Week 8: Blood Flow Through Heart
Match the term in the left column to the blanks near their definition on the right.
1. End diastolic volume (EDV): the volume of blood in one ventricle before contraction 2. Heart rate (HR): the number of heart beats per minute 3. Stroke volume (SV): the volume of blood per heart beat pumped out by one ventricle 4. End systolic volume (ESV): the volume of blood in one ventricle after contraction 5. Cardiac output (CO): the volume of blood per minute pumped out by one ventricle 6. Venous return (VR): the volume of blood per minute flowing into one atrium
Match the cardiac components in the left column to the blanks near their functions on the right.
1. SA node: Set(s) the pace for the entire heart 2. Purkinje fibers: Convey(s) the impulse throughout the ventricular walls 3. Bundle branches: Convey(s) the impulse down the interventricular septum 4. AV node: Delay(s) occurs here while atria contract 5. Internodal pathways: Link(s) between the SA node and AV node 6. AV bundle : Electrical link(s) between atria and ventricles
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.
Which part of the intrinsic conduction system delays the impulse briefly before it moves on to the ventricles?
AV node
Which of these structures conduct(s) action potentials the slowest?
AV node Action potentials slow down as they pass through the AV node. This gives the atria time to finish contracting before the ventricles are depolarized.
Increased pressure in the ventricles would close what valve(s)?
AV valves only
So why is Mr. G's mitral regurgitation causing a systolic murmur? Remember, a murmur is caused by abnormal turbulent blood flow.
Because his mitral valve leaks, when the ventricles contract, they push blood back up through it into the left atrium.
Calculate the cardiac output if heart rate (HR) is 90 beats per minute, stroke volume (SV) is 110 ml/beatml/beat, end diastolic volume (EDV) is 140 mlml, and end systolic volume (ESV) is 30 mlml.
CO = SV (EDV - ESV) x HR 9.9 L/min
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+ channels in their sarcolemma that continue to allow influx of Ca2+ ions after Na+ channels are inactivated.
Which of the following can be heard with a stethoscope most easily?
Closing of atrioventricular valves
Which of the following is an effect of epinephrine, norepinephrine, and thyroxine?
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.
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.
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.
Which of the following is correct about the filling of the ventricles?
Most blood flows passively into the ventricles through open AV valves. 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
Which of the following graphs depict the cardiac cycle of an individual with chronic hypertension in which blood pressure is 140/90?
Pressure and volume curve throughout the cardiac cycle, heart rate is 85 bpm, ventricular pressure curve starts just above zero, curves up slightly and back down to where it started, then has a large rounded curve up to 140 and back down. The atrial pressure starts just above zero and then curves up to about 15 and slopes back down, this repeats and is followed by a slow increase and then a larger increase. Aortic pressure starts at 130 and travels down to 90 then follows the ventricular curve up to 140 then back up to 130 and back down. The ventricular volume slopes up from 60 to 120 and then back down again.
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.
A person notices his or her heart beat because he or she senses blood being pumped by the heart. Excessive caffeine intake can lead to irregular heart rhythms (arrhythmias) that patients perceive as "skipped beats." Given that caffeine is a stimulant, which of the following mechanisms best explains the reason for the feeling that the heart skipped a beat?
Purkinje fibers initiate spontaneous action potentials, which cause the ventricles to contract early.
Refer to Focus Figure 18.2, specifically the graph reflecting pressure changes in the cardiac cycle. Why is the dicrotic notch important?
Reflects an increase in aortic pressure as blood rebounds against the closed aortic semilunar valve
Which part of the conduction system initiates the depolarizing impulse, which spreads throughout the heart?
SA node
Which part of the intrinsic conduction system normally initiates the depolarizing impulse that causes a heartbeat?
SA node
Which of the following is true during ventricular systole?
The AV valves are closed.
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.
Refer to Focus Figure 18.2, specifically the pressure in the left atrium. Which statement best explains the second rise in atrial pressure on the line graph?
The bicuspid/mitral valve closes; blood is contained within the closed chamber, exerting pressure against the atrial wall.
Which of the following is equivalent to the ventricular volume during isovolumetric contraction?
The end diastolic volume (EDV)
Now that you have reviewed normal blood flow, why does a patient with left-sided heart failure have a low systolic blood pressure?
The left side of the heart pumps blood into the body, so when it fails, less blood will be pumped into the arteries.
Mr. G talks in short bursts with frequent breaths. He tells you he used to feel breathless when he was walking, but now he has been having more and more trouble breathing even when he is lying down at night. When you listened to his lungs you heard fluid in them. Could this be due to his heart failure, or is it another problem? Choose the best answer.
The left side of the heart receives blood from the lungs and pumps it out to the body, so if it fails, blood will remain in the lungs.
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 than it would be if the vagus nerve were severed.
Isovolumetric relaxation is characterized by which of the following?
The semilunar and AV valves are closed.
During the ventricular ejection phase of the cardiac cycle, which of the following is true?
The semilunar valves are open.
Drag and drop the labels into the appropriate blanks in the sentences. Each term will be used once.
The semilunar valves open during the ventricular ejection phase of the cardiac cycle, allowing blood to exit the ventricles. End diastolic volume and the first heart sound are observed during the isovolumetric contraction phase of the cardiac cycle. The dicrotic notch occurs during the isovolumetric relaxation phase of the cardiac cycle. The P wave and subsequent atrial contraction are evident during the ventricular filling phase of the cardiac cycle.
You take Mr. V into the second exam room while the doctor talks to Mr. G. You can tell right away that Mr. V is breathing better than Mr. G because he does not have to stop talking to take a breath. He complains that he is having trouble with walking −− his legs feel heavy. And he has gained 6 pounds in a week, even though he has been sticking to the diet the doctor gave him. "My pants aren't any tighter," he says, "but my socks and shoes sure are! I've had to switch to these sandals. I'm too old for my feet to be growing. I don't get why Mr. G isn't having the same problem, since we're both rheumies −− rheumatic fever guys."When you examine Mr. V he has pitting edema of both ankles and feet. They were slightly swollen on his last visit, but not this badly. His jugular veins are distended.Mr. V's chart says he has been diagnosed with tricuspid stenosis (narrowed tricuspid valve) secondary to rheumatic fever. His blood pressure is the same as it was the last time he came in, and so is his heart rate. His lungs sound normal, but you hear a diastolic murmur when you listen to his heart.Why would tricuspid stenosis cause a diastolic murmur?
The tricuspid valve is partly blocked, so when blood is flowing through it, there will be a noise of turbulent blood flow. Blood flows through the tricuspid during diastole, so that is when you hear the murmur.
When the atria contract, which of the following is true?
The ventricles are in diastole.
Mr. G's online file also has the results of his recent blood tests. The only thing that looks abnormal is something called ANP −− atrial natriuretic peptide. It is elevated. Why would this hormone be elevated in Mr. G, and what is it doing to him?
This hormone comes from the overstretched atrium and makes Mr. G lose more Na+ and water in his urine, lowering blood volume and reducing the load on the atrium.
Atrial pressure is greater than ventricular pressure during which phase of the cardiac cycle?
atrial contraction
The beginning of the QRS complex of the electrocardiogram (ECG) immediately precedes which of the following events?
closing of the atrioventricular valves The QRS complex is a recording of ventricular depolarization. This depolarization begins just prior to the ventricular contraction it initiates. As the ventricles contract, the increase in ventricular pressure closes the atrioventricular valves, beginning isovolumetric contraction. As ventricular pressure increases above the corresponding blood vessel, only then do the semilunar valves open, initiating ventricular ejection.
An increase in sympathetic stimulation of the heart would increase stroke volume by increasing __________.
contractility
How would a decrease in blood volume affect both stroke volume and cardiac output?
decreased stroke volume and no change in cardiac output 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.
Mr. V has also had a recent echocardiogram and blood work. With tricuspid stenosis, what changes do you expect to see in the echocardiogram report? Choose the best answer.
dilated right atrium because blood is not flowing down into the right ventricle fast enough
What does the ECG wave tracing represent?
electrical activity in the heart
Which of the following is equivalent to the ventricular volume during isovolumetric relaxation?
end systolic volume (ESV)
Which of the following would increase heart rate?
epinephrine and norepinephrine
When threshold is reached at the SA node (an autorhythmic cell), what channels open causing further depolarization of the membrane?
fast calcium
In what direction does blood flow through the heart?
from a region of high pressure to a region of low pressure
Action potentials generated by the autorhythmic cells spread to the contractile cells through what structures in the membrane?
gap junctions
What causes the aortic semilunar valve to close?
greater pressure in the aorta than in the left ventricle Backflow of blood in the aorta (towards the left ventricle) closes the aortic semilunar valve.
How would an increase in the sympathetic nervous system increase stroke volume?
increased contractility 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
Which of the following would increase cardiac output to the greatest extent?
increased heart rate and increased stroke volume
Put the phases of the cardiac cycle in the correct order, starting after ventricular filling.
isovolumetric contraction, ventricular ejection, isovolumetric relaxation
As part of a blood drive on campus for the American Red Cross, you and your friends have just donated 500 mlml of blood. You are now relaxing at the student lounge, waiting for A&P lab to begin. Unfortunately, even though you are thirsty, you haven't bothered to buy yourself a drink. Other than a little soreness of the skin and tissue around your median cubital vein, you feel fine. How has your 500 mlml decrease in blood volume most likely affected your cardiac output, heart rate, and stroke volume?
no change in cardiac output, increased heart rate, decreased stroke volume Donating blood does not alter resting cardiac output. However, the decreased blood volume does decrease venous return and end diastolic volume. This decreases preload, thereby lowering stroke volume. By itself, decreased stroke volume would decrease cardiac output. But remember, the body still requires a resting blood flow of around 5 L/minL/min. To meet this demand, homeostatic mechanisms quickly restore cardiac output to resting levels. For example, heart rate is increased as parasympathetic influence is removed and sympathetic activity is increased. Even though your blood volume is a bit low, your body has no problem compensating to meet your resting metabolic needs. Running away from a tiger? Now that might be a different story.
One of the changes that occurs in the pacemaker potential (unstable resting membrane potential) in the SA node (an autorhythmic cell) is a decreased efflux of what ion?
potassium
The anatomy of the intrinsic conduction system causes contraction of the ventricles to begin at the apex and move superiorly. Why is this important?
so blood is forced upward, toward the semilunar valves
In order to cause cardiac muscle contraction, the contractile cells must also depolarize. What causes the depolarization of the contractile cells?
the flow of positive ions from adjacent cells
What structure in the intrinsic cardiac conduction system determines heart rate?
the sinoatrial (SA) node
What is the main function of heart valves?
to prevent backward flow of blood
What does the QRS complex represent in the ECG wave tracing?
ventricular depolarization
Isovolumetric relaxation and ventricular filling (two phases of the cardiac cycle) take place during __________.
ventricular diastole
Most of the decrease in ventricular volume takes place during which phase of the cardiac cycle?
ventricular ejection
Ventricular pressure is greater than aortic pressure during which phase of the cardiac cycle?
ventricular ejection
Most of the increase in left ventricular volume takes place during what phase of the cardiac cycle?
ventricular filling
Repolarization of an autorhythmic cell is due to the opening of which channels?
voltage-gated potassium channels
At what point in the cardiac cycle does the AV valve open?
when atrial pressure becomes greater than ventricular pressure
At what point in the cardiac cycle does the semilunar valve close?
when pressure in the ventricle becomes less than aortic pressure
At what point in the cardiac cycle does the semilunar valve open?
when ventricular pressure becomes greater than aortic pressure
At what point during the cardiac cycle does the AV valve close?
when ventricular pressure becomes greater than atrial pressure
