CVR practice questions and answers already graded A+

A 53-year-old woman is found, by arteriography, to have 50% narrowing of her left renal artery. What is the expected change in blood flow through the stenotic artery? (A) Decrease to ½ (B) Decrease to ¼ (C) Decrease to 1⁄8 (D) Decrease to 1⁄16 (E) No change (D) Decrease to 1⁄16 If the radius of the artery decreased by 50% (1/2), then resistance would increase by 24, or 16 (R = 8nl/pie r4). Because blood flow is inversely proportional to resistance (Q = #P/R), flow will decrease to 1/16 of the original value. When a person moves from a supine position to a standing position, which of the following compensatory changes occurs? (A) Decreased heart rate (B) Increased contractility (C) Decreased total peripheral resistance (TPR) (D) Decreased cardiac output (E) Increased PR intervals (B) Increased contractility When a person moves to a standing position, blood pools in the leg veins, causing decreased venous return to the heart, decreased cardiac output, 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. At which site is systolic blood pressure the highest? (A) Aorta (B) Central vein (C) Pulmonary artery (D) Right atrium (E) Renal artery (F) Renal vein (E) Renal artery 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. 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 (A) sinoatrial (SA) node (B) atrioventricular (AV) node (C) bundle of His (D) Purkinje system (E) ventricular muscle (B) atrioventricular (AV) node 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. If the ejection fraction increases, there will be a decrease in (A) cardiac output (B) end-systolic volume (C) heart rate (D) pulse pressure (E) stroke volume (F) systolic pressure (B) end-systolic volume 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. An electrocardiogram (ECG) on a person shows ventricular extrasystoles. 6. The extrasystolic beat would produce (A) increased pulse pressure because contractility is increased (B) increased pulse pressure because heart rate is increased (C) decreased pulse pressure because ventricular filling time is increased (D) decreased pulse pressure because stroke volume is decreased (E) decreased pulse pressure because the PR interval is increased (D) decreased pulse pressure because stroke volume is decreased 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 An electrocardiogram (ECG) on a person shows ventricular extrasystoles. After an extrasystole, the next "normal" ventricular contraction produces (A) increased pulse pressure because the contractility of the ventricle is increased (B) increased pulse pressure because total peripheral resistance (TPR) is decreased (C) increased pulse pressure because compliance of the veins is decreased (D) decreased pulse pressure because the contractility of the ventricle is increased (E) decreased pulse pressure because TPR is decreased A) increased pulse pressure because the contractility of the ventricle is increased The postextrasystolic contraction produces increased pulse pressure because contractility is increased. Extra Ca2+ enters the cell during the extrasystolic beat. Contractility is directly related to the amount of intracellular Ca2+ available for binding to troponin C. An increase in contractility is demonstrated on a Frank-Starling diagram by (A) increased cardiac output for a given end diastolic volume (B) increased cardiac output for a given end systolic volume (C) decreased cardiac output for a given end-diastolic volume (D) decreased cardiac output for a given end-systolic volume (A) increased cardiac output for a given end diastolic volume 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. On the graph showing left ventricular volume and pressure, isovolumetric contraction occurs between points (A) 4 ' 1 (B) 1 ' 2 (C) 2 ' 3 (D) 3 ' 4 (B) 1 ' 2 Isovolumetric contraction occurs during ventricular systole, before the aortic valve opens. Ventricular pressure increases, but volume remains constant because blood cannot be ejected into the aorta against a closed valve. 10. The aortic valve closes at point (A) 1 (B) 2 (C) 3 (D) 4 (C) 3 Closure of the aortic valve occurs once ejection of blood from the ventricle has occurred and the left ventricular pressure has decreased to less than the aortic pressure. The first heart sound corresponds to point (A) 1 (B) 2 (C) 3 (D) 4 (A) 1 The first heart sound corresponds to closure of the atrial-ventricular valves. Before this closure occurs, the ventricle fills (phase 4 ' 1). After the valves close, isovolumetric contraction begins and ventricular pressure increases (phase 1 ' 2). If the heart rate is 70 beats/min, then the cardiac output of this ventricle is closest to (A) 3.45 L/min (B) 4.55 L/min (C) 5.25 L/min (D) 8.00 L/min (E) 9.85 L/min (C) 5.25 L/min Stroke volume is the volume ejected from the ventricle and is represented on the pressure-volume loop as phase 2 ' 3; end-diastolic volume is about 140 mL and end-systolic volume is about 65 mL; the difference, or stroke volume, is 75 mL. Cardiac output is calculated as stroke volume × heart rate or 75 mL × 70 beats /min = 5250 mL/min or 5.25 L/min. In a capillary, Pc is 30 mm Hg, Pi is −2 mm Hg, (pie)c is 25 mm Hg, and (pie)i is 2 mm Hg. What is the direction of fluid movement and the net driving force? (A) Absorption; 6 mm Hg (B) Absorption; 9 mm Hg (C) Filtration; 6 mm Hg (D) Filtration; 9 mm Hg (E) There is no net fluid movement (D) Filtration; 9 mm Hg Starling equation Net pressure = (Pc- Pi) - (pie c -pie i) (30-(-2) - (25-2) 32-23 =+9 Because the net pressure is positive, filtration out of the capillary will occur. In a capillary, Pc is 30 mm Hg, Pi is −2 mm Hg, (pie)c is 25 mm Hg, and (pie)i is 2 mm Hg. If Kf is 0.5 mL/min/mm Hg, what is the rate of water flow across the capillary wall? (A) 0.06 mL/min (B) 0.45 mL/min (C) 4.50 mL/min (D) 9.00 mL/min (E) 18.00 mL/min (C) 4.50 mL/min Water flow= Kf x Net pressure 0.5 x 9 = 4.50 The tendency for blood flow to be turbulent is increased by (A) increased viscosity (B) increased hematocrit (C) partial occlusion of a blood vessel (D) decreased velocity of blood flow (C) partial occlusion of a blood vessel Reynolds number is increased. viscosity the state of being thick, sticky Factors that increase the Reynolds number and produce turbulent flow are decreased viscosity (hematocrit) and increased velocity. (lower viscosity makes the fluid velocity higher.) Partial occlusion of a blood vessel increases the Reynolds number (and turbulence) because the decrease in cross-sectional area results in increased blood velocity (v = Q/A). A 66-year-old man, who has had a sympathectomy, experiences a greater than- normal fall in arterial pressure upon standing up. The explanation for this occurrence is (A) an exaggerated response of the renin- angiotensin-aldosterone system (B) a suppressed response of the renin- angiotensin-aldosterone system (C) an exaggerated response of the baroreceptor mechanism (D) a suppressed response of the baroreceptor mechanism (D) a suppressed response of the baroreceptor mechanism sympathectomy procedure to cut or block a nerve in the middle of your body. It's done to treat problems such as severe sweating (hyperhidrosis) and severe facial blushing. sympathectomy, the sympathetic component of the baroreceptor mechanism is absent. 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. The ventricles are completely depolarized during which isoelectric portion of the electrocardiogram (ECG)? (A) PR interval (B) QRS complex (C) QT interval (D) ST segment (E) T wave (D) ST segment 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. In which of the following situations is pulmonary blood flow greater than aortic blood flow? (A) Normal adult (B) Fetus (C) Left-to-right ventricular shunt (D) Right-to-left ventricular shunt (E) Right ventricular failure (F) Administration of a positive inotropic agent (C) Left-to-right ventricular shunt 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 The change indicated by the dashed lines on the cardiac output/venous return curves shows (dotted line up) (A) decreased cardiac output in the "new" steady state (B) decreased venous return in the "new" steady state (C) increased mean systemic pressure (D) decreased blood volume (E) increased myocardial contractility (C) increased mean systemic pressure The shift in the venous return curve to the right is consistent with an increase in blood volume and, as a consequence, mean systemic pressure. Both cardiac output and venous return are increased in the new steady state (and are equal to each other). Contractility is unaffected. A 30-year-old female patient's electrocardiogram (ECG) shows two P waves preceding each QRS complex. The interpretation of this pattern is (A) decreased firing rate of the pacemaker in the sinoatrial (SA) node (B) decreased firing rate of the pacemaker in the atrioventricular (AV) node (C) increased firing rate of the pacemaker in the SA node (D) decreased conduction through the AV node (E) increased conduction through the His- Purkinje system (D) decreased conduction through the AV node 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. An acute decrease in arterial blood pressure elicits which of the following compensatory changes? (A) Decreased firing rate of the carotid sinus nerve (B) Increased parasympathetic outflow to the heart (C) Decreased heart rate (D) Decreased contractility (E) Decreased mean systemic pressure (A) Decreased firing rate of the carotid sinus nerve 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). The tendency for edema to occur will be increased by (A) arteriolar constriction (B) increased venous pressure (C) increased plasma protein concentration (D) muscular activity (B) increased venous pressure 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 pie c. Arteriolar constriction would decrease Pc and decrease filtration. Dehydration would increase plasma protein concentration (by hemoconcentration) and thereby increase pie c and decrease filtration. Inspiration "splits" the second heart sound because (A) the aortic valve closes before the pulmonic valve (B) the pulmonic valve closes before the aortic valve (C) the mitral valve closes before the tricuspid valve (D) the tricuspid valve closes before the mitral valve (E) filling of the ventricles has fast and slow components (A) the aortic valve closes before the pulmonic valve Because the aortic valve closes before the pulmonic valve, the sound can be split by inspiration. During exercise, total peripheral resistance (TPR) decreases because of the effect of (A) the sympathetic nervous system on splanchnic arterioles (B) the parasympathetic nervous system on skeletal muscle arterioles (C) local metabolites on skeletal muscle arterioles (D) local metabolites on cerebral arterioles (E) histamine on skeletal muscle arterioles (C) local metabolites on skeletal muscle arterioles 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 Curve A in the figure represents (A) aortic pressure (B) ventricular pressure (C) atrial pressure (D) ventricular volume (A) aortic pressure The electrocardiogram (ECG) tracing serves as a reference. The QRS complex marks ventricular depolarization, followed immediately by ventricular contraction. Aortic pressure increases steeply after QRS, as blood is ejected from the ventricles. After reaching peak pressure, aortic pressure decreases as blood runs off into the arteries. The characteristic dicrotic notch ("blip" in the aortic pressure curve) appears when the aortic valve closes. Aortic pressure continues to decrease as blood flows out of the aorta. Curve B in the figure represents (A) left atrial pressure (B) ventricular pressure (C) atrial pressure (D) ventricular volume (D) ventricular volume Ventricular volume increases slightly with atrial systole (P wave), is constant during isovolumetric contraction (QRS), and then decreases dramatically after the QRS, when blood is ejected from the ventricle. An increase in arteriolar resistance, without a change in any other component of the cardiovascular system, will produce (A) a decrease in total peripheral resistance (TPR) (B) an increase in capillary filtration (C) an increase in arterial pressure (D) a decrease in afterload (C) an increase in arterial pressure An increase in arteriolar resistance will increase total peripheral resistance (TPR). Arterial pressure = cardiac output × TPR, so arterial pressure will also increase. Capillary filtration decreases when there is arteriolar constriction because Pc decreases. Afterload of the heart would be increased by an increase in TPR The following measurements were obtained in a male patient: Central venous pressure: 10 mm Hg Heart rate: 70 beats/min Systemic arterial [O2] = 0.24 mL O2/mL Mixed venous [O2] = 0.16 mL O2/mL Whole body O2 consumption: 500 mL/min What is this patient's cardiac output? (A) 1.65 L/min (B) 4.55 L/min (C) 5.00 L/min (D) 6.25 L/min (E) 8.00 L/min (D) 6.25 L/min Fick principle if whole body oxygen (O2) consumption and [O2] 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. Central venous pressure and heart rate are not needed for this calculation. CO= whole body 02 consumption / system arterial - mixed venous Which of the following is the result of an inward Na+ current? (A) Upstroke of the action potential in the sinoatrial (SA) node (B) Upstroke of the action potential in Purkinje fibers (C) Plateau of the action potential in ventricular muscle (D) Repolarization of the action potential in ventricular muscle (E) Repolarization of the action potential in the SA node (B) Upstroke of the action potential in Purkinje fibers 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 Ca2+ current. The plateau of the ventricular action potential is the result of a slow inward Ca2+ current. Repolarization in all cardiac tissues is the result of an outward K+ current. 30. The dashed line in the figure illustrates the effect of (A) increased total peripheral resistance (TPR) (B) increased blood volume C) increased contractility (D) a negative inotropic agent (E) increased mean systemic pressure C) increased contractility An upward shift of the cardiac output curve is consistent with an increase in myocardial contractility; for any right atrial pressure (sarcomere length), the force of contraction is increased. Such a change causes an increase in stroke volume and cardiac output. Increased blood volume and increased mean systemic pressure are related and would cause a rightward shift in the venous return curve. A negative inotropic agentmwould cause a decrease in contractility and a downward shift of the cardiac output curve. The x-axis in the figure (right atrial pressure) could have been labelled (A) end-systolic volume (B) end-diastolic volume (C) pulse pressure (D) mean systemic pressure (E) heart rate (B) end-diastolic volume End-diastolic volume and right atrial pressure are related and can be used interchangeably. The greatest pressure decrease in the circulation occurs across the arterioles because (A) they have the greatest surface area (B) they have the greatest cross-sectional area (C) the velocity of blood flow through them is the highest (D) the velocity of blood flow through them is the lowest (E) they have the greatest resistance (E) they have the greatest resistance The decrease in pressure at any level of the cardiovascular system is caused by the resistance of the blood vessels (delta P = Q × R). The greater the resistance is, the greater the decrease in pressure is. 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. Pulse pressure is (A) the highest pressure measured in the arteries (B) the lowest pressure measured in the arteries (C) measured only during diastole (D) determined by stroke volume (E) decreased when the capacitance of the arteries decreases (F) the difference between mean arterial pressure and central venous pressure (D) determined by stroke volume 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 In the sinoatrial (SA) node, phase 4 depolarization (pacemaker potential) is attributable to (A) an increase in K+ conductance (B) an increase in Na+ conductance (C) a decrease in Cl- conductance (D) a decrease in Ca2+ conductance (E) simultaneous increases in K+ and Cl- conductances (B) an increase in Na+ conductance 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. A healthy 35-year-old man is running a marathon. During the run, there is a increase in his splanchnic vascular resistance. Which receptor is responsible for the increased resistance? (A) alpha1 Receptors (B) beta 1 Receptors (C) beta 2 Receptors (D) Muscarinic receptors (A) alpha1 Receptors During exercise, the sympathetic nervous system is activated. The observed increase in splanchnic vascular resistance is due to sympathetic activation of alpha 1 receptors on splanchnic arterioles During which phase of the cardiac cycle is aortic pressure highest? (A) Atrial systole (B) Isovolumetric ventricular contraction (C) Rapid ventricular ejection (D) Reduced ventricular ejection (E) Isovolumetric ventricular relaxation (F) Rapid ventricular filling (G) Reduced ventricular filling (diastasis) (D) Reduced ventricular ejection 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 ventricular ejection phase. Myocardial contractility is best correlated with the intracellular concentration of (A) Na+ (B) K+ (C) Ca2+ (D) Cl- (E) Mg2+ (C) Ca2+ Contractility of myocardial cells depends on the intracellular [Ca2+], which is regulated by Ca2+ entry across the cell membrane during the plateau of thenaction potential and by Ca2+ uptake into and release from the sarcoplasmic reticulum (SR). Ca2+ binds to troponin C and removes the inhibition of actin-myosin interaction, allowing contraction (shortening) to occur Which of the following is an effect of histamine? (A) Decreased capillary filtration (B) Vasodilation of the arterioles (C) Vasodilation of the veins (D) Decreased Pc (E) Interaction with the muscarinic receptors on the blood vessels (B) Vasodilation of the arterioles 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). Carbon dioxide (CO2) regulates blood flow to which one of the following organs? (A) Heart (B) Skin (C) Brain (D) Skeletal muscle at rest (E) Skeletal muscle during exercise (C) Brain 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+ 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. Cardiac output of the right side of the heart is what percentage of the cardiac output of the left side of the heart? (A) 25% (B) 50% (C) 75% (D) 100% (E) 125% (D) 100% 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. The physiologic function of the relatively slow conduction through the atrioventricular (AV) node is to allow sufficient time for (A) runoff of blood from the aorta to the arteries (B) venous return to the atria (C) filling of the ventricles (D) contraction of the ventricles (E) repolarization of the ventricles (C) filling of the ventricles 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. Blood flow to which organ is controlled primarily by the sympathetic nervous system rather than by local metabolites? (A) Skin (B) Heart (C) Brain (D) Skeletal muscle during exercise (A) Skin 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. Which of the following parameters is decreased during moderate exercise? (A) Arteriovenous O2 difference (B) Heart rate (C) Cardiac output (D) Pulse pressure (E) Total peripheral resistance (TPR) (E) Total peripheral resistance (TPR) 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 O2, more O2 can be extracted and used by the contracting muscle. A 72-year-old woman, who is being treated with propranolol, finds that she cannot maintain her previous exercise routine. Her physician explains that the drug has reduced her cardiac output. Blockade of which receptor is responsible for the decrease in cardiac output? (A) alpha1 Receptors (B) beta1 Receptors (C) beta2 Receptors (D) Muscarinic receptors (E) Nicotinic receptors (B) beta1 Receptors Propranolol is an adrenergic antagonist that blocks both beta 1 and beta2 receptors. When propranolol is administered to reduce cardiac output, it inhibits beta 1 receptors in the sinoatrial (SA) node (heart rate) and in ventricular muscle (contractility During which phase of the cardiac cycle is ventricular volume lowest? (A) Atrial systole (B) Isovolumetric ventricular contraction (C) Rapid ventricular ejection (D) Reduced ventricular ejection (E) Isovolumetric ventricular relaxation (F) Rapid ventricular filling (G) Reduced ventricular filling (diastasis (E) Isovolumetric ventricular relaxation Which of the following changes will cause an increase in myocardial O2 consumption? (A) Decreased aortic pressure (B) Decreased heart rate (C) Decreased contractility (D) Increased size of the heart (E) Increased influx of Na+ during the upstroke of the action potential (D) Increased size of the heart Myocardial O2 consumption is determined by the amount of tension developed by the heart. It increases when there are increases in aortic pressure (increased afterload), when there is increased heart rate or stroke volume (which increases cardiac output), or when the size (radius) of the heart is increased (T = P × 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). Which of the following substances crosses capillary walls primarily through water-filled clefts between the endothelial cells? (A) O2 (B) CO2 (C) CO (D) Glucose (D) Glucose Because O2, 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 water-filled clefts, or pores, between the cells. 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 mterm-46m 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? (A) Decreased total peripheral resistance (B) Increased venoconstriction (C) Increased contractility (D) Increased afterload (E) Decreased venous return (E) Decreased venous return 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. 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? (A) Aldosterone-secreting tumor (B) Adrenal adenoma secreting aldosterone and cortisol (C) Pheochromocytoma (D) Left renal artery stenosis (E) Right renal artery stenosis (D) Left renal artery stenosis 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 (are tumor that usually starts in the cells of one of your adrenal glands) 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. During which phase of the ventricular action potential is the membrane potential closest to the K+ equilibrium potential? (A) Phase 0 (B) Phase 1 (C) Phase 2 (D) Phase 3 (E) Phase 4 (E) Phase 4 Phase 4 is the resting membrane potential. Because the conductance K+ is highest, the membrane potential approaches the equilibrium potential for K+. During which phase of the ventricular action potential is the conductance to Ca2+ highest? (A) Phase 0 (B) Phase 1 (C) Phase 2 (D) Phase 3 (E) Phase 4 (C) Phase 2 Phase 2 is the plateau of the ventricular action potential. During this phase, the conductance to Ca2+ increases transiently. Ca2+ that enters the cell during the plateau is the trigger that releases more Ca2+ from the sarcoplasmic reticulum (SR) for the contraction. Which phase of the ventricular action potential coincides with diastole? (A) Phase 0 (B) Phase 1 (C) Phase 2 (D) Phase 3 (E) Phase 4 (E) Phase 4 Phase 4 is electrical diastole Propranolol has which of the following effects? (A) Decreases heart rate (B) Increases left ventricular ejection fraction (C) Increases stroke volume (D) Decreases splanchnic vascular resistance (E) Decreases cutaneous vascular resistance (A) Decreases heart rate Propranolol, a beta adrenergic antagonist, blocks all sympathetic effects that are mediated by a beta 1 or beta 2 receptor. The sympathetic effect on the sinoatrial (SA) node is to increase heart rate via a beta1 receptor; therefore, propranolol decreases heart rate. Ejection fraction reflects ventricular contractility, which is another effect of beta 1 receptors; thus, propranolol decreases contractility, ejection fraction, and stroke volume. Splanchnic and cutaneous resistance are mediated by alpha 1 receptors Which receptor mediates slowing of the heart? (A) alpha 1 Receptors (B) beta 1 Receptors (C) beta 2 Receptors (D) Muscarinic receptors (D) Muscarinic receptors Acetylcholine (ACh) causes slowing of the heart via muscarinic receptors in the sinoatrial (SA) node Which of the following agents or changes has a negative inotropic effect on the heart? (A) Increased heart rate (B) Sympathetic stimulation (C) Norepinephrine (D) Acetylcholine (ACh) (E) Cardiac glycosides (D) Acetylcholine (ACh) 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 [Ca2+]. 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 Ca2+ by the sarcoplasmic reticulum (SR) [for later release]. Cardiac glycosides increase intracellular [Ca2+] by inhibiting the Na+-K+ pump, thereby inhibiting Na+-Ca2+ exchange (a mechanism that pumps Ca2+ out of the cell). The low-resistance pathways between myocardial cells that allow for the spread of action potentials are the (A) gap junctions (B) T tubules (C) sarcoplasmic reticulum (SR) (D) intercalated disks (E) mitochondria (A) gap junctions low-resistance sites of current spread Which agent is released or secreted after a hemorrhage and causes an increase in renal Na+ reabsorption? (A) Aldosterone (B) Angiotensin I (C) Angiotensinogen (D) Antidiuretic hormone (ADH) (E) Atrial natriuretic peptide A) Aldosterone Angiotensin I and aldosterone are increased in response to a decrease in renal perfusion pressure. Angiotensinogen is the precursor for angiotensin I. 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 wouldmnot be anticipated after blood loss. During which phase of the cardiac cycle does the mitral valve open? (A) Atrial systole (B) Isovolumetric ventricular contraction (C) Rapid ventricular ejection (D) Reduced ventricular ejection (E) Isovolumetric ventricular relaxation (F) Rapid ventricular filling (G) Reduced ventricular filling (diastasis) (E) Isovolumetric ventricular relaxation 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. A hospitalized patient has an ejection fraction of 0.4, a heart rate of 95 beats/min, and a cardiac output of 3.5 L/min. What is the patient's end-diastolic volume? (A) 14 mL (B) 37 mL (C) 55 mL (D) 92 mL (E) 140 mL (D) 92 mL First, calculate stroke volume from the cardiac output and heart rate: Cardiac output = stroke volume × heart rate; = 36.8 Then, calculate end-diastolic volume from stroke volume and ejection fraction: Ejection fraction = stroke volume/end-diastolic volume thus end-diastolic volume = stroke volume/ejection fraction = 36.8 mL/0.4 = 92 mL A scientist observes a myocyte beating in cell culture. Which step is the most direct necessary component of relaxation for this cell? A Influx of sodium ions B Efflux of potassium ions C Influx of calcium ions from the sacroplasmic reticulum D Influx of calcium ions from outside the myocyte E Efflux of calcium ions E Efflux of calcium ions Cardiac muscle relaxation occurs when intracellular Ca2+ levels return to baseline. Since Ca2+ enters the cytoplasm to trigger contraction, it must then leave the cytoplasm to return to baseline. After the myocyte is depolarized, L-type Ca2+ channels (long-acting, voltage gated, active in Phase 2 of the action potential) open to allow Ca2+ to enter the cell, which leads to calcium-induced-calcium-release (CICR) via the ryanodine receptor (ligand gated, active in Phase 2 as well), a phenomenon unique to cardiac myocytes (compared to skeletal muscle). Eventually, intracellular Ca2+ binds troponin, which allows actin and myosin to bind and contract. To relax, Ca2+ leaves the cytoplasm via several mechanisms: 1) the Na+/Ca2+ exchanger, which allows 1 Ca2+ to exit for every 3 Na+ that enter, 2) the Ca2+ ATP-ase pump in the cell membrane, which pumps Ca2+ out of the cell, and 3) the Ca2+ ATP-ase pump in the sarcoplasmic reticulum (SR) membrane, which pumps Ca2+ into the SR. Answers A and B incorrect because K+ actually must enter the myocyte and Na+ must leave it (via Na+/K+ ATPase) to establish the Na+ gradient that drives the Na+/Ca2+ exchanger. Answers C and D Ca2+ must enter the cell, first from outside the myocyte, and then from the SR (via CICR) for the cell to contract, but not to relax A scientist observes a myocyte beating in cell culture. Which step is the most direct necessary component of contraction for this cell? A Influx of sodium ions B Efflux of potassium ions C Influx of calcium ions from the sacroplasmic reticulum D Influx of calcium ions from outside the myocyte E Efflux of calcium ions D Influx of calcium ions from outside the myocyte Ca2+ must enter the cell, first from outside the myocyte, and then from the SR (via CICR) for the cell to contract A scientist is studying how electrical activity propagates across the heart. He isolates fibers from different areas of the heart with the following characteristics. A)Dysfunction leads to fixed PR intervals prior to a dropped beat; (B)Dysfunction leads to tachycardia with a dramatically widened QRS complex; (C)Dysfunction leads to increasing PR intervals prior to a dropped beat; (D) Dysfunction leads to tachycardia with a sawtooth pattern on electrocardiogram. Which of the following is the proper order of these tissues from fastest action potential propagation to slowest action potential propagation. A) A >D > B>C B) A >D > C>B C) B > C>D>A D) B > D > C>A A) A >D > B>C Purkinje fibers are the fastest Purkinje system, 2.4 m/s fixed PR intervals prior to a dropped beat atrial muscle 1.2 m/s, tachycardia with a sawtooth pattern venticular muscle, 0.4 m/s tachycardia with a dramatically widened QRS complex; AV Node, 0.05 m/s increasing PR intervals prior to a dropped beat A cardiologist measures action potential propagation velocity in various regions of the heart in a 24-year-old male. Which of the following set of measurements corresponds to the velocities found in the atrial muscle, AV Node, Purkinje system, and ventricular muscle, respectively? A) 2.4 m/s, 0.4 m/s, 0.05 m/s, 1.2 m/s B 1.2 m/s, 0.05 m/s, 2.4 m/s, 0.4 m/s С 0.5 m/s, 1.1 m/s, 2.2 m/s, 3 m/s D 0.4 m/s, 2.4 m/s, 0.05 m/s, 1.2 m/s E) 0.05 m/s, 1.2 m/s, 2.4 m/s, 3.3 m/s B 1.2 m/s, 0.05 m/s, 2.4 m/s, 0.4 m/s A 68-year-old woman presents to the emergency center with shortness of breath, light-headedness, and chest pain described as being like "an elephant sitting on her chest." She is diagnosed with a myocardial infarction. S he is given oxygen and an aspirin to chew and is not felt to be a candidate for thrombolytic therapy. Her heart rate is 40 beats per minute (bpm). Although there are P waves, they seem to be dissociated from the QRS complexes on the electrocardiograph (ECG). The patient is diagnosed with complete heart block, probably as a result of her myocardial infarction. The patient is taken to the intensive care unit for stabilization, and plans are made for pacemaker insertion. ◆ Where are the normal pacemaker and the backup pacemakers of the heart located? ◆ Why does this patient have a bradycardia? ◆ What parts of the heart have the fastest and slowest conduction velocities? ◆ Location of pacemakers: Normal, sinoatrial (SA) node; other pacemakers (in order of recruitment), atrioventricular (AV) node, bundle of His-Purkinje system ◆ Cause of bradycardia: If the AV node is injured by the infarction, both its ability to conduct and its ability to serve as a backup pacemaker may be lost, allowing a slow intrinsic pacemaker in the bundle of His or the Purkinje system to generate the ventricular heartbeat. ◆ Extreme conduction velocities: Fastest in the Purkinje system and slowest at the AV node.