PHGY 215 Cardiac Physiology Module 05 PDF

PHGY 215 oiw PRINCIPLES OF MAMMALIAN PHYSIOLOGY I MODULE 05 CARDIAC PHYSIOLOGY Please note: This course was designed to be interacted and engaged with using the online modules. This Module Companion Guide is a resource created to complement the online slides. If there is a discrepancy between this guide and the online module, please refer to the module. How can you help protect the integrity and quality of your Queen’s University course? Do not distribute this Module Companion Guide to any students who are not enrolled in PHGY 215 as it is a direct violation of the Academic Integrity Policy of Queen’s University. Students found in violation can face sanctions. For more information, please visit https://www.queensu.ca/academic- calendar/health-sciences/bhsc/. MODULE 05 COMPANION GUIDE PHGY 215 TABLE OF CONTENTS INTRODUCTION..................................................................................................................................................... 5 Learning Outcomes........................................................................................................................................... 5 Module Assignments........................................................................................................................................ 5 Case Study Discussion Board Series........................................................................................................... 5 Integrated Lab Report.................................................................................................................................. 6 Module Outline.................................................................................................................................................. 6 SECTION 01: Introduction to Cardiovascular System........................................................................................ 7 Section 01: Introduction to Cardiovascular System...................................................................................... 7 The Circulatory System..................................................................................................................................... 7 Functions of the Circulatory System............................................................................................................... 7 Organization of the Circulatory System.......................................................................................................... 8 Blood Flow is Both Serial and Parallel............................................................................................................ 9 Series and Parallel Circuits........................................................................................................................... 9 Activity: The Functions of the Circulatory System.......................................................................................10 SECTION 02: Structure of The Heart.................................................................................................................12 Section 02: Structure of the Heart.................................................................................................................12 The Heart: A Double Pump............................................................................................................................12 The Major Vessels of the Heart......................................................................................................................13 Flow of Blood Through the Body...................................................................................................................13 Blood Flow is Unidirectional..........................................................................................................................14 Heart Valves.....................................................................................................................................................15 Clinical Application: Heart Valves..................................................................................................................17 Question: What Do You Know About Cardiac Muscle?...............................................................................17 Cardiac Muscle Fibres.....................................................................................................................................18 Intercalated Discs............................................................................................................................................19 Cardiac Muscle Fibre Arrangement...............................................................................................................19 The Pericardial Sac..........................................................................................................................................20 SECTION 03: Electrical Activity of The Heart.....................................................................................................22 Section 03: Electrical Activity of The Heart...................................................................................................22 Question: Introduction to Electrical Activity of the Heart...........................................................................22 Cardiac Autorhythmic Cells............................................................................................................................22 The Cardiac Conduction System....................................................................................................................23 PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 2 MODULE 05 COMPANION GUIDE PHGY 215 Normal Pacemaker Activity of the Heart......................................................................................................24 Cardiac Excitation Requirements..................................................................................................................25 Question: Cardiac Excitation Requirements................................................................................................25 Atrial Excitation................................................................................................................................................26 Question: Cardiac Excitation Requirements................................................................................................27 Ventricular Excitation......................................................................................................................................27 Conduction Pathway of the Heart.................................................................................................................28 The Heart in Action.........................................................................................................................................28 The Cardiac Action Potential..........................................................................................................................29 Cardiac Excitation-Contraction Coupling......................................................................................................30 The Relationship Between Action Potential Duration and Length of Contraction..................................31 The Electrocardiogram (ECG)..........................................................................................................................31 The First ECG................................................................................................................................................32 The Modern Day ECG..................................................................................................................................33 The ECG Recording..........................................................................................................................................33 Summary of ECG Recordings..........................................................................................................................34 Components of an ECG Recording Part 1.....................................................................................................35 Components of an ECG Recording Part 2.....................................................................................................35 Heart Rate and Rhythm Disturbances..........................................................................................................37 SECTION 04: Mechanical Activity of The Heart.................................................................................................39 Section 04: Mechanical Activity of The Heart...............................................................................................39 Introduction to Mechanical Activity of the Heart........................................................................................39 The Cardiac Cycle............................................................................................................................................39 The Mechanical Activity of the Heart............................................................................................................40 Question: The Functions of the Circulatory System....................................................................................41 Heart Sounds...................................................................................................................................................42 Clinical Application - Heart Murmurs............................................................................................................43 SECTION 05: Cardiac Output..............................................................................................................................44 Section 05: Cardiac Output............................................................................................................................44 Cardiac Output................................................................................................................................................44 Regulation of Heart Rate and Cardiac Output.............................................................................................45 Parasympathetic Regulation of the Heart....................................................................................................45 Sympathetic Regulation of the Heart............................................................................................................47 PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 3 MODULE 05 COMPANION GUIDE PHGY 215 Control of Heart Rate......................................................................................................................................49 Control of Stroke Volume...............................................................................................................................50 Intrinsic Control of Stroke Volume and End-Diastolic Volume..................................................................50 Question: The Frank-Starling Law of the Heart...........................................................................................51 The Regulation of EDV.....................................................................................................................................52 Ejection Fraction..............................................................................................................................................53 Extrinsic Control of Stroke Volume...............................................................................................................53 Activity: Cardiac Output..................................................................................................................................54 Question: Cardiac Output and Heart Failure...............................................................................................55 SECTION 06: Nourishing The Heart...................................................................................................................56 Section 06: Nourishing The Heart.................................................................................................................56 Coronary Blood Supply...................................................................................................................................56 The Coronary Circulation...............................................................................................................................57 Cardiac Demand for Oxygen..........................................................................................................................57 Question: Cardiac Excitation Requirements................................................................................................58 Question: Myocardial Infarctions / “Heart Attacks”....................................................................................58 Summary..........................................................................................................................................................59 Module 05: Important Formulas...................................................................................................................59 Learning Outcomes.........................................................................................................................................60 CONCLUSION.......................................................................................................................................................61 PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 4 MODULE 05 COMPANION GUIDE PHGY 215 INTRODUCTION Please see the online learning module for the full experience of interactions within this document. This content was retrieved from Introduction Slide 1 of 4 of the online learning module. We have now discussed the peripheral nervous system, including the efferent division, which innervates muscle tissue via motor neurons. Not all muscles, however, are innervated this way. In this module, we will focus on the structure, function, and innervation of one such example: the heart. The heart is a muscular organ about the size of a closed fist, located in the thoracic cavity between the lungs. Its function is to pump blood through the body in order for muscles and organs to receive oxygen and nutrients and rid themselves of waste. In this module, we will first start by discussing the role and structure of the heart. We will then discuss the unique electrical network which controls the rhythmical beating of the heart. Next, we will discuss the mechanical activity of the heart and how the amount of blood which leaves the heart is strictly regulated, yet dynamic, to respond to the body’s needs. Lastly, we will discuss how the heart itself acquires nutrients crucial to its function. LEARNING OUTCOMES This content was retrieved from Introduction Slide 2 of 4 of the online learning module. The end of Module 05, you should be able to: Discuss the role of the heart in the circulatory system and outline the flow of blood throughout the body. Describe the flow of excitation and contraction that occurs during the cardiac cycle to demonstrate an understanding of the heart as an electro-mechanical organ. Explain the statement “what enters the heart, the heart pumps out” in order to describe how the heart itself can regulate cardiac output. Identify key components of the coronary circulation and how they contribute to the heart’s ability to satisfy its high metabolic needs. MODULE ASSIGNMENTS This content was retrieved from Introduction Slide 3 of 4 of the online learning module. Each module in this course has associated assessments that relates to the content you will be learning. Some of these assessments may only be relevant to one module whereas others will build upon concepts you will learn as you advance through the course. More details about each assignment can be found in the assignment description on the course website. Integrated Lab Report - Refer to Page 6 Case Study Discussion Board Series - Refer to Page 6 Activities throughout the Module: Note that text responses and interactions will not be graded unless otherwise notified. However, they are recorded in the module and viewable by your instructor. CASE STUDY DISCUSSION BOARD SERIES PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 5 MODULE 05 COMPANION GUIDE PHGY 215 Subpage of Introduction Slide 3 of 6 - Assignment 1/1 Students will be placed in small groups and assigned biweekly case studies and a corresponding set of questions. Each student’s is required to answer at least one of the associated questions, and respond to at least one peer's post. Students will be marked on the quality of their posts and their efforts to participate in discussion with their group members. Navigate to the assignment description in the PHGY 215 learning environment for more details INTEGRATED LAB REPORT Subpage of Introduction Slide 3 of 6 - Assignment 1/1 This lab and report aims to introduce students to simulated laboratory data and analysis, which will be extend from course content. Students will complete an integrated lab, in which they will be given data and answer guiding questions posed in the lab. Students will then write an individual lab report based on their analysis and responses to the guiding questions provided. Navigate to the assignment description in the PHGY 215 learning environment for more details MODULE OUTLINE This content was retrieved from Introduction Slide 4 of 4 of the online learning module. Section 01: Introduction to Cardiovascular System Section 02: Structure of The Heart Section 03: Electrical Activity of The Heart Section 04: Mechanical Activity of The Heart Section 05: Cardiac Output Section 06: Nourishing The Heart PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 6 MODULE 05 COMPANION GUIDE PHGY 215 SECTION 01: INTRODUCTION TO CARDIOVASCULAR SYSTEM SECTION 01: INTRODUCTION TO CARDIOVASCULAR SYSTEM This content was retrieved from Section 1 Slide 1 of 6 of the online learning module. By the end of Section 01, you should be able to: Describe the main functions of the circulatory system. Describe how oxygenated and deoxygenated blood flows through the heart. Explain what is meant by “the systemic circulation delivers blood in parallel”. Assigned Readings: Human Physiology: From Cells to Systems, 4th Canadian Edition By Sherwood and Ward Section 8.1: Pages 345-346 THE CIRCULATORY SYSTEM This content was retrieved from Section 1 Slide 2 of 6 of the online learning module. The circulatory system is the lifeline of the body. It is responsible for the transportation of materials upon which cells throughout the body are vitally dependent. It has three basic components: Review each component to learn more. The Heart The heart is the pump that generates the pressure necessary to move blood throughout the circulatory system. It is the focus of this module. The Blood Vessels The blood vessels are the conduits through which the blood passes to deliver nutrients to cells and to carry their metabolic wastes away. We fill focus on this vascular system in Module 06. The Blood Blood is the transport media in which materials are moved throughout the body. Everything is either dissolved in, suspended in, or bound within the blood for long distance movement. We will not be covering blood specifically in this course but you may read Chapter 10 of the textbook if you are interested. Reference: Oman. (2017). How to Prevent Heart and Blood Vessels Diseases. Retrieved August 31, 2017, from https://naturesgist.com/2017/03/02/prevent-heart-blood-vessels-diseases/ FUNCTIONS OF THE CIRCULATORY SYSTEM PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 7 MODULE 05 COMPANION GUIDE PHGY 215 This content was retrieved from Section 1 Slide 3 of 6 of the online learning module. The circulatory system has several important functions and reaches all of the tissues in the body. Review these functions. 1. Gas exchange: delivery of oxygen, removal of carbon dioxide. 2. Nutrient and water delivery and absorption: by cells. 3. Removal of heat and metabolic waste: exercising muscle generates excess heat and the constant supply of fresh blood flowing through the muscle can help remove this heat as well as metabolic wastes. 4. Immunity and defense: the blood transports key immune cells that can quickly identify and neutralize foreign particles. 5. Cell communication: cells from one part of the body can communicate with other more distant cells by releasing chemical messages into the blood. ORGANIZATION OF THE CIRCULATORY SYSTEM This content was retrieved from Section 1 Slide 4 of 6 of the online learning module. The circulatory system is what is called a closed loop system consisting of two pumps - the left and right sides of the heart - and two circulation systems. The two circulation systems are the pulmonary circulatory system, which moves blood to and from the lungs, and the systemic circulatory system, which moves blood throughout the rest of the body. In the broader sense, we consider blood flow to be serial throughout the circulatory system as blood that leaves the left side of the heart flows through the systemic circulation into the right side of the heart. It then flows into the lungs before returning to the left side of the heart. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 8 MODULE 05 COMPANION GUIDE PHGY 215 Reference: Circulation [Online Image]. (2014). Retrieved on September 15 2017 from https://empoweryourknowledgeandhappytrivia.wordpress.com/tag/science/page/13/ BLOOD FLOW IS BOTH SERIAL AND PARALLEL This content was retrieved from Section 1 Slide 5 of 6 of the online learning module. While we consider the system as a whole to be in serial, the systemic circulation is actually designed to deliver blood in parallel. When blood leaves the left side of the heart, it flows through branching blood vessels which direct the blood to all the tissues and organs of the body simultaneously. After leaving these tissues and organs, these branched blood vessels come back together to deliver all of the blood back to the right side of the heart. We will be exploring this concept in more detail in Module 06. The rest of this module will focus on the heart. Learn about the serial and parallel circuits - Refer to Pages 9-10 Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. SERIES AND PARALLEL CIRCUITS Subpage of Section 1 Slide 5 of 6 - Series and Parallel Circuits 1/1 As discussed, the circulatory system is considered to be serial and parallel. The difference between the two types of circuits can easily be explained using electrical circuits. Series Circuit In a series circuit, electrons can only flow down one path. In this circuit, electrons flow in a counterclockwise direction; from point 4 to point 1. This is similar to the circulatory system as a whole. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 9 MODULE 05 COMPANION GUIDE PHGY 215 Parallel Circuit In a parallel circuit, electrons can flow down many paths. In this circuit, electrons flow in a counterclockwise direction, from point 8 to point 1, but can flow down any of the intermediate paths to ultimately reach point 1. This is similar to the systemic circulatory system. Reference: All about circuits - What are series and parallel circuits? (n.d.). Retrieved on Sept 30 2017 from https://www.allaboutcircuits.com/textbook/direct-current/chpt-5/what-are-series-and-parallel- circuits/ ACTIVITY: THE FUNCTIONS OF THE CIRCULATORY SYSTEM This content was retrieved from Section 1 Slide 6 of 6 of the online learning module. Now that you have a general sense of the organization and function of the circulatory system, we can move on to discussing the structure of the heart. Before continuing to the next section, please attempt the following activity to test your understanding. Drop down on each function to indicate if it is, or is not, a function of the circulatory system. Feedback: PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 10 MODULE 05 COMPANION GUIDE PHGY 215 Is a function of the circulatory system: Gas exchange Nutrient delivery Immunity Removal of metabolic wastes Water absorption Heat dissipation Cell communication Is not a function of the circulatory system: Digestion Detoxification Nutrient Breakdown Storage of white blood cells Production of white blood cells Production of insulin PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 11 MODULE 05 COMPANION GUIDE PHGY 215 SECTION 02: STRUCTURE OF THE HEART SECTION 02: STRUCTURE OF THE HEART This content was retrieved from Section 2 Slide 1 of 13 of the online learning module. By the end of Section 02, you should be able to: Describe the cardiac valves and how they achieve their purpose. Describe the unique properties of cardiac muscle cells in relation to their function. Explain how cardiac muscle cells communicate with each other. Assigned Readings: Human Physiology: From Cells to Systems, 4th Canadian Edition By Sherwood and Ward Section 8.2: Pages 346-351 THE HEART: A DOUBLE PUMP This content was retrieved from Section 2 Slide 2 of 13 of the online learning module. We will discuss the structure of the heart in terms of its function. The heart, even though it is a single organ, can be considered to be two pumps, the left and right sides of the heart, separated by the septum. Each of these pumps is divided into an upper chamber, called the atrium, and a lower chamber, called the ventricle. Atria receive the blood that is returning to the heart and transfer it to the ventricles, which pump the blood out of the heart. The vessels that take blood away from the heart are called arteries and the vessels that return blood to the heart are called veins. Watch this video: Solidify and enhance your understanding of the structures of the heart Page Link: https://www.youtube.com/embed/rguztY8aqpk PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 12 MODULE 05 COMPANION GUIDE PHGY 215 Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. THE MAJOR VESSELS OF THE HEART This content was retrieved from Section 2 Slide 3 of 13 of the online learning module. Before discussing how the heart is able to pump blood throughout the body, it is essential that we first explore the major blood vessels which bring blood to and from the heart. There is a common misconception that veins only carry deoxygenated blood and arteries only carry oxygenated blood. In reality, veins always carry blood towards the heart whereas arteries always carry blood away from the heart, regardless of whether it is oxygenated or not. Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. FLOW OF BLOOD THROUGH THE BODY This content was retrieved from Section 2 Slide 4 of 13 of the online learning module. In Section 1 of this module, we gave you an overview of the circulatory system and we will now put it in context of cardiac anatomy. Follow the blood through the structures of the heart. 1. Oxygen rich blood is pumped from the left ventricle into the very large artery called the aorta. 2. This oxygen-rich blood is then delivered to the various tissues and organs. 3. At the level of the tissues and organs, oxygen and other nutrients are removed from the blood while carbon dioxide and other waste products are added to the blood. 4. The blood is now oxygen-poor. It circulates in the veins and eventually returns to the right atria via two large veins called the venae cavae (not pictured). 5. The blood is then pumped into the right ventricle and then pumped again out through the PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 13 MODULE 05 COMPANION GUIDE PHGY 215 pulmonary artery, taking the blood to the lungs. 6. In the lungs, the carbon dioxide is removed and oxygen is again added to the blood. 7. The now oxygen-rich blood flows through the pulmonary vein into the left atria where it is pumped into the left ventricle to start the circuit again. Study Tips & Tools Use this image to review the flow of blood throughout the body. Pay particular attention to how the circulatory system allows for the delivery of oxygen and removal of carbon dioxide from body tissues. Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. BLOOD FLOW IS UNIDIRECTIONAL This content was retrieved from Section 2 Slide 5 of 13 of the online learning module. In order to maintain constant delivery of oxygen-rich blood to the tissues and organs, it is very important that blood only flows in one direction. Within the heart, this is ensured by the presence of the cardiac valves. There are four pressure-operated valves within the heart. What this means is that when the pressure is great enough, the valves open to let blood flow through but when the pressure decreases, the valves shut to stop blood from flowing backwards. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 14 MODULE 05 COMPANION GUIDE PHGY 215 Learn more about the direction of blood flow through the cardiac valves. Valve is open: When the pressure is greater behind the valve, it opens. Valve is closed: When the pressure is greater in front of the valve, it closes. Note that when pressure is greater in front of the valve, it does not open in the opposite direction; that is, it is a one way valve. Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. HEART VALVES This content was retrieved from Section 2 Slide 6 of 13 of the online learning module. There are two types of valves in the heart. Learn more. Atrioventricular Valves The atrioventricular (AV) valves are located between the atria and the ventricles. When the pressure inside the atria is greater than in the ventricles, these valves open and blood flows from the atria into the ventricles. When ventricular pressure increases to become more than the pressure in the atria then the valves close. Both of these valves are connected to the papillary muscles* of the ventricular walls via chordae tendineae* to prevent them from everting. The right AV valve is also called the tricuspid valve because it has three cusps or leaflets. The left AV valve only has two leaflets and is called the bicuspid valve. This valve is also commonly known as the mitral valve. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 15 MODULE 05 COMPANION GUIDE PHGY 215 Semilunar Valves The semilunar valves are the valves that are between the ventricles and the arteries leaving them. The pulmonary valve lies between the right ventricle and the pulmonary artery while the aortic valve lies between the left ventricle and the aorta. They are called semilunar valves due to their shape. They both contain three leaflets that resemble half-moons. Unlike the AV valves, there are no chordae tendineae. The shape of these valves alone prevents them from inverting when arterial pressure is greater than ventricular pressure. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 16 MODULE 05 COMPANION GUIDE PHGY 215 Definitions:* Papillary Muscles: Muscles located in the ventricles of the heart. Chordae Tendineae: Cord-like tendons that connect the papillary muscles to the atrioventricular valves in the heart. They are also known as the heart strings. Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. CLINICAL APPLICATION: HEART VALVES This content was retrieved from Section 2 Slide 7 of 13 of the online learning module. A heart valve normally allows blood to flow in only one direction through the heart. However, complications due to disease can occur and are one of the causes of heart failure. Valvular heart disease (V H D) is a general term which refers to the dysfunction of any of the valves within the heart and primarily arises in one of two forms: regurgitation and stenosis. Learn about these two complications. Regurgitation Regurgitation occurs when a valve does not close properly which causes blood to flow back into the compartment from which it came. This can occur in any of the four valves and can cause a decrease in blood leaving the heart, irregular heart rhythms, and unnecessary stress on the walls of the compartment due to volume overload, all of which can eventually lead to cardiac failure. Stenosis Stenosis is another form of V H D where there is a narrowing of the valve due to a thickening or inflammation of the valve. Like regurgitation, stenosis can occur in any of the heart valves. Stenosis inhibits the flow of blood out of the ventricle or the atria. The heart is therefore forced to pump blood with an increased force in order to maintain flow to the rest of the body. QUESTION: WHAT DO YOU KNOW ABOUT CARDIAC MUSCLE? This content was retrieved from Section 2 Slide 8-9 of 13 of the online learning module. Now that we have discussed the gross anatomy of the heart and the flow of blood throughout the body, we will now explore the specific features of cardiac muscle tissue that allow the heart to function as it does. Recall that at the end of Module 04 we introduced cardiac muscle. What are some of the key features of cardiac muscle that were discussed? Feedback: Some key features of cardiac muscle are: It is striated with thick and thin filaments organized into sarcomeres It contains troponin and tropomyosin as the primary site where C a 2+ activates cross bridge activity PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 17 MODULE 05 COMPANION GUIDE PHGY 215 It has t-tubules and a well defined S R It contain lots of mitochondria It has a well defined length-tension relationship C a2+ comes from both the E C F and the S R It is interconnected by gap junctions to allow spread of excitation Cardiac muscle is innervated by the A N S to modify rate and strength of contraction Its muscle fibres are connected in a branched manner CARDIAC MUSCLE FIBRES This content was retrieved from Section 2 Slide 10 of 13 of the online learning module. Cardiac muscle cells have well defined sarcomeres, just like skeletal muscle cells, discussed in Module 04. However, unlike skeletal muscle fibres, a single cardiac muscle cell does not run the length of the heart. They are much smaller. Instead, cardiac muscle cells are connected end-to-end to form a branching network of cardiac fibres. These end-to-end connections are at specialized structures called intercalated discs. Switch between histological and diagrammatic images of cardiac muscle fibers. References: PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 18 MODULE 05 COMPANION GUIDE PHGY 215 Muscle tissue, cardiac muscle | Histologia | Pinterest | Muscle tissue, Med school and Radiology. (n.d.). Retrieved September 7, 2017, from https://www.pinterest.com/pin/324259241905801342/ Cardiac muscle cells. (n.d.). Retrieved September 8, 2017, from http://smart.servier.com/smart_image/cellules-coeur/ INTERCALATED DISCS This content was retrieved from Section 2 Slide 11 of 13 of the online learning module. At intercalated discs are composed of two types of membrane junctions that we discussed in Module 01: desmosomes and gap junctions. The desmosomes mechanically hold the cells together while the gap junctions allow the cells to communicate and spread action potentials from cell-to-cell, permitting each wave of excitation to spread very quickly through the atria and ventricles. This attribute allows the chamber to contract in a wave-like motion which allows blood to be efficiently pushed out of the chamber. Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. CARDIAC MUSCLE FIBRE ARRANGEMENT This content was retrieved from Section 2 Slide 12 of 13 of the online learning module. How do you think the muscle fibres of the heart are arranged in order to create the necessary pressure to pump blood throughout the body? View the answer to the posed question. View Answer The muscle fibres of the heart are arranged in a spiral fashion around its circumference. Because of this, when the muscle fibres contract they cause a squeezing or wringing of the heart that generates pressure in the chambers. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 19 MODULE 05 COMPANION GUIDE PHGY 215 References: Anatomy and Physiology (2006). Heart Musculature [Online Image]. Retrieved on September 13, 2017, from http://philschatz.com/anatomy-book/contents/m46676.html Anatomy and Physiology (2007). Ventricular Muscle Thickness [Online Image]. Retrieved on September 13 2017 from http://philschatz.com/anatomy-book/contents/m46676.html THE PERICARDIAL SAC This content was retrieved from Section 2 Slide 13 of 13 of the online learning module. The heart is almost constantly in motion, and thus needs protection from the rest of the chest cavity. This is accomplished by the pericardial sac, which is a double-walled membrane. The two layers of the pericardium, the fibrous and the serous layers, protect by lubricating the heart to prevent friction during activity. Learn about the fibrous layer and the serous layer. Fibrous Layer This layer anchors the heart to the surrounding walls to keep it in place during movement, as well as to prevent it from overfilling with blood. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 20 MODULE 05 COMPANION GUIDE PHGY 215 Serous Layer The serous pericardium is divided into two layers: the parietal pericardium and the visceral pericardium. These layers lubricate the heart with pericardial fluid, shown in orange, and prevent friction during activity. Read an article about pericarditis - pay special attention to the etiology and diagnostic criteria. Clinical Application Complications can arise with the pericardial sacs; the most common being pericarditis which is an inflammation of the pericardium. Page Link: https://proxy.queensu.ca/login?url=http://dx.doi.org/10.1001/jama.2015.12763 References: The Cleveland Clinic (n.d.). [Pericardium layers of the heart]. Retrieved on September 21, 2017, from http://www.clevelandclinicmeded.com/medicalpubs/diseasemanagement/cardiology/pe ricardial-disease/ Imazio, M., Gaita, F., & LeWinter, M. (2015). Evaluation and treatment of pericarditis: a systematic review. Jama, 314(14), 1498-1506. doi: 10.1001/jama.2015.12763. Retrieved August 12 2019 from https://proxy.queensu.ca/login?url=http://dx.doi.org/10.1001/jama.2015.12763 PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 21 MODULE 05 COMPANION GUIDE PHGY 215 SECTION 03: ELECTRICAL ACTIVITY OF THE HEART SECTION 03: ELECTRICAL ACTIVITY OF THE HEART This content was retrieved from Section 3 Slide 1 of 24 of the online learning module. By the end of Section 03, you should be able to: Describe the cardiac conduction system. Describe the cardiac action potential and its underlying currents. Explain excitation-contraction coupling. Explain what electrical activity occurs to result in the lead II ECG trace. Assigned Readings: Human Physiology: From Cells to Systems, 4th Canadian Edition By Sherwood and Ward Section 8.3: Pages 352-361 QUESTION: INTRODUCTION TO ELECTRICAL ACTIVITY OF THE HEART This content was retrieved from Section 3 Slide 2-3 of 24 of the online learning module. The heart is what we call an electro-mechanical organ. That is, it has both an electrical activity, in that it generates and conducts action potentials in a manner similar to nerves, yet the heart is also a large muscle that contracts. Because of these properties, it contains two different types of cardiac muscle cells: those that are primarily contractile and do the mechanical work, discussed in Section 2, and those that are electrical to generate and propagate action potentials to the contractile cells. It is the second type of cells which we will discuss in this section. This being said, nervous system input can modify the electrical activity of the heart in a few ways. Though you will learn more about this in Section 5, use what you have learned about the nervous system thus far to name a few situations when the SNS or PNS could affect heart rate. What makes the heart interesting in terms of electrical activity is that it generates and propagates electrical signals independently. That is, the heart is not dependent upon either the CNS or PNS for its function. Feedback: View Our Answer Physical and emotional stress can cause changes in heart rate. This stress can be due to exercise, fear, injury, and even illness. Exercise increases heart rate to bring additional blood, and therefore oxygen, to working muscles and to rid them of CO2 and other waste. Fear increases heart rate due to the “fight or flight” response which releases epinephrine from the adrenal glands. Epinephrine stimulates the SN S and raises the heart rate. Illness and injury cause an increase in blood flow to peripheral tissues, which increases heart rate via the SNS. CARDIAC AUTORHYTHMIC CELLS This content was retrieved from Section 3 Slide 4 of 24 of the online learning module. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 22 MODULE 05 COMPANION GUIDE PHGY 215 Specialized cardiac muscle cells that can generate action potentials are known as autorhythmic. Instead of a flat, constant resting membrane potential, these cells contain ion channels that cause the membrane potential to slowly depolarize until the threshold potential is reached and an action potential is fired. The precise nature of this depolarizing current, however, is still not clear. It is thought that autorhythmic cells contain If channels, which we described in Module 04. Once these channels are activated, both Na+ and K+ enter the cell resulting in a depolarization of the membrane potential. Recent research suggests that the activation of If channels could either be due to the hyperpolarization-activated cyclic nucleotide-gated channel (HCN) family or, possibly, that a type of Ca2+ channel, the T-type Ca2+ channel, is involved. What is also unique about these cells is that the upstroke of the action potential is due to another type of Ca2+ channel, the L-type Ca2+ channel, instead of Na+ channels as seen in neurons and cardiac contractile cells. Definition: If Channels: Channels with unusual properties which allow current (I) to flow. The researchers who first described the ion current through these channels initially did not understand its behavior and named it funny current - hence the subscript f. Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. THE CARDIAC CONDUCTION SYSTEM This content was retrieved from Section 3 Slide 5 of 24 of the online learning module. Autorhythmic cells are localized in very specific regions of the heart. Learn where autorhythmic cells are found. Sinoatrial node The sinoatrial (SA) node is a very small area located in the right atrial wall near the opening of the superior venae cavae. Atrioventricular node PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 23 MODULE 05 COMPANION GUIDE PHGY 215 The atrioventricular (AV) node is a small area located in the right atrium where the right atria and right ventricle come together. Note: it is often described as being located in the interatrial septum due to its location in the centre of the heart. Bundle of His The bundle of His consists of specialized cells that arise from the AV node. It divides into two bundle branches that travel down each side of the septum to the bottom of the heart where they curve around and travel back towards the atria. Purkinje fibres The purkinje fibres are small fibres that branch off the bundle of His and spread along the inner (endocardial) surface of the ventricles. Study Tips & Tools This is an important concept! Come back to this page while study to check your understanding of the cardiac conduction system. Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. NORMAL PACEMAKER ACTIVITY OF THE HEART This content was retrieved from Section 3 Slide 6 of 24 of the online learning module. It is important to remember that several types of autorhythmic cells work together to create a unified electrical signal. The autorhythmic cells in the SA node have the fastest rate of depolarization (i.e. the reach threshold fastest). These cells are considered the pacemaker cells of the heart because they control heart rate and keep it at around 70-80 beats/minute for the average person. Once an action potential is generated in these cells, it conducts through the rest of the cardiac conduction system, overriding the pacemaker activity of other autorhythmic cells. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 24 MODULE 05 COMPANION GUIDE PHGY 215 As long as the SA node is functioning fine, it controls the rate at which the heart beats. Without pacemaker activity, the heart would not beat at all. Watch this video: How the electrical signal from the SA node, depicted with a glowing yellow circle, acts as the pacemaker of the cell. Page Link: https://www.youtube.com/embed/WvvzODYqmbg CARDIAC EXCITATION REQUIREMENTS This content was retrieved from Section 3 Slide 7 of 24 of the online learning module. Once initiated, an action potential spreads throughout the heart. In order for efficient cardiac contraction, three criteria must be satisfied. Review each criterion to learn why it must be satisfied. Atrial excitation and contraction should be complete before the onset of ventricular contractions In order for the ventricles to fill with blood completely, the blood from the atria must be moved into the ventricles. During relaxation of the heart, the pressure in the ventricles is lower in than the atria so the AV valves are open. This allows the passive flow of blood from the atria to the ventricles. Passive blood flow accounts for around 80% of total ventricular filling with the remaining 20% coming from when the atria contract. If the ventricles were to contract at the same time as the atria, then incomplete ventricular filling would occur. During a normal heartbeat, the atria contract about 160 m/sec before the ventricles contract. Excitation of the cardiac muscles fibres needs to be coordinated In order for the heart to act efficiently as a pump, the chambers need to have a coordinated contraction. If different regions of a ventricular wall were to depolarize and contract at different times, then it would not be possible for the ventricles to eject the blood. This uncoordinated depolarization is called ventricular fibrillation, which we will discuss near the end of this section. The pair of atria and the pair of ventricles must be functionally coordinated In order for the blood to move throughout the body, the two pumps of the heart must work together and move the same amount of blood at the same time. In order for this to happen, both atria contract at the same time, then both ventricles contract at the same time. QUESTION: CARDIAC EXCITATION REQUIREMENTS This content was retrieved from Section 3 Slide 8-9 of 24 of the online learning module. What do you think would happen if the ventricles contracted out of sync? Feedback: View Our Answer If the right and left ventricles contract at different times, such as is the case with a bundle branch block (a block in one of the branches of the bundle of His), the blood pumping to the lungs to be oxygenated, PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 25 MODULE 05 COMPANION GUIDE PHGY 215 and the blood pumping through the aorta would occur at different times. These blocks can cause unnecessary stress on the ventricular walls and may require a pacemaker to re-coordinate the contraction of the ventricles. Alone, these blocks are generally not dangerous, however they can be a symptom of a much larger problem such as a heart failure, a valve problem, lung disease, or other cardiac conditions. ATRIAL EXCITATION This content was retrieved from Section 3 Slide 10 of 24 of the online learning module. Keeping all three criteria for efficient cardiac contraction in in mind, the normal spread of excitation throughout the heart occurs to ensure that heart function is as efficient as possible. We will now look at how this happens by first discussing atrial excitation. Once the SA node fires an action potential, this wave of excitation travels throughout the atria by two main mechanisms: Learn how this wave of excitation is able to travel throughout the atria. Gap Junctions The gap junctions between atrial cells. Pathways The interatrial and internodal pathways. These pathways act like nervous tissue in that they move the excitation wave faster than possible by gap junctions alone. The interatrial pathway extends from the right atrium to the left atrium and ensures that the wave of excitation spreads across both atria at the same time. This ensures that the atria contract at the same time. The internodal pathway connects the SA node to the AV node. Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 26 MODULE 05 COMPANION GUIDE PHGY 215 QUESTION: CARDIAC EXCITATION REQUIREMENTS This content was retrieved from Section 3 Slide 11-12 of 24 of the online learning module. The muscle cells of the atria are separated from the muscle cells of the ventricle by a dense region of connective tissue that lies between the atria and ventricles. Consequently, the AV node and the bundle of His are the only means by which an electrical signal can move from the atria to the ventricles. Even though the electrical signal moves from the SA node to the AV node very quickly, the rate of conduction slows down through the AV node. This is called the AV nodal delay. Using what you have learned, what do you think is the purpose of this delay? Feedback: View Our Answer Its purpose is to make sure that the atria have had a chance to contract prior to the ventricles. This maximizes the atrial emptying of blood into the ventricles. Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. VENTRICULAR EXCITATION This content was retrieved from Section 3 Slide 13 of 24 of the online learning module. The ventricles are a substantially larger mass of muscle than the atria. They are also hollow chambers. Because of their size and shape, if the ventricles relied on gap junctions alone to spread the wave of excitation, the top part of the heart would have contracted before the wave of excitation reached the bottom. The bundle of His and the purkinje fibres solve this problem. After the AV nodal delay, the wave of excitation spreads down both the right and left bundles of His PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 27 MODULE 05 COMPANION GUIDE PHGY 215 and the purkinje fibres. The purkinje fibres, however, do not terminate on all of the ventricular muscle cells. Gap junction communication is therefore required in order to spread the wave of excitation to the rest of the cells not innervated by the purkinje fibres. This ventricular conduction system ensures that the both the ventricles contract at the same time. Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. CONDUCTION PATHWAY OF THE HEART This content was retrieved from Section 3 Slide 14 of 24 of the online learning module. Various structures within the heart must act together in order for the heart to contract in a regular fashion. Drag and drop the labels below to their corresponding places in the diagram. Word Bin: S a Node, Interatrial Pathway, AV node, Left Atrium, Bundle of His, Left Ventricle, Purkinje Fibres, Right Ventricle, Electrically Nonconductive Fibrous Tissue, Right Atrium, Internodal Pathway Feedback: Clockwise from top: Interatrial Pathway, AV Node, Left Atrium, Bundle of His, Left Ventricle, Purkinje Fibres, Right Ventricle, Electrically Nonconductive Fibrous Tissue, Right Atrium, Internodal Pathway, S a Node Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. THE HEART IN ACTION This content was retrieved from Section 3 Slide 15 of 24 of the online learning module. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 28 MODULE 05 COMPANION GUIDE PHGY 215 Now that you have learned about the different chambers of the heart and how the electrical signal is conducted, we will see the heart in action. Watch this video: Ultrasound recording. While watching the video, be sure to notice the difference in tissue thickness between the atria and ventricles. Also, be sure to try and identify the pericardium. Page Link: https://www.youtube.com/watch?v=ew6uJvZDhmw THE CARDIAC ACTION POTENTIAL This content was retrieved from Section 3 Slide 16 of 24 of the online learning module. The cardiac action potential is substantially different in shape compared to those generated by nerve cells. It is also very different in shape compared to the pacemaker cells of the SA node. These differences are caused by the different kinds of voltage-gated ion channels found in ventricular muscle cells. The resting membrane potential for a cardiac myocyte (muscle cell) is around -80 m V. These cells have no pacemaker currents, so the resting membrane potential remains steady until the cell is excited. Learn about the three stages of the cardiac action potential. 1. When a cardiac myocyte is excited and reaches threshold, voltage-gated N a+ channels open and the membrane potential rapidly depolarizes towards +50 mV. 2. This rapid depolarization activates other ion channels. It activates a transient outward K + channel that rapidly moves K+ out of the cell to counter the influx of Na+. It also activates L-type Ca2+ channels and what is called a delayed rectifying K+ channel. These currents create a balance of the membrane potential where the membrane potential is neither depolarizing nor repolarizing. It becomes steady at what is called the plateau potential. 3. Eventually, the transient outward K+ and L-type Ca2+ currents inactivate and the outward K+ movement through the delayed rectifier allows the cell to hyperpolarize and reach its resting membrane potential once again. Now that we have looked at the electrical activity of a cardiac myocyte, let us now see how this electrical signal can cause a contraction. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 29 MODULE 05 COMPANION GUIDE PHGY 215 Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. CARDIAC EXCITATION -CONTRACTION COUPLING This content was retrieved from Section 3 Slide 17 of 24 of the online learning module. Cardiac myocytes undergo a very well defined pattern of excitation-contraction (EC) coupling, which is the process by which an action potential triggers a myocyte to contract. Recall from Module 04 that skeletal muscle cells have T-tubule systems that allow for the spread of excitation and an increase of intracellular Ca2+ necessary for contraction. Cardiac myocytes also have a well-defined T-tubule system. Learn about how a myocyte is activated to initiate contraction. Action potential in cardiac contractile cell: During the plateau phase of the action potential, L-type Ca2+ channels, located within the T tubules, open. Release of Ca2+ The opening of L-type Ca2+ channels allow Ca2+ to enter the cell. Interaction with contractile apparatus: This Ca2+ can directly interact with the contractile apparatus. Large release of Ca2+ The release of C a2+ can interacts with ryanodine receptors* on the S R membrane which activates them and triggers an additional large release of Ca2+ from internal stores. This process is called Ca2+ - induced Ca2+ -release (CICR). Contraction This influx of Ca2+ initiates cardiac muscle contraction. When Ca2+ is removed from the cytosol, either by PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 30 MODULE 05 COMPANION GUIDE PHGY 215 moving it across the plasma membrane or pumping it back into the SR, contraction ends. It is important to note that cardiac muscle cells are dependent upon Ca2+ entering the cell to initiate contraction, this is in contrast to skeletal muscle cells where the electrical signal alone causes release of Ca2+ from the SR. Definition:* Ryanodine Receptors: Intracellular calcium channels found in excitable muscle tissue. THE RELATIONSHIP BETWEEN ACTION POTENTIAL DURATION AND LENGTH OF CONTRACTION This content was retrieved from Section 3 Slide 18 of 24 of the online learning module. When discussing skeletal muscle contraction, we mentioned that skeletal muscle fibres can undergo summation and tetanus. Cardiac muscle cannot because it would lead to contractile patterns in the heart that are not only inefficient, but also life-threatening. It is the length of the cardiac action potential that prevents twitch summation. As already mentioned, cardiac myocytes have long action potentials due to the prominent plateau phase. During this plateau phase, the depolarized membrane potential keeps the voltage-gated N a+ channels in an inactivated state so that even if another wave of excitation came, they will not open. This period during which a cardiac myocyte cannot be re-stimulated is called the refractory period. The refractory period is long enough that most of the muscle contraction has been completed. Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. THE ELECTROCARDIOGRAM ( ECG) PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 31 MODULE 05 COMPANION GUIDE PHGY 215 This content was retrieved from Section 3 Slide 19 of 24 of the online learning module. So far we have been looking at the electrical and mechanical activity at the single myocyte level. Because the heart is highly coordinated and basically serves a single function - contraction to circulate blood - it makes far more sense to look at the electrical and mechanical properties of the organ as a whole. We will begin by looking at the electrocardiogram (ECG). The tissue mass of the heart is quite large and it undergoes a distinctive pattern of electrical activity in order to bring about coordinated contractions. Consequently, this electrical pattern generates an electrical field that is transmitted throughout the body fluids and can actually be “sensed” at the surface of the skin. Learn about how the first ECG was detected as well as how the modern day ECG is detected. The First ECG - Refer to Pages 32-33 Modern Day ECG - Refer to Page 33 You will be shown a tracing of an ECG later on in this section. THE FIRST ECG Subpage of Section 3 Slide 19 of 24 - The First ECG 1/1 For a historical perspective, it was Willem Einthoven who invented the first ECG, for which he was awarded a Nobel Prize. Einthoven used his knowledge of the heart’s electrical activity and constructed a device that used three electrical leads to detect this activity. These electrical leads were placed on the right arm, left arm, and left leg with a ground electrode on the right leg. These form what were called the Einthoven Triangle for lead location and form the basis of the limb leads of the modern ECG. Using these limb leads, you can record the changes of electrical activity that are occurring between them. As well, they allow you to take a look at the electrical activity through different planes of the heart. Review the standard three leads. Lead 1: right arm to left arm Lead 2: right arm to left leg Lead 3: left arm to left leg PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 32 MODULE 05 COMPANION GUIDE PHGY 215 Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. THE MODERN DAY ECG Subpage of Section 3 Slide 19 of 24 - The Modern Day ECG 1/1 The modern ECG still uses the same principles developed by Einthoven, but goes beyond the original three limb leads and now consists of a 12 lead ECG that is a very powerful diagnostic tool. Interestingly, the 12 lead ECG arises from only 9 physical leads. There are the three limb leads I-III we have already mentioned, as well as six leads on the chest around the heart as shown in the diagram. The remaining three leads are mathematically derived from leads I, II, and III. An ECG measures the electrical activity of the heart but indirectly as it is measuring changes of electrical potentials that originate in the heart but must be transmitted through the body to the surface where they can be measured. It measures a summation of all electrical activity at any given time, which allows one to observe the spread of electrical activity throughout the heart. This ultimately allows us to identify cardiac abnormalities which we will learn about later in this section. Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. THE ECG RECORDING This content was retrieved from Section 3 Slide 20 of 24 of the online learning module. The nomenclature for the different parts or deflections of an ECG recording are still those introduced by Einthoven. The standard ECG recording that is shown is that taken from lead II. ECG tracings revolve around the isoelectric, or 0 voltage line. Generally, depolarization is observed as upward (positive) deflections, and repolarizations are observed as downward (negative) reflections. Let us now go through the lead II ECG tracing with what we already have learned about cardiac electrical activity. Learn about the different components of an ECG. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 33 MODULE 05 COMPANION GUIDE PHGY 215 1. The initiation of a heart beat is the firing of the SA node. However, the size of the SA node and its electrical activity is too small to be detected at the body’s surface, and so it isn’t seen. However, the SA node does trigger both of the atria to undergo excitation and their depolarization is observed as the P wave. 2. While the atria are depolarized, there is no net movement of charge so the ECG remains flat again until the AV node delay has occurred. Following this delay, the wave of excitation travels down bundle of His and Purkinje fibres to depolarize the ventricles. This current is observed as the QRS complex. 3. Again, while the ventricles are depolarized there is no net current. Thus the ECG trace is flat until the ventricles repolarize, as depicted by the T wave. Once they have repolarized, there is no net current again until the SA node fires again to start the process over. 4. Portions of an ECG recording are often grouped together as cardiac abnormalities tend to present themselves as changes in these segments. The P R segment indicates the AV node delay. The S T segment indicates the time during which ventricles are contracting and emptying. The T P interval indicates the time during which ventricles are relaxing and filling. The Q T segment indicates the electrical depolarization and repolarization of the ventricles. 5. We talked about ventricular repolarization, but what about atrial repolarization? The muscle mass of the ventricles is much greater than the atria and the atria repolarize while the ventricles are depolarizing, so atrial repolarization is lost in the summation of the electrical activity. Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. SUMMARY OF ECG RECORDINGS This content was retrieved from Section 3 Slide 21 of 24 of the online learning module. So far we have discussed the cardiac conduction system as well as how an ECG is used to measure the electrical activity of the heart. In this video, the different parts of an ECG recording are summarized once again. While watching, pay particular attention to what electrical activity occurs to result in each component of an ECG trace. Watch this video: Summary of the cardiac conduction system and its correlation with an ECG PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 34 MODULE 05 COMPANION GUIDE PHGY 215 Page Link : https://www.youtube.com/embed/v3b-YhZmQu8 COMPONENTS OF AN ECG RECORDING PART 1 This content was retrieved from Section 3 Slide 22 of 24 of the online learning module. As you just learned, there are various identifiable parts of an ECG recording. Drag and drop the labels to their corresponding places in the diagram. Word Bin: P, R, T, Q, S Feedback: Clockwise from top: R, T, S, Q, P Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. COMPONENTS OF AN ECG RECORDING PART 2 This content was retrieved from Section 3 Slide 23 of 24 of the online learning module. Drag and drop each component of an ECG recording to match its corresponding cardiac event. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 35 MODULE 05 COMPANION GUIDE PHGY 215 Word Bin: T wave, T P interval, P wave, S T segment, P R segment, QRS complex, Q T interval Ventricular repolarization Atrial depolarization Time during which ventricles are relaxing and filling Time during which ventricles are contracting and emptying Ventricular depolarization (atria repolarizing simultaneously). AV nodal delay. Electrical depolarization and repolarization of the ventricles. Feedback: T Wave Ventricular repolarization P Wave Atrial depolarization T P Interval Time during which ventricles are relaxing and filling S T Segments Time during which ventricles are contracting and emptying QRS Complex Ventricular depolarization (atria repolarizing simultaneously). P R Segment AV nodal delay. Q T Interval Electrical depolarization and repolarization of the ventricles. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 36 MODULE 05 COMPANION GUIDE PHGY 215 HEART RATE AND RHYTHM DISTURBANCES This content was retrieved from Section 3 Slide 24 of 24 of the online learning module. Though the heart is meant to follow a regular rate and rhythm, several abnormalities can occur. Learn about how different cardiac abnormalities can affect both the rhythm and the rate of the heart. Tachycardia Tachycardia is a heart rate that exceeds the normal resting heart rate. In adults, this is a heart rate exceeding 100 b p m. It can be due to something as simple as exercise or caffeine, or something more complex, like an electrical abnormality within the heart. Tachycardia can decrease cardiac output* due to reduced ventricular filling. An ECG is used to classify the type of tachycardia; either wide or narrow based on the QRS complex. In the image we see a narrow complex tachycardia which we can identify with the narrow QRS complex. Extrasystole Extrasystole is a relatively common event where a heartbeat is initiated by the Purkinje fibres rather than the SA node. This can be a sign of reduced oxygenation to the heart muscle, but can also be found in healthy hearts. They are felt as palpitations in the chest. In extrasystole, the ventricles contract before the atria and therefore are not optimally filled with blood which ultimately reduces cardiac output (CO). This can be dangerous if frequent, however these abnormal heart beats do not normally pose a threat to healthy individuals. Ventricular Fibrillation Ventricular fibrillation (V-fib) occurs when the heart is quivering rather than pumping due to abnormal electrical activity in the ventricles. It can result in cardiac arrest with loss of consciousness and no pulse. V-fib can occur due a variety of conditions, such as coronary artery disease, or intracranial bleeds. An ECG can be used to classify this irregularity which shows an irregular, unformed QRS complex, without any clear P waves. Complete Heart Block Also known as third degree atrioventricular block (AV block), a complete heart block is a condition in which the impulse generated at the SA node does not travel to the ventricles. Because the impulse is blocked, the pacemaker cells in the AV node independently activate the ventricles. This allows for two independent rhythms to be seen on an ECG: P wave with regular P to P intervals. A QRS complex which does not always follow a P wave. Patients with a complete heart block often experience abnormally low heart rates and blood pressure. Definition:* PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 37 MODULE 05 COMPANION GUIDE PHGY 215 Cardiac Output: The volume of blood that is pumped by each ventricle over a minute of time. Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 38 MODULE 05 COMPANION GUIDE PHGY 215 SECTION 04: MECHANICAL ACTIVITY OF THE HEART SECTION 04: MECHANICAL ACTIVITY OF THE HEART This content was retrieved from Section 4 Slide 1 of 7 of the online learning module. By the end of Section 04, you should be able to: Within the context of the electrical activity of the heart, describe the mechanical activity of the cardiac cycle. Describe why there are periods of isovolumetric contraction and relaxation. Describe why heart sounds can be heard. Assigned Readings: Human Physiology: From Cells to Systems, 4th Canadian Edition By Sherwood and Ward Section 8.4: Pages 361-365 INTRODUCTION TO MECHANICAL ACTIVITY OF THE HEART This content was retrieved from Section 4 Slide 2 of 7 of the online learning module. The previous section focused on the electrical activity of the heart, but now we will turn our attention to the mechanical activity that is caused by the electrical activity. We will focus on the contractions and relaxations and how they change the flow of blood through the heart. THE CARDIAC CYCLE This content was retrieved from Section 4 Slide 3 of 7 of the online learning module. The cardiac cycle consists of alternating periods of contraction (also called systole) and relaxation (also PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 39 MODULE 05 COMPANION GUIDE PHGY 215 called diastole). As we go through this process, we will also be discussing various pressures that are generated during cardiac systole and diastole. To make things a little simpler, we will focus on just the left side of the heart. Recall that both the right and left sides contract at the exact same time so the process is the same, and just differs in the names of valves and blood vessels on the right side. On the next slide you will learn about the mechanical activities of the heart. These images will help guide you to remember the direction of blood flow with every heartbeat. Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. THE MECHANICAL ACTIVITY OF THE HEART This content was retrieved from Section 4 Slide 4 of 7 of the online learning module. Learn how the pressure in the different compartments of the heart changes during the course of one heart beat. 1. Just before the start of the P-wave of the electrocardiogram, blood is flowing from the pulmonary veins into the left atrium and, because the AV valve is currently open, blood is passively flowing into the left ventricle. When the atria contract (the P wave) pressure is generated in the left atria and blood is forcefully squeezed into the left ventricle to increase both left ventricular blood volume and pressure. This continues throughout the AV nodal delay. 2. While the atria are depolarized, there is no net movement of charge so the ECG remains flat again until the AV node delay has occurred. Following this delay, the wave of excitation travels down bundle of His and purkinje fibres to depolarize the ventricles. This current is observed as the QRS complex. 3. At the end of the AV nodal delay, the wave of excitation is spread throughout the entire left ventricle and contraction begins. This contraction creates enough pressure to close the AV valve and prevent backwards blood flow but it isn’t yet strong enough to open the aortic valve. Because both valves are closed, this is the period called isovolumetric (same volume) contraction. Eventually, the pressure generated in the left ventricle becomes larger than that in the aorta, which allows the aortic valve to open. The result is the squeezing of blood from the left ventricle into the aorta. 4. When the ventricle relaxes enough, its pressure drops below that of the atria and the AV valve reopens to begin the cycle again. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 40 MODULE 05 COMPANION GUIDE PHGY 215 Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. QUESTION: THE FUNCTIONS OF THE CIRCULATORY SYSTEM This content was retrieved from Section 4 Slide 5 of 7 of the online learning module. Using your knowledge of how blood is pumped into and out of the heart, order the images of blood flow from when deoxygenated blood first enters the heart to when it leaves through the aorta using the descriptions in the ‘Word Bin.’. Word Bin: 3, 5, 1, 4, 2 PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 41 MODULE 05 COMPANION GUIDE PHGY 215 Feedback: Left to right: 3. Isovolumetric ventricular contraction, 5. Isovolumetric ventricular relaxation, 1. Passive filling during ventricular and atrial diastole, 4. Ventricular ejection, 2. Atrial contraction HEART SOUNDS This content was retrieved from Section 4 Slide 6 of 7 of the online learning module. Like the ECG, there is another non-invasive diagnostic technique that is effective in diagnosing heart function and that is the heart sounds that can be heard using a stethoscope. The heart valves are mechanical barriers that open and close to ensure one way flow of blood. When the valves open they do so quietly, but when they close they create vibrations within the walls of the ventricles and arteries that can be heard. When the valves open the pressure allows for smooth or laminar flow, whereas the closing of the blood causes turbulent flow that causes the vibrations. Learn about the two different heart sounds. 1. The first heart sound heard occurs when the AV valves close (remember both left and right are closing at the same time) and make a sound that is described as “lub”. This signals the beginning of ventricular systole. 2. The second heart sound occurs when the semilunar valves close and make a sound that is describes as “dub”. This signals the onset of ventricular diastole. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 42 MODULE 05 COMPANION GUIDE PHGY 215 Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. CLINICAL APPLICATION - HEART MURMURS This content was retrieved from Section 4 Slide 7 of 7 of the online learning module. Watch the three videos provided, which demonstrate typical heart sounds versus heart sounds with a murmur. Anytime a valve is not functioning correctly the typical lub-dub heart sounds are altered. A common valve defect is when a valve does not open fully. As we saw in Section 2, these are stenotic valves. When this happens, the opening through which the blood must flow is restricted, which increases its velocity and the amount of turbulent blood flow. This type of turbulence causes a whistling-like sound. Another common valve defect is when a valve does not close completely, which is called an insufficient or leaky valve. When a valve cannot close completely it allows the backward flow of blood, also known as regurgitation, which is turbulent and creates a swishing or gurgling type of sound. Watch this video: Typical heart sounds Watch this video: Heart sounds with aortic stenosis murmur Watch this video: Heart sounds with mitral valve regurgitation murmur Page Links: https://www.youtube.com/embed/xER8Bp4L2kM https://www.youtube.com/embed/MJg257pyt4I https://www.youtube.com/embed/vL0s_nEkC8Q PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 43 MODULE 05 COMPANION GUIDE PHGY 215 SECTION 05: CARDIAC OUTPUT SECTION 05: CARDIAC OUTPUT This content was retrieved from Section 5 Slide 1 of 17 of the online learning module. By the end of Section 05, you should be able to: Explain how cardiac output is calculated. Describe the Frank-Starling law of the heart. Explain why end diastolic volume is so important for the regulation of cardiac contractility. Explain how cardiac output is regulated. Assigned Readings: Human Physiology: From Cells to Systems, 4th Canadian Edition By Sherwood and Ward Section 8.5: Pages 365-372 CARDIAC OUTPUT This content was retrieved from Section 5 Slide 2 of 17 of the online learning module. In the previous two sections of this module we discussed the electrical and mechanical properties of the heart and how they are coordinated in order to serve the primary function of the heart: to pump blood. In this section, we will focus on the heart’s function as a pump and how this pump can be regulated. The volume of blood that is pumped by each ventricle over a minute of time is called the cardiac output (CO) and this output is the same for both the left and right sides of the heart. Use the buttons to see how heart rate and stroke volume contribute to cardiac output. Heart Rate (HR) x Stroke Volume (SV) = Cardiac Output (CO) HR At rest, the heart rate is 70 beats per minute (bpm). This increases with an increase in activity. SV Each time a ventricle contracts, it ejects a certain amount of blood. This is called stroke volume. At rest, stroke volume is approximately 70 ml. CO This amounts to almost 5L of blood being pumped out of each ventricle every minute at rest which is roughly the entire blood volume of an average person (5-5.5L). During exercise, CO can exceed 20L/min! This increase is to either an increase in HR, SV, or both. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 44 MODULE 05 COMPANION GUIDE PHGY 215 REGULATION OF HEART RATE AND CARDIAC OUTPUT This content was retrieved from Section 5 Slide 3 of 17 of the online learning module. Recall that the SA node is the pacemaker of the heart and that it spontaneously depolarizes around 70 times each minute. Therefore, in order to change heart rate, you need to influence the rate at which the SA node depolarizes. The heart is innervated by both the sympathetic and parasympathetic nervous systems. The parasympathetic system, via the vagus nerve, has rich innervation to the atria, specifically the SA and AV nodes with just a small amount of innervation to the ventricles. The sympathetic system innervates the atria, including both nodes, but it more richly innervates the ventricles. Reference: Nature Publishing Group. (2011). Scheme of autonomic innervation of the heart [Online Image]. Retrieved from http://doi.org/10.1161/CIRCRESAHA.113.302549 PARASYMPATHETIC REGULATION OF THE HEART This content was retrieved from Section 5 Slide 4 of 17 of the online learning module. Parasympathetic stimulation has four effects on the heart. Learn about these four effects. Slowing Heart Rate Within the atrial muscle cells, parasympathetic stimulation also increases K + permeability. The main PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 45 MODULE 05 COMPANION GUIDE PHGY 215 effect this has here is that this increased K+ permeability will cause the action potential to repolarize faster than normal, as seen in red in the diagram. This means that the plateau phase where Ca2+ enters is shorter so less Ca2+ enters the cells and therefore their strength of contraction is less. Reducing the AV Nodes Excitability The effects on the AV node are essentially the same as the SA node in that the increased K+ permeability hyperpolarizes the AV node membrane and makes the node less excitable. Shortening Atrial Action Potentials When the parasympathetic system releases acetylcholine at the SA node, it decreases heart rate by increasing K+ permeability. This hyperpolarizes the membrane potential making it harder to reach threshold and by opposing the If current. Thus, the slope of the pacing current is decreased, meaning it takes longer to reach threshold. Both of these effects are occurring at the same time and both cause a decrease in the pacing rate of the SA node. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 46 MODULE 05 COMPANION GUIDE PHGY 215 Very Little Stimulation of The Ventricles There is very little parasympathetic innervation to the ventricular muscle cells so parasympathetic stimulation has little to no effect on the ventricles. The majority of its innervation is on the SA node, which initiates atrial contraction, and the AV node. References: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. Austin Community College - Cardiovascular System (Heart) (n.d.). Retrieved on September 7 2017 from https://www.austincc.edu/apreview/PhysText/Cardiac.html ZooFari. (2009). Effect of class 1b antiarrhythmic agents on the cardiac action potential [online image]. Retrieved August 9, 2019, from https://en.wikipedia.org/wiki/Sodium_channel_blocker Nature Publishing Group. (2011). Scheme of autonomic innervation of the heart [Online Image]. Retrieved from http://doi.org/10.1161/CIRCRESAHA.113.302549 SYMPATHETIC REGULATION OF THE HEART PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 47 MODULE 05 COMPANION GUIDE PHGY 215 This content was retrieved from Section 5 Slide 5 of 17 of the online learning module. The sympathetic system also has four effects on the heart. Learn about these four effects. Pay special attention to how these differ from the ways in which the parasympathetic system affects the heart. Increasing Heart Rate The release of norepinephrine at the SA node enhances both of the pacing currents (If and T-type Ca2+ currents). When these currents increase, the pacing current is stronger and the membrane potential reaches threshold faster. The slope of the pacing current is increased and the pacing rate of the heart is increased. Increasing the AV Nodes Excitability The release of norepinephrine at the AV node also increases its excitability by decreasing the AV node delay (i.e. shortening the P R segment), allowing the wave of excitation to reach the ventricles faster. Enhancing Conduction Speeds PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 48 MODULE 05 COMPANION GUIDE PHGY 215 Similar to the AV node, in which the delay was decreased by increasing the conduction speed of the AV node cells, the conduction speed in the rest of the cells of the cardiac conduction system, the bundle of His, and purkinje fibres, are also increased. This means that the wave of excitation reaches them faster. Increasing Contractility of Cardiac Muscles For both the atria and the ventricles, sympathetic stimulation increases the contractile strength of the muscle cells. This is primarily due to increasing Ca2+ permeability during the plateau phase of the action potential. This allows more Ca2+ to enter the muscle cells to both directly enhance contractility and to enhance CICR*. For both the atria and the ventricles, when their strength of contraction increases they are able to squeeze harder and eject more blood. Within the ventricles, this means the end systolic volume is lower because stroke volume was increased. Definition:* CICR: Calcium-induced calcium-release (recall from Section 3). References: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. Clinical ECG Interpretation - The PR interval (n.d.). Retrieved on September 8 2017 from https://ecgwaves.com/lessons/the-pr-interval/ CONTROL OF HEART RATE This content was retrieved from Section 5 Slide 6 of 17 of the online learning module. As we have seen, parasympathetic stimulation decreases heart rate while sympathetic stimulation increases it. This control is at the level of the SA node. There are many different reasons for an increase in heart rate. Learn about a few different ways in which heart rate can be increased or decreased. Injury To The Vagus Nerve At rest, the parasympathetic system dominates and the average HR is about 70 b p m. If the vagus nerve was cut, the influence of the parasympathetic system would be removed and the resting heart rate would increase. The endogenous pacing rate of the SA node is around 100 beats per minute but at PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 49 MODULE 05 COMPANION GUIDE PHGY 215 rest the parasympathetic system reduces it to around 70 b p m. Activity When it becomes necessary to increase HR to deliver O2 to working muscles during activity, there is a decrease in parasympathetic input and an increase in sympathetic input allowing the sympathetic system to dominate and raise HR. Fever When core body temperature gets too high, as is the case with a fever, HR will increase to increase the amount of blood flow to the tissues and dissipate heat through the skin. The relative activities of the parasympathetic and sympathetic branches of the autonomic nervous system are coordinated by the cardiovascular control centre located in the brain stem. Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. CONTROL OF STROKE VOLUME This content was retrieved from Section 5 Slide 7 of 17 of the online learning module. Stroke volume (SV) is the volume of blood pumped out of each ventricle during each heartbeat. Stroke volume is under two types of control. Learn about the different ways in which stroke volume is controlled. Extrinsic Control This refers to factors outside the heart that influence contractility. The primary extrinsic control is the sympathetic nervous system. Intrinsic Control This refers to factors outside the heart that influence contractility. The primary extrinsic control is the sympathetic nervous system. INTRINSIC CONTROL OF STROKE VOLUME AND END -DIASTOLIC VOLUME This content was retrieved from Section 5 Slide 8 of 17 of the online learning module. There is a direct correlation between the EDV and SV: as more blood returns to the heart, more blood is pumped out (remember though, the ventricles never empty fully during systole!). The volume of blood in the ventricle at any given time causes the chamber to distend and this puts a stretch on the cardiac muscle fibres. This stretch changes the length-tension relationship of the cardiac muscle fibres. Recall from Module 04, a skeletal muscle is normally at its optimal length (Io) in the length-tension relationship. If its length is either increased or decreased then the amount of developed tension decreases. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 50 MODULE 05 COMPANION GUIDE PHGY 215 At rest, the length-tension relationship of cardiac muscle is well below Io. As cardiac muscle is stretched, because of more blood in the ventricle, muscle fibre length increases and a greater contraction can occur. Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. QUESTION: THE FRANK -STARLING LAW OF THE HEART This content was retrieved from Section 5 Slide 9-10 of 17 of the online learning module. The Frank-Starling law of the heart is the relationship between EDV and SV such that increasing EDV increases SV, the greater the diastolic filling, the greater the systolic emptying. This law of the heart allows for beat-to-beat regulation of stroke volume. Using what you have learned thus far, discuss what you think would occur if the right ventricle was to pump an increased volume of blood into the pulmonary circulation? Would there be an increase or decrease in EDV in the left ventricle? What about the SV? Feedback: An increase of blood volume from the right ventricle would return to the left atria to be pumped to the left ventricle and increase end diastolic volume and thus stroke volume. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 51 MODULE 05 COMPANION GUIDE PHGY 215 Reference: Sherwood, L. (2015). Human Physiology: From Cells to Systems. Nelson Education Ltd. THE REGULATION OF EDV This content was retrieved from Section 5 Slide 11 of 17 of the online learning module. There are essentially two forces that affect EDV. Read about these forces. Preload Preload is the amount of blood returning to the ventricle. This is also called venous return and will be discussed in greater detail in Module 06. Preload is increased by increasing venous return and therefore EDV and stroke volume. Preload stretches the right or left ventricles to its greatest dimensions. Afterload Afterload is the force that the ventricle is pushing against. If there is increased pressure in the aorta then the left ventricle is contracting against this extra load. The net result is that the aortic valve will shut early and the stroke volume is decreased. However, if the normal volume of blood returns to the heart during diastole, the EDV is increased and so will be the force of the next contraction. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 52 MODULE 05 COMPANION GUIDE PHGY 215 Reference: Slide Player - Preload and Afterload (n.d.). Retrieved on September 15 2017 from http://slideplayer.com/slide/3835776/ EJECTION FRACTION This content was retrieved from Section 5 Slide 12 of 17 of the online learning module. Several times now it has been mentioned that the ventricles never fully empty of blood during systole. The ejection fraction is the amount of blood that is pumped out of the ventricles relative to the amount of blood that was in the ventricle before contraction. Ejection fraction is a very clinically relevant parameter and can be measured by echocardiography. It can also be calculated: At rest, the normal ejection fraction is around 60% meaning that there is a substantial amount of blood remaining in the ventricles after systole. This remaining 40% can be considered a reserve for when the body needs to increase cardiac output. CLINICAL APPLICATION The ejection fraction can change and is very important for diseases such as heart failure. Learn more about the role of normal versus abnormal ejection fractions and congestive heart disease. Page Link: https://proxy.queensu.ca/login?url=https://doi.org/10.1016/S0735-1097(99)00118-7 Reference: M D Health (n.d.). [Illustration comparing a healthy and congestive heart]. Retrieved on September 7 2017 from http://www.md-health.com/Congestive-Heart-Failure.html EXTRINSIC CONTROL OF STROKE VOLUME This content was retrieved from Section 5 Slide 13-14 of 17 of the online learning module. As already mentioned, extrinsic control of stroke volume is essentially the influence of the sympathetic nervous system. PRINCIPLES OF MAMMALIAN PHYSIOLOGY I | PHGY 215 MODULE 05 PAGE 53 MODULE 05 COMPANION GUIDE PHGY 215 Recall what you have learned about sympathetic stimulation. What are some of the ways in which it stimulates the heart? Feedback: View Our Answer Some ways in which sympathetic stimulation regulates the heart are: Increase the force of contraction Increase stroke volume Shift the Frank-Starling curve upwards Increase AV node excitability Increase contractility of cardiac muscles The effects of extrinsic and intrinsic control can occur at the same time for an even greater increase of stroke volume. ACTIVITY: CARDIAC OUTPUT This content was retrieved from Section 5 Slide 15 of 17 of the online learning module. You have now learned that there are many factors, such as parasympathetic activity, stroke volume, and end diastolic volume, which affect cardiac output (CO); either increasing it or decreasing it. For each change in cardiac activity, indicate if cardi

PHGY 215 Cardiac Physiology Module 05 PDF

Document Details

Tags

Related

Summary

Full Transcript

Upgrade to continue