MAP #4 - The Heart

Which of the following is not part of the conduction system of the heart?

AV Valve

Which part of the intrinsic conduction system delays the impulse briefly before it moves on to the ventricles?

AV node (Yes, the AV node slows down the impulse giving the atria time to contract before the ventricles contract.)

Trace the pathway of stimulation through the heart. Which of these pathways shows stimulation in the correct order?

AV node, AV bundle, interventricular septum, subendocardial conducting network (This is the correct order of stimulation of the heart muscle. The signal to the AV node would begin in the SA node.)

Increased pressure in the ventricles would close what valve(s)?

AV valves only (Yes, increased pressure in the ventricles would close the AV valves.)

In a healthy individual which of the following would be low?

Afterload (High afterload is a characteristic of poor cardiovascular health; in a healthy person, afterload would be low.) definition: Afterload is the pressure against which the heart must work to eject blood during systole (systolic pressure).

In contrast to a skeletal muscle cell action potential, why does the action potential for a cardiac muscle cell contain a "plateau" phase?

Cardiac muscle cells contain slow Ca2+Ca2+ channels in their sarcolemma that continue to allow influx of Ca2+Ca2+ ions after Na+Na+ channels are inactivated. (Fast voltage-gated Na+Na+ channels are open only for a very brief time before they are inactivated, but the resulting depolarization opens slow Ca2+Ca2+ channels that start a positive feedback cycle that temporarily keeps the membrane potential high.)

Autonomic regulation of heart rate is via two reflex centers found in the pons.

False

What is the effect of high blood pressure on cardiac output?

High blood pressure increases afterload and reduces cardiac output (CO). (High blood pressure does produce a resistant force to systolic contractions, thus increasing afterload and end systolic volume (ESV). If ESV increases, stroke volume decreases.)

How does heart rate affect stroke volume?

How does heart rate affect stroke volume? A high heart rate reduces the end diastolic volume (EDV) and stroke volume (SV), because there is less time for ventricular filling. (A slow heart rate allows more time for ventricular filling. Conversely, a faster heart rate allows less time. The amount the heart fills during diastole (EDV) has a direct impact on stroke volume.)

Why does a graph of the membrane potential of living pacemaker cells never demonstrate a flat line?

Hyperpolarization of pacemaker cells triggers the opening of slow Na+ channels and starts a new slow depolarization phase. (At the end of an action potential, as repolarization and hyperpolarization occur, slow Na+ channels open, causing the membrane potential to immediately start to increase again (called the pacemaker potential), eventually triggering another action potential.)

A 55-year-old male was admitted to the hospital with heart failure. He complains of increasing shortness of breath on exertion, and of needing to sleep on three pillows at night. On physical assessment, the nurse determines that his ankles and feet are very swollen. Which of these symptoms either reflect left-sided and/or right-sided heart failure?

Left side failure results in shortness of breath. Right side failure results in edema in the extremities.

Which of the following is correct about the filling of the ventricles?

Most blood flows passively into the ventricles through open AV valves. (Yes, most of the ventricular filling is passive; atrial contraction adds just a little more blood.)

Contraction of the atria results from which wave of depolarization on the ECG tracing?

P wave (Yes, the P wave represents atrial depolarization, which leads to atrial contraction.)

Describe the pressures in the atria and ventricles that would cause the opening of the AV valves.

Pressure in the atria would be greater than the pressure in the ventricles. (Yes, higher pressure in the atria than in the ventricles forces the AV valves to open and blood moves into the ventricles.)

Your patient has been diagnosed with right ventricular failure. Which of the following abnormalities is not a direct result of this problem?

Pulmonary edema (fluid in the alveoli) (The other items listed here all result when the right ventricle cannot "keep up" with the volume of blood presented by the vena cavae. Left ventricular failure directly causes blood to "back up" into the pulmonary veins, increasing pressure in the pulmonary capillaries and causing fluid to be pushed from the blood to the alveoli.)

Which part of the conduction system initiates the depolarizing impulse, which spreads throughout the heart?

SA node (Yes, the SA Node spontaneously depolarizes, causing the wave of depolarization that spreads through the rest of the conduction system and heart.)

An older woman complains of shortness of breath and intermittent fainting spells. Her doctor runs various tests and finds that the AV node is not functioning properly. What is the suggested treatment?

Surgery to implant an artificial pacemaker

Which of the following is true during ventricular systole?

The AV valves are closed. (At the beginning of ventricular systole, the one-way AV valves are forced shut. The AV valves remain shut throughout ventricular systole. This prevents blood from flowing back into the atria when the ventricles contract.)

Part A - Blood Entering the Right Atrium

The ___superior VC___ carries oxygen-poor venous blood from above the diaphragm from areas of the upper body and extremities into the right atrium. The ____coronary sinus___ carries oxygen-poor venous blood of the coronary circulation into the right atrium. The ___inferior VC___ carries oxygen-poor venous blood from below the diaphragm from the areas of the lower body and extremities into the right atrium.

What is the role of the atrioventricular bundle?

The atrioventricular bundle provides the only pathway for electrical signals to pass from the atria to the ventricles. (The atrial cardiac cells are not connected by gap junctions to the ventricular cardiac cells. The only means by which the electrical signals of the heart can pass from atria to ventricles is the atrioventricular bundle.)

Which of the following is equivalent to the ventricular volume during isovolumetric contraction?

The end diastolic volume (EDV) (Isovolumetric contraction occurs at the beginning of ventricular systole when the ventricular volume is at its maximum value−the end diastolic volume (EDV). Because no volume changes occur during isovolumetric contraction, ventricular volume remains at this value throughout the phase.)

Which statement best describes the autonomic nervous system's role in regulating heart rate?

The parasympathetic division normally inhibits the heart, keeping it beating at a slower rate than it would be on its own. (The inhibitory signals from the vagus nerve inhibit the heart rate, thus keeping the heart rate lower then it would be if the vagus nerve were severed.)

Which of the following descriptions of cardiac pacemaker cells is INCORRECT?

The rapid depolarization phase of the pacemaker cell action potential is due to Na+ influx through Na+ channels (The action potential begins with a slow depolarization towards threshold, called the pacemaker potential (or prepotential). At threshold (approximately -40 mV), Ca2+ channels open, allowing explosive entry of Ca2+ from the extracellular space. As a result, in pacemaker cells, it is the influx of Ca2+ (rather than Na+) that produces the rapid depolarization phase of the action potential.)

Isovolumetric relaxation is characterized by which of the following?

The semilunar and AV valves are closed. (During isovolumetric relaxation, all valves into and out of the ventricles remain closed. This prevents blood from flowing backward through the heart.)

During the ventricular ejection phase of the cardiac cycle, which of the following is true?

The semilunar valves are open (During ventricular ejection, blood flows from the ventricles into the arteries. To do so, the blood must pass through the semilunar valves, which must be open during this phase. Narrowing of the left semilunar valve reduces blood flow out of the heart, a disease condition known as aortic stenosis.)

When the atria contract, which of the following is true?

The ventricles are in diastole. (Atrial contraction fills each of the ventricles to their maximum capacity−the end diastolic volume (EDV). This occurs towards the end of ventricular diastole while the ventricles are still relaxed.)

A patient was admitted to the hospital with chest pains. On admission, his pulse was 110 and blood pressure was 96/64. According to his history, his normal pulse rate is usually between 80 and 88 and his blood pressure runs from 120/70 to 130/80. Why did these changes in BP and HR occur?

To maintain the same cardiac output, the heart rate would need to increase to compensate for a decreased stroke volume.

Part B - Right-Sided Anatomical Features

Tricusp. valve, Pulmon. SL valve, RV, Pulmon., Lung Cap. Inferior VC artery Bed Pulmonary trunk

As pressure in the aorta rises due to atherosclerosis, more ventricular pressure is required to open the aortic valve.

True

Tissues damaged by myocardial infarction are replaced by connective tissue.

True

As soon as ventricular pressure falls below atrial pressure, the atrioventricular valve will open and ventricular filling will begin.

True (At any given time, the pressures on either side of a heart valve determine whether a valve is open or closed. During ventricular systole, pressure in the ventricle increases. As soon as ventricular pressure rises above atrial pressure, the AV valve closes. During ventricular diastole, pressure in the ventricle decreases. As soon as ventricular pressure drops below atrial pressure, the AV valve opens, and ventricular filling begins.)

Hemorrhage with a large loss of blood causes ________.

a lowering of blood pressure due to change in cardiac output

Atrial pressure is greater than ventricular pressure during which phase of the cardiac cycle?

atrial contraction (Blood always flows from high to low pressure. During atrial contraction, blood flows from atria (high pressure) to ventricles (low pressure). Similarly, this same pressure gradient exists during ventricular filling.)

What is afterload?

back pressure exerted by arterial blood (Afterload refers to the back pressure exerted by arterial blood, or the pressure that must be overcome for the ventricles to eject blood.)

The first heart sound (the "lub" of the "lub-dup") is caused by __________.

closure of the atrioventricular valves (The first heart sound (the "lub" of the "lub-dup") is generated by the closure of the atrioventricular valves.)

Normal heart sounds are caused by which of the following events?

closure of the heart valves

If cardiac muscle is deprived of its normal blood supply, damage would primarily result from ________.

decreased delivery of oxygen

How would a decrease in blood volume affect both stroke volume and cardiac output?

decreased stroke volume and no change in cardiac output (Yes, a decreased blood volume would decrease the end diastolic volume, thus lowering the stroke volume. Although this would initially lead to a decrease in the cardiac output, heart rate would increase because of increased activity of the sympathetic nervous system in an effort to maintain cardiac output.)

What does the ECG wave tracing represent?

electrical activity in the heart (Yes, the ECG waves show the depolarization and repolarization in various areas of the heart.)

Which of the following is equivalent to the ventricular volume during isovolumetric relaxation?

end systolic volume (ESV) (Isovolumetric relaxation occurs at the beginning of ventricular diastole when the ventricular volume is at its minimum value−the end systolic volume (ESV). Because no volume changes occur during isovolumetric relaxation, ventricular volume remains at this value throughout the phase.)

Which of the following would increase heart rate?

epinephrine (Sympathetic stimulation (i.e., exercise) can lead to the release of epinephrine and norepinephrine, both of which increase heart rate.)

Which of the following would increase heart rate?

epinephrine and norepinephrine (Yes, secreted by the adrenal medulla as a result of sympathetic stimulation, these hormones act as part of the sympathetic response, increasing heart rate.)

A premature ventricular contraction is classified as a(n) __________.

extrasystole (Premature ventricular contraction is a type of extrasystole. Extrasystole, or premature contraction, can be caused by ectopic pacemakers (also called ectopic foci). An ectopic focus can result when the SA node is defective. Alternatively, some drugs (such as caffeine and nicotine) can generate an ectopic focus. Any defect in the intrinsic conduction system of the heart can generate an irregular heart rhythm (an arrhythmia). Damage to the AV node can lead to a heart block. In a complete heart block, impulses do not reach the ventricles and they beat at their intrinsic rate, which is too slow to maintain adequate circulation.)

In what direction does blood flow through the heart?

from a region of high pressure to a region of low pressure (Blood moves through the heart from atria to ventricles and out large arteries, always from areas of high pressure to areas of lower pressure through one-way valves.)

What causes the aortic semilunar valve to close?

greater pressure in the aorta than in the left ventricle (Yes, backflow of blood in the aorta (towards the left ventricle) closes the aortic semilunar valve)

Which of the following is an effect of epinephrine, norepinephrine, and thyroxine?

increase contractility (Epinephrine, norepinephrine, and thyroxine secreted by the sympathetic nervous system directly increase contractility and heart rate, for the overall effect of increasing cardiac output. Likewise, end systolic volume would decrease with increased contractility.)

How would an increase in the sympathetic nervous system increase stroke volume?

increased contractility (Yes, an increase in sympathetic nervous system activity would increase contractility (by increasing available calcium), thus increasing stroke volume. Contractility causes an increase in stroke volume by decreasing end systolic volume; it does not change end diastolic volume.)

By what mechanism would an increase in venous return increase stroke volume?

increased end diastolic volume (Yes, an increase in venous return increases the end diastolic volume. The fibers are stretched more, resulting in an increase in the force of contraction (preload, or the Frank-Starling Mechanism).

Which of the following would increase cardiac output to the greatest extent?

increased heart rate and increased stroke volume (Yes, cardiac output = heart rate x stroke volume.)

Put the phases of the cardiac cycle in the correct order, starting after ventricular filling.

isovolumetric contraction, ventricular ejection, isovolumetric relaxation (Yes, the ventricles must contract and eject blood before they relax and fill again.)

Art-labeling Activity: Figure 18.15

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Art-labeling Activity: Figure 18.17

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During contraction of heart muscle cells ________.

some calcium enters the cell from the extracellular space and triggers the release of larger amounts of calcium from intracellular stores

If the length of the absolute refractory period in cardiac muscle cells was the same as it is for skeletal muscle cells ________.

tetanic contractions might occur, which would stop the heart's pumping action

If the vagal nerves to the heart were cut, the result would be that ________.

the heart rate would increase by about 25 beats per minute.

What structure in the intrinsic cardiac conduction system determines heart rate?

the sinoatrial (SA) node (The SA node is composed of pacemaker cells that initiate and set the initial pace, or the sinus rhythm, of the heartbeat.)

Which of the following is not an age-related change affecting the heart?

thinning of the valve flaps

If we were able to artificially alter the membrane permeability of pacemaker cells so that sodium influx is more rapid, ________.

threshold is reached more quickly and heart rate would increase

What is the main function of heart valves?

to prevent backward flow of blood (Heart valves are one-way valves that prevent blood from flowing backward. For example, the AV valves only allow blood to flow from the atria to the ventricles. And the semilunar valves only allow blood to flow from the ventricles to the aorta and pulmonary trunk. When valves do not completely close, blood flows backward through the heart, creating an abnormal "sloshing" sound known as a heart murmur.)

What does the QRS complex represent in the ECG wave tracing?

ventricular depolarization (Yes, the QRS complex represents depolarization in the ventricles, which have greater mass than the atria.)

Isovolumetric relaxation and ventricular filling (two phases of the cardiac cycle) take place during __________.

ventricular diastole (Yes, both occur during ventricular diastole when the ventricles are not actively contracting and ejecting blood.)

The decrease in ventricular volume takes place during which phase of the cardiac cycle?

ventricular ejection (As the ventricles contract, blood is forced through the semilunar valves and out into the arteries, resulting in a reduction in ventricular blood volume. At the end of this phase, ventricular volume is at a minimum−the "end-systolic volume" (ESV).)

Ventricular pressure is greater than aortic pressure during which phase of the cardiac cycle?

ventricular ejection (While pressure in the ventricle is greater than pressure in the aorta, the semilunar valve remains open. This allows blood to be ejected from the ventricle.)

Most of the increase in left ventricular volume takes place during what phase of the cardiac cycle?

ventricular filling (During ventricular filling the AV valves remain open, which allows blood to flow from the atria into the ventricles. The passive flow of blood during this phase (before atrial contraction) accounts for roughly 80 percent of the increase in ventricular volume.)

At what point in the cardiac cycle does the AV valve open?

when atrial pressure becomes greater than ventricular pressure (Blood flows through the heart in one direction (atria-ventricles-large arteries) and from high to low pressure. When pressure in the atrium becomes greater than ventricular pressure, the AV valve opens; and blood flows from the atrium into the ventricle.)

At what point in the cardiac cycle does the semilunar valve close?

when pressure in the ventricle becomes less than aortic pressure (When pressure in the ventricle drops below aortic pressure, the semilunar valve shuts. This prevents blood from flowing backward through the heart.)

At what point in the cardiac cycle does the semilunar valve open?

when ventricular pressure becomes greater than aortic pressure (When pressure in the ventricle exceeds pressure in the aorta, the semilunar valve opens. This allows blood to be ejected from the ventricle.)

At what point during the cardiac cycle does the AV valve close?

when ventricular pressure becomes greater than atrial pressure (When ventricular pressure rises above atrial pressure, the AV valve closes. This prevents blood from flowing backward through the heart.)

Concept Map to describe ionic movement during action potentials in cardiac pacemaker and contractile cells, and trace the conduction pathway

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Concept Map to name and explain the effects of various factors regulating stroke volume and heart rate.

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Drag the appropriate labels to their respective targets. MATCHING/LABELING ECG readings:

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Focus Figure 18.1: Blood Flow through the Heart (multiple parts for section w questions below)

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IP: Intrinsic Conduction System of the Heart - Video and questions below

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IP: Regulation of Cardiac Output - Video and Q's below

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Video Tutor: Cardiac Cycle (part 1: volume changes) - Copy - Video and Questions below

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Video Tutor: Cardiac Cycle (part 2: pressure changes) - Video and Questions below

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A patient is prescribed a calcium channel blocker to prevent angina (chest pain) by decreasing the demand for oxygen. What is the explanation for this pharmacological effect?

A drug that inhibits the entry of calcium ions into the cytoplasm of cardiac cells decreases the force of myocardial contractility, thereby decreasing the oxygen demand, relieving the chest pain.