Block 3 Cardio Physio BRS
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Myocardial contractility is best correlated with the intracellular concentration of
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Na+
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K+
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Ca2+
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Cl-
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Mg2+
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This quiz titled 'Block 3 Cardio Physio BRS' assesses knowledge in cardiovascular physiology, focusing on arterial dynamics, cardiac function, and ECG interpretation. It is designed for medical students preparing for exams, enhancing understanding of key physiological concepts and clinical applications.
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- 2.
The physiologic function of the relatively slow conduction through the atrioventricular (AV) node is to allow sufficient time for
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Runoff of blood from the aorta to the arteries
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Venous return to the atria
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Filling of the ventricles
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Contraction of the ventricles
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Repolarization of the ventricles
Correct Answer
A. Filling of the ventriclesExplanation
The atrioventricular (AV) delay (which corresponds to the PR interval)
allows time for filling of the ventricles from the atria. If the ventricles contracted before
they were filled, stroke volume would decrease.Rate this question:
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- 3.
Arteriography of a patient's left renal arteryshows narrowing of the radius of the artery by 50%. What is the expected change in blood flowthrough the stenotic artery?
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Decrease to 1/2
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Decrease to 1/4
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Decrease to 1/8
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Decrease to 1/16
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No change
Correct Answer
A. Decrease to 1/16Explanation
If the radius of the artery decreased by 50% (1/2), then resistance would increase by 2(4th) , or 16 (R = 8nl /(pi)r4).
Because blood flow is inversely proportional to resistance (Q = (delta)P/R),
flow will decrease to 1/16th, the original value.Rate this question:
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- 4.
Propranolol has which of the following effects?
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Decreases heart rate
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Increases left ventricular ejection fraction
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Increases stroke volume
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Decreases splanchnic vascular resistance
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Decreases cutaneous vascular resistance
Correct Answer
A. Decreases heart rateExplanation
Propranolol, a 13- adrenergic antagonist, blocks all
sympathetic effects that are mediated by a 13 1 or p2 receptor. The sympathetic effect on the sinoatrial
(SA) node is to increase heart rate via a p i receptor; therefore, propranolol decreases heart
rate. Ejection fraction reflects ventricular contractility, which is another effect of 13 1 receptors;
thus, propranolol decreases contractility, ejection fraction, and stroke volume. Splanchnic and
cutaneous resistance are mediated by a 1 receptors.Rate this question:
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- 5.
The tendency for blood flow to be turbulent is increased by
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Increased viscosity
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Increased hematocrit
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Partial occlusion of a blood vessel
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Decreased velocity of blood flow
Correct Answer
A. Partial occlusion of a blood vesselExplanation
Turbulent flow is predicted when the Reynold's number is increased.
Factors that increase the Reynold's number and produce turbulent flow are decreased
viscosity (hematocrit) and increased velocity. Partial occlusion of a blood vessel increases the
Reynold's number (and turbulence) because the decrease in cross-sectional area results in increased
blood velocity (v = Q/A).Rate this question:
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- 6.
An increase in arteriolar resistance, without a change in any other component of the cardiovascular system, will produce
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A decrease in total peripheral resistance (TPR)
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An increase in capillary filtration
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An increase in arterial pressure
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A decrease in afterload
Correct Answer
A. An increase in arterial pressureExplanation
An increase in arteriolar resistance will increase total peripheral
resistance (TPR). Arterial pressure = cardiac output x TPR, so arterial pressure will also increase.
Capillary filtration decreases when there is arteriolar constriction because P c decreases.
Afterload of the heart would be increased by an increase in TPR.Rate this question:
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- 7.
Which of the following parameters is decreased during moderate exercise?
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Arteriovenous 02 difference
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Heart rate
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Cardiac output
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Pulse pressure
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Total peripheral resistance (TPR)
Correct Answer
A. Total peripheral resistance (TPR)Explanation
In anticipation of exercise, the central command increases sympathetic
outflow to the heart and blood vessels, causing an increase in heart rate and contractility.
Venous return is increased by muscular activity and contributes to an increase in cardiac output
by the Frank-Starling mechanism. Pulse pressure is increased because stroke volume is increased.
Although increased sympathetic outflow to the blood vessels might be expected to increase
total peripheral resistance (TPR), it does not because there is an overriding vasodilation
of the skeletal muscle arterioles as a result of the buildup of vasodilator metabolites (lactate, K+,
adenosine). Because this vasodilation improves the delivery of 0 2, more 02 can be extracted and
used by the contracting muscle.Rate this question:
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- 8.
Which of the following agents or changes has a negative inotropic effect on the heart?
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Increased heart rate
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Sympathetic stimulation
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Norepinephrine
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Acetylcholine (ACh)
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Cardiac glycosides
Correct Answer
A. Acetylcholine (ACh)Explanation
A negative inotropic effect is one that decreases myocardial contractility.
Contractility is the ability to develop tension at a fixed muscle length. Factors that decrease
contractility are those that decrease the intracellular [Ca 2-1. Increasing heart rate increases
intracellular [Ca2+] because more Ca2± ions enter the cell during the plateau of each
action potential. Sympathetic stimulation and norepinephrine increase intracellular [Ca2+] by
increasing entry during the plateau and increasing the storage of Ca 2+ by the sarcoplasmic reticulum
(SR) [for later release]. Cardiac glycosides increase intracellular [Ca 2÷] by inhibiting the
Na+–K+ pump, thereby inhibiting Na+–Ca21- exchange (a mechanism that pumps Ca2+ out of the
cell). Acetylcholine (ACh) has a negative inotropic effect on the atria.Rate this question:
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- 9.
A person's electrocardiogram (ECG) has no P wave, but has a normal QRS complex and a normal T wave. Therefore, his pacemaker is located in the
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Sinoatrial (SA) node
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Atrioventricular (AV) node
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Bundle of His
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Purkinje system
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Ventricular muscle
Correct Answer
A. Atrioventricular (AV) nodeExplanation
The absent P wave indicates that the atrium is not depolarizing and,
therefore, the pacemaker cannot be in the sinoatrial (SA) node. Because the QRS and T waves
are normal, depolarization and repolarization of the ventricle must be proceeding in the normal
sequence. This situation can occur if the pacemaker is located in the atrioventricular (AV) node.
If the pacemaker were located in the bundle of His or in the Purkinje system, the ventricles would
activate in an abnormal sequence (depending on the exact location of the pacemaker) and the
QRS wave would have an abnormal configuration. Ventricular muscle does not have pacemaker
properties.Rate this question:
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- 10.
The ventricles are completely depolarized during which isoelectric portion of the electrocardiogram (ECG)?
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PR interval
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QRS complex
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QT interval
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ST segment
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T wave
Correct Answer
A. ST segmentExplanation
The PR segment (part of the PR interval) and the ST segment are
the only portions of the electrocardiogram (ECG) that are isoelectric. The PR interval includes
the P wave (atrial depolarization) and the PR segment, which represents conduction through the
atrioventricular (AV) node; during this phase, the ventricles are not yet depolarized. The ST segment
is the only isoelectric period when the entire ventricle is depolarized.Rate this question:
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- 11.
Inspiration "splits" the second heart sound because
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The aortic valve closes before the pulmonic valve
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The pulmonic valve closes before the aortic valve
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The mitral valve closes before the tricuspid valve
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The tricuspid valve closes before the mitral valve
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Filling of the ventricles has fast and slow components
Correct Answer
A. The aortic valve closes before the pulmonic valveExplanation
The second heart sound is associated with closure of the aortic and
pulmonic valves. Because the aortic valve closes before the pulmonic valve, the sound can be split
by inspiration.Rate this question:
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- 12.
During exercise, total peripheral resistance (TPR) decreases because of the effect of
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the sympathetic nervous system on splanchnic arterioles
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The parasympathetic nervous system on skeletal muscle arterioles
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Local metabolites on skeletal muscle arterioles
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Local metabolites on cerebral arterioles
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Histamine on skeletal muscle arterioles
Correct Answer
A. Local metabolites on skeletal muscle arteriolesExplanation
During exercise, local metabolites accumulate in the exercising
muscle and cause local vasodilation and decreased arteriolar resistance of the skeletal muscle.
Because muscle mass is large, it contributes a large fraction of the total peripheral resistance
(TPR). Therefore, the skeletal muscle vasodilation results in an overall decrease in TPR, even
though there is sympathetic vasoconstriction in other vascular beds.Rate this question:
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- 13.
An acute decrease in arterial blood pressure elicits which of the following compensatory changes?
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Decreased firing rate of the carotid sinus nerve
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Increased parasympathetic outflow to the heart
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Decreased heart rate
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Decreased contractility
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Decreased mean systemic pressure
Correct Answer
A. Decreased firing rate of the carotid sinus nerveExplanation
A decrease in blood pressure causes decreased stretch of the
carotid sinus baroreceptors and decreased firing of the carotid sinus nerve. In an attempt to restore
blood pressure, the parasympathetic outflow to the heart is decreased and sympathetic outflow
is increased. As a result, heart rate and contractility will be increased. Mean systemic pressure
will increase because of increased sympathetic tone of the veins (and a shift of blood to the
arteries).Rate this question:
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- 14.
Cardiac output of the right side of the heart is what percentage of the cardiac output of the left side of the heart?
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25%
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50%
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75%
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100%
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125%
Correct Answer
A. 100%Explanation
Cardiac output of the left and right sides of the heart is equal. Blood
ejected from the left side of the heart to the systemic circulation must be oxygenated by passage
through the pulmonary circulation.Rate this question:
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- 15.
The low-resistance pathways between myocardial cells that allow for the spread of action potentials are the
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Gap junctions
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T tubules
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Sarcoplasmic reticulum (SR)
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Intercalated disks
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Mitochondria
Correct Answer
A. Gap junctionsExplanation
The gap junctions occur at the intercalated disks between cells
and are low-resistance sites of current spread.Rate this question:
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- 16.
When a person moves from a supine position to a standing position, which of the following compensatory changes occurs?
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Decreased heart rate
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Increased contractility
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Decreased total peripheral resistance (TPR)
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Decreased cardiac output
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Increased PR intervals
Correct Answer
A. Increased contractilityExplanation
When a person moves to a standing position, blood pools
in the leg veins, causing decreased venous return to the heart, decreased cardiac output, and decreased
arterial pressure. The baroreceptors detect the decrease in arterial pressure, and the vasomotor
center is activated to increase sympathetic outflow and decrease parasympathetic outflow.
There is an increase in heart rate (resulting in a decreased PR interval), contractility, and
total peripheral resistance (TPR). Because both heart rate and contractility are increased, cardiac
output will increase toward normal.Rate this question:
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- 17.
Which of the following changes will cause an increase in myocardial 02 consumption?
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Decreased aortic pressure
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Decreased heart rate
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Decreased contractility
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Increased size of the heart
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Increased influx of Na+ during the upstroke of the action potential
Correct Answer
A. Increased size of the heartExplanation
Myocardial 02 consumption is determined by the amount of tension
developed by the heart. It increases when there are increases in aortic pressure (increased afterload),
increased heart rate or stroke volume (which increase cardiac output), or when the size
(radius) of the heart is increased (T = P x r). Influx of Na + ions during an action potential is a
purely passive process, driven by the electrochemical driving forces on Na + ions. Of course, maintenance
of the inwardly directed Na + gradient over the long term requires the Na +–K+ pump,
which is energized by adenosine triphosphate (ATP).Rate this question:
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- 18.
Which of the following is an effect of histamine?
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Decreased capillary filtration
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Vasodilation of the arterioles
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Vasodilation of the veins
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Decreased Pc
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Interaction with the muscarinic receptors on the blood vessels
Correct Answer
A. Vasodilation of the arteriolesExplanation
Histamine causes vasodilation of the arterioles, which increases
Pc and capillary filtration. It also causes constriction of the veins, which contributes to
the increase in Pc. Acetylcholine (ACh) interacts with muscarinic receptors (although these are
not present on vascular smooth muscle).Rate this question:
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- 19.
Carbon dioxide (CO 2) regulates blood flow to which one of the following organs?
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Heart
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Skin
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Brain
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Skeletal muscle at rest
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Skeletal muscle during exercise
Correct Answer
A. BrainExplanation
Blood flow to the brain is autoregulated by the PCO2.
If metabolism increases (or arterial pressure decreases), the PCO2 will increase and cause cerebral
vasodilation. Blood flow to the heart and to skeletal muscle during exercise is also regulated
metabolically, but adenosine and hypoxia are the most important vasodilators for the heart.
Adenosine, lactate, and K+ the are the most important vasodilators for exercising skeletal muscle.
Blood flow to the skin is regulated by the sympathetic nervous system rather than by local
metabolites.Rate this question:
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- 20.
An increase in contractility is demonstrated on a Frank-Starling diagram by
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Increased cardiac output for a given enddiastolic volume
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Increased cardiac output for a given endsystolic volume
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Decreased cardiac output for a given enddiastolic volume
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Decreased cardiac output for a given endsystolic Volume
Correct Answer
A. Increased cardiac output for a given enddiastolic volumeExplanation
An increase in contractility produces an increase in cardiac output
for a given end-diastolic volume, or pressure. The Frank-Starling relationship demonstrates
the matching of cardiac output (what leaves the heart) with venous return (what returns to the
heart). An increase in contractility (positive inotropic effect) will shift the curve upward.Rate this question:
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- 21.
In which of the following situations is pulmonary blood flow greater than aortic blood flow?
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Normal adult
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Fetus
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Left-to-right ventricular shunt
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Right-to-left ventricular shunt
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Right ventricular failure
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Administration of a positive inotropic
Correct Answer
A. Left-to-right ventricular shuntExplanation
In a left-to-right ventricular shunt, a defect in the ventricular septum
allows blood to flow from the left ventricle to the right ventricle instead of being ejected into the
aorta. The "shunted" fraction of the left ventricular output is therefore added to the output of the
right ventricle, making pulmonary blood flow (the cardiac output of the right ventricle) higher
than systemic blood flow (the cardiac output of the left ventricle). In normal adults, the outputs
of both ventricles are equal in the steady state. In the fetus, pulmonary blood flow is near zero.
Right ventricular failure results in decreased pulmonary blood flow. Administration of a positive
inotropic agent should have the same effect on contractility and cardiac output in both ventricles.Rate this question:
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- 22.
The greatest pressure decrease in the circulation occurs across the arterioles because
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They have the greatest surface area
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They have the greatest cross-sectional area
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The velocity of blood flow through them is the highest
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The velocity of blood flow through them is the lowest
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They have the greatest resistance
Correct Answer
A. They have the greatest resistanceExplanation
The decrease in pressure at any level of the cardiovascular
system is caused by the resistance of the blood vessels (AP = Q x R). The greater the resistance,
the greater the decrease in pressure. The arterioles are the site of highest resistance in the vasculature.
The arterioles do not have the greatest surface area or cross-sectional area (the capillaries
do). Velocity of blood flow is lowest in the capillaries, not in the arterioles.Rate this question:
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- 23.
The tendency for edema to occur will be increased by
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Arteriolar constriction
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Increased venous pressure
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Increased plasma protein concentration
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Muscular activity
Correct Answer
A. Increased venous pressureExplanation
Edema occurs when more fluid is filtered out of the
capillaries than can be returned to the circulation by the lymphatics. Filtration is increased by
changes that increase Pc or decrease are. Arteriolar constriction would decrease P, and decrease
filtration. Dehydration would increase plasma protein concentration (by hemoconcentration)
and thereby increase ire and decrease filtration. Increased venous pressure would increase Pe
and filtration.Rate this question:
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- 24.
During which phase of the cardiac cycle is ventricular volume lowest?
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Atrial systole
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Isovolumetric ventricular contraction
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Rapid ventricular ejection
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Reduced (slow) ventricular ejection
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Isovolumetric ventricular relaxation
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Rapid ventricular filling
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Reduced (slow) ventricular filling (diastasis)
Correct Answer
A. Isovolumetric ventricular relaxationExplanation
Ventricular volume is at its lowest value while the ventricle is relaxed
(diastole), just before ventricular filling beginsRate this question:
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- 25.
A patient experiences orthostatic hypotension after a sympathectomy. The explanation for this occurrence is
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An exaggerated response of the reninangiotensin- aldosterone system
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A suppressed response of the renin-angiotensin- aldosterone system
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An exaggerated response of the baroreceptor mechanism
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A suppressed response of the baroreceptor mechanism
Correct Answer
A. A suppressed response of the baroreceptor mechanismExplanation
Orthostatic hypotension is a decrease in arterial pressure that occurs
when a person moves from a supine to a standing position. A person with a normal baroreceptor
mechanism responds to a decrease in arterial pressure through the vasomotor center by
increasing sympathetic outflow and decreasing parasympathetic outflow. The sympathetic component
helps to restore blood pressure by increasing heart rate, contractility, total peripheral resistance
(TPR), and mean systemic pressure. In a patient who has undergone a sympathectomy,
the sympathetic component of the baroreceptor mechanism is absentRate this question:
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- 26.
The following measurements were obtained in a male patient: Heart rate: 70 beats/min Pulmonary vein [0 2] = 0.24 ml 02/m1 Pulmonary artery [02] = 0.16 ml 02/ml Whole body 02 consumption: 500 ml/min What is this patient's cardiac output?
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1.65 L/min
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4.55 L/min
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5.00 L/min
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6.25 L/min
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8.00 L/min
Correct Answer
A. 6.25 L/minExplanation
Cardiac output is calculated by the Fick principle if whole body oxygen
(02) consumption and [02] in the pulmonary artery and pulmonary vein are measured. Mixed
venous blood could substitute for a pulmonary artery sample, and peripheral arterial blood could
substitute for a pulmonary vein sample. Heart rate is not needed for this calculation.
Cardiac output = 500 ml/min_______________
0.24 ml 02/ml – 0.16 ml 02/ml
= 6250 ml/min or 6.25 L/minRate this question:
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- 27.
In the sinoatrial (SA) node, phase 4 depolarization (pacemaker potential) is attributable to
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An increase in K + conductance
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An increase in Na + conductance
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A decrease in Cl- conductance
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A decrease in Ca2+ conductance
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Simultaneous increases in K + and Cl conductances
Correct Answer
A. An increase in Na + conductanceExplanation
Phase 4 depolarization is responsible for the pacemaker property
of sinoatrial (SA) nodal cells. It is caused by an increase in Na + conductance and an inward
Na+ current (If), which depolarizes the cell membrane.Rate this question:
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- 28.
Which receptor is blocked when propranolol is administered to reduce cardiac output?
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A1 receptors
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B1(1) receptors
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B2 receptors
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Muscarinic receptors
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Nicotinic receptors
Correct Answer
A. B1(1) receptorsExplanation
Propranolol is an adrenergic antagonist that blocks
both B1and B2 receptors. When propanolol is administered to reduce cardiac output, it inhibits
B1 receptors in the sinoatrial (SA) node (heart rate) and in ventricular muscle (contractility).Rate this question:
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- 29.
If the ejection fraction increases, there will be a decrease in
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Cardiac output
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End-diastolic volume
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End-systolic volume
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Heart rate
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Pulse pressure
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Stroke volume
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Systolic pressure
Correct Answer
A. End-systolic volumeExplanation
An increase in ejection fraction means that a higher fraction of the
end-diastolic volume is ejected in the stroke volume (e.g., because of the administration of a positive
inotropic agent). When this situation occurs, the volume remaining in the ventricle after
systole, the end-systolic volume, will be reduced. Cardiac output, pulse pressure, stroke volume,
and systolic pressure will be increased.Rate this question:
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- 30.
Which receptor mediates constriction of arteriolar smooth muscle?
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A1 Receptors
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B1 Receptors
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B2 receptors
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Muscarinic receptors
Correct Answer
A. A1 ReceptorsExplanation
The a l receptors for norepinephrine are excitatory
on vascular smooth muscle and cause vasoconstriction. There are also B2 receptors on the arterioles
of skeletal muscle, but they produce vasodilation.Rate this question:
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- 31.
Which agent is released or secreted after a hemorrhage and causes an increase in renal Na+ reabsorption?
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Aldosterone
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Angiotensin I
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Angiotensin II
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Antidiuretic hormone (ADH)
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Atrial natriuretic peptide
Correct Answer
A. AldosteroneExplanation
Angiotensin I, angiotensin II, and aldosterone are increased
in response to a decrease in renal perfusion pressure. Antidiuretic hormone (ADH) is released
when atrial receptors detect a decrease in blood volume. Of these, only aldosterone increases Na+
reabsorption. Atrial natriuretic peptide is released in response to an increase in atrial pressure,
and an increase in its secretion would not be anticipated after blood loss.Rate this question:
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- 32.
An electrocardiogram (ECG) on a person shows ventricular extrasystoles. The next "normal" ventricular contraction that occurs after the extrasystole would produce
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Increased pulse pressure because the contractility of the ventricle is increased
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Increased pulse pressure because total peripheral resistance (TPR) is decreased
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Increased pulse pressure because compliance of the veins is decreased
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Decreased pulse pressure because the contractility of the ventricle is increased
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Decreased pulse pressure because TPR is decreased
Correct Answer
A. Increased pulse pressure because the contractility of the ventricle is increasedExplanation
The post-extrasystolic contraction produces increased pulse
pressure because contractility is increased. Extra Ca 2+ enters the cell during the extrasystolic
beat. Contractility is directly related to the amount of intracellular Ca 2+ available for binding to
troponin C.Rate this question:
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- 33.
Pulse pressure is
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The highest pressure measured in the arteries
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The lowest pressure measured in the arteries
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Measured only during diastole
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Determined by stroke volume
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Decreased when the capacitance of the arteries decreases
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The difference between mean arterial pressure and central venous pressure
Correct Answer
A. Determined by stroke volumeExplanation
Pulse pressure is the difference between the highest (systolic) and
lowest (diastolic) arterial pressures. It reflects the volume ejected by the left ventricle (stroke volume).
Pulse pressure increases when the capacitance of the arteries decreases, such as with aging.Rate this question:
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- 34.
Blood flow to which organ is controlled primarily by the sympathetic nervous system rather than by local metabolites?
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Skin
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Heart
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Brain
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Skeletal muscle during exercise
Correct Answer
A. SkinExplanation
Circulation of the skin is controlled primarily by the sympathetic
nerves. The coronary and cerebral circulations are primarily regulated by local metabolic
factors. Skeletal muscle circulation is regulated by metabolic factors (local metabolites) during
exercise, although at rest it is controlled by the sympathetic nerves.Rate this question:
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- 35.
Which of the following substances crosses capillary walls primarily through water-filled clefts between the endothelial cells?
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02
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CO2
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CO
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Glucose
Correct Answer
A. GlucoseExplanation
Because 0 2, CO2, and CO are lipophilic, they cross capillary
walls primarily by diffusion through the endothelial cell membranes. Glucose is water-soluble;
it cannot cross through the lipid component of the cell membrane and is restricted to the waterfilled
clefts, or pores, between the cells.Rate this question:
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- 36.
At which site is systolic blood pressure the highest?
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Aorta
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Central vein
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Pulmonary artery
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Right atrium
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Renal artery
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Renal vein
Correct Answer
A. Renal arteryExplanation
Pressures on the venous side of the circulation (e.g., central
vein, right atrium, renal vein) are lower than pressures on the arterial side. Pressure in the pulmonary
artery (and all pressures on the right side of the heart) are much lower than their counterparts
on the left side of the heart. In the systemic circulation, systolic pressure is actually
slightly higher in the downstream arteries (e.g., renal artery) than in the aorta because of the reflection
of pressure waves at branch points.Rate this question:
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- 37.
An electrocardiogram (ECG) on a person shows ventricular extrasystoles. The extrasystolic beat would produce
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Increased pulse pressure because contractility is increased
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Increased pulse pressure because heart rate is increased
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Decreased pulse pressure because ventricular filling time is increased
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Decreased pulse pressure because stroke volume is decreased
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Decreased pulse pressure because the PR interval is increased
Correct Answer
A. Decreased pulse pressure because stroke volume is decreasedExplanation
On the extrasystolic beat, pulse pressure decreases because there
is inadequate ventricular filling time—the ventricle beats "too soon." As a result, stroke volume
decreases.Rate this question:
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- 38.
A person's electrocardiogram (ECG) shows two P waves preceding each QRS complex. The interpretation of this pattern is
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Decreased firing rate of the pacemaker in the sinoatrial (SA) node
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Decreased firing rate of the pacemaker in the atrioventricular (AV) node
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Increased firing rate of the pacemaker in the SA node
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Decreased conduction through the AV node
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Increased conduction through the His- Purkinje system
Correct Answer
A. Decreased conduction through the AV nodeExplanation
A pattern of two P waves preceding each QRS complex indicates
that only every other P wave is conducted through the atrioventricular (AV) node to the
ventricle. Thus, conduction velocity through the AV node must be decreased.Rate this question:
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- 39.
Which of the following is the result of an inward Na+ current?
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Upstroke of the action potential in the sinoatrial (SA) node
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Upstroke of the action potential in Purkinje fibers
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Plateau of the action potential in ventricular muscle
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Repolarization of the action potential in ventricular muscle
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Repolarization of the action potential in the SA node
Correct Answer
A. Upstroke of the action potential in Purkinje fibersExplanation
The upstroke of the action potential in the atria, ventricles,
and Purkinje fibers is the result of a fast inward Na + current. The upstroke of the action
potential in the sinoatrial (SA) node is the result of an inward Ca 2+ current. The plateau of the
ventricular action potential is the result of a slow inward Ca 2+ current. Repolarization in all cardiac
tissues is the result of an outward K + current.Rate this question:
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- 40.
A 24-year-old woman presents to the emergency department with severe diarrhea. When she is supine (lying down), her blood pressure is 90/60 mm Hg (decreased) and her heart rate is 100 beats/min (increased). When she is moved to a standing position, her heart rate further increases to 120 beats/min. Which of the following accounts for the further increase in heart rate upon standing?
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Decreased total peripheral resistance
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Increased venoconstriction
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Increased contractility
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Increased afterload
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Decreased venous return
Correct Answer
A. Decreased venous returnExplanation
Diarrhea causes a loss of extracellular fluid volume, which produces a decrease in arterial pressure. The decrease in arterial pressure activates the baroreceptor mechanism, which produces an increase in heart rate when the patient is supine. When she stands up, blood pools in her leg veins and produces a decrease in venous return, a decrease in cardiac output (by the Frank-Starling mechanism), and a further decrease in arterial pressure.
The further decrease in arterial pressure causes further activation of the baroreceptor mechanism
and a further increase in heart rate.Rate this question:
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- 41.
Which receptor mediates slowing of the heart?
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A1 Receptors
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B1 Receptors
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B2 Receptors
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Muscarinic receptors
Correct Answer
A. Muscarinic receptorsExplanation
Acetylcholine (ACh) causes slowing of the heart via
muscarinic receptors in the sinoatrial (SA) node.
.
BLOCKING the B1 slows the heart, (this is pharmacy NOT physiology)Rate this question:
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- 42.
A 60-year-old businessman is evaluated by his physician, who determines that his blood pressure is significantly elevated at 185/130 mm Hg. Laboratory tests reveal an increase in plasma renin activity, plasma aldosterone level, and left renal vein renin level. His right renal vein renin level is decreased. What is the most likely cause of the patient's hypertension?
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Aldosterone-secreting tumor
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Adrenal adenoma secreting aldosterone and cortisol
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Pheochromocytoma
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Left renal artery stenosis
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Right renal artery stenosis
Correct Answer
A. Left renal artery stenosisExplanation
In this patient, hypertension is most likely caused by left renal artery
stenosis, which led to increased renin secretion by the left kidney. The increased plasma renin activity
causes an increased secretion of aldosterone, which increases Na + reabsorption by the renal
distal tubule. The increased Na+ reabsorption leads to increased blood volume and blood pressure.
The right kidney responds to the increase in blood pressure by decreasing its renin secretion. Right
renal artery stenosis causes a similar pattern of results, except that renin secretion from the right
kidney, not the left kidney, is increased. Aldosterone-secreting tumors cause increased levels of aldosterone,
but decreased plasma renin activity (as a result of decreased renin secretion by both kidneys).
Pheochromocytoma is associated with increased circulating levels of catecholamines, which
increase blood pressure by their effects on the heart (increased heart rate and contractility) and
blood vessels (vasoconstriction); the increase in blood pressure is sensed by the kidneys and results
in decreased plasma renin activity and aldosterone levels.Rate this question:
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- 43.
During which phase of the cardiac cycle is aortic pressure highest?
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Atrial systole
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Isovolumetric ventricular contraction
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Rapid ventricular ejection
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Reduced (slow) ventricular ejection
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Isovolumetric ventricular relaxation
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Rapid ventricular filling
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Reduced (slow) ventricular filling (diastasis)
Correct Answer
A. Reduced (slow) ventricular ejectionExplanation
Aortic pressure reaches its highest level immediately after the
rapid ejection of blood during left ventricular systole. This highest level actually coincides with
the beginning of the reduced (slow) ventricular ejection phase.Rate this question:
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- 44.
During which phase of the cardiac cycle does the mitral valve open?
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Atrial systole
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Isovolumetric ventricular contraction
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Rapid ventricular ejection
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Reduced ventricular ejection
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Isovolumetric ventricular relaxation
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Rapid ventricular filling
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Reduced ventricular filling (diastasis)
Correct Answer
A. Isovolumetric ventricular relaxationExplanation
The mitral [atrioventricular (AV)] valve opens when left atrial pressure
becomes higher than left ventricular pressure. This situation occurs when the left ventricular
pressure is at its lowest level—when the ventricle is relaxed, blood has been ejected from
the previous cycle, and before refilling has occurred.Rate this question:
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Current Version
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Mar 20, 2023Quiz Edited by
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Nov 10, 2011Quiz Created by
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