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Questions and Answers
What is the purpose of an Electrocardiogram (ECG)?
What is the purpose of an Electrocardiogram (ECG)?
Systole is the phase of the cardiac cycle when the heart is relaxed.
Systole is the phase of the cardiac cycle when the heart is relaxed.
False
What are the two main events associated with the ECG waveforms?
What are the two main events associated with the ECG waveforms?
Depolarization and repolarization
The volume of blood in the heart at the end of systole is called the ______.
The volume of blood in the heart at the end of systole is called the ______.
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Match the following components of the cardiac cycle with their definitions:
Match the following components of the cardiac cycle with their definitions:
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Which neurotransmitter is primarily released by parasympathetic neurons to influence heart rate?
Which neurotransmitter is primarily released by parasympathetic neurons to influence heart rate?
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The sympathetic nervous system decreases heart rate and strength of contractions.
The sympathetic nervous system decreases heart rate and strength of contractions.
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What is the role of the pacemaker in the heart?
What is the role of the pacemaker in the heart?
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The ________ nerve is associated with the activation of the parasympathetic nervous system during heart rate modulation.
The ________ nerve is associated with the activation of the parasympathetic nervous system during heart rate modulation.
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Match the component to its respective function:
Match the component to its respective function:
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What effect does sympathetic division have on the heart?
What effect does sympathetic division have on the heart?
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Stimulation of the cardioinhibitory center results in an increase in heart rate.
Stimulation of the cardioinhibitory center results in an increase in heart rate.
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Which receptors are stimulated by norepinephrine in the heart?
Which receptors are stimulated by norepinephrine in the heart?
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What is the primary function of valves in large veins?
What is the primary function of valves in large veins?
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Valves in venous circulation help to counteract the effects of gravity on venous return.
Valves in venous circulation help to counteract the effects of gravity on venous return.
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What is lymph?
What is lymph?
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Valves in the lymphatic system are created by the __________ of endothelial cells.
Valves in the lymphatic system are created by the __________ of endothelial cells.
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Match the following features with their descriptions:
Match the following features with their descriptions:
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What triggers the opening of valves in the initial lymphatics?
What triggers the opening of valves in the initial lymphatics?
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The arrangement of endothelial cells in initial lymphatics allows for two-way flow of fluid.
The arrangement of endothelial cells in initial lymphatics allows for two-way flow of fluid.
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What prevents the backflow of blood in veins?
What prevents the backflow of blood in veins?
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What occurs during the first phase of ventricular systole?
What occurs during the first phase of ventricular systole?
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During ventricular diastole, the ventricles are relaxed and filled passively.
During ventricular diastole, the ventricles are relaxed and filled passively.
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What happens to the semilunar valves during the second phase of ventricular systole?
What happens to the semilunar valves during the second phase of ventricular systole?
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During _______, blood flows into the relaxed atria.
During _______, blood flows into the relaxed atria.
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Match the following phases of the cardiac cycle with their descriptions:
Match the following phases of the cardiac cycle with their descriptions:
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During which stage do the AV valves open?
During which stage do the AV valves open?
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Reverse blood flow pushes the cusps of the semilunar valves together during ventricular diastole—early.
Reverse blood flow pushes the cusps of the semilunar valves together during ventricular diastole—early.
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What is the main event that occurs at 370 msec in the cardiac cycle?
What is the main event that occurs at 370 msec in the cardiac cycle?
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Which component of the heart has the fastest rate of action potential discharge?
Which component of the heart has the fastest rate of action potential discharge?
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The AV node has a higher rate of action potential discharge than the Bundle of His.
The AV node has a higher rate of action potential discharge than the Bundle of His.
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What phase follows the slow depolarization in cardiac autorhythmic cells?
What phase follows the slow depolarization in cardiac autorhythmic cells?
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The _____ phase of the action potential occurs in contractile cardiac muscle cells after the rapid rising phase.
The _____ phase of the action potential occurs in contractile cardiac muscle cells after the rapid rising phase.
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Match the following cardiac cells with their respective rates of action potential discharge:
Match the following cardiac cells with their respective rates of action potential discharge:
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What characterizes the action potential in contractile cardiac muscle cells during the plateau phase?
What characterizes the action potential in contractile cardiac muscle cells during the plateau phase?
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In autorhythmic cells, the action potential has a slower rate of depolarization compared to contractile cells.
In autorhythmic cells, the action potential has a slower rate of depolarization compared to contractile cells.
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What is the phase called when the membrane potential returns to a negative value after depolarization?
What is the phase called when the membrane potential returns to a negative value after depolarization?
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What occurs immediately after atrial systole ends?
What occurs immediately after atrial systole ends?
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The stroke volume is the amount of blood ejected from the heart during each heartbeat.
The stroke volume is the amount of blood ejected from the heart during each heartbeat.
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What are the heart sounds S1 and S2 commonly referred to as?
What are the heart sounds S1 and S2 commonly referred to as?
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During isovolumetric relaxation, the ______ valves close.
During isovolumetric relaxation, the ______ valves close.
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What happens during ventricular ejection?
What happens during ventricular ejection?
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The left AV valve opens during atrial systole.
The left AV valve opens during atrial systole.
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What is the end-diastolic volume?
What is the end-diastolic volume?
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Study Notes
PA 533 Cardiology 2
- This course covers Cardiology Physiology using Medical Physiology chapters 17, 19, and 21-23.
Objectives
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A. Overview of the Autonomic Nervous System
- Compare and contrast sympathetic and parasympathetic nervous systems' influence on the cardiovascular system.
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B. The Cardiac Cycle, The Heart as a Pump
- Graph a cardiac cycle, labeling systole, diastole, and associated pressures.
- Relate ECG waveforms to the mechanical events of the cardiac cycle and correlate heart sounds.
- Describe the coordination of events leading to heart contraction.
- Describe factors contributing to and inhibiting cardiac contractility.
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C. Hemodynamics of the Cardiovascular System
- Describe factors used in calculating cardiac output.
- Describe pressure, resistance, and flow relationships across the cardiovascular system.
- Outline factors influencing resistance to blood flow.
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D. Regulation of Arterial Pressure and Cardiac Output
- Understand the dynamics involved with regulating cardiac output.
- Locate arterial baroreceptors and explain their influence on pressure regulation.
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E. Arteries and Veins, The Lymphatic System
- Discuss how blood flow velocity changes with vessel diameter.
- Compare and contrast pulmonary and systemic circulation pressures.
- Describe factors influencing compliance of arteries and veins.
- Describe the role of valves in venous and lymphatic circulation.
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F. Microcirculation and Local Control
- Describe factors influencing oxygen and carbon dioxide exchange in capillaries.
- Identify physical and chemical regulators of microcirculation.
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G. Electrical Events in the Heart, The Electrocardiogram
- Graph and define distinct phases of cardiac action potential.
- Follow the electrical impulse's propagation through the heart and relate to the ECG waveform.
ANS Control of the Cardiovascular System
- Parasympathetic and sympathetic innervation modify heart rate, strength of contractions, and vessel diameter.
- The pacemaker sets the heart rate but can be altered.
- Impulses from the autonomic nervous system modify pacemaker activity.
Autonomic control of heart rate
- Parasympathetic division slows heart rate.
- Sympathetic division accelerates heart rate.
Parasympathetic and Sympathetic Neurotransmitters
- Parasympathetic neurons release acetylcholine (ACh), slowing spontaneous depolarization.
- Sympathetic neurons release norepinephrine (NE), increasing depolarization rate.
Effects of ACh and NE on Nodal and Contractile Cells
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Acetylcholine:
- Stimulates muscarinic receptors.
- Decreases heart rate.
- Decreases force of contractions.
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Norepinephrine:
- Stimulates beta receptors.
- Increases heart rate.
- Increases force of contractions.
Cardiac Centers in the Medulla Oblongata
- Stimulation activates sympathetic neurons (cardiac nerve), increasing heart rate.
- Stimulation activates parasympathetic neurons (vagus nerve), decreasing heart rate.
Heart Rate
- Determined by balance between inhibitory effects of vagus nerve and stimulatory effects of cardiac nerve.
- Parasympathetic discharge is dominant under resting conditions.
- Increasing sympathetic and decreasing parasympathetic activity increases heart rate.
- Increasing parasympathetic and decreasing sympathetic activity decreases heart rate.
Sympathetic Control of Blood Vessels
- Sympathetic activation stimulates smooth muscle cells to constrict and reduce vessel diameter (vasoconstriction).
- Relaxation of smooth muscle increases lumen diameter (vasodilation).
The Cardiac Cycle
- The period between one heartbeat and the next, including contraction and relaxation.
- Two phases: systole (contraction) and diastole (relaxation).
- Lasts around 800 msec at 75 bpm.
- All phases shorten with increased heart rate, particularly diastole.
Blood Pressure
- Rises during systole, falls during diastole.
- Controlled by timing of contractions and one-way valves.
Phases of the Cardiac Cycle
- Atrial systole, atrial diastole, ventricular systole, ventricular diastole.
The Electrocardiogram (ECG)
- An electrical recording of the heart's activity.
- Detects cardiac muscle depolarization and repolarization, displayed on graph paper.
Electrode Placement for Recording a Standard ECG
- Electrodes are placed on the chest and limbs to accurately record the electrical activity of the heart.
ECG Printout
- A strip of graph paper displaying electrical events.
- Major components and measurements are essential for analysis.
Cardiac Output
- Volume of blood pumped by each ventricle per minute.
- Equivalent volume flows through pulmonary and systemic circulation.
- Determined by heart rate multiplied by stroke volume.
Pressure, Resistance, and Flow
- Blood flow driven by pressure across variable resistance.
- Flow (F) is output from the left side of the heart.
- Pressure (P) is force exerted by blood on vessel walls.
- Resistance (R) opposes blood flow.
- Flow is directly proportional to pressure gradient and inversely to vascular resistance.
Resistance to Blood Flow
- Opposition to blood flow through a vessel.
- Depends on blood viscosity, vessel length, and vessel radius.
- Radius is the most influential factor; a small change in radius significantly affects blood flow.
- Resistance proportional to 1/r4 (radius to the power of 4).
Regulation of Cardiac Output
- Cardiac output depends on heart rate and stroke volume.
- ANS controls heart rate.
- Stroke volume is controlled intrinsically (venous return) and extrinsically (sympathetic stimulation).
Intrinsic Control
- Degree of diastolic filling determines cardiac muscle fiber length.
- Increased venous return increases fiber length.
- This leads to stronger contractions and increased stroke volume (Frank-Starling law of the heart).
Extrinsic Control
- Sympathetic stimulation enhances heart contractility and increases stroke volume, as well as venous return.
- Combined effect influences cardiac output.
Baroreceptor Control of Arterial Pressure
- Pressure sensors (baroreceptors) in carotid sinus and aortic arch.
- Part of a neural feedback mechanism.
- Regulate mean arterial pressure.
Negative Feedback Loop
- Increased mean arterial pressure triggers vasodilation and bradycardia (slowing of heart rate).
- Decreased mean arterial pressure triggers vasoconstriction and tachycardia (increased heart rate).
The Vascular Tree
- Arteries, arterioles, capillaries, venules, and veins.
- Arteries distribute blood, microcirculation facilitates diffusion and filtration, veins collect blood.
- Physical properties closely follow the branching level.
Key Parameters
- Number, radius, cross-sectional area of vessels, velocity of blood flow and blood volume, pressure, and structure/elastic properties of vascular walls.
- Number of vessels increases dramatically from aorta to capillaries; radius decreases; cross-sectional area decreases even more, with the largest area in capillaries.
- The combined cross-sectional area of daughter vessels always exceeds that of the parent vessel at each branch point.
- Steepest increase in total cross-sectional area occurs in microcirculation.
Pressures in Pulmonary and Systemic Circulation
- Intravascular pressures in the systemic circuit are higher than in the pulmonary circuit.
- Total resistance in systemic circulation is far higher than in pulmonary circulation.
- Upstream driving pressure is approximately 95 mm Hg in systemic and 15 mm Hg in pulmonary circulation.
- Circulation divided into high-pressure (left ventricle to systemic arterioles) and low-pressure (systemic capillaries to left atrium) systems.
Compliance of Arteries and Veins
- How easily vessel walls stretch in response to blood volume and pressure changes.
- Expressed as volume change over pressure change.
- Arteries have low volume capacity but withstand large pressure differences.
- Veins have high volume capacity but withstand smaller pressure differences; compliance is higher in veins of the low-pressure range but low in the higher-pressure range.
Role of Valves in Fluid Movement
- Large veins contain one-way valves spaced at intervals.
- Valves prevent backflow and assist movement toward the heart, counteracting gravity's effect on venous return.
- Valves ensure blood flows in the correct direction.
Capillary Bed Gas Exchange
- Capillaries are the sites of exchange between blood and body cells.
- Exchange happens via diffusion across thin walls.
- Factors enhancing diffusion include minimization of distance and maximization of surface area.
- Capillaries' thin walls and branching enhance this process.
Regulation of Microcirculation
- Vascular smooth muscle cells (VSMCs) exhibit spontaneous rhythmic tension variations, influencing vascular resistance.
- Active VSMC contraction adjusts resistance upstream of capillary beds, controlling blood flow (perfusion).
Cardiac Action Potentials
- Pacemaker activity of SA node, AV node, and bundle of His.
- Action potential of contractile cells (atrial and ventricular).
- Pacemaker potential has an initial phase of slow depolarization to threshold, a rising phase, and a falling phase of repolarization.
- Action potential in contractile cells exhibits a rapid rising phase, a plateau phase, and a rapid falling phase of repolarization.
Electrical Activity of the Heart
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Cardiac action potential originates in the sinoatrial (SA) node.
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Spontaneous depolarization and firing of action potentials occur at a rate of 80-100 times per minute.
Propagation of the Cardiac Action Potential
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Spontaneous action potential conducts from cell to cell in the right atrium; then spreads to the left atrium via gap junctions; both atria depolarize and contract simultaneously.
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Signal arrives at atrioventricular (AV) node.
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Internodal pathways conduct action potential from SA to AV node, causing sequential contraction of the ventricles.
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AV nodal delay (approximately 100 msec) ensures atrial contraction is complete before ventricular contraction begins.
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Impulse travels from AV node to His-Purkinje system; this system transmits action potential throughout both ventricles allowing them to contract synchronously.
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This entire process is vital for the heart's coordinated pumping action.
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Description
Test your knowledge on cardiac physiology, including the purpose of Electrocardiograms (ECG), phases of the cardiac cycle, and the role of neurotransmitters in heart rate modulation. This quiz also covers components of the cardiac cycle and their functions, providing a comprehensive overview of heart mechanics.