Health Science I: Body Circulation Lecture Notes PDF

Lecture 7: Body circulation- the heart Dr Isabel Hwang Division of Education School of Biomedical Sciences Faculty of Medicine, CUHK [email protected] E-mail: [email protected] Office number: 3943 6795 Important Notice: These slides contain copyright materia...

Lecture 7: Body circulation- the heart Dr Isabel Hwang Division of Education School of Biomedical Sciences Faculty of Medicine, CUHK [email protected] E-mail: [email protected] Office number: 3943 6795 Important Notice: These slides contain copyright materials. Access is limited to students of MEDF1011, unless 1 otherwise specified. Copyright © 2016 The Chinese University of Hong Kong Lecture Outline MAP can be approximated by both systolic and diastolic pressure MAP can be regulated through short-term and long-term regulatory mechanisms The baroreceptor reflex Excitation-contraction (EC) of the heart Action potential of the SA node Action potential of the cardiac muscle cell (myocardial cell) The cardiac cycle Electrical event Mechanical event Importance of the Wiggers diagram Copyright © 2024 The Chinese University of Hong Kong 2 Pre-class assignment on Blackboard Micromodules 6 3 Concept recall (lecture 6): MAP is the P that drives blood flow in the systemic circuit F = P / R P = F x R MAP = CO x TPR MAP = HR x SV x TPR 4  Q. Can you name a few examples that cause a fall in MAP (hypotension)? MAP = CO x TPR  Venous return  Atrial pressure  End-diastolic pressure CO = HR x SV 5 The cardiovascular (CV) system Functions: To delivers O2, nutrients To removes CO2 and other wastes To transport hormones and other molecules To allow temperature balance To allow fluid balance (Lecture 8) To allow acid-base balance (Lecture 9) To allow immune function 6 A cardiac cycle: systole and diastole The orderly depolarizations (electrical events) of the heart triggers a recurring cardiac cycle (mechanical events) Electrical event is followed by Electrical mechanical event Mechanical Initiated by the inherent Caused by cardiac muscle pacemaker cell called sinoatrial cells (myocardial) which are (SA) node which are non- contractile contractile Consists of systole and Achieved by the intrinsic diastole conduction system Extrinsic control +/- +/- 7 The heart Is shaped like an inverted cone Base is larger and flat Apex in the inferior and tapers to a blunt, rounded point 8 The heart has 4 chambers Muscle layer (contractile) The direction of arrow represents the route of blood flow 9 Atria are the receiving chambers Chambers through which blood flow from veins to ventricles Atrial contraction adds to ventricular filling but is not significant Small and thin muscular wall 10 Ventricles are the pumping/ discharging chambers Chambers whose contractions produce the pressures that drive blood flow through the pulmonary and systemic vascular systems and back to the heart Occupy most of the bulk and volume of the heart Q. Why LV has more muscular mass than RV? Right ventricle Left ventricle Pumps blood into the pulmonary trunk Pumps blood into the aorta (largest (large artery that splits into the artery in the body) pulmonary arteries) that carry to lungs Thicker muscle wall 11 Cardiac valves Ensure uni-directional (one way) blood flow through the heart Open and close in response to pressure gradients (P) Atrioventricular (AV) valves Semilunar (SL) valves Prevent backflow into atria Prevent backflow into when ventricles contract ventricles when ventricles Tricuspid valve (right AV valve) relax and bicuspid valve (left AV Aortic and pulmonary valve valve, mitral valve) 12 Excitation-contraction (EC) coupling Refers to the mechanism by which a cardiac action potential stimulates (initiates) cardiac contraction There are two types of cardiac action potentials: Excitation (step 1) Excitation (step 2) Contraction (Step 3) Relaxed Action potential of pacemaker Action potential of cardiac cell called sinoatrial node muscle cell (contractile) (non-contractile) contracted 13 Excitation-contraction (EC) coupling Gap junctions are protein channels linking cytosol of adjacent cells and allows action potentials to spread from one cell to another 14 Path of blood flow Both sides of the heart pump at the same time to give the same stroke volume (SV) and cardiac output (CO) Venous return Color change (blue to red) due to oxygenation of blood Please check slide 9 for the types of blood vessels 15 Electrical events of the heart Heart depolarizes and contracts at a resting range of 60-100 beats per minute (bpm) But this rhythm can also be altered by the autonomic nervous system (ANS) which is part of the peripheral nervous system i.e. sympathetic and parasympathetic input The SA node fires at an intrinsic depolarization rate = 100/min i.e. no extrinsic control on heart; HR = 100 In reality, the SA node is under control of ANS and hormones At rest: parasympathetic system dominates giving a heart rate of about 70-75 bpm During stress: sympathetic system takes over; HR increases 16 The SA node is the intrinsic cardiac pacemaker The pacemaker (SA node) spontaneously generate action potentials that lead to depolarization of cardiac cells The intrinsic conduction system help spread depolarization across the entire heart The SA node is located in the right atrium near the entrance of the superior vena cava The AP then spreads from the SA node throughout the atria and then into and throughout the ventricles Q. What is the path of spread of this excitation? 17 Spread of electrical excitation through the heart by the conduction system The intrinsic conduction system contains both nodal cells and conducting fibers 18 Electrical excitation of the heart can be detected by an electrocardiogram (ECG) 19 Wave components of an ECG in one cardiac cycle R P T Q S Components Representations P wave Atrial depolarization QRS complex Ventricular depolarization T wave Ventricular repolarization 20 Action potential produced by the SA node Q. Can you identify RMP here? Q. What additional ion is involved here that is not present in neuron? There are 3 phases that from the action potential of the SA node Pacemaker potential → Depolarization → Repolarization 21 Effects of autonomic nervous system on the SA nodal cell action potentials Increase in frequency of action potentials fired by Sympathetic activation the SA node Decrease in frequency of action potentials fired by Parasympathetic activation the SA node 22 Action potential of the cardiac muscle cell There are 5 phases that from the action potential of the cardiac muscle cell Depolarisation→ small repolarisation → plateau→ repolarization → resting membrane potential 23 23 Mechanical events of the cardiac cycle (systole) 24 24 Mechanical events of the cardiac cycle (diastole) 25 Summary of the mechanical events in a cardiac cycle The contraction and relaxation of the heart affects blood pressure, blood volume in the cardiac chambers and aorta 26  1 The left atrium and ventricle are both relaxed 2 The AV valve is held open by P and blood fills into atrium and then to the ventricle 3 The aortic valve is closed as aortic pressure is still higher than ventricular pressure 27  4 Aortic pressure is decreasing as blood is moving out into arteries 5 Ventricular pressure is building up as more blood is filling into the ventricle 6 Near the end of diastole, SA node fires and atria depolarize, P wave appears on ECG 28  7 Contraction of atria raises atrial pressure 8 Small increase in atrial pressure adds more volume into the ventricle 9 This marks the end of diastole, so the volume of blood in the ventricle is called “end-diastolic volume (EDV)” 29  10 From the AV node, depolarization spreads to the ventricle, QRS complex appear on the ECG and ventricle contracts 11 Ventricular pressure rises which exceeds atrial pressure 12 This P forces the AV valve to close and prevent backflow of blood into the atrium 30  13 Aortic valve remains closed and a brief period when all valves are closed (called isovolumetric ventricular contraction) 14 Rapidly increasing ventricular pressure exceeds aortic pressure 15 This P forces the aortic valve to open, and ventricular ejection occurs 31  16 Ventricular volume curve shows ventricular ejection is rapid at first and then slows down 17 The volume of blood that remains in the ventricle after its ejection is called end-systolic volume (ESV) 18 As blood enters the aorta, the aortic pressure increases along with the ventricular pressure 32  19 Peak ventricular and aortic pressure is reached 20 Reduced rate of ejection as it is the last part of the systole 21 Volume and pressure in the aorta begins to drop as the rate of blood ejected from the ventricle becomes slower than the rate at which blood drains out of the arteries into the tissues 33  22 T wave represents ventricular repolarization 23 Ventricles relax and its pressure drops, this forces the aortic valve to close. 24 The AV valve also remains closed as the ventricular pressure is still higher than the atrial pressure. All valves are closed briefly and this is called isovolumetric ventricular relaxation. 34  25 Decreasing ventricular pressure becomes lower than atrial pressure 26 This P opens the AV valve. 27 Venous blood enters ventricle from the atrium 28 Ventricular filling continues 35 Stroke volume and ejection fraction EDV SV = EDV − ESV ESV Ejection fraction (EF): percent of EDV pumped EF provides a clinical index of cardiac contractility (i.e. the force of contraction of the heart muscle) SV EF = EDV 36 Mean arterial blood pressure (MAP) Pressure that propels blood to tissues can be approximated by the following equation: MAP = 1/3 systolic pressure + 2/3 diastolic pressure Pulse pressure (PP) and MAP both decline with increasing distance from the heart due to PP resistance Eg. SP/DP = 120/80; MAP = 93 mm Hg Systolic and diastolic pressure can be measured by a sphygmomanometer 37 37  Learning outcomes Define systolic, diastolic and pulse pressure with normal values Briefly describe the function of a gap junction Reproduce the MAP equation using systolic and diastolic pressures as values for calculation Write a flow diagram to summarize a baroreceptor reflex when the MAP of a person falls below normal range. Define excitation-contraction (EC) coupling of the heart Draw the action potentials of both SA node and cardiac muscle cell and compare the ions and their channels involved in each phase. Identify the different phases clearly in your drawing. Sequence the intrinsic conduction system of the heart starting from the SA node Identify different components of an ECG in one heartbeat and state the electrical event each component represents. Define stroke volume and recall the stroke volume equation Define EDV, ESV, isovolumetric ventricular contraction and isovolumetric ventricular relaxation Define ejection fraction of a resting heart Important Notice: These slides contain copyright materials. Access is limited to students of MEDF1011 unless otherwise specified. 38  End of this lecture Copyright © 2024 The Chinese University of Hong Kong 39