is a protective sac that encloses and protects the heart. The pericardium consists of two membranes (visceral pericardium and parietal pericardium), between which there is a fluid-filled cavity. The fluid helps to cushion the heart, and also lubricates its outer surface.<\/li>\r\n<\/ul>\r\n
Heart Chambers<\/h2>\r\nAs shown in Figure 14.3.3 the four chambers of the heart include two upper chambers called atria (singular, [pb_glossary id=\"4408\"]atrium[\/pb_glossary])<\/strong>, and two lower chambers called\u00a0[pb_glossary id=\"4409\"]ventricles[\/pb_glossary].<\/strong> The atria are also referred to as receiving chambers, because blood coming into the heart first enters these two chambers. The right atrium receives deoxygenated blood from the upper and lower body through the superior [pb_glossary id=\"4410\"]vena cava[\/pb_glossary] and inferior vena cava, respectively. The left atrium receives oxygenated blood from the lungs through the [pb_glossary id=\"4411\"]pulmonary veins[\/pb_glossary]. The ventricles are also referred to as discharging chambers, because blood leaving the heart passes out through these two chambers. The right ventricle discharges blood to the lungs through the [pb_glossary id=\"4412\"]pulmonary artery[\/pb_glossary], and the left ventricle discharges blood to the rest of the body through the [pb_glossary id=\"4413\"]aorta[\/pb_glossary]. The four chambers are separated from each other by dense connective tissue consisting mainly of [pb_glossary id=\"3970\"]collagen[\/pb_glossary].\r\n\r\n[caption id=\"attachment_4414\" align=\"aligncenter\" width=\"663\"] Figure 14.3.3 This cross-sectional diagram of the heart shows its four chambers and four valves. The white arrows indicate the direction of blood flow through the heart chambers.<\/em>[\/caption]\r\nHeart Valves<\/h2>\r\n[caption id=\"attachment_4423\" align=\"alignleft\" width=\"370\"] Figure 14.3.4 If the veins and arteries of the heart were removed, a top-down view of the heart would reveal the four valves that are critical in preventing backflow of blood. Note the three cusps of the tricuspid AV valve and the 2 cusps of the bicuspid AV valve. Also note the size difference between the AV valves and the semilunar valves.<\/em>[\/caption]\r\n\r\nFigure 14.3.4 shows the location of the heart's four valves in a top-down view, looking down at the heart as if the arteries and veins feeding into and out of the heart were removed. The heart valves allow blood to flow from the atria to the ventricles, and from the ventricles to the pulmonary artery and aorta. The valves are constructed in such a way that blood can flow through them in only one direction, thus preventing the backflow of blood. Figure 14.3.5 shows how valves open to let blood into the appropriate chamber, and then close to prevent blood from moving in the wrong direction and the next chamber contracts.\u00a0 The four valves are the:\r\n\r\n \t- [pb_glossary id=\"4415\"]Tricuspid atrioventricular valve[\/pb_glossary]<\/strong>, (can be shortened to tricuspid AV valve) which allows blood to flow from the right atrium to the right ventricle.<\/li>\r\n \t
- [pb_glossary id=\"4416\"]Bicuspid atrioventricular valve[\/pb_glossary] <\/strong>(also know as the mitral valve), which allows blood to flow from the left atrium to the left ventricle.<\/li>\r\n \t
- [pb_glossary id=\"4417\"]Pulmonary semilunar valve[\/pb_glossary]<\/strong>, which allows blood to flow from the right ventricle to the pulmonary artery.<\/li>\r\n \t
- [pb_glossary id=\"4418\"]Aortic semilunar valve[\/pb_glossary]<\/strong>, which allows blood to flow from the left ventricle to the aorta.<\/li>\r\n<\/ol>\r\n[caption id=\"attachment_4419\" align=\"aligncenter\" width=\"411\"] Figure 14.3.5 The valves of the heart prevent backflow of blood. The open when the chamber before them contracts (systole) and then close when that chamber relaxes (diastole).<\/em>[\/caption]\r\n\r\n\r\n\r\n[caption id=\"attachment_4426\" align=\"alignright\" width=\"384\"] Figure 14.3.6 The chordae tendoneae, shown in this diagram in white, play a critical role in reinforcing the AV valves of the heart.<\/em>[\/caption]\r\n\r\nThe two atrioventricular (AV) valves prevent backflow when the ventricles are contracting, while the semilunar valves prevent backflow from vessels.\u00a0 This means that the AV valves must withstand much more pressure than do the semilunar valves.\u00a0 In order to withstand the force of the ventricles contracting (to prevent blood from backflowing into the atria), the AV valves are reinforced with structures called [pb_glossary id=\"4424\"]chordae tendineae[\/pb_glossary] \u2014 tendon-like cords of connective tissue which anchor the valve and prevent it from [pb_glossary id=\"4425\"]prolapse[\/pb_glossary].\u00a0 Figure 14.3.6 shows the structure and location of the chordae tendoneae.\r\n\r\nThe chordae tendoneae are under such force that they need special attachments to the interior of the ventricles where they anchor.\u00a0 [pb_glossary id=\"4430\"]Papillary muscles[\/pb_glossary] are specialized muscles in the interior of the ventricle that provide a strong anchor point for the chordae tendineae.\r\n
Coronary\u00a0Circulation<\/h1>\r\n<\/div>\r\nThe [pb_glossary id=\"5631\"]cardiomyocyte<\/strong>[\/pb_glossary]s of the muscular walls of the heart are very active cells, because they are responsible for the constant beating of the heart. These cells need a continuous supply of oxygen and\u00a0nutrients. The carbon dioxide and waste products they produce also must be continuously removed. The\u00a0blood vessels\u00a0that carry blood to and from the heart muscle cells make up the [pb_glossary id=\"4421\"]coronary\u00a0circulation[\/pb_glossary]. Note that the blood vessels of the coronary circulation supply heart tissues with blood, and are different from the blood vessels that carry blood to and from the chambers of the heart as part of the general circulation.\u00a0[pb_glossary id=\"4422\"]Coronary arteries[\/pb_glossary] <\/strong>supply oxygen-rich blood to the heart muscle cells. Coronary veins remove deoxygenated blood from the heart\u00a0muscles\u00a0cells.\r\n\r\n \t- There are two [pb_glossary id=\"4422\"]coronary arteries[\/pb_glossary] \u2014 a right coronary artery that supplies the right side of the heart, and a left coronary artery that supplies the left side of the heart. These arteries branch repeatedly into smaller and smaller arteries and finally into capillaries, which exchange gases,\u00a0nutrients, and waste products with cardiomyocytes.<\/li>\r\n \t
- At the back of the heart, small cardiac veins drain into larger veins, and finally into the great cardiac vein, which empties into the right atrium. At the front of the heart, small cardiac veins drain directly into the right atrium.<\/li>\r\n<\/ul>\r\n\r\n
Blood Circulation Through the Heart<\/h1>\r\n<\/div>\r\nFigure 14.3.7 shows how blood circulates through the chambers of the heart. The right atrium collects blood from two large veins, the superior vena cava (from the upper body) and the inferior vena cava (from the lower body). The blood that collects in the right atrium is pumped through the tricuspid valve into the right ventricle. From the right ventricle, the blood is pumped through the pulmonary valve into the pulmonary artery. The pulmonary artery carries the blood to the lungs, where it enters the pulmonary circulation, gives up carbon dioxide, and picks up oxygen. The oxygenated blood travels back from the lungs through the pulmonary veins (of which there are four), and enters the left atrium of the heart. From the left atrium, the blood is pumped through the mitral valve into the left ventricle. From the left ventricle, the blood is pumped through the aortic valve into the aorta, which subsequently branches into smaller arteries that carry the blood throughout the rest of the body. After passing through capillaries and exchanging substances with cells, the blood returns to the right atrium via the superior vena cava and inferior vena cava, and the process begins anew.\r\n\r\n[caption id=\"attachment_4431\" align=\"alignnone\" width=\"3000\"] Figure 14.3.7 The flow chart in this diagram summarizes the pathway blood takes as it flows into, through, and out of the heart. Trace the path of blood flow in the diagram of the heart as you follow it through the flow chart.<\/em>[\/caption]\r\n\r\n\r\nCardiac Cycle<\/h1>\r\n<\/div>\r\nThe cardiac cycle refers to a single complete heartbeat, which includes one iteration of the lub and dub sounds heard through a stethoscope. During the cardiac cycle, the atria and ventricles work in a coordinated fashion so that blood is pumped efficiently through and out of the heart. The cardiac cycle includes two parts, called diastole and systole, which are illustrated in the diagrams in Figure 14.3.8.\r\n\r\n \t- During\u00a0[pb_glossary id=\"4442\"]diastole[\/pb_glossary],<\/strong>\u00a0the atria contract and pump blood into the ventricles, while the ventricles relax and fill with blood from the atria.<\/li>\r\n \t
- During\u00a0[pb_glossary id=\"4443\"]systole[\/pb_glossary],<\/strong>\u00a0the atria relax and collect blood from the lungs and body, while the ventricles contract and pump blood out of the heart.<\/li>\r\n<\/ul>\r\n[caption id=\"attachment_4444\" align=\"aligncenter\" width=\"495\"] Figure 14.3.8 Diastole is referred to the filling stage, because this is when the ventricles fill with blood. Systole is referred to the pumping stage because this is when the ventricles pump blood out of the heart.<\/em>[\/caption]\r\n\r\nElectrical Stimulation of the Heart<\/span>\r\n\r\nThe normal, rhythmical beating of the heart is called\u00a0[pb_glossary id=\"4445\"]sinus rhythm[\/pb_glossary].<\/strong>\u00a0It is established by the heart\u2019s\u00a0[pb_glossary id=\"4446\"]pacemaker[\/pb_glossary]<\/strong> cells, which are located in an area of the heart called the [pb_glossary id=\"4195\"]sinoatrial node[\/pb_glossary] (shown in Figure 14.3.9). The pacemaker cells create electrical signals with the movement of electrolytes (sodium, potassium, and calcium ions) into and out of the cells. For each [pb_glossary id=\"4447\"]cardiac cycle[\/pb_glossary], an electrical signal rapidly travels first from the sinoatrial node, to the right and left atria so they contract together. Then, the signal travels to another node, called the [pb_glossary id=\"4448\"]atrioventricular node[\/pb_glossary] (Figure 14.3.9), and from there to the right and left ventricles (which also contract together), just a split second after the atria contract.\r\n\r\n[caption id=\"attachment_4449\" align=\"aligncenter\" width=\"416\"] Figure 14.3.9 The sinoatrial (SA) node causes the atria to contract and then signals the atrioventricular (AV) nodes to initiate the contraction of the ventricles.<\/em>[\/caption]\r\n\r\nThe normal [pb_glossary id=\"4445\"]sinus rhythm[\/pb_glossary] of the heart is influenced by the [pb_glossary id=\"2935\"]autonomic\u00a0nervous system[\/pb_glossary]\u00a0through sympathetic and parasympathetic nerves. These nerves arise from two paired cardiovascular centers in the [pb_glossary id=\"3075\"]medulla[\/pb_glossary] of the brainstem. The parasympathetic nerves act to decrease the heart rate, and the sympathetic nerves act to increase the heart rate. Parasympathetic input normally predominates. Without it, the pacemaker cells of the heart would generate a resting heart rate of about 100 beats per minute, instead of a normal resting heart rate of about 72 beats per minute. The cardiovascular centers receive input from receptors throughout the body, and act through the sympathetic nerves to increase the heart rate, as needed.\u00a0Increased physical activity, for example, is detected by receptors in\u00a0muscles,\u00a0joints, and tendons. These receptors send\u00a0nerve impulses\u00a0to the cardiovascular centers, causing sympathetic nerves to increase the heart rate, and allowing more blood to flow to the muscles.\r\n\r\nBesides the autonomic\u00a0nervous system, other factors can also affect the heart rate. For example, [pb_glossary id=\"2958\"]thyroid[\/pb_glossary] hormones and [pb_glossary id=\"5869\"]adrenal[\/pb_glossary] hormones (such as epinephrine) can stimulate the heart to beat faster. The heart rate also increases when\u00a0blood pressure\u00a0drops or the body is dehydrated or overheated. On the other hand, cooling of the body and relaxation \u2014 among other factors \u2014 can contribute to a decrease in the heart rate.\r\n\r\n
Feature: Human Biology in the News<\/h1>\r\n<\/div>\r\nWhen a patient\u2019s heart is too diseased or damaged to sustain life, a heart transplant is likely to be the only long-term solution. The first successful heart transplant was undertaken in South Africa in 1967. There are over 2,200 Canadians walking around today because of life-saving heart transplant surgery.\u00a0 Approximately 180 heart transplant surgeries are performed each year, but there are still so many Canadians on the transplant list that some die while waiting for a heart. The problem is that far too few hearts are available for transplant \u2014 there is more demand (people waiting for a heart transplant) than supply (organ donors). Sometimes, recipient hopefuls will receive a device called a Total Artificial Heart (see Figure 14.3.10), which can buy them some time until a donor heart becomes available.\r\n\r\n[caption id=\"attachment_7737\" align=\"alignnone\" width=\"1023\"] Figure 14.3.10 A Total Artificial Heart, shown here, can be used for short periods of time in order to maintain a patient until a donor heart becomes available.<\/em>[\/caption]\r\n\r\nWatch the video below \"Total artificial heart option...\" from Stanford Health Care to see how it works:\r\n\r\nhttps:\/\/youtu.be\/1PtxaxcPnGc\r\nTotal artificial heart option at Stanford (Includes surgical graphic footage), Stanford Health Care, 2014.<\/p>\r\n\r\n
\r\n\r\n14.3 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- The [pb_glossary id=\"2987\"]heart[\/pb_glossary] is a muscular organ behind the sternum and slightly to the left of the center of the chest. Its function is to pump blood through the blood vessels of the\u00a0[pb_glossary id=\"5927\"]cardiovascular system[\/pb_glossary].<\/li>\r\n \t
- The wall of the heart consists of three layers. The middle layer, the [pb_glossary id=\"4191\"]myocardium[\/pb_glossary], is the thickest layer and consists mainly of [pb_glossary id=\"5925\"]cardiac muscle[\/pb_glossary]. The interior of the heart consists of four chambers, with an upper [pb_glossary id=\"4408\"]atrium[\/pb_glossary] and lower [pb_glossary id=\"4409\"]ventricle[\/pb_glossary] on each side of the heart. Blood enters the heart through the atria, which pump it to the ventricles. Then the ventricles pump blood out of the heart. Four valves in the heart keep blood flowing in the correct direction and prevent backflow.<\/li>\r\n \t
- The coronary circulation consists of blood vessels that carry blood to and from the heart muscle cells, and is different from the general circulation of blood through the heart chambers. There are two coronary arteries that supply the two sides of the heart with oxygenated blood. Cardiac veins drain deoxygenated blood back into the heart.<\/li>\r\n \t
- Deoxygenated blood flows into the right atrium through veins from the upper and lower body (superior and inferior [pb_glossary id=\"4410\"]vena cava[\/pb_glossary], respectively), and oxygenated blood flows into the left atrium through four pulmonary veins from the lungs. Each atrium pumps the blood to the ventricle below it. From the right ventricle, deoxygenated blood is pumped to the lungs through the two pulmonary arteries. From the left ventricle, oxygenated blood is pumped to the rest of the body through the aorta.<\/li>\r\n \t
- The [pb_glossary id=\"4447\"]cardiac cycle[\/pb_glossary] refers to a single complete heartbeat. It includes [pb_glossary id=\"4442\"]diastole[\/pb_glossary] \u2014 when the atria contract \u2014 and [pb_glossary id=\"4443\"]systole[\/pb_glossary], when the ventricles contract.<\/li>\r\n \t
- The normal, rhythmic beating of the heart is called [pb_glossary id=\"4445\"]sinus rhythm[\/pb_glossary]. It is established by the heart\u2019s [pb_glossary id=\"4446\"]pacemaker cells[\/pb_glossary] in the [pb_glossary id=\"4195\"]sinoatrial node[\/pb_glossary]. Electrical signals from the pacemaker cells travel to the atria, and cause them to contract. Then, the signals travel to the [pb_glossary id=\"4448\"]atrioventricular node[\/pb_glossary] and from there to the ventricles, causing them to contract. Electrical stimulation from the [pb_glossary id=\"2935\"]autonomic\u00a0nervous system[\/pb_glossary]\u00a0and hormones from the\u00a0[pb_glossary id=\"5985\"]endocrine system[\/pb_glossary]\u00a0can also influence heartbeat.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n14.3 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- What is the heart, where is located, and what is its function?<\/li>\r\n \t
- [h5p id=\"613\"]<\/li>\r\n \t
- Describe the coronary circulation.<\/li>\r\n \t
- Summarize how blood flows into, through, and out of the heart.<\/li>\r\n \t
- Explain what controls the beating of the heart.<\/li>\r\n \t
- What are the two types of cardiac muscle cells in the myocardium?\u00a0What are the differences between these two types of cells?<\/li>\r\n \t
- Explain why the blood from the cardiac veins empties into the right atrium of the heart. Focus on function (rather than anatomy) in your answer.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n14.3 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=1bnzVjOJ6NM\r\nNoel Bairey Merz: The single biggest health threat women face, TED, 2012.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=jJm7zBcN6-M\r\n
Watch a Transcatheter Aortic Valve Replacement (TAVR) Procedure at St. Luke's in Cedar Rapids, Iowa, UnityPoint Health - Cedar Rapids, 2018.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=zU6mmix04PI\r\n
A Change of Heart: My Transplant Experience | Thomas Volk | TEDxUWLaCrosse, TEDx Talks, 2018.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=biGuwQhuAsk\r\n
Heart Transplant Recipient Meets Donor Family For The First Time, WMC Health, 2018.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 14.3.1<\/strong>\r\n\r\n \t- Female clinician dressed in scrubs using a stethoscope<\/a> by Amanda Mills, USCDCP, on Pixnio<\/a> is used under a CC0<\/a> public domain certification license (https:\/\/creativecommons.org\/licenses\/publicdomain\/).<\/li>\r\n \t
- Human heart beating loud and strong<\/a> (audio) by Daniel Simion on Soundbible.com is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.<\/span><\/li>\r\n<\/ul>\r\nFigure 14.3.2<\/strong>\r\n\r\nBlausen_0470_HeartWall<\/a> by BruceBlaus<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\nFigure 14.3.3<\/strong>\r\n\r\nDiagram_of_the_human_heart_(cropped).svg<\/a> by Wapcaplet<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0 <\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license.\r\n\r\nFigure 14.3.4<\/strong>\r\n\r\nHeart_Valves<\/a>\u00a0by OpenStax College<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\nFigure 14.3.5<\/strong>\r\n\r\nCG_Heart Valve Animation<\/a> by DrJanaOfficial<\/a> on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n\r\nFigure 14.3.6<\/strong>\r\n\r\nHeart_tee_four_chamber_view<\/a> by Patrick J. Lynch, medical illustrator from Yale University School of Medicine, on Wikimedia Commons is used under a CC BY 2.5<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.5) license.\r\n\r\nFigure 14.3.7<\/strong>\r\n\r\nCirculation of blood through the heart<\/a> by Christinelmiller<\/a> on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license. [Original image<\/a> in the bottom right is by Wapcaplet<\/a> \/ CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/)]\r\n\r\nFigure 14.3.8<\/strong>\r\n\r\nHuman_healthy_pumping_heart_en.svg<\/a>\u00a0by Mariana Ruiz Villarreal [LadyofHats<\/a>] on Wikimedia Common is released into the public domain<\/a>\u00a0(https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 14.3.9<\/strong>\r\n\r\nCardiac_Conduction_System<\/a> by Cypressvine<\/a> on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n \r\n\r\nReferences<\/span>\r\n
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, June 19). Figure <\/span><\/span>19.12<\/span><\/span>\u00a0<\/span>Heart valves <\/span><\/span>with the atria and major vessels removed [digital image].\u00a0 In Anatomy and Physiology<\/em> (Section 19.1). OpenStax. https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/19-1-heart-anatomy#fig-ch20_01_04<\/span><\/span><\/p>\r\nBlausen.com Staff. (2014). Medical gallery of Blausen Medical 2014. WikiJournal of Medicine 1<\/em> (2). DOI:10.15347\/wjm\/2014.010. ISSN 2002-4436.<\/p>\r\nHeart and Stroke Foundation of Canada. (n.d.). https:\/\/www.heartandstroke.ca\/\r\nSliwa, K., Zilla, P. (2017, December 7). 50th anniversary of the first human heart transplant\u2014How is it seen today? European Heart Journal, 38<\/em>(46):<\/em>3402\u20133404. https:\/\/doi.org\/10.1093\/eurheartj\/ehx695<\/p>\r\nStanford Health Care. (2014, December 3). Total artificial heart option at Stanford (Includes surgical graphic footage). YouTube. https:\/\/www.youtube.com\/watch?v=1PtxaxcPnGc&feature=youtu.be<\/p>\r\n
TED. (2012, March 21). Noel Bairey Merz: The single biggest health threat women face. YouTube. https:\/\/www.youtube.com\/watch?v=1bnzVjOJ6NM&feature=youtu.be<\/p>\r\n
TEDx Talks. (2018, April 18). A change of heart: My transplant experience | Thomas Volk | TEDxUWLaCrosse. YouTube. https:\/\/www.youtube.com\/watch?v=zU6mmix04PI&feature=youtu.be<\/p>\r\n
UMagazine. (2015, Fall). The cutting edge: Patient first to bridge from experimental total artificial heart to transplant. UCLA Health. https:\/\/www.uclahealth.org\/u-magazine\/patient-first-to-bridge-from-experimental-total-artificial-heart-to-transplant<\/p>\r\n
UnityPoint Health - Cedar Rapids. (2018, February 7). Watch a transcatheter aortic valve replacement (TAVR) Procedure at St. Luke's in Cedar Rapids, Iowa. YouTube.\u00a0 https:\/\/www.youtube.com\/watch?v=jJm7zBcN6-M&feature=youtu.be<\/p>\r\n
WMC Health. (2018, September 13). Heart transplant recipient meets donor family for the first time. YouTube. https:\/\/www.youtube.com\/watch?v=biGuwQhuAsk&feature=youtu.be<\/p>\r\n \r\n\r\n \r\n\r\n ","rendered":"
<\/p>\nFigure 14.3.1 Healthy hearts are happy hearts. What do you hear?<\/figcaption><\/figure>\n\u00a0<\/em><\/em><\/p>\n\n
Structure of the Heart<\/h1>\r\n<\/div>\r\nThe heart has a thick muscular wall that consists of several layers of tissue. Internally, the heart is divided into four chambers through which\u00a0blood\u00a0flows. Because of heart valves, blood flows in just one direction through the chambers.\r\nHeart Wall<\/h2>\r\n[caption id=\"attachment_4407\" align=\"alignright\" width=\"424\"] Figure 14.3.2 The wall of the heart is made up mainly of myocardium, which consists largely of cardiac muscle.<\/em>[\/caption]\r\n\r\nAs shown in Figure 14.3.2, the wall of the heart is made up of three layers, called the endocardium, myocardium, and pericardium.\r\n\r\n \t- The\u00a0[pb_glossary id=\"4193\"]endocardium[\/pb_glossary]<\/strong>\u00a0is the innermost layer of the heart wall. It is made up primarily of simple epithelial\u00a0cells. It covers the heart chambers and valves. A thin layer of connective tissue joins the endocardium to the myocardium.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"4191\"]myocardium[\/pb_glossary]<\/strong> is the middle and thickest layer of the heart wall. It consists of [pb_glossary id=\"5925\"]cardiac muscle[\/pb_glossary] surrounded by a framework of collagen. There are two types of cardiac muscle cells in the myocardium: cardiomyocytes \u2014 which have the ability to contract easily \u2014 and pacemaker cells, which conduct electrical impulses that cause the cardiomyocytes to contract. About 99 per cent of cardiac muscle cells are cardiomyocytes, and the remaining one per cent is pacemaker cells. The myocardium is supplied with blood vessels and nerve fibres via the pericardium.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"4194\"]pericardium[\/pb_glossary]<\/strong>\u00a0is a protective sac that encloses and protects the heart. The pericardium consists of two membranes (visceral pericardium and parietal pericardium), between which there is a fluid-filled cavity. The fluid helps to cushion the heart, and also lubricates its outer surface.<\/li>\r\n<\/ul>\r\n
Heart Chambers<\/h2>\r\nAs shown in Figure 14.3.3 the four chambers of the heart include two upper chambers called atria (singular, [pb_glossary id=\"4408\"]atrium[\/pb_glossary])<\/strong>, and two lower chambers called\u00a0[pb_glossary id=\"4409\"]ventricles[\/pb_glossary].<\/strong> The atria are also referred to as receiving chambers, because blood coming into the heart first enters these two chambers. The right atrium receives deoxygenated blood from the upper and lower body through the superior [pb_glossary id=\"4410\"]vena cava[\/pb_glossary] and inferior vena cava, respectively. The left atrium receives oxygenated blood from the lungs through the [pb_glossary id=\"4411\"]pulmonary veins[\/pb_glossary]. The ventricles are also referred to as discharging chambers, because blood leaving the heart passes out through these two chambers. The right ventricle discharges blood to the lungs through the [pb_glossary id=\"4412\"]pulmonary artery[\/pb_glossary], and the left ventricle discharges blood to the rest of the body through the [pb_glossary id=\"4413\"]aorta[\/pb_glossary]. The four chambers are separated from each other by dense connective tissue consisting mainly of [pb_glossary id=\"3970\"]collagen[\/pb_glossary].\r\n\r\n[caption id=\"attachment_4414\" align=\"aligncenter\" width=\"663\"] Figure 14.3.3 This cross-sectional diagram of the heart shows its four chambers and four valves. The white arrows indicate the direction of blood flow through the heart chambers.<\/em>[\/caption]\r\nHeart Valves<\/h2>\r\n[caption id=\"attachment_4423\" align=\"alignleft\" width=\"370\"] Figure 14.3.4 If the veins and arteries of the heart were removed, a top-down view of the heart would reveal the four valves that are critical in preventing backflow of blood. Note the three cusps of the tricuspid AV valve and the 2 cusps of the bicuspid AV valve. Also note the size difference between the AV valves and the semilunar valves.<\/em>[\/caption]\r\n\r\nFigure 14.3.4 shows the location of the heart's four valves in a top-down view, looking down at the heart as if the arteries and veins feeding into and out of the heart were removed. The heart valves allow blood to flow from the atria to the ventricles, and from the ventricles to the pulmonary artery and aorta. The valves are constructed in such a way that blood can flow through them in only one direction, thus preventing the backflow of blood. Figure 14.3.5 shows how valves open to let blood into the appropriate chamber, and then close to prevent blood from moving in the wrong direction and the next chamber contracts.\u00a0 The four valves are the:\r\n\r\n \t- [pb_glossary id=\"4415\"]Tricuspid atrioventricular valve[\/pb_glossary]<\/strong>, (can be shortened to tricuspid AV valve) which allows blood to flow from the right atrium to the right ventricle.<\/li>\r\n \t
- [pb_glossary id=\"4416\"]Bicuspid atrioventricular valve[\/pb_glossary] <\/strong>(also know as the mitral valve), which allows blood to flow from the left atrium to the left ventricle.<\/li>\r\n \t
- [pb_glossary id=\"4417\"]Pulmonary semilunar valve[\/pb_glossary]<\/strong>, which allows blood to flow from the right ventricle to the pulmonary artery.<\/li>\r\n \t
- [pb_glossary id=\"4418\"]Aortic semilunar valve[\/pb_glossary]<\/strong>, which allows blood to flow from the left ventricle to the aorta.<\/li>\r\n<\/ol>\r\n[caption id=\"attachment_4419\" align=\"aligncenter\" width=\"411\"] Figure 14.3.5 The valves of the heart prevent backflow of blood. The open when the chamber before them contracts (systole) and then close when that chamber relaxes (diastole).<\/em>[\/caption]\r\n\r\n\r\n\r\n[caption id=\"attachment_4426\" align=\"alignright\" width=\"384\"] Figure 14.3.6 The chordae tendoneae, shown in this diagram in white, play a critical role in reinforcing the AV valves of the heart.<\/em>[\/caption]\r\n\r\nThe two atrioventricular (AV) valves prevent backflow when the ventricles are contracting, while the semilunar valves prevent backflow from vessels.\u00a0 This means that the AV valves must withstand much more pressure than do the semilunar valves.\u00a0 In order to withstand the force of the ventricles contracting (to prevent blood from backflowing into the atria), the AV valves are reinforced with structures called [pb_glossary id=\"4424\"]chordae tendineae[\/pb_glossary] \u2014 tendon-like cords of connective tissue which anchor the valve and prevent it from [pb_glossary id=\"4425\"]prolapse[\/pb_glossary].\u00a0 Figure 14.3.6 shows the structure and location of the chordae tendoneae.\r\n\r\nThe chordae tendoneae are under such force that they need special attachments to the interior of the ventricles where they anchor.\u00a0 [pb_glossary id=\"4430\"]Papillary muscles[\/pb_glossary] are specialized muscles in the interior of the ventricle that provide a strong anchor point for the chordae tendineae.\r\n
Coronary\u00a0Circulation<\/h1>\r\n<\/div>\r\nThe [pb_glossary id=\"5631\"]cardiomyocyte<\/strong>[\/pb_glossary]s of the muscular walls of the heart are very active cells, because they are responsible for the constant beating of the heart. These cells need a continuous supply of oxygen and\u00a0nutrients. The carbon dioxide and waste products they produce also must be continuously removed. The\u00a0blood vessels\u00a0that carry blood to and from the heart muscle cells make up the [pb_glossary id=\"4421\"]coronary\u00a0circulation[\/pb_glossary]. Note that the blood vessels of the coronary circulation supply heart tissues with blood, and are different from the blood vessels that carry blood to and from the chambers of the heart as part of the general circulation.\u00a0[pb_glossary id=\"4422\"]Coronary arteries[\/pb_glossary] <\/strong>supply oxygen-rich blood to the heart muscle cells. Coronary veins remove deoxygenated blood from the heart\u00a0muscles\u00a0cells.\r\n\r\n \t- There are two [pb_glossary id=\"4422\"]coronary arteries[\/pb_glossary] \u2014 a right coronary artery that supplies the right side of the heart, and a left coronary artery that supplies the left side of the heart. These arteries branch repeatedly into smaller and smaller arteries and finally into capillaries, which exchange gases,\u00a0nutrients, and waste products with cardiomyocytes.<\/li>\r\n \t
- At the back of the heart, small cardiac veins drain into larger veins, and finally into the great cardiac vein, which empties into the right atrium. At the front of the heart, small cardiac veins drain directly into the right atrium.<\/li>\r\n<\/ul>\r\n\r\n
Blood Circulation Through the Heart<\/h1>\r\n<\/div>\r\nFigure 14.3.7 shows how blood circulates through the chambers of the heart. The right atrium collects blood from two large veins, the superior vena cava (from the upper body) and the inferior vena cava (from the lower body). The blood that collects in the right atrium is pumped through the tricuspid valve into the right ventricle. From the right ventricle, the blood is pumped through the pulmonary valve into the pulmonary artery. The pulmonary artery carries the blood to the lungs, where it enters the pulmonary circulation, gives up carbon dioxide, and picks up oxygen. The oxygenated blood travels back from the lungs through the pulmonary veins (of which there are four), and enters the left atrium of the heart. From the left atrium, the blood is pumped through the mitral valve into the left ventricle. From the left ventricle, the blood is pumped through the aortic valve into the aorta, which subsequently branches into smaller arteries that carry the blood throughout the rest of the body. After passing through capillaries and exchanging substances with cells, the blood returns to the right atrium via the superior vena cava and inferior vena cava, and the process begins anew.\r\n\r\n[caption id=\"attachment_4431\" align=\"alignnone\" width=\"3000\"] Figure 14.3.7 The flow chart in this diagram summarizes the pathway blood takes as it flows into, through, and out of the heart. Trace the path of blood flow in the diagram of the heart as you follow it through the flow chart.<\/em>[\/caption]\r\n\r\n\r\nCardiac Cycle<\/h1>\r\n<\/div>\r\nThe cardiac cycle refers to a single complete heartbeat, which includes one iteration of the lub and dub sounds heard through a stethoscope. During the cardiac cycle, the atria and ventricles work in a coordinated fashion so that blood is pumped efficiently through and out of the heart. The cardiac cycle includes two parts, called diastole and systole, which are illustrated in the diagrams in Figure 14.3.8.\r\n\r\n \t- During\u00a0[pb_glossary id=\"4442\"]diastole[\/pb_glossary],<\/strong>\u00a0the atria contract and pump blood into the ventricles, while the ventricles relax and fill with blood from the atria.<\/li>\r\n \t
- During\u00a0[pb_glossary id=\"4443\"]systole[\/pb_glossary],<\/strong>\u00a0the atria relax and collect blood from the lungs and body, while the ventricles contract and pump blood out of the heart.<\/li>\r\n<\/ul>\r\n[caption id=\"attachment_4444\" align=\"aligncenter\" width=\"495\"] Figure 14.3.8 Diastole is referred to the filling stage, because this is when the ventricles fill with blood. Systole is referred to the pumping stage because this is when the ventricles pump blood out of the heart.<\/em>[\/caption]\r\n\r\nElectrical Stimulation of the Heart<\/span>\r\n\r\nThe normal, rhythmical beating of the heart is called\u00a0[pb_glossary id=\"4445\"]sinus rhythm[\/pb_glossary].<\/strong>\u00a0It is established by the heart\u2019s\u00a0[pb_glossary id=\"4446\"]pacemaker[\/pb_glossary]<\/strong> cells, which are located in an area of the heart called the [pb_glossary id=\"4195\"]sinoatrial node[\/pb_glossary] (shown in Figure 14.3.9). The pacemaker cells create electrical signals with the movement of electrolytes (sodium, potassium, and calcium ions) into and out of the cells. For each [pb_glossary id=\"4447\"]cardiac cycle[\/pb_glossary], an electrical signal rapidly travels first from the sinoatrial node, to the right and left atria so they contract together. Then, the signal travels to another node, called the [pb_glossary id=\"4448\"]atrioventricular node[\/pb_glossary] (Figure 14.3.9), and from there to the right and left ventricles (which also contract together), just a split second after the atria contract.\r\n\r\n[caption id=\"attachment_4449\" align=\"aligncenter\" width=\"416\"] Figure 14.3.9 The sinoatrial (SA) node causes the atria to contract and then signals the atrioventricular (AV) nodes to initiate the contraction of the ventricles.<\/em>[\/caption]\r\n\r\nThe normal [pb_glossary id=\"4445\"]sinus rhythm[\/pb_glossary] of the heart is influenced by the [pb_glossary id=\"2935\"]autonomic\u00a0nervous system[\/pb_glossary]\u00a0through sympathetic and parasympathetic nerves. These nerves arise from two paired cardiovascular centers in the [pb_glossary id=\"3075\"]medulla[\/pb_glossary] of the brainstem. The parasympathetic nerves act to decrease the heart rate, and the sympathetic nerves act to increase the heart rate. Parasympathetic input normally predominates. Without it, the pacemaker cells of the heart would generate a resting heart rate of about 100 beats per minute, instead of a normal resting heart rate of about 72 beats per minute. The cardiovascular centers receive input from receptors throughout the body, and act through the sympathetic nerves to increase the heart rate, as needed.\u00a0Increased physical activity, for example, is detected by receptors in\u00a0muscles,\u00a0joints, and tendons. These receptors send\u00a0nerve impulses\u00a0to the cardiovascular centers, causing sympathetic nerves to increase the heart rate, and allowing more blood to flow to the muscles.\r\n\r\nBesides the autonomic\u00a0nervous system, other factors can also affect the heart rate. For example, [pb_glossary id=\"2958\"]thyroid[\/pb_glossary] hormones and [pb_glossary id=\"5869\"]adrenal[\/pb_glossary] hormones (such as epinephrine) can stimulate the heart to beat faster. The heart rate also increases when\u00a0blood pressure\u00a0drops or the body is dehydrated or overheated. On the other hand, cooling of the body and relaxation \u2014 among other factors \u2014 can contribute to a decrease in the heart rate.\r\n\r\n
Feature: Human Biology in the News<\/h1>\r\n<\/div>\r\nWhen a patient\u2019s heart is too diseased or damaged to sustain life, a heart transplant is likely to be the only long-term solution. The first successful heart transplant was undertaken in South Africa in 1967. There are over 2,200 Canadians walking around today because of life-saving heart transplant surgery.\u00a0 Approximately 180 heart transplant surgeries are performed each year, but there are still so many Canadians on the transplant list that some die while waiting for a heart. The problem is that far too few hearts are available for transplant \u2014 there is more demand (people waiting for a heart transplant) than supply (organ donors). Sometimes, recipient hopefuls will receive a device called a Total Artificial Heart (see Figure 14.3.10), which can buy them some time until a donor heart becomes available.\r\n\r\n[caption id=\"attachment_7737\" align=\"alignnone\" width=\"1023\"] Figure 14.3.10 A Total Artificial Heart, shown here, can be used for short periods of time in order to maintain a patient until a donor heart becomes available.<\/em>[\/caption]\r\n\r\nWatch the video below \"Total artificial heart option...\" from Stanford Health Care to see how it works:\r\n\r\nhttps:\/\/youtu.be\/1PtxaxcPnGc\r\nTotal artificial heart option at Stanford (Includes surgical graphic footage), Stanford Health Care, 2014.<\/p>\r\n\r\n
\r\n\r\n14.3 Summary<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- The [pb_glossary id=\"2987\"]heart[\/pb_glossary] is a muscular organ behind the sternum and slightly to the left of the center of the chest. Its function is to pump blood through the blood vessels of the\u00a0[pb_glossary id=\"5927\"]cardiovascular system[\/pb_glossary].<\/li>\r\n \t
- The wall of the heart consists of three layers. The middle layer, the [pb_glossary id=\"4191\"]myocardium[\/pb_glossary], is the thickest layer and consists mainly of [pb_glossary id=\"5925\"]cardiac muscle[\/pb_glossary]. The interior of the heart consists of four chambers, with an upper [pb_glossary id=\"4408\"]atrium[\/pb_glossary] and lower [pb_glossary id=\"4409\"]ventricle[\/pb_glossary] on each side of the heart. Blood enters the heart through the atria, which pump it to the ventricles. Then the ventricles pump blood out of the heart. Four valves in the heart keep blood flowing in the correct direction and prevent backflow.<\/li>\r\n \t
- The coronary circulation consists of blood vessels that carry blood to and from the heart muscle cells, and is different from the general circulation of blood through the heart chambers. There are two coronary arteries that supply the two sides of the heart with oxygenated blood. Cardiac veins drain deoxygenated blood back into the heart.<\/li>\r\n \t
- Deoxygenated blood flows into the right atrium through veins from the upper and lower body (superior and inferior [pb_glossary id=\"4410\"]vena cava[\/pb_glossary], respectively), and oxygenated blood flows into the left atrium through four pulmonary veins from the lungs. Each atrium pumps the blood to the ventricle below it. From the right ventricle, deoxygenated blood is pumped to the lungs through the two pulmonary arteries. From the left ventricle, oxygenated blood is pumped to the rest of the body through the aorta.<\/li>\r\n \t
- The [pb_glossary id=\"4447\"]cardiac cycle[\/pb_glossary] refers to a single complete heartbeat. It includes [pb_glossary id=\"4442\"]diastole[\/pb_glossary] \u2014 when the atria contract \u2014 and [pb_glossary id=\"4443\"]systole[\/pb_glossary], when the ventricles contract.<\/li>\r\n \t
- The normal, rhythmic beating of the heart is called [pb_glossary id=\"4445\"]sinus rhythm[\/pb_glossary]. It is established by the heart\u2019s [pb_glossary id=\"4446\"]pacemaker cells[\/pb_glossary] in the [pb_glossary id=\"4195\"]sinoatrial node[\/pb_glossary]. Electrical signals from the pacemaker cells travel to the atria, and cause them to contract. Then, the signals travel to the [pb_glossary id=\"4448\"]atrioventricular node[\/pb_glossary] and from there to the ventricles, causing them to contract. Electrical stimulation from the [pb_glossary id=\"2935\"]autonomic\u00a0nervous system[\/pb_glossary]\u00a0and hormones from the\u00a0[pb_glossary id=\"5985\"]endocrine system[\/pb_glossary]\u00a0can also influence heartbeat.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n14.3 Review Questions<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\n \t- What is the heart, where is located, and what is its function?<\/li>\r\n \t
- [h5p id=\"613\"]<\/li>\r\n \t
- Describe the coronary circulation.<\/li>\r\n \t
- Summarize how blood flows into, through, and out of the heart.<\/li>\r\n \t
- Explain what controls the beating of the heart.<\/li>\r\n \t
- What are the two types of cardiac muscle cells in the myocardium?\u00a0What are the differences between these two types of cells?<\/li>\r\n \t
- Explain why the blood from the cardiac veins empties into the right atrium of the heart. Focus on function (rather than anatomy) in your answer.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n14.3 Explore More<\/span><\/h1>\r\n<\/header>\r\n\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=1bnzVjOJ6NM\r\nNoel Bairey Merz: The single biggest health threat women face, TED, 2012.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=jJm7zBcN6-M\r\n
Watch a Transcatheter Aortic Valve Replacement (TAVR) Procedure at St. Luke's in Cedar Rapids, Iowa, UnityPoint Health - Cedar Rapids, 2018.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=zU6mmix04PI\r\n
A Change of Heart: My Transplant Experience | Thomas Volk | TEDxUWLaCrosse, TEDx Talks, 2018.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=biGuwQhuAsk\r\n
Heart Transplant Recipient Meets Donor Family For The First Time, WMC Health, 2018.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 14.3.1<\/strong>\r\n\r\n \t- Female clinician dressed in scrubs using a stethoscope<\/a> by Amanda Mills, USCDCP, on Pixnio<\/a> is used under a CC0<\/a> public domain certification license (https:\/\/creativecommons.org\/licenses\/publicdomain\/).<\/li>\r\n \t
- Human heart beating loud and strong<\/a> (audio) by Daniel Simion on Soundbible.com is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.<\/span><\/li>\r\n<\/ul>\r\nFigure 14.3.2<\/strong>\r\n\r\nBlausen_0470_HeartWall<\/a> by BruceBlaus<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\nFigure 14.3.3<\/strong>\r\n\r\nDiagram_of_the_human_heart_(cropped).svg<\/a> by Wapcaplet<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0 <\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license.\r\n\r\nFigure 14.3.4<\/strong>\r\n\r\nHeart_Valves<\/a>\u00a0by OpenStax College<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\nFigure 14.3.5<\/strong>\r\n\r\nCG_Heart Valve Animation<\/a> by DrJanaOfficial<\/a> on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n\r\nFigure 14.3.6<\/strong>\r\n\r\nHeart_tee_four_chamber_view<\/a> by Patrick J. Lynch, medical illustrator from Yale University School of Medicine, on Wikimedia Commons is used under a CC BY 2.5<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.5) license.\r\n\r\nFigure 14.3.7<\/strong>\r\n\r\nCirculation of blood through the heart<\/a> by Christinelmiller<\/a> on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license. [Original image<\/a> in the bottom right is by Wapcaplet<\/a> \/ CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/)]\r\n\r\nFigure 14.3.8<\/strong>\r\n\r\nHuman_healthy_pumping_heart_en.svg<\/a>\u00a0by Mariana Ruiz Villarreal [LadyofHats<\/a>] on Wikimedia Common is released into the public domain<\/a>\u00a0(https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 14.3.9<\/strong>\r\n\r\nCardiac_Conduction_System<\/a> by Cypressvine<\/a> on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n \r\n\r\nReferences<\/span>\r\n
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, June 19). Figure <\/span><\/span>19.12<\/span><\/span>\u00a0<\/span>Heart valves <\/span><\/span>with the atria and major vessels removed [digital image].\u00a0 In Anatomy and Physiology<\/em> (Section 19.1). OpenStax. https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/19-1-heart-anatomy#fig-ch20_01_04<\/span><\/span><\/p>\r\nBlausen.com Staff. (2014). Medical gallery of Blausen Medical 2014. WikiJournal of Medicine 1<\/em> (2). DOI:10.15347\/wjm\/2014.010. ISSN 2002-4436.<\/p>\r\nHeart and Stroke Foundation of Canada. (n.d.). https:\/\/www.heartandstroke.ca\/\r\nSliwa, K., Zilla, P. (2017, December 7). 50th anniversary of the first human heart transplant\u2014How is it seen today? European Heart Journal, 38<\/em>(46):<\/em>3402\u20133404. https:\/\/doi.org\/10.1093\/eurheartj\/ehx695<\/p>\r\nStanford Health Care. (2014, December 3). Total artificial heart option at Stanford (Includes surgical graphic footage). YouTube. https:\/\/www.youtube.com\/watch?v=1PtxaxcPnGc&feature=youtu.be<\/p>\r\n
TED. (2012, March 21). Noel Bairey Merz: The single biggest health threat women face. YouTube. https:\/\/www.youtube.com\/watch?v=1bnzVjOJ6NM&feature=youtu.be<\/p>\r\n
TEDx Talks. (2018, April 18). A change of heart: My transplant experience | Thomas Volk | TEDxUWLaCrosse. YouTube. https:\/\/www.youtube.com\/watch?v=zU6mmix04PI&feature=youtu.be<\/p>\r\n
UMagazine. (2015, Fall). The cutting edge: Patient first to bridge from experimental total artificial heart to transplant. UCLA Health. https:\/\/www.uclahealth.org\/u-magazine\/patient-first-to-bridge-from-experimental-total-artificial-heart-to-transplant<\/p>\r\n
UnityPoint Health - Cedar Rapids. (2018, February 7). Watch a transcatheter aortic valve replacement (TAVR) Procedure at St. Luke's in Cedar Rapids, Iowa. YouTube.\u00a0 https:\/\/www.youtube.com\/watch?v=jJm7zBcN6-M&feature=youtu.be<\/p>\r\n
WMC Health. (2018, September 13). Heart transplant recipient meets donor family for the first time. YouTube. https:\/\/www.youtube.com\/watch?v=biGuwQhuAsk&feature=youtu.be<\/p>\r\n \r\n\r\n \r\n\r\n ","rendered":"
<\/p>\nFigure 14.3.1 Healthy hearts are happy hearts. What do you hear?<\/figcaption><\/figure>\n\u00a0<\/em><\/em><\/p>\n\n
Figure 14.3.2 The wall of the heart is made up mainly of myocardium, which consists largely of cardiac muscle.<\/em>[\/caption]\r\n\r\nAs shown in Figure 14.3.2, the wall of the heart is made up of three layers, called the endocardium, myocardium, and pericardium.\r\n- \r\n \t
- The\u00a0[pb_glossary id=\"4193\"]endocardium[\/pb_glossary]<\/strong>\u00a0is the innermost layer of the heart wall. It is made up primarily of simple epithelial\u00a0cells. It covers the heart chambers and valves. A thin layer of connective tissue joins the endocardium to the myocardium.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"4191\"]myocardium[\/pb_glossary]<\/strong> is the middle and thickest layer of the heart wall. It consists of [pb_glossary id=\"5925\"]cardiac muscle[\/pb_glossary] surrounded by a framework of collagen. There are two types of cardiac muscle cells in the myocardium: cardiomyocytes \u2014 which have the ability to contract easily \u2014 and pacemaker cells, which conduct electrical impulses that cause the cardiomyocytes to contract. About 99 per cent of cardiac muscle cells are cardiomyocytes, and the remaining one per cent is pacemaker cells. The myocardium is supplied with blood vessels and nerve fibres via the pericardium.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"4194\"]pericardium[\/pb_glossary]<\/strong>\u00a0is a protective sac that encloses and protects the heart. The pericardium consists of two membranes (visceral pericardium and parietal pericardium), between which there is a fluid-filled cavity. The fluid helps to cushion the heart, and also lubricates its outer surface.<\/li>\r\n<\/ul>\r\n
Heart Chambers<\/h2>\r\nAs shown in Figure 14.3.3 the four chambers of the heart include two upper chambers called atria (singular, [pb_glossary id=\"4408\"]atrium[\/pb_glossary])<\/strong>, and two lower chambers called\u00a0[pb_glossary id=\"4409\"]ventricles[\/pb_glossary].<\/strong> The atria are also referred to as receiving chambers, because blood coming into the heart first enters these two chambers. The right atrium receives deoxygenated blood from the upper and lower body through the superior [pb_glossary id=\"4410\"]vena cava[\/pb_glossary] and inferior vena cava, respectively. The left atrium receives oxygenated blood from the lungs through the [pb_glossary id=\"4411\"]pulmonary veins[\/pb_glossary]. The ventricles are also referred to as discharging chambers, because blood leaving the heart passes out through these two chambers. The right ventricle discharges blood to the lungs through the [pb_glossary id=\"4412\"]pulmonary artery[\/pb_glossary], and the left ventricle discharges blood to the rest of the body through the [pb_glossary id=\"4413\"]aorta[\/pb_glossary]. The four chambers are separated from each other by dense connective tissue consisting mainly of [pb_glossary id=\"3970\"]collagen[\/pb_glossary].\r\n\r\n[caption id=\"attachment_4414\" align=\"aligncenter\" width=\"663\"]
Figure 14.3.3 This cross-sectional diagram of the heart shows its four chambers and four valves. The white arrows indicate the direction of blood flow through the heart chambers.<\/em>[\/caption]\r\nHeart Valves<\/h2>\r\n[caption id=\"attachment_4423\" align=\"alignleft\" width=\"370\"]
Figure 14.3.4 If the veins and arteries of the heart were removed, a top-down view of the heart would reveal the four valves that are critical in preventing backflow of blood. Note the three cusps of the tricuspid AV valve and the 2 cusps of the bicuspid AV valve. Also note the size difference between the AV valves and the semilunar valves.<\/em>[\/caption]\r\n\r\nFigure 14.3.4 shows the location of the heart's four valves in a top-down view, looking down at the heart as if the arteries and veins feeding into and out of the heart were removed. The heart valves allow blood to flow from the atria to the ventricles, and from the ventricles to the pulmonary artery and aorta. The valves are constructed in such a way that blood can flow through them in only one direction, thus preventing the backflow of blood. Figure 14.3.5 shows how valves open to let blood into the appropriate chamber, and then close to prevent blood from moving in the wrong direction and the next chamber contracts.\u00a0 The four valves are the:\r\n- \r\n \t
- [pb_glossary id=\"4415\"]Tricuspid atrioventricular valve[\/pb_glossary]<\/strong>, (can be shortened to tricuspid AV valve) which allows blood to flow from the right atrium to the right ventricle.<\/li>\r\n \t
- [pb_glossary id=\"4416\"]Bicuspid atrioventricular valve[\/pb_glossary] <\/strong>(also know as the mitral valve), which allows blood to flow from the left atrium to the left ventricle.<\/li>\r\n \t
- [pb_glossary id=\"4417\"]Pulmonary semilunar valve[\/pb_glossary]<\/strong>, which allows blood to flow from the right ventricle to the pulmonary artery.<\/li>\r\n \t
- [pb_glossary id=\"4418\"]Aortic semilunar valve[\/pb_glossary]<\/strong>, which allows blood to flow from the left ventricle to the aorta.<\/li>\r\n<\/ol>\r\n[caption id=\"attachment_4419\" align=\"aligncenter\" width=\"411\"]
Figure 14.3.5 The valves of the heart prevent backflow of blood. The open when the chamber before them contracts (systole) and then close when that chamber relaxes (diastole).<\/em>[\/caption]\r\n\r\n\r\n\r\n[caption id=\"attachment_4426\" align=\"alignright\" width=\"384\"] Figure 14.3.6 The chordae tendoneae, shown in this diagram in white, play a critical role in reinforcing the AV valves of the heart.<\/em>[\/caption]\r\n\r\nThe two atrioventricular (AV) valves prevent backflow when the ventricles are contracting, while the semilunar valves prevent backflow from vessels.\u00a0 This means that the AV valves must withstand much more pressure than do the semilunar valves.\u00a0 In order to withstand the force of the ventricles contracting (to prevent blood from backflowing into the atria), the AV valves are reinforced with structures called [pb_glossary id=\"4424\"]chordae tendineae[\/pb_glossary] \u2014 tendon-like cords of connective tissue which anchor the valve and prevent it from [pb_glossary id=\"4425\"]prolapse[\/pb_glossary].\u00a0 Figure 14.3.6 shows the structure and location of the chordae tendoneae.\r\n\r\nThe chordae tendoneae are under such force that they need special attachments to the interior of the ventricles where they anchor.\u00a0 [pb_glossary id=\"4430\"]Papillary muscles[\/pb_glossary] are specialized muscles in the interior of the ventricle that provide a strong anchor point for the chordae tendineae.\r\nCoronary\u00a0Circulation<\/h1>\r\n<\/div>\r\nThe [pb_glossary id=\"5631\"]cardiomyocyte<\/strong>[\/pb_glossary]s of the muscular walls of the heart are very active cells, because they are responsible for the constant beating of the heart. These cells need a continuous supply of oxygen and\u00a0nutrients. The carbon dioxide and waste products they produce also must be continuously removed. The\u00a0blood vessels\u00a0that carry blood to and from the heart muscle cells make up the [pb_glossary id=\"4421\"]coronary\u00a0circulation[\/pb_glossary]. Note that the blood vessels of the coronary circulation supply heart tissues with blood, and are different from the blood vessels that carry blood to and from the chambers of the heart as part of the general circulation.\u00a0[pb_glossary id=\"4422\"]Coronary arteries[\/pb_glossary] <\/strong>supply oxygen-rich blood to the heart muscle cells. Coronary veins remove deoxygenated blood from the heart\u00a0muscles\u00a0cells.\r\n
- \r\n \t
- There are two [pb_glossary id=\"4422\"]coronary arteries[\/pb_glossary] \u2014 a right coronary artery that supplies the right side of the heart, and a left coronary artery that supplies the left side of the heart. These arteries branch repeatedly into smaller and smaller arteries and finally into capillaries, which exchange gases,\u00a0nutrients, and waste products with cardiomyocytes.<\/li>\r\n \t
- At the back of the heart, small cardiac veins drain into larger veins, and finally into the great cardiac vein, which empties into the right atrium. At the front of the heart, small cardiac veins drain directly into the right atrium.<\/li>\r\n<\/ul>\r\n\r\n
Blood Circulation Through the Heart<\/h1>\r\n<\/div>\r\nFigure 14.3.7 shows how blood circulates through the chambers of the heart. The right atrium collects blood from two large veins, the superior vena cava (from the upper body) and the inferior vena cava (from the lower body). The blood that collects in the right atrium is pumped through the tricuspid valve into the right ventricle. From the right ventricle, the blood is pumped through the pulmonary valve into the pulmonary artery. The pulmonary artery carries the blood to the lungs, where it enters the pulmonary circulation, gives up carbon dioxide, and picks up oxygen. The oxygenated blood travels back from the lungs through the pulmonary veins (of which there are four), and enters the left atrium of the heart. From the left atrium, the blood is pumped through the mitral valve into the left ventricle. From the left ventricle, the blood is pumped through the aortic valve into the aorta, which subsequently branches into smaller arteries that carry the blood throughout the rest of the body. After passing through capillaries and exchanging substances with cells, the blood returns to the right atrium via the superior vena cava and inferior vena cava, and the process begins anew.\r\n\r\n[caption id=\"attachment_4431\" align=\"alignnone\" width=\"3000\"]
Figure 14.3.7 The flow chart in this diagram summarizes the pathway blood takes as it flows into, through, and out of the heart. Trace the path of blood flow in the diagram of the heart as you follow it through the flow chart.<\/em>[\/caption]\r\n\r\n\r\nCardiac Cycle<\/h1>\r\n<\/div>\r\nThe cardiac cycle refers to a single complete heartbeat, which includes one iteration of the lub and dub sounds heard through a stethoscope. During the cardiac cycle, the atria and ventricles work in a coordinated fashion so that blood is pumped efficiently through and out of the heart. The cardiac cycle includes two parts, called diastole and systole, which are illustrated in the diagrams in Figure 14.3.8.\r\n
- \r\n \t
- During\u00a0[pb_glossary id=\"4442\"]diastole[\/pb_glossary],<\/strong>\u00a0the atria contract and pump blood into the ventricles, while the ventricles relax and fill with blood from the atria.<\/li>\r\n \t
- During\u00a0[pb_glossary id=\"4443\"]systole[\/pb_glossary],<\/strong>\u00a0the atria relax and collect blood from the lungs and body, while the ventricles contract and pump blood out of the heart.<\/li>\r\n<\/ul>\r\n[caption id=\"attachment_4444\" align=\"aligncenter\" width=\"495\"]
Figure 14.3.8 Diastole is referred to the filling stage, because this is when the ventricles fill with blood. Systole is referred to the pumping stage because this is when the ventricles pump blood out of the heart.<\/em>[\/caption]\r\n\r\nElectrical Stimulation of the Heart<\/span>\r\n\r\nThe normal, rhythmical beating of the heart is called\u00a0[pb_glossary id=\"4445\"]sinus rhythm[\/pb_glossary].<\/strong>\u00a0It is established by the heart\u2019s\u00a0[pb_glossary id=\"4446\"]pacemaker[\/pb_glossary]<\/strong> cells, which are located in an area of the heart called the [pb_glossary id=\"4195\"]sinoatrial node[\/pb_glossary] (shown in Figure 14.3.9). The pacemaker cells create electrical signals with the movement of electrolytes (sodium, potassium, and calcium ions) into and out of the cells. For each [pb_glossary id=\"4447\"]cardiac cycle[\/pb_glossary], an electrical signal rapidly travels first from the sinoatrial node, to the right and left atria so they contract together. Then, the signal travels to another node, called the [pb_glossary id=\"4448\"]atrioventricular node[\/pb_glossary] (Figure 14.3.9), and from there to the right and left ventricles (which also contract together), just a split second after the atria contract.\r\n\r\n[caption id=\"attachment_4449\" align=\"aligncenter\" width=\"416\"] Figure 14.3.9 The sinoatrial (SA) node causes the atria to contract and then signals the atrioventricular (AV) nodes to initiate the contraction of the ventricles.<\/em>[\/caption]\r\n\r\nThe normal [pb_glossary id=\"4445\"]sinus rhythm[\/pb_glossary] of the heart is influenced by the [pb_glossary id=\"2935\"]autonomic\u00a0nervous system[\/pb_glossary]\u00a0through sympathetic and parasympathetic nerves. These nerves arise from two paired cardiovascular centers in the [pb_glossary id=\"3075\"]medulla[\/pb_glossary] of the brainstem. The parasympathetic nerves act to decrease the heart rate, and the sympathetic nerves act to increase the heart rate. Parasympathetic input normally predominates. Without it, the pacemaker cells of the heart would generate a resting heart rate of about 100 beats per minute, instead of a normal resting heart rate of about 72 beats per minute. The cardiovascular centers receive input from receptors throughout the body, and act through the sympathetic nerves to increase the heart rate, as needed.\u00a0Increased physical activity, for example, is detected by receptors in\u00a0muscles,\u00a0joints, and tendons. These receptors send\u00a0nerve impulses\u00a0to the cardiovascular centers, causing sympathetic nerves to increase the heart rate, and allowing more blood to flow to the muscles.\r\n\r\nBesides the autonomic\u00a0nervous system, other factors can also affect the heart rate. For example, [pb_glossary id=\"2958\"]thyroid[\/pb_glossary] hormones and [pb_glossary id=\"5869\"]adrenal[\/pb_glossary] hormones (such as epinephrine) can stimulate the heart to beat faster. The heart rate also increases when\u00a0blood pressure\u00a0drops or the body is dehydrated or overheated. On the other hand, cooling of the body and relaxation \u2014 among other factors \u2014 can contribute to a decrease in the heart rate.\r\n\r\nFeature: Human Biology in the News<\/h1>\r\n<\/div>\r\nWhen a patient\u2019s heart is too diseased or damaged to sustain life, a heart transplant is likely to be the only long-term solution. The first successful heart transplant was undertaken in South Africa in 1967. There are over 2,200 Canadians walking around today because of life-saving heart transplant surgery.\u00a0 Approximately 180 heart transplant surgeries are performed each year, but there are still so many Canadians on the transplant list that some die while waiting for a heart. The problem is that far too few hearts are available for transplant \u2014 there is more demand (people waiting for a heart transplant) than supply (organ donors). Sometimes, recipient hopefuls will receive a device called a Total Artificial Heart (see Figure 14.3.10), which can buy them some time until a donor heart becomes available.\r\n\r\n[caption id=\"attachment_7737\" align=\"alignnone\" width=\"1023\"]
Figure 14.3.10 A Total Artificial Heart, shown here, can be used for short periods of time in order to maintain a patient until a donor heart becomes available.<\/em>[\/caption]\r\n\r\nWatch the video below \"Total artificial heart option...\" from Stanford Health Care to see how it works:\r\n\r\nhttps:\/\/youtu.be\/1PtxaxcPnGc\r\nTotal artificial heart option at Stanford (Includes surgical graphic footage), Stanford Health Care, 2014.<\/p>\r\n\r\n
\r\n\r\n 14.3 Summary<\/span><\/h1>\r\n<\/header>\r\n
\r\n- \r\n \t
- The [pb_glossary id=\"2987\"]heart[\/pb_glossary] is a muscular organ behind the sternum and slightly to the left of the center of the chest. Its function is to pump blood through the blood vessels of the\u00a0[pb_glossary id=\"5927\"]cardiovascular system[\/pb_glossary].<\/li>\r\n \t
- The wall of the heart consists of three layers. The middle layer, the [pb_glossary id=\"4191\"]myocardium[\/pb_glossary], is the thickest layer and consists mainly of [pb_glossary id=\"5925\"]cardiac muscle[\/pb_glossary]. The interior of the heart consists of four chambers, with an upper [pb_glossary id=\"4408\"]atrium[\/pb_glossary] and lower [pb_glossary id=\"4409\"]ventricle[\/pb_glossary] on each side of the heart. Blood enters the heart through the atria, which pump it to the ventricles. Then the ventricles pump blood out of the heart. Four valves in the heart keep blood flowing in the correct direction and prevent backflow.<\/li>\r\n \t
- The coronary circulation consists of blood vessels that carry blood to and from the heart muscle cells, and is different from the general circulation of blood through the heart chambers. There are two coronary arteries that supply the two sides of the heart with oxygenated blood. Cardiac veins drain deoxygenated blood back into the heart.<\/li>\r\n \t
- Deoxygenated blood flows into the right atrium through veins from the upper and lower body (superior and inferior [pb_glossary id=\"4410\"]vena cava[\/pb_glossary], respectively), and oxygenated blood flows into the left atrium through four pulmonary veins from the lungs. Each atrium pumps the blood to the ventricle below it. From the right ventricle, deoxygenated blood is pumped to the lungs through the two pulmonary arteries. From the left ventricle, oxygenated blood is pumped to the rest of the body through the aorta.<\/li>\r\n \t
- The [pb_glossary id=\"4447\"]cardiac cycle[\/pb_glossary] refers to a single complete heartbeat. It includes [pb_glossary id=\"4442\"]diastole[\/pb_glossary] \u2014 when the atria contract \u2014 and [pb_glossary id=\"4443\"]systole[\/pb_glossary], when the ventricles contract.<\/li>\r\n \t
- The normal, rhythmic beating of the heart is called [pb_glossary id=\"4445\"]sinus rhythm[\/pb_glossary]. It is established by the heart\u2019s [pb_glossary id=\"4446\"]pacemaker cells[\/pb_glossary] in the [pb_glossary id=\"4195\"]sinoatrial node[\/pb_glossary]. Electrical signals from the pacemaker cells travel to the atria, and cause them to contract. Then, the signals travel to the [pb_glossary id=\"4448\"]atrioventricular node[\/pb_glossary] and from there to the ventricles, causing them to contract. Electrical stimulation from the [pb_glossary id=\"2935\"]autonomic\u00a0nervous system[\/pb_glossary]\u00a0and hormones from the\u00a0[pb_glossary id=\"5985\"]endocrine system[\/pb_glossary]\u00a0can also influence heartbeat.<\/li>\r\n<\/ul>\r\n<\/div>\r\n<\/div>\r\n
\r\n 14.3 Review Questions<\/span><\/h1>\r\n<\/header>\r\n
\r\n- \r\n \t
- What is the heart, where is located, and what is its function?<\/li>\r\n \t
- [h5p id=\"613\"]<\/li>\r\n \t
- Describe the coronary circulation.<\/li>\r\n \t
- Summarize how blood flows into, through, and out of the heart.<\/li>\r\n \t
- Explain what controls the beating of the heart.<\/li>\r\n \t
- What are the two types of cardiac muscle cells in the myocardium?\u00a0What are the differences between these two types of cells?<\/li>\r\n \t
- Explain why the blood from the cardiac veins empties into the right atrium of the heart. Focus on function (rather than anatomy) in your answer.<\/li>\r\n<\/ol>\r\n<\/div>\r\n<\/div>\r\n
\r\n 14.3 Explore More<\/span><\/h1>\r\n<\/header>\r\n
\r\n\r\nhttps:\/\/www.youtube.com\/watch?v=1bnzVjOJ6NM\r\nNoel Bairey Merz: The single biggest health threat women face, TED, 2012.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=jJm7zBcN6-M\r\n
Watch a Transcatheter Aortic Valve Replacement (TAVR) Procedure at St. Luke's in Cedar Rapids, Iowa, UnityPoint Health - Cedar Rapids, 2018.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=zU6mmix04PI\r\n
A Change of Heart: My Transplant Experience | Thomas Volk | TEDxUWLaCrosse, TEDx Talks, 2018.<\/p>\r\nhttps:\/\/www.youtube.com\/watch?v=biGuwQhuAsk\r\n
Heart Transplant Recipient Meets Donor Family For The First Time, WMC Health, 2018.<\/p>\r\n\r\n<\/div>\r\n<\/div>\r\n \r\n\r\n<\/div>\r\n
Attributions<\/h2>\r\nFigure 14.3.1<\/strong>\r\n
- \r\n \t
- Female clinician dressed in scrubs using a stethoscope<\/a> by Amanda Mills, USCDCP, on Pixnio<\/a> is used under a CC0<\/a> public domain certification license (https:\/\/creativecommons.org\/licenses\/publicdomain\/).<\/li>\r\n \t
- Human heart beating loud and strong<\/a> (audio) by Daniel Simion on Soundbible.com is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.<\/span><\/li>\r\n<\/ul>\r\nFigure 14.3.2<\/strong>\r\n\r\nBlausen_0470_HeartWall<\/a> by BruceBlaus<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\nFigure 14.3.3<\/strong>\r\n\r\nDiagram_of_the_human_heart_(cropped).svg<\/a> by Wapcaplet<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0 <\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license.\r\n\r\nFigure 14.3.4<\/strong>\r\n\r\nHeart_Valves<\/a>\u00a0by OpenStax College<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\nFigure 14.3.5<\/strong>\r\n\r\nCG_Heart Valve Animation<\/a> by DrJanaOfficial<\/a> on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n\r\nFigure 14.3.6<\/strong>\r\n\r\nHeart_tee_four_chamber_view<\/a> by Patrick J. Lynch, medical illustrator from Yale University School of Medicine, on Wikimedia Commons is used under a CC BY 2.5<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.5) license.\r\n\r\nFigure 14.3.7<\/strong>\r\n\r\nCirculation of blood through the heart<\/a> by Christinelmiller<\/a> on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license. [Original image<\/a> in the bottom right is by Wapcaplet<\/a> \/ CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/)]\r\n\r\nFigure 14.3.8<\/strong>\r\n\r\nHuman_healthy_pumping_heart_en.svg<\/a>\u00a0by Mariana Ruiz Villarreal [LadyofHats<\/a>] on Wikimedia Common is released into the public domain<\/a>\u00a0(https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 14.3.9<\/strong>\r\n\r\nCardiac_Conduction_System<\/a> by Cypressvine<\/a> on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n \r\n\r\nReferences<\/span>\r\n
Betts, J. G., Young, K.A., Wise, J.A., Johnson, E., Poe, B., Kruse, D.H., Korol, O., Johnson, J.E., Womble, M., DeSaix, P. (2013, June 19). Figure <\/span><\/span>19.12<\/span><\/span>\u00a0<\/span>Heart valves <\/span><\/span>with the atria and major vessels removed [digital image].\u00a0 In Anatomy and Physiology<\/em> (Section 19.1). OpenStax. https:\/\/openstax.org\/books\/anatomy-and-physiology\/pages\/19-1-heart-anatomy#fig-ch20_01_04<\/span><\/span><\/p>\r\n
Blausen.com Staff. (2014). Medical gallery of Blausen Medical 2014. WikiJournal of Medicine 1<\/em> (2). DOI:10.15347\/wjm\/2014.010. ISSN 2002-4436.<\/p>\r\nHeart and Stroke Foundation of Canada. (n.d.). https:\/\/www.heartandstroke.ca\/\r\n
Sliwa, K., Zilla, P. (2017, December 7). 50th anniversary of the first human heart transplant\u2014How is it seen today? European Heart Journal, 38<\/em>(46):<\/em>3402\u20133404. https:\/\/doi.org\/10.1093\/eurheartj\/ehx695<\/p>\r\n
Stanford Health Care. (2014, December 3). Total artificial heart option at Stanford (Includes surgical graphic footage). YouTube. https:\/\/www.youtube.com\/watch?v=1PtxaxcPnGc&feature=youtu.be<\/p>\r\n
TED. (2012, March 21). Noel Bairey Merz: The single biggest health threat women face. YouTube. https:\/\/www.youtube.com\/watch?v=1bnzVjOJ6NM&feature=youtu.be<\/p>\r\n
TEDx Talks. (2018, April 18). A change of heart: My transplant experience | Thomas Volk | TEDxUWLaCrosse. YouTube. https:\/\/www.youtube.com\/watch?v=zU6mmix04PI&feature=youtu.be<\/p>\r\n
UMagazine. (2015, Fall). The cutting edge: Patient first to bridge from experimental total artificial heart to transplant. UCLA Health. https:\/\/www.uclahealth.org\/u-magazine\/patient-first-to-bridge-from-experimental-total-artificial-heart-to-transplant<\/p>\r\n
UnityPoint Health - Cedar Rapids. (2018, February 7). Watch a transcatheter aortic valve replacement (TAVR) Procedure at St. Luke's in Cedar Rapids, Iowa. YouTube.\u00a0 https:\/\/www.youtube.com\/watch?v=jJm7zBcN6-M&feature=youtu.be<\/p>\r\n
WMC Health. (2018, September 13). Heart transplant recipient meets donor family for the first time. YouTube. https:\/\/www.youtube.com\/watch?v=biGuwQhuAsk&feature=youtu.be<\/p>\r\n \r\n\r\n \r\n\r\n ","rendered":"
<\/p>\n
Figure 14.3.1 Healthy hearts are happy hearts. What do you hear?<\/figcaption><\/figure>\n \u00a0<\/em><\/em><\/p>\n
\n - Human heart beating loud and strong<\/a> (audio) by Daniel Simion on Soundbible.com is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.<\/span><\/li>\r\n<\/ul>\r\nFigure 14.3.2<\/strong>\r\n\r\nBlausen_0470_HeartWall<\/a> by BruceBlaus<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\nFigure 14.3.3<\/strong>\r\n\r\nDiagram_of_the_human_heart_(cropped).svg<\/a> by Wapcaplet<\/a> on Wikimedia Commons is used under a CC BY-SA 3.0 <\/a> (http:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/) license.\r\n\r\nFigure 14.3.4<\/strong>\r\n\r\nHeart_Valves<\/a>\u00a0by OpenStax College<\/a> on Wikimedia Commons is used under a CC BY 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by\/3.0) license.\r\n\r\nFigure 14.3.5<\/strong>\r\n\r\nCG_Heart Valve Animation<\/a> by DrJanaOfficial<\/a> on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n\r\nFigure 14.3.6<\/strong>\r\n\r\nHeart_tee_four_chamber_view<\/a> by Patrick J. Lynch, medical illustrator from Yale University School of Medicine, on Wikimedia Commons is used under a CC BY 2.5<\/a> (https:\/\/creativecommons.org\/licenses\/by\/2.5) license.\r\n\r\nFigure 14.3.7<\/strong>\r\n\r\nCirculation of blood through the heart<\/a> by Christinelmiller<\/a> on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license. [Original image<\/a> in the bottom right is by Wapcaplet<\/a> \/ CC BY-SA 3.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/3.0\/)]\r\n\r\nFigure 14.3.8<\/strong>\r\n\r\nHuman_healthy_pumping_heart_en.svg<\/a>\u00a0by Mariana Ruiz Villarreal [LadyofHats<\/a>] on Wikimedia Common is released into the public domain<\/a>\u00a0(https:\/\/en.wikipedia.org\/wiki\/Public_domain).\r\n\r\nFigure 14.3.9<\/strong>\r\n\r\nCardiac_Conduction_System<\/a> by Cypressvine<\/a> on Wikimedia Commons is used under a CC BY-SA 4.0<\/a> (https:\/\/creativecommons.org\/licenses\/by-sa\/4.0) license.\r\n\r\n \r\n\r\nReferences<\/span>\r\n
- Female clinician dressed in scrubs using a stethoscope<\/a> by Amanda Mills, USCDCP, on Pixnio<\/a> is used under a CC0<\/a> public domain certification license (https:\/\/creativecommons.org\/licenses\/publicdomain\/).<\/li>\r\n \t
- During\u00a0[pb_glossary id=\"4443\"]systole[\/pb_glossary],<\/strong>\u00a0the atria relax and collect blood from the lungs and body, while the ventricles contract and pump blood out of the heart.<\/li>\r\n<\/ul>\r\n[caption id=\"attachment_4444\" align=\"aligncenter\" width=\"495\"]
- During\u00a0[pb_glossary id=\"4442\"]diastole[\/pb_glossary],<\/strong>\u00a0the atria contract and pump blood into the ventricles, while the ventricles relax and fill with blood from the atria.<\/li>\r\n \t
- [pb_glossary id=\"4416\"]Bicuspid atrioventricular valve[\/pb_glossary] <\/strong>(also know as the mitral valve), which allows blood to flow from the left atrium to the left ventricle.<\/li>\r\n \t
- The\u00a0[pb_glossary id=\"4191\"]myocardium[\/pb_glossary]<\/strong> is the middle and thickest layer of the heart wall. It consists of [pb_glossary id=\"5925\"]cardiac muscle[\/pb_glossary] surrounded by a framework of collagen. There are two types of cardiac muscle cells in the myocardium: cardiomyocytes \u2014 which have the ability to contract easily \u2014 and pacemaker cells, which conduct electrical impulses that cause the cardiomyocytes to contract. About 99 per cent of cardiac muscle cells are cardiomyocytes, and the remaining one per cent is pacemaker cells. The myocardium is supplied with blood vessels and nerve fibres via the pericardium.<\/li>\r\n \t
![Blausen_0470_HeartWall<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Blausen_0470_HeartWall.png\"){kind=link}
![Diagram_of_the_human_heart_(cropped).svg<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Diagram_of_the_human_heart_(cropped).svg\"){kind=link}
![Heart_Valves<\/a>\u00a0by](\"https:\/\/commons.wikimedia.org\/wiki\/File:2011_Heart_Valves.jpg\"){kind=link}
![CG_Heart Valve Animation<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:CG_Heart.gif\"){kind=link}
![Heart_tee_four_chamber_view<\/a> by Patrick J. Lynch, medical illustrator from Yale University School of Medicine, on Wikimedia Commons is used under a](\"https:\/\/commons.wikimedia.org\/wiki\/File:Heart_tee_four_chamber_view.jpg\"){kind=link}
![Circulation of blood through the heart<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Circulation_of_blood_through_the_heart.png\"){kind=link}
![Human_healthy_pumping_heart_en.svg<\/a>\u00a0by Mariana Ruiz Villarreal [](\"https:\/\/commons.wikimedia.org\/wiki\/File:Human_healthy_pumping_heart_en.svg\"){kind=link}
![Cardiac_Conduction_System<\/a> by](\"https:\/\/commons.wikimedia.org\/wiki\/File:Cardiac_Conduction_System.jpg\"){kind=link}