Human Anatomy & Physiology Chapter 17: The Cardiovascular System PDF

Human Anatomy & Physiology Second Edition Chapter 17 The Cardiovascular System I:The Heart PowerPoint® Lectures...

Human Anatomy & Physiology Second Edition Chapter 17 The Cardiovascular System I:The Heart PowerPoint® Lectures created by Suzanne Pundt, University of Texas at Tyler Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Study Guide: What you need to learn from this chapter 1. Where the heart is located, How it appears from outside? Which side of the heart dominates the anterior view? 2. What is Pericardium? What are the two layers of connective tissue that cover the heart? Why is there fluid between these two layers? 3. Anatomy of the heart, What are the four chambers of the heart? ? Know the landmarks of each chamber, that is, where do you find papillary muscles? What about pectinate muscles? The fossa ovalis? Coronary sinus ? , etc. What is structural difference between the Left and Right Ventricles? 4. Heart valves (How do they differ)? 5. What are major blood vessels connected to the heart? What are Aortic Sinuses? 6. What are coronary sulcus & interventricular sulcus 7. Know all the components of systemic, pulmonary, and coronary circulation and understand what each of those circulatory pathways do for the body (coronary circulation supplies the heart muscle cells with blood). 8. Cardiac Muscle tissue; How do cardiac muscle cells differ from skeletal muscles? 9. What are two Types of Cardiac Muscle Cells? what are their functions? 10. What are the components of the Conducting System, How heart beat is initiated and established, How pacemaker potential is being established, Do you understand the autorhythmicity of the heart? Does the spontaneous depolarization of pacemaker cells make the heart beat faster or slower than our resting heart rate? how impulse is conducted through the heart, how nerves control heart beat? Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  11. How Action potential is produced in in cardiac muscle (Contractile Cells)? How does a cardiac muscle cell’s action potential differ from that of a skeletal muscle? Understand why this is vital to heart function. If you are given the graph in figure 20-15, be able to tell not only what is happening in the heart at each step but also understand what channels in the cells are driving this process. Be able to describe what a refractory period is and why it is important to the heart (think complete tetanus). 12. What is Cardiac cycle? What are its phases ? Can you describe the cardiac cycle in terms of systole and diastole? Generally know the phases in order and what that means in terms of chambers being contracted or relaxed. What is isovolumetric contractions, know that the pressure increases or decreases in the ventricle.Think about being in a car under water. When the pressure of the water is the same on the inside and the outside, you can open the door (valve). Why do people with poorly performing atria go undiagnosed? (because ventricle filling is mostly passive) Is this true of people with damaged ventricles? If given a graph like that in figure 20-17, can you describe what is going on in the heart at each point? 13. Heart sounds; What do the sounds we hear in the stethoscope (lubb dubb) indicate? 14. What is cardiac output and what two factors influence it? What controls the heart rate? (Autonomic innervation, hormones and venous return) What is stroke volume and what factors influence it? What is the difference between preload and afterload? Which one increases stroke volume and which one decreases stroke volume? Which does elevated afterload indicate? Generally know what EDV and ESV mean for the left ventricle and what they can tell us about the heart health. How adjustments in stroke volume and cardiac output are coordinated at different levels of physical activity. 15. How are most heart attacks caused? How do you tell the difference between a heart attack and general chest pain/angina? 16. What is an ECG or EKG? What does it measure? what are its features? Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved 2:07 / 6:51 2:13 Useful links Cardiovascular System Overview, Animation https://www.youtube.com/watch?v=G4dFVeP9Vdo............................Heart real time https://www.youtube.com/watch?v=28CYhgjrBLA................................. Cardiovascular animation https://www.youtube.com/watch?v=UxzZyrX2Q_w.......................... Heart Anatomy Part 1 model https://www.youtube.com/watch?v=fx5OR6eOfz8..................................... Heart Anatomy Part 2 model https://www.youtube.com/watch?v=SNrTbeL2h84..... Electrocardiogram https://www.youtube.com/watch?v=H_VsHmoRQKk............................. What happens during a Heart Attack? https://www.youtube.com/watch?v=ilnEruQg4ls ……………………………… CIRCULATORY SYSTEM ANATOMY: Coronary circulation arteries and cardiac veins vessel model description http://www.youtube.com/watch?v=kUQe6I6vv74............................................ Blocked Coronary Arteries https://www.youtube.com/watch?v=lFblnQcs48Y..................................... heart dissection: external structures and blood vessels https://www.youtube.com/watch? v=fo4GyqqXsKM&feature=iv&src_vid=lFblnQcs48Y&annotation_id=annotation_3065495893..................................... heart dissection: internal structures https://www.youtube.com/watch?v=-vsHgj1f0XE............................ heart dissection http://www.austincc.edu/apreview/NursingAnimations/cardiac_cycle.swf............cardiac cycle ….. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Garden Current/Flow= F Pressure= P Resistance=R F= P/R F P R Volume= V V P Water- hose- pump Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Location, Basic Structure and function of the Heart Figure 17.1c Location and basic anatomy of the heart in the thoracic cavity. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved MODULE 17.1 OVERVIEW OF THE HEART Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Cardiovascular System – Consists of  heart, blood vessels, and blood – Heart pumps blood (liquid carrying oxygen and nutrients) into blood vessels (system of tubes that distributes it throughout cardiovascular system) Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Functions of the Heart That's a hefty job for a fist-sized muscle!!! Under a minute, your heart can pump blood to every cell (about 37.2 – 70 Trillion Cells) in your body. Over the course of a day, about 100,000 heart beats, shuttle 8000 liters of blood through about 60,000 miles of branching blood vessels that link together the cells of our organs and body parts. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Functions of the Heart Heart helps maintain homeostasis of pressure that blood exerts on blood vessels (blood pressure) – Rate and force of heart’s contraction are major factors that influence blood pressure and blood flow to organs Heart (specifically atria) also acts as endocrine organ; produces atrial natriuretic peptide (ANP)  lowers blood pressure by decreasing sodium ion retention in kidneys  Reduces osmotic water reabsorption and volume and pressure of blood in blood vessels Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Location and Basic Structure of the Heart Heart—somewhat cone-shaped organ; Situated slightly to left side in thoracic cavity; posterior to sternum in mediastinum; rests on diaphragm Apex—point of cone; points toward left hip; Base is posterior side (not inferior) facing posterior rib cage Relatively small, only about size of fist; generally weighs from 250 to 350 grams (slightly less than 1 pound) Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Location and Basic Structure of the Heart Posterior mediastinum Esophagus Aorta (arch segment removed) Left pulmonary artery Right pleural cavity Right Left pleural cavity lung Left lung Left pulmonary vein Bronchus of lung Right pulmonary artery Pulmonary trunk Aortic arch Left atrium Right pulmonary vein Left ventricle Superior vena cava Pericardial cavity Epicardium Right atrium Right ventricle Pericardial sac Anterior mediastinum A superior view of the organs in the mediastinum; portions of the lungs have been removed to reveal blood vessels and airways. The heart is situated in the anterior part of the mediastinum, immediately posterior to the sternum. Figure 17.1b Location and basic anatomy of the heart in the thoracic cavity. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Heart’s Great Vessels, Chambers, and Valves Largest structures in heart are four chambers Chambers—superior right and left atria (singular, atrium) and inferior right and left ventricles Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Heart’s Great Vessels, Chambers, and Valves Ventricles are larger than atria and have much thicker walls; makes ventricles much stronger pumps Greater strength is needed to generate pressure that pumps blood around pulmonary and systemic circuits Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Heart’s Great Vessels, Chambers, and Valves Externally, indentation known as atrioventricular sulcus is boundary between atria and ventricles (coronary sulcus) Interventricular sulcus—external depression between right and left ventricles Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Heart’s Great Vessels, Chambers, and Valves Great vessels—main veins and arteries; – bring blood to and from heart – Arteries: Carry blood away from heart – Veins: Carry blood to heart – Capillaries: Interconnect the smallest arteries and the smallest vein Vessels and organs that transport oxygenated blood are color- coded red in textbook; those that carry deoxygenated blood are blue Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Heart’s Great Vessels, Chambers, and Valves Four Chambers of the Heart 1. Atria of the heart Atria are the receiving chambers of the heart Are expandable outer auricle (atrial appendage) Right atrium Collects blood from body Left atrium Collects blood from lungs Interatrial septum separates atria Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  The Heart’s Great Vessels, Chambers, and Valves 2. Ventricles of the Heart – Right ventricle Pumps blood to lungs – Left ventricle Pumps blood to upper part and body Interventricular septum separates ventricles Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Heart’s Great Vessels, Chambers, and Valves Major Vessels of the heart Veins: 1. Superior and Inferior venae cava 2. Pulmonary veins split to two Right and two left Arteries: 3. Pulmonary trunk (split to right and left pulmonary arteries) 4. Ascending aorta (split to three branches) Brachiocephalic Left common carotid Left Subclavian arteries Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Heart’s Great Vessels, Chambers, and Valves Major systemic veins: two veins that drain majority of systemic circuit are superior and inferior venae cavae; both have large openings into posterior aspect of right atrium: – Superior vena cava (SVC)— drains deoxygenated blood from veins superior to diaphragm – Inferior vena cava (IVC)— drains deoxygenated blood from veins inferior to diaphragm Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Heart’s Great Vessels, Chambers, and Valves Pulmonary trunk—largest vessel in pulmonary circuit; receives deoxygenated blood pumped from right ventricle – Originates from right ventricle on anterior aspect of heart, nearly along midline – Splits into right and left pulmonary arteries; bring deoxygenated blood to right and left lungs, respectively – Pulmonary arteries branch extensively inside lungs to become tiny pulmonary capillaries where gases are exchanged Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Heart’s Great Vessels, Chambers, and Valves Oxygenated blood in pulmonary capillaries returns to heart via a set of pulmonary veins – Most people have four; two from each lung – Drain oxygenated blood into posterior part of left atrium Aorta supplies entire systemic circuit with oxygenated blood – Largest and thickest artery in systemic circuit and in entire body – Arises from left ventricle as ascending aorta; curves to left and makes U-turn as aortic arch Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Heart’s Great Vessels, Chambers, and Valves Figure 17.5c The external anatomy of the heart. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Heart’s Great Vessels, Chambers, and Valves Two types of valves prevent blood from flowing backward 1. AV valves 2. Semilunar valves Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Heart’s Great Vessels, Chambers, and Valves No valves needed between atria and veins that drain blood into them Backflow of blood generally doesn’t occur in veins draining into atria – Atria are under very low pressure; blood mostly flows into atria with help of gravity and pressure in veins Atria receive blood from veins, and pump blood into ventricles through valves – Valves have flaps that close when ventricles contract; keep blood from moving backward – Contracting ventricles then eject blood into arteries; Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  The Heart’s Great Vessels, Chambers, and Valves 1. AV valves consist of flaps (cusps); – Forceful ventricular contractions could drive blood backward into atria; prevented by valves between atria and ventricles (right and left) – composed of endocardium overlying core of collagenous connective tissue – Each valve is named for number of cusps:  Tricuspid valve—between right atrium and right ventricle contains three cusps  Bicuspid valve—between left atrium and left ventricle has two cusps; more commonly called mitral valve (clinical name) Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  The Heart’s Great Vessels, Chambers, and Valves Chordae tendineae—fibrous, tendon-like structures attached to inferior end of each cusp – Attached to papillary muscles that contract just before ventricles begin ejecting blood – Creates tension on chordae tendineae keeping valves closed Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  The Heart’s Great Vessels, Chambers, and Valves Semilunar valves; Backflow of blood into ventricles from pulmonary artery and aorta can also occur; – Blood flows backward when ventricles relax as result of higher pressure in arteries and gravity; semilunar valves prevent this. – “Semilunar” refers to half-moon shape of their three cusps; also composed of endocardium and central collagenous core – Named according to artery in which they reside  Pulmonary valve—between right ventricle and pulmonary trunk  Aortic valve—posterior to pulmonary; between left ventricle and aorta Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Heart’s Great Vessels, Chambers, and Valves Frontal Sections through Left Atrium and Ventricle Figure 17.7b Anatomy of the atrioventricular and semilunar valves. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Heart’s Great Vessels, Chambers, and Valves Figure 17.5b The external anatomy of the heart. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  The Heart’s Great Vessels, Chambers, and Valves Atria are not symmetrical in size, shape, or location: – Right atrium is larger, thinner-walled, and more anterior than left atrium – Left atrium is thicker-walled, somewhat smaller, and located mostly on posterior side of heart; makes up much of heart’s base (posterior surface) – Externally, each atrium has muscular pouch (auricle); named for resemblance to external ear; expand to give atria more space to hold blood; auricle of right atrium is much larger than that of left atrium Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Heart’s Great Vessels, Chambers, and Valves The Right Atrium – Pectinate muscles  Contain prominent muscular ridges Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Heart’s Great Vessels, Chambers, and Valves The Right Atrium: Openings Superior vena cava: Vein receives blood from head, neck, upper limbs, and chest Inferior vena cava : Vein receives blood from trunk, viscera, and lower limbs Coronary sinus: Cardiac veins return blood to coronary sinus Foramen ovale: Before birth, is an opening through interatrial septum – Connects the two atria, Seals off at birth forming fossa ovalis Right atrioventricular (AV) valve or tricuspid valve Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Heart’s Great Vessels, Chambers, and Valves The Left Atrium Blood gathers into left and right pulmonary veins Is delivered to left atrium Blood from left atrium passes to left ventricle through left atrioventricular (AV) valve A two-cusped bicuspid valve or mitral valve Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  The Heart’s Great Vessels, Chambers, and Valves Ventricles—like atria, ventricles are asymmetrical; Right ventricle is wider with thinner walls than left ventricle because of pressure differences in pulmonary and systemic circuits – Right ventricle has little resistance against which to pump; – left ventricle pumps against much greater resistance – Left ventricle has to work harder than right ventricle; therefore has greater muscle mass; walls are about three times thicker than those of right ventricle Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Figure 20-6c The Sectional Anatomy of the Heart Ascending aorta Left coronary artery branches (red) Cusp of aortic valve and great cardiac vein (blue) Inferior vena cava Fossa ovalis Cusp of left AV (bicuspid) valve Pectinate muscles Chordae tendineae Coronary sinus RIGHT ATRIUM Papillary muscles Cusps of right AV (tricuspid) valve LEFT VENTRICLE Interventricular Trabeculae carneae septum RIGHT VENTRICLE A frontal section, anterior view. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  The Heart’s Great Vessels, Chambers, and Valves Ventricles (continued) – Internally, both ventricles have ridged surface created by irregular protrusions of cardiac muscle tissue (trabeculae carneae) – Interventricular septum—thick, muscular wall; separates right and left ventricles; contracts with rest of ventricular muscle; helps expel blood into pulmonary trunk and Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Aorta  The Heart’s Great Vessels, Chambers, and Valves Moderator band A muscular ridge that extends horizontally from inferior portion of the interventicular septum to right ventricle Connect to papillary muscles Contains part of conducting system Coordinates contractions of papillary muscles and Chordae tendineae Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  The Pericardium, Heart Wall, and Heart Skeleton Pericardium—Membranous structure surrounding heart. Is a double-walled sac containing the heart and the roots of the great vessels Protects and anchors the heart Prevent overfilling Anatomy: 1. Fibrous Pericardium 3. Pericardial cavity dense network of collagen fibers between parietal and visceral layers, contains 2. Serous Pericardium; pericardial fluid Parietal pericardium Visceral pericardium (epicardium) Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Figure 20-4a The Heart Wall Parietal pericardium Dense fibrous layer Areolar tissue Mesothelium Myocardium Pericardial cavity (cardiac muscle tissue) Epicardium Cardiac muscle cells (visceral pericardium) Connective tissues Mesothelium Areolar tissue Endocardium Areolar tissue Endothelium Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Pericardium, Heart Wall, and Heart Skeleton Fibrous pericardium—outer layer – Composed of collagen bundles that make it tough; – Anchor heart to diaphragm and great vessels – Low distensibility—doesn’t change shape or size considerably when stretching forces applied; helps to prevent chambers of heart from overfilling with blood Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Pericardium, Heart Wall, and Heart Skeleton Serous pericardium—thin inner serous membrane; produces serous fluid: – Parietal pericardium—fused to inner surface of fibrous pericardium; encases heart-like sac; at great vessels, it folds under itself and forms another layer that adheres directly to heart – Visceral pericardium—innermost layer; also known as epicardium; considered most superficial layer of heart wall Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Pericardium, Heart Wall, and Heart Skeleton – Pericardial cavity—between parietal and visceral pericardia; contains very thin layer of serous fluid (pericardial fluid); fluid acts as lubricant, decreasing friction as heart moves – Visceral pericardium rests on top of thin layer of areolar connective tissue; contains large fat deposits Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Pericardium, Heart Wall, and Heart Skeleton Figure 17.4b, c The pericardium and the layers of the heart wall. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Pericardium, Heart Wall, and Heart Skeleton Myocardium—deep to connective tissue; second and thickest layer of heart wall Myocardium components: – Cardiac muscle tissue and fibrous skeleton – Cardiac muscle tissue consists of cardiac muscle cells (myocytes) and their surrounding extracellular matrix – Cardiac muscle cells are attached to and woven through fibrous skeleton; composed of dense irregular collagenous connective tissue; Fibrous skeleton functions:  Providing structural support  Acting as insulator for heart’s electrical activity Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Pericardium, Heart Wall, and Heart Skeleton Lumen of heart is lined by Endocardium; third and deepest layer of heart wall – Composed of special type of simple squamous epithelium (endothelium) and several layers of connective tissue with elastic and collagen fibers – Endothelial cells of endocardium are continuous with endothelial cells that line blood vessels; share many functions Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Circulation of Blood through the Pulmonary and Systemic Circuits Heart pumps blood through two separate sets of vessels (circuits) Heart is divided functionally into right and left sides Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Circulation of Blood through the Pulmonary and Systemic Circuits Pulmonary circuit; Right side of heart is pulmonary pump; pumps blood into series of blood vessels leading to and within lung Pulmonary arteries of pulmonary circuit deliver oxygen-poor and carbon dioxide-rich (deoxygenated) blood to lungs Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Circulation of Blood through the Pulmonary and Systemic Circuits – Gas exchange takes place between tiny air sacs in lung (alveoli) and smallest vessels of pulmonary circuit (pulmonary capillaries)  Oxygen diffuses from air in alveoli into blood in pulmonary capillaries  Carbon dioxide diffuses from blood in pulmonary capillaries to air in alveoli, to be expired – Veins of pulmonary circuit deliver this oxygen-rich (oxygenated) blood to left side of heart Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Circulation of Blood through the Pulmonary and Systemic Circuits Left side of heart is systemic pump; receives oxygenated blood from pulmonary veins; pumps it into blood vessels that serve rest of body (systemic circuit) (Figure 17.3b) – In systemic circuit, arteries deliver oxygenated blood to smallest blood vessels (systemic capillaries) – Here gas exchange occurs again, in reverse:  Oxygen diffuses from blood into tissues  Carbon dioxide diffuses from tissues into blood Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Circulation of Blood through the Pulmonary and Systemic Circuits – Blood delivers nutrients, picks up wastes to be excreted, and distributes hormones to their target cells throughout body – As result of gas exchange in tissues, blood is deoxygenated and veins of systemic circuit then deliver it back to right side of heart, to be pumped into pulmonary circuit Pulmonary circuit is low-pressure circuit because it pumps blood only to lungs Systemic circuit is a high-pressure circuit because it has to pump blood to entire rest of body Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Big Picture of Blood Flow through the Heart Figure 17.8 The Big Picture of Blood Flow through the Heart. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Big Picture of Blood Flow through the Heart Figure 17.8 The Big Picture of Blood Flow through the Heart. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Circulation of Blood through the Pulmonary and Systemic Circuits (4 of 8) Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Circulation of Blood through the Pulmonary and Systemic Circuits (8 of 8) Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Cardiac Tamponade If pericardial cavity becomes filled with excess fluid, cardiac tamponade may result Potential causes: trauma, certain cancers, kidney failure, recent thoracic surgery, and HIV Regardless of cause, result is same—fibrous pericardium is strong but not very flexible, so excess fluid in pericardial cavity squeezes heart; reduces capacity of ventricles to fill with blood, decreasing amount of blood pumped with each beat Treatment may include removal of excess fluid via needle inserted into pericardial cavity Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Thoracotomy Thoracic cavity is opened in surgical procedure known as thoracotomy Performed when surgeon must gain access to thoracic organs, surrounding blood vessels, or anterior side of thoracic vertebral column Generally involves incision in chest wall and cutting through either sternum or ribs; separated and held apart with instrument called retractor (or “rib spreader”); creates “window” into thoracic cavity When procedure is completed, chest wall is closed, and chest tube must be inserted to prevent air from leaking into thoracic cavity and potentially causing collapse of lung Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Valvular Heart Diseases Valvular heart diseases impair function of one or more of valves; may be congenital (present at birth) or acquired from disease process (infection, cancer, or disorders of immune system) Two major types of valvular defects: insufficiency and stenosis – Insufficient valve—fails to close fully; allows blood to leak backward – Stenotic valve—calcium deposits in cusps; makes them hard and inflexible; blood flows through stenotic valve with difficulty; often heart has to pump harder to eject blood through it Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Valvular Heart Diseases Both types of valvular heart diseases may cause heart murmur (audible “swooshing” of blood when heart beats) Other signs and symptoms vary with type and severity of disease; may include enlargement of heart, fatigue, dizziness, and heart palpitations Mitral and aortic valves are most commonly affected by valvular heart disease Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Coronary Circulation Heart’s chambers are filled with blood, but myocardium is too thick for oxygen and nutrients to diffuse from inside chambers to all of organ’s cells For this reason, heart is supplied by a set of blood vessels collectively called coronary circulation Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Coronary Circulation Figure 17.9b The coronary circulation. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  coronary sinus Aortic sinuses Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Coronary Circulation Coronary vessels (coronary arteries): – Ascending aorta—main systemic artery into which left ventricle pumps blood – Immediately after ascending aorta emerges from left ventricle, two branches (right and left coronary arteries) arise; travel in right and left atrioventricular sulci, respectively Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  The Coronary Circulation Aortic Sinuses Dilations of the ascending aorta, which occurs just above the aortic valve. prevent valve cusps from sticking to aorta Three aortic sinuses: The left posterior ; gives rise to the left coronary artery. The right posterior; noncoronary sinus The anterior: gives rise to the right coronary artery. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Left coronary Coronary circulation Aortic arch artery Pulmonary Ascending trunk aorta Left Coronary Arteries Right coronary Circumflex artery artery circumflex artery (Cx) Atrial arteries Anterior interventricular Anterior artery Anterior interventicular artery cardiac veins Great cardiac Small vein Right Coronary Arteries cardiac vein Marginal Coronary vessels supplying artery and draining the anterior Several branches including surface of the heart. Circumflex artery Coronary sinus Right Marginal artery Great cardiac vein Marginal artery Posterior interventricular Artery Posterior interventricular artery Cardiac Veins Posterior cardiac Great cardiac vein vein Small cardiac Left vein ventricle Middle cardic vein Right coronary artery Middle cardiac vein Marginal artery Small cardiac vein Coronary vessels supplying and draining Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved the posterior surface of the heart. The Coronary Circulation Right coronary artery travels inferiorly and laterally along right atrioventricular sulcus; gives off several branches that supply right atrium and ventricle (Figure 17.9a): – Largest branch is marginal artery; typically arises near inferior margin (border) of heart – After marginal artery branches off, right coronary artery curls around to posterior heart; travels in posterior interventricular sulcus as posterior interventricular artery Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Coronary Circulation Shortly after left coronary artery emerges from ascending aorta, it generally branches into two vessels: – Anterior interventricular artery (left anterior descending artery, or LAD) travels along anterior interventricular sulcus; at apex of heart, it generally curls around and travels short distance along posterior interventricular sulcus – Circumflex artery curves along left atrioventricular sulcus and flexes around heart; supplies left atrium and parts of left ventricle; in some people, replaces right coronary artery in supplying branch that becomes posterior interventricular artery Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  The Coronary Circulation Coronary arterial supply is complicated by formation of anastomoses (systems of channels formed between blood vessels) – Coronary arteries may form anastomoses with one another, with branches from pericardium, or even with arteries from outside coronary circulation entirely – When blood flow to myocardium is insufficient, occasionally new anastomoses will form to provide alternate routes of blood flow (collateral circulation) to myocardium – Collaterals help protect muscle cells from damage that could result from blocked vessels Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Coronary Circulation Coronary vessels (coronary veins) (Figure 17.9b): – Majority of heart’s veins empty into large venous structure on posterior heart (coronary sinus); drains into posterior right atrium – Coronary sinus receives blood from three major veins:  Great cardiac vein  Small cardiac vein  Middle cardiac vein Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Coronary Circulation – Coronary sinus receives blood from three major veins – Large great cardiac vein ascends along anterior interventricular sulcus; travels to posterior side of heart along left atrioventricular sulcus; drains left atrium and much of both ventricles  Small cardiac vein travels along right atrioventricular sulcus; drains right atrium and parts of right ventricle  Middle cardiac vein travels along posterior interventricular groove; drains mostly posterior left ventricle Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  The Coronary Circulation Build-up of fatty material (plaques) in coronary arteries results in coronary artery disease (CAD); – leading cause of death worldwide – CAD decreases blood flow to myocardium; results in inadequate oxygenation of myocardium; known as myocardial ischemia – When present, symptoms generally come in form of chest pain (angina pectoris) Normal Artery Narrowing of Artery Tunica Atherosclerotic externa plaque Tunica media Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Cross section Cross section  The Coronary Circulation Most dangerous potential consequence of CAD is myocardial infarction (MI; heart attack) – MIs occur when plaques in coronary arteries rupture and clot forms; obstructs blood flow to myocardium; myocardial tissue supplied by that artery infarct (die) Symptoms include chest pain that radiates along dermatomes to left arm or left side of neck, shortness of breath, sweating, anxiety, and nausea and/or vomiting women may not present with chest pain; may suffer back, jaw, or arm pain instead Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Coronary Circulation – Survival after MI depends on extent and location of damage  Cardiac muscle cells generally do not undergo mitosis  Dead cells are replaced with fibrous, noncontractile scar tissue – Death of part of myocardium increases workload of remaining heart muscle – Risk factors for CAD and MI include smoking, high blood pressure, poorly controlled diabetes, high levels of certain lipids in blood, obesity, age over 40 for males and over 50 for females, genetics, and male gender Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Coronary Circulation – CAD is definitively diagnosed via angiography; small tube is fed through artery in systemic circuit into ascending aorta, and into coronary arteries; special dye is injected into arteries, and their condition is examined by x-ray – Treatments include lifestyle modifications and appropriate medications; if these approaches fail, invasive treatments are considered (next slide) Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Coronary Circulation – Coronary angioplasty—commonly performed invasive procedure; – balloon is inflated in blocked artery; – piece of wire-mesh tubing (stent) may be inserted into artery to keep it open – Coronary artery bypass grafting— more invasive treatment; other vessels are grafted onto diseased coronary artery to bypass blockage and provide alternate route for blood flow Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Myocardial infarction – Causes intense, persistent pain, even at rest – Pain is not always felt May go undiagnosed and untreated – Often diagnosed with ECG and blood studies – Damaged myocardial cells release enzymes into circulation Cardiac troponin T Cardiac troponin I A form of creatinine phosphokinase, CK-MB Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved 76  Treatment of CAD and myocardial infarction  Treatment of CAD and myocardial infarction – About 25 percent of MI patients die before obtaining medical assistance 65 percent of MI deaths among people under age 50 occur within an hour  Risk factor modification – Stop smoking – Treat high blood pressure – Adjust diet to lower cholesterol and promote weight loss – Reduce stress – Increase physical activity Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved 77 Myocardial infarction – Consequences depend on site and nature of circulatory blockage – If near the start of one of the coronary arteries Damage will be widespread, and heart may stop beating – If blockage involves small arterial branch Individual may survive the immediate crisis But may have complications such as reduced contractility and cardiac arrhythmias Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved 78 Drug treatments are used to – Reduce coagulation (e.g., aspirin and coumadin) – Block sympathetic stimulation (propranolol or metoprolol) – Cause vasodilation (e.g., nitroglycerin) – Block calcium ion movement into muscle cells (calcium ion channel blockers) – Relieve pain and help dissolve clots (in MI) Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved 79  Cardiac Physiology 1. Electrical Events 2. Mechanical Events: The Cardiac Cycle 3. Heart Sounds 4. Cardiac output Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Module 17.3 Cardiac Muscle Tissue Anatomy and Electrophysiology Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Characteristics of Cardiac Muscle Cells Heartbeat: A single contraction of the heart First the atria Then the ventricles Two Types of Cardiac Muscle Cells: Conducting system : Controls and coordinates heartbeat Contractile cells: Produce contractions that propel blood Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Characteristics of Cardiac Muscle Cells Typically branched cells with single nucleus; shorter and wider than skeletal muscle fibers – Contain abundant myoglobin (protein that carries oxygen) – Nearly half of cytoplasmic volume is composed of mitochondria; reflect high energy demands Intercalated disc Gap junction Opposing plasma Intercalated discs membranes Desmosomes Cardiac muscle tissue LM  575 Cardiac muscle tissue Structure of an intercalated disc Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Cardiac Muscle Tissue Possess unique structures Cardiac muscle cell (intercalated discs) that join adjacent Mitochondria cardiac muscle cells; join pacemaker Intercalated disc (sectioned) cells to contractile cells, and contractile cells to one another Intercalated discs contain Desmosomes—hold cardiac Nucleus Cardiac muscle muscle cells together cell (sectioned) Gap junctions—allow ions to Bundles of myofibrils rapidly pass from one cell to Intercalated discs another, permitting communication Cardiac muscle cells among cardiac muscle cells Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Histology of Cardiac Muscle Tissue and Cells Figure 17.10 Cardiac muscle cells. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Histology of Cardiac Muscle Tissue and Cells Like skeletal muscle fibers and other excitable cells, cardiac muscle cells contain selective gated ion channels in sarcolemma Opening and closing action of these ion channels is responsible for both pacemaker and contractile cardiac action potentials – Voltage-gated sodium ion channels—open in response to voltage changes across membrane; in all cardiac muscle cells except certain pacemaker cells – Calcium ion channels—demonstrate voltage-gated opening but time- gated closing; close after certain period regardless of voltage – All types of cardiac muscle cells have one or more types of potassium ion channels; some ligand-gated; others voltage-gated Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Histology of Cardiac Muscle Tissue and Cells Cardiac muscle cells, like skeletal muscle fibers, have striations (alternating light and dark bands when viewed under microscope) As with skeletal muscle fibers, striations are due to arrangement of contractile proteins within cardiac muscle cells – Structural similarities reflect physiological similarities; skeletal and cardiac muscle tissues have same general function; both generate tension through sliding-filament mechanism of contraction; Structure-Function Core Principle Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Study Boost: Revisiting Electrophysiology (1 of 3) Terminology: Voltage—difference in electrical potential between two points Membrane potential—voltage (charge) difference that exists across membranes of all cells, including excitable cells Resting membrane potential—membrane potential of excitable cell at rest (not being stimulated); averages between −60 and −90 mV: difference in concentration of ions across plasma membrane Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Study Boost: Revisiting Electrophysiology (2 of 3) Terminology (continued): Current—flow of ions or electrons with chemical or electrical gradient Depolarization—change in resting membrane potential to value less negative than when at rest; occurs when positive charges (generally, sodium and/or calcium ions) rush into cell Repolarization—return of cell to its negative resting membrane potential; occurs when positive charges (potassium ions) leave cell Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Study Boost: Revisiting Electrophysiology (3 of 3) Review of ion gradients (Gradients Core Principle): – Concentration of sodium and calcium ions in extracellular fluid (ECF) is higher than in cytosol; concentration of potassium ions in ECF is lower than in cytosol  Sodium and calcium ions tend to follow their concentration gradients to enter cell when their channels open  Potassium ions follow their concentration gradient and leave cell when their channels open – Sodium and potassium ion gradients are maintained by Na+/K+ pump; calcium ion gradient by separate active transport pump Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue Contractile cells—great majority (99%) of cardiac muscle cells – Action potential in contractile cardiac muscle cell results from reversal in membrane potential—inside of plasma membrane swings from negative (about −85 mV) to momentarily positive (ranging from 0 to +20 mV) – Voltage-gated ion channels in sarcolemma and unequal concentrations of sodium and potassium ions on either side of membrane drive ions in or out of cell through channels Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue Action potential in cardiomyocytes How action potential in cardiac muscle (Contractile Cells) is produced? Rapid Depolarization The Plateau Repolarization Cause: Na+ entry Cause: Ca2+ entry Cause: K loss + Duration: 3–5 msec Duration: ~175 msec Duration: 75 msec Ends with: Closure of Ends with: Closure Ends with: Closure voltage-gated fast of slow calcium of slow potassium sodium channels channels channels mV Relative refractory Absolute refractory period period Stimulus Time (msec) Events in an action potential in a ventricular muscle cell. KEY Absolute refractory period Relative Copyright © 2019, 2016 Pearson refractory Education, Inc. All Rights Reserved period Electrophysiology of Cardiac Muscle Tissue Sequence of events of contractile cell action potential proceeds as follows (Figure 17.13): – Rapid depolarization phase—pacemaker cell action potentials cause voltage changes in adjacent cells; voltage-gated sodium ion channels in sarcolemma are activated; causes rapid and massive influx of sodium ions; leads to rapid membrane depolarization – Initial repolarization phase—small, initial repolarization immediately after depolarization spike; due to abrupt inactivation of sodium ion channels and to very small outflow of potassium ions through selected potassium ion channels (open only briefly) Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue Sequence of events (continued): – Plateau phase—depolarization is sustained at about 0 mV in plateau phase; critically important phase is mostly due to slow opening of calcium ion channels and resulting influx of calcium ions – Repolarization phase—final phase of action potential; both sodium and calcium ion channels return to resting states and most of potassium ion channels open; allows positively charged potassium ions to exit cardiac muscle cell; membrane potential returns to its resting value of about −85 mV Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue Figure 17.13 A contractile cell action potential. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue Sequence of events of contractile cell action potential resembles that of skeletal muscle fiber action potential with one important exception: plateau phase – If cardiac action potentials lasted only about 1–5 msec, like skeletal muscle fiber action potentials, resting heart rate would be about 15 times faster than it should be at rest Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue – Plateau phase lengthens cardiac action potential to about 200– 300 msec; slows heart rate; provides time required for heart to fill with blood – Plateau phase also increases strength of heart’s contraction; prolonged action potential makes muscle twitch last longer; can develop more force; allows more calcium ions to enter cell; needed for contraction via sliding-filament mechanism – Plateau phase also effectively prevents tetany (sustained contraction) in heart by lengthening refractory period (time during which excitable cell cannot be stimulated to contract again) Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue Refractory Period – Absolute refractory period  Cardiac muscle cells cannot respond  Sodium channels are already open or are closed  Long (200msec) – Relative refractory period  Response depends on degree of stimulus  Voltage gated sodium channel are closed but can be opened  Short (50sec) – Refractory period in cardiac muscle cells is so long that cells cannot maintain sustained contraction; allows heart to relax and ventricles to refill with blood before cardiac muscle cells are stimulated to contract again Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology Heart does not require conscious intervention to elicit cardiac muscle to contract; cardiac muscle exhibits autorhythmicity; sets its own rhythm without need for input from nervous system Cardiac muscle cells contract in response to electrical excitation in form of action potentials Unlike skeletal muscle and many smooth muscle cells, cardiac muscle cells do not require stimulation from nervous system to generate action potentials Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Electrophysiology of Cardiac Muscle Tissue Pacemaker cells: Cardiac electrical activity is coordinated by very small, Unique population of cardiac muscle cells – Pacemaker cells undergo rhythmic, spontaneous depolarizations that lead to action potentials; – spread quickly through heart by cardiac conduction system (group of interconnected pacemaker cells) – Action potentials rhythmically and spontaneously also spread to contractile cells. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue Action potentials are transmitted from pacemaker cells to contractile cells through intercalated discs that unite them – Gap junctions in these discs allow electrical activity generated by pacemaker cells to rapidly spread to all cardiac muscle cells via electrical synapses – Permits heart to contract as unit and produce coordinated heartbeat; reason cells of heart are sometimes referred to as functional syncytium (term for large, multinucleated cell) Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Electrophysiology of Cardiac Muscle Tissue Pacemaker potential—much different from that of contractile cell Depolarization in pacemaker cell occurs much more slowly; – due in part to lack of voltage-gated sodium ion channels in pacemaker sarcolemma – Pacemaker cell action potentials lack plateau phase and membrane potential oscillates—never remains at resting level; instead occurs in cycle, with last event triggering first – Occurs because of nonspecific cation channels; unique to pacemaker cells Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Physiology of Conduction System Movement of ions (principally Ca++and K+, and to a Lesser extent Na+) across the membrane through ion channels Are responsible for the changes in membrane potential of autorhythmic cells in conducting system during the different phases SA node initiate action potentials depolarizes first ,establishing heart rate Have unstable resting potentials called pacemaker potentials Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Pacemaker potentials (Prepotential) During resting potential of conducting cells, slow inflow of calcium (rather than sodium) gradually depolarizes membrane toward threshold with out compensating out flow of K+ Once the membrane potential reaches threshold triggers the action potential Threshold Prepotential (spontaneous depolarization) Time (sec) Changes in the membrane potential of a pacemaker cell in the SA node that is establishing a heart rate of 72 beats per minute. Note the presence of a prepotential, a gradual spontaneous depolarization. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue Pacemaker potential (continued) – Slow initial depolarization phase— pacemaker potential starts with plasma membrane in hyperpolarized state—at minimum membrane potential  Opens nonspecific calcium channels in membrane; allow cations to leak into cell and potassium ions to leak out  Results in overall slow depolarization to threshold – Full depolarization phase—when membrane reaches threshold, voltage-gated calcium ion channels open; allows calcium ions to enter cell; causes membrane to fully depolarize Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Electrophysiology of Cardiac Muscle Tissue Pacemaker potential (continued) – Repolarization phase—calcium ion channels are time-gated for closing; after certain time (about 100–150 msec), they close; at same time, voltage-gated potassium ion channels begin to open; allows potassium ions to exit cell, and membrane begins to repolarize – Minimum potential phase— potassium ion channels remain open until membrane reaches its minimum potential (membrane is hyperpolarized); opens nonspecific cation channels, and cycle begins again Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue Figure 17.11 A pacemaker cell action potential. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue Figure 17.11 A pacemaker cell action potential. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue Pacemaker cells make up only about 1% of total number of cardiac muscle cells – Three populations of these cells in heart; capable of spontaneously generating action potentials, thereby setting pace of heart – Three cell populations are collectively called cardiac conduction system – SA node generates 60–100 action potentials per minute – AV node generates 40–60 action potentials per minute – Purkinje fiber depolarize at 20-40 per min Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue Cardiac conduction system Sinoatrial Sinoatrial (SA) node, (SA) node Atrioventricular (AV) node, Internodal pathways Internodal pathways, AV bundle (bundle of His) Atrioventricular (AV) node bundle branches, AV bundle purkinje fibers Bundle branches Purkinje fibers Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue Sinoatrial node (SA node)—in upper right atrium, slightly inferior and lateral to opening of superior vena cava  Under normal conditions, SA node has fastest intrinsic rate of depolarization—about 60 or more times per minute  Rate is subject to influence from sympathetic and parasympathetic nervous systems Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue Cardiac conduction system cells populations (continued): – Atrioventricular node (AV node)— posterior and medial to tricuspid valve; slower than SA node; intrinsic rate of only about 40 action potentials per minute – Purkinje fiber system—slowest group of pacemaker cells; depolarize only about 20 times per minute;  atypical pacemakers because their action potentials rely on different ion channels and they function in slightly different way Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue Purkinje fiber system: – Atrioventricular bundle (AV bundle)—penetrates heart’s fibrous skeleton in inferior interatrial septum and superior interventricular septum – Right and left bundle branches—course along right and left sides of interventricular septum, respectively – Terminal branches (Purkinje system )—penetrate ventricles and finally come into contact with contractile cardiac muscle cells Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue Figure 17.12 The cardiac conduction system. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue Pacing Heart: Sinus rhythm—each population of pacemaker cells can potentially pace heart (make it beat at certain rate); one that depolarizes fastest sets heart rate; other pacemakers will pace heart only if fastest pacemaker ceases to function – SA node is normal pacemaker of entire heart; electrical rhythms generated and maintained by SA node are known as sinus rhythms – AV node and Purkinje fiber system normally only conduct action potentials generated by SA node; if SA node ceases to function, AV node can successfully pace heart, albeit somewhat slowly Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue – Note that AV bundle of Purkinje system is only connection between AV node and ventricles  If blocked, SA node cannot pace ventricles even if functioning normally  Purkinje fiber system is capable of pacing heart, but its slow rate of depolarization is not adequate to sustain life beyond short period of time  Occasionally, group of regular contractile cells or pacemaker cells other than SA node will attempt to pace heart at same time as SA node; “extra” pacemaker is called ectopic pacemaker; can cause irregular heart rhythms Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue Under normal conditions, SA node generates action potential; spreads rapidly via gap junctions to surrounding atrial cells – Impulses are conducted by specialized atrial conducting fibers to AV node; altogether require about 0.03 second – Once impulse reaches AV node, conduction slows considerably as result of:  Low number of gap junctions between AV nodal cells  Presence of nonconducting fibrous skeleton that surrounds AV node Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue – This slow conduction (AV node delay) generally lasts about 0.13 second  Allows atria to depolarize (and contract) before ventricles; gives ventricles time to fill with blood  Also helps to prevent current from flowing backward from AV bundle into AV node and atria – Action potential is then conducted from AV bundle to right and left bundle branches – Depolarization spreads along Purkinje fibers to contractile cardiac muscle cells of ventricles Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue The Sinoatrial (SA) Node, cardiac pacemaker – Contains pacemaker cells, establish the heart rate SA node activity and atrial SA activation begin. node Time = 0 Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue Stimulus spreads across the atrial surfaces (internodal Pathways) and reaches the AV node. AV node Elapsed time = 50 msec There is a 100-msec delay at the AV node (Important in adjusting contraction time between AV atria and ventricles) bundle Atrial contraction begins. Bundle branches Elapsed time = 150 msec Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue The impulse travels along the interventricular septum within the AV bundle and the bundle branches to the Purkinje fibers and, via the moderator band, to the papillary muscles of the right ventricle. Moderator Elapsed time = 175 msec band Right ventricle papillary muscles receive the impulse through moderator band and contract before the rest of ventricular muscles impulse will be conducted to chordae tendineae bracing AV valve Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue The impulse is distributed by Purkinje fibers and relayed throughout the ventricular myocardium. Atrial contraction is completed, and ventricular contraction begins. Purkinje Elapsed time = 225 msec fibers – Ventricular contraction begins from the apex and spread toward the base Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Heart Rate – SA node generates 80–100 action potentials per minute – AV node generates 40–60 action potentials per minute – Purkinje fiber depolarize at 20-40 per min – Under normal conditions, cells of AV bundles, the bundle branches and the most purkinje cells do not depolarize spontaneously and follow heart rate from SA node Extrinsic innervation of the heart – Heart is stimulated by the sympathetic cardioacceleratory center – Heart is inhibited by the parasympathetic cardioinhibitory center – Parasympathetic stimulation slows heart rate (75/min) Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Autonomic Innervation Cardiac centers of medulla oblongata Cardioacceleratory center controls sympathetic neurons (increases heart rate) Cardioinhibitory center controls parasympathetic neurons (slows heart rate) Both ANS divisions innervate the SA and AV nodes and the atrial and ventricular muscle cells Cardiac centers adjust cardiac activity by affecting Autonomic tone Dual innervations maintains resting tone by releasing Ach(acetylcholine) and NE (Norepinephrine) at the nodes and myocardium. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Parasympathetic (through Vagus (N X) ) effects dominate in healthy, resting individual. (80-100bpm of SA node is changing to 70-80bpm) Cardiac reflexes Cardiac centers adjust the heart activity through the information received by (Baroreceptors) monitor Blood pressure (Chemoreceptors) monitor Arterial oxygen and carbon dioxide levels Fine adjustments by ANS meet needs of other higher systems The medulla receives information from other brain regions (e.g., hypothalamus). The hypothalamus and higher centers modify the activity of the medullary centers and are particularly important in stimulating cardiovascular responses to emotion and stress (e.g., exercise, thermal stress). Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Higher systems Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved How do the sympathetic and parasympathetic divisions alter the heart rate – Heart Rate depends on  Resting membrane potential of nodal cells  Rate of spontaneous depolarization of nodal cells  Duration of repolarization of nodal cells Normal (resting) Prepotential (spontaneous Membrane depolarization) potential (mV) Threshold Heart rate: 75 bpm Pacemaker cells have membrane potentials closer to threshold than those of other cardiac muscle cells (–60 mV versus –90 mV). Their plasma membranes undergo spontaneous depolarization to threshold, producing action potentials at a frequency determined by (1) the resting-membrane potential and (2) the rate of depolarization. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  ANS effects on the SA Node by changing the ionic permeability of cells Parasympathetic stimulation Acetylcholine ,ACh (parasympathetic stimulation) Slows the heart by opening K+ channels Parasympathetic stimulation Membrane potential (mV) Threshold Hyperpolarization Heart rate: 40 bpm Slower depolarization Parasympathetic stimulation releases ACh, which extends repolarization and decreases the rate of spontaneous depolarization. The heart rate slows. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Sympathetic stimulation Norepinephrine, NE (sympathetic stimulation) Speeds the heart by binding to beta-1 receptors, leading to opening sodium/calcium channels Sympathetic stimulation Membrane potential (mV) Threshold Reduced repolarization More rapid Heart rate: 120 bpm depolarization Time (sec) Sympathetic stimulation releases NE, which shortens repolarization and accelerates the rate of spontaneous depolarization. As a result, the heart rate increases. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved The Conducting System  Disturbances in heart rhythm – Bradycardia—abnormally slow heart rate – Tachycardia—abnormally fast heart rate – Ectopic pacemaker Abnormal cells generate high rate of action potentials Bypasses conducting system Disrupts timing of ventricular contractions Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved 131  Excitation-contraction coupling—mechanism for cardiac muscle cell contraction is very similar to that of skeletal muscle fiber; occurs by sliding-filament mechanism – In stimulated cardiac muscle cell, depolarization propagates through sarcolemma and dives into cell along T-tubules; causes sarcoplasmic reticulum to release calcium ions – Ions bind to troponin; allows actin and myosin to bind and crossbridge cycle to begin Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Electrophysiology of Cardiac Muscle Tissue Excitation-contraction coupling (continued) – Sarcoplasmic reticulum of cardiac muscle cells is much less extensive than in skeletal muscle fibers; does not release enough calcium ions to produce reliably strong contraction – Remaining calcium ions needed for contraction diffuse into cell during action potential through calcium ion channels from extracellular fluid in T-tubules – For this reason, concentration of calcium ions in cardiac extracellular fluid plays significant role in determining strength of contraction; one reason why calcium ion homeostasis is so critical Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  The Energy for Cardiac Contractions – Aerobic energy of heart  From mitochondrial breakdown of fatty acids and glucose  Oxygen from circulating hemoglobin  Cardiac muscles store oxygen in myoglobin Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Module 17.4 Mechanical Physiology of the Heart: The Cardiac Cycle Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Introduction to Mechanical Physiology Mechanical physiology—actual processes by which blood fills cardiac chambers and is pumped out of them – Heartbeat; Cardiac muscle cells contract as unit to produce one coordinated contraction : muscle cells are arranged in spiral pattern, producing “wringing” action in heart when it contracts – Pressure changes caused by contractions drive blood flow through heart, with valves preventing backflow – Cardiac cycle—sequence of events within heart from one heartbeat to next Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  The Cardiac Cycle (Mechanical Events steps) 1. Systole (contraction) 2. Diastole (relaxation) Phases of the Cardiac Cycle Atrial systole Atrial diastole Ventricular systole Ventricular diastole At 75 beats per minute (bpm) cardiac cycle lasts about 800 msec When the heart rate increases, all the phases of the cardiac cycle are shortened. The greatest reduction occurs in the length of time spent in diastole Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Pressure Changes, Blood Flow, and Valve Function Each cardiac cycle consists of one period of relaxation (diastole) and one period of contraction (systole) for each chamber of heart (Figures 17.17, 17.18) – Atrial and ventricular diastoles and systoles occur at different times as result of AV node delay; both sides of heart are working to pump blood into their respective circuits simultaneously – Cycle is divided into four main phases; defined by actions of ventricles and positions of valves: – filling, contraction, ejection, and relaxation Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Pressure Changes, Blood Flow, and Valve Function Blood flows in response to pressure gradients as ventricles contract and relax, pressure in chambers changes, causing blood to push on valves and open or close them (Figure 17.15) Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Pressure Changes, Blood Flow, and Valve Function When ventricles contract, their pressures rise above those in right and left atria and in pulmonary trunk and aorta; causes blood to flow from ventricles to vessels and produces two changes in valves: – Both AV valves are forced shut by blood pushing against them – Both semilunar valves are forced open by outgoing blood Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Pressure Changes, Blood Flow, and Valve Function When ventricles relax, opposite occurs; pressures in ventricles fall below those in atria and in pulmonary trunk and aorta – Higher pressure in atria forces AV valves open, allowing blood to drain from atria into relaxed ventricles – Higher pressures in pulmonary trunk and aorta push cusps of semilunar valves closed Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Ventricular filling phase Ventricular diastole—late Cardiac cycle All chambers are relaxed 800msec AV valves open Semi lunar valves are closed Passive atrial filling Passive ventricular filling Cardiac cycle Nearly 80% of total blood volume of atria drains passively in this manner into Ventricular ventricles diastole—late: During ventricular diastole the pressure within the left ventricle is lower than that in aorta, allowing blood to circulate in the heart itself via the coronary arteries. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Cardiac cycle Atrial systole Atrial systole begins: Start Atrial contraction begins Right and left AV valves are open Semi lunar valves are closed Atria eject blood into ventricles Filling ventricles, little back flow into 0 800 msec 100 the vein (20% of blood volume ) msec msec Atrial systole ends AV valves close At end of atrial systole, each ventricle Cardiac contains about 120 ml of blood (end- cycle diastolic volume (EDV)); ventricular volume at end of ventricular diastole Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Cardiac cycle Figure 17.17 Events of the cardiac cycle. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Ventricular Systole Cardiac cycle Beginning of ventricular systole occurs during shortest phase of cardiac cycle (isovolumetric contraction) Atrial systole ends, 100 Atrial diastole Pressure in ventricles rises rapidly as msec begins ventricles begin to contract; high pressure closes AV valves and causes S1 heart Cardiac sound cycle Ventricular systole— first phase: Ventricular pressure is not yet high enough to push open semilunar valves, so both sets of valves are closed and ventricular volume does not change (same volume = isovolumetric) Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Cardiac cycle Figure 17.17 Events of the cardiac cycle. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Cardiac cycle Ventricular ejection At beginning of ventricular ejection phase Pressure in ventricles rises to level Cardiac cycle higher than in pulmonary trunk and aorta; pushes semilunar valves open; rapid outflow of blood from ventricles occurs 370 As phase continues, pressure in msec pulmonary trunk and aorta approaches that in ventricles; at this point, ejection of blood into Ventricular systole— vessels decreases considerably second phase: Approximately 70 ml of blood pumped from each ventricle; about 50 ml of blood remains in each ventricle (end-systolic volume (ESV)) Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Cardiac cycle Figure 17.17 Events of the cardiac cycle. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Cardiac cycle Ventricular Diastole (early) Final phase (isovolumetric relaxation) is brief; Ventricles stop contracting and begin to relax. Ventricular pressure falls. Cardiac cycle Semilunar valves snap shut; S2 heart sound is heard AV valves remain closed 370 msec Blood is neither being ejected from nor entering into ventricles; volume briefly remains constant Dicrotic notch, temporary pressure Ventricular diastole—early: rise in aorta as a result of elastic arterial walls recoil. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Cardiac cycle Figure 17.17 Events of the cardiac cycle. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  Cardiac cycle Figure 17.17 Events of the cardiac cycle. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved isovolumetric contraction Isovolumic relaxation: Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved Pressure Changes, Blood Flow, and Valve Function Figure 17.18 Comparison of pressure changes in left and right ventricles during the cardiac cycle. Copyright © 2019, 2016 Pearson Education, Inc. All Rights Reserved  ATRIAL ATRIAL ATRIAL DIASTOLE Pressure and Volume Relationships DIASTOLEin the Cardiac Cycle (Part 3 of 4). SYSTOLE VENTRICULAR VENTRICULAR DIASTOLE SYSTOLE 120 5 Aortic valve opens Aorta 90 1 Atrial contraction begins. 2 Atria eject blood into ventricles. Pressure (mm Hg) 60 3 Atrial systole ends; AV valves close. Left 4 Isovolumetric ventricular contraction occurs. ventricle 4 5 Ventricular ejection occurs. 6 Semilunar valves close. 7 Isovolumetric relaxation occurs. 30 Left AV Left atrium valve closes 8 AV valves open; passive ventricular filling occurs. 2 1 3 0 130 End-diastolic 3 volume volume (mL) 2 ventricular 1 Left Stroke volume 50 0 100 200 300 Copyright © 2019