McCance Ch. 31 Cardiac Practice Questions
Which statements are true concerning the method in which substances pass between capillaries and the interstitial fluid? (Select all that apply.) a. Substances pass through junctions between endothelial cells. b. Substances pass through pores or oval windows (fenestrations). c. Substances pass between vesicles by active transport across the endothelial cell membrane. d. Substances pass across the endothelial cell membrane by osmosis. e. Substances pass through endothelial cell membranes by diffusion.
Correct answer: a. Substances pass through junctions between endothelial cells. b. Substances pass through pores or oval windows (fenestrations). c. Substances pass between vesicles by active transport across the endothelial cell membrane. e. Substances pass through endothelial cell membranes by diffusion. Why it's correct: Substances can pass between capillaries and interstitial fluid in multiple ways: Through Junctions Between Endothelial Cells (A): Substances like ions and small solutes can pass through the junctions or gaps between endothelial cells, especially in the case of 'leaky' capillaries found in organs like the liver. Through Pores or Oval Windows (Fenestrations) (B): Some capillaries have fenestrations that allow the passage of small molecules and ions. These are especially prevalent in organs like the kidneys. In Vesicles Moved by Active Transport Across the Endothelial Cell Membrane (C): Endocytosis and exocytosis are processes that use energy to transport materials in vesicles across the endothelial cell membrane. By Diffusion Through the Endothelial Cell Membrane (E): Lipid-soluble substances can diffuse directly through the endothelial cell membrane. Why others are wrong: d. Substances pass across the endothelial cell membrane by osmosis: Osmosis refers specifically to the movement of water across a semipermeable membrane, driven by differences in solute concentration. While water does move across capillary walls, the statement is incorrect in the context of "substances" as it generalizes beyond water. Osmosis isn't the primary mechanism for the passage of most substances between capillaries and interstitial fluid.
Which intracardiac pressure is generated by the atrial contraction? a. A wave b. C wave c. Y descent d. X descent
Correct answer: A. A wave Why it's correct: The A wave is generated by atrial contraction and is seen on the atrial pressure curve. It represents the final push of blood into the ventricles before they contract (ventricular systole). Why others are wrong: b. C wave: The C wave occurs during early ventricular systole and represents a slight rise in atrial pressure as the tricuspid valve bulges back into the atrium. It's not generated by atrial contraction. c. Y descent: The Y descent is a downward deflection in atrial pressure that occurs during early ventricular diastole as the tricuspid valve opens and blood flows from the atrium into the ventricle. It's not associated with atrial contraction. d. X descent: The X descent is another downward deflection in atrial pressure that occurs during ventricular systole and early ventricular diastole. It does not represent atrial contraction.
What is the major effect of a calcium channel blocker such as verapamil on cardiac contractions? a. Increases the rate of cardiac contractions. b. Decreases the strength of cardiac contractions. c. Stabilizes the rhythm of cardiac contractions. d. Stabilizes the vasodilation during cardiac contractions.
Correct answer: B. Decreases the strength of cardiac contractions Why it's correct: Calcium channel blockers like verapamil inhibit the L-type calcium channels, thereby reducing the influx of calcium ions into the cardiac myocytes (muscle cells). Calcium is essential for muscle contraction, so blocking its entry weakens the force of cardiac contractions. Why others are wrong: a. Increases the rate of cardiac contractions: Calcium channel blockers usually have a negative chronotropic effect, meaning they decrease heart rate, rather than increase it. c. Stabilizes the rhythm of cardiac contractions: While some calcium channel blockers are used in arrhythmias, their primary effect is not to stabilize the rhythm but to decrease the strength and rate of cardiac contractions. d. Stabilizes the vasodilation during cardiac contractions: Calcium channel blockers do cause vasodilation, but this is not their major effect on cardiac contractions per se. Their primary action is to reduce the strength of cardiac contractions.
An early diastole peak caused by filling of the atrium from peripheral veins is identified by which intracardiac pressure? a. A wave b. V wave c. C wave d. X descent
Correct answer: B. V wave Why it's correct: The V wave represents the phase where the atria are filling from peripheral veins. This occurs during early diastole and results in a peak in atrial pressure, which is represented by the V wave on an atrial pressure curve. Why others are wrong: a. A wave: The A wave is associated with atrial contraction and is therefore not related to the filling of the atrium from peripheral veins during early diastole. c. C wave: The C wave occurs during early ventricular systole and represents the slight rise in atrial pressure as the tricuspid valve bulges into the atrium. It's not related to early diastolic filling. d. X descent: The X descent is a downward deflection in atrial pressure that occurs during ventricular systole and early ventricular diastole. It does not represent the filling of the atrium from peripheral veins.
Which function of the cardiovascular system is often affected by ischemia? a. Cardiac output (CO) b. Stroke volume (SV) c. Heart rate (HR) d. Cardiac index (CI)
Correct answer: C. Heart rate (HR) Why it's correct: Ischemia, which refers to insufficient blood flow to a part of the body, often affects the heart rate (HR) because the myocardium (heart muscle) is sensitive to changes in oxygen supply. Reduced oxygen supply, as happens during ischemia, can result in alterations in the heart's electrical conduction system, leading to various arrhythmias and fluctuations in heart rate. The sympathetic nervous system may also be activated in response to the stress of ischemia, which can further elevate the heart rate. Why others are wrong: a. Cardiac output (CO): Cardiac output is the product of stroke volume (SV) and heart rate (HR). Although ischemia can indirectly affect cardiac output, it does so through alterations in heart rate or contractility. However, cardiac output is not the most directly affected parameter in ischemia; rather, it's the heart rate that's more directly affected. b. Stroke volume (SV): Stroke volume refers to the amount of blood ejected by the left ventricle with each contraction. While it's true that prolonged ischemia can affect contractility and thereby influence stroke volume, the more immediate and often-noted effect of ischemia is on the heart rate. d. Cardiac index (CI): Cardiac index is cardiac output adjusted for body surface area. While this is an important measure of cardiovascular function, it is not the most direct function affected by ischemia. CI could be affected indirectly through changes in HR and CO, but again, HR is the most directly affected parameter.
What physical sign is the result of turbulent blood flow through a vessel? a. Increased blood pressure during periods of stress b. Bounding pulse felt on palpation c. Cyanosis observed on excretion d. Murmur heard on auscultation
Correct answer: D. Murmur heard on auscultation Why it's correct: Turbulent blood flow results in an audible sound known as a murmur. Murmurs are most commonly detected during auscultation of the heart or blood vessels. The turbulence is often caused by a narrowing or obstruction in a blood vessel, or by abnormal anatomy of the heart itself, such as valve defects. Why others are wrong: a. Increased blood pressure during periods of stress: While stress can result in increased blood pressure, it is not a direct indicator of turbulent blood flow. Increased blood pressure has numerous other causes and is not specific to turbulence. b. Bounding pulse felt on palpation: A bounding pulse can be indicative of a variety of cardiovascular conditions, such as increased stroke volume or hyperkinetic states. However, it is not a specific sign of turbulent blood flow in a vessel. c. Cyanosis observed on excretion: Cyanosis refers to bluish discoloration of the skin due to inadequate oxygenation and has nothing to do with turbulent blood flow in a vessel.
Which intracardiac pressure is produced because of the descent of the tricuspid valve ring and by the ejection of blood from both ventricles? a. V wave b. C wave c. Y descent d. X descent
Correct answer: D. X descent Why it's correct: The X descent is a feature observed on atrial pressure curves and is produced during ventricular systole and early diastole. As both ventricles contract to eject blood, the tricuspid valve ring moves downwards into the ventricles, leading to a decrease in atrial pressure. This event is represented by the X descent on an atrial pressure curve. The downward movement of the tricuspid valve ring and ejection of blood from both ventricles contribute to this characteristic pressure change. Why others are wrong: a. V wave: The V wave is related to venous return into the atrium and occurs in early diastole. It does not represent the descent of the tricuspid valve ring or the ejection of blood from the ventricles. b. C wave: The C wave occurs during early ventricular systole and represents the tricuspid valve briefly bulging into the right atrium. While it does involve ventricular action and the tricuspid valve, it doesn't specifically represent the descent of the tricuspid valve ring or the ejection of blood from both ventricles. c. Y descent: The Y descent occurs during early ventricular diastole and represents the rapid emptying of the atrium into the ventricle as the tricuspid valve opens. It's not generated by the descent of the tricuspid valve ring nor by the ejection of blood from both ventricles.
Reflex control of total cardiac output and total peripheral resistance is controlled by what mechanism? a. Parasympathetic stimulation of the heart, arterioles, and veins b. Sympathetic stimulation of the heart, arterioles, and veins c. Autonomic control of the heart only d. Somatic control of the heart, arterioles, and veins
Correct answer: b. Sympathetic stimulation of the heart, arterioles, and veins Why it's correct: The autonomic nervous system (ANS) plays a pivotal role in controlling the heart rate, cardiac output, and the diameter of blood vessels. The sympathetic nervous system, a division of the ANS, acts to increase heart rate, strengthen the force of cardiac contractions, and constrict blood vessels, thereby increasing blood pressure and redistributing blood flow to essential organs during times of stress or increased activity. When the sympathetic nervous system stimulates the heart, it releases norepinephrine, which binds to beta-adrenergic receptors in the heart, leading to increased heart rate and contractility. Additionally, the sympathetic nervous system also stimulates the arterioles and veins, leading to vasoconstriction. This vasoconstriction increases peripheral resistance, which in turn increases blood pressure. The overall effect of sympathetic stimulation is to increase cardiac output and total peripheral resistance, ensuring that vital organs receive an adequate blood supply during times of increased demand. Why others are wrong: a. Parasympathetic stimulation of the heart, arterioles, and veins: The parasympathetic nervous system, another division of the ANS, primarily serves to slow down the heart rate and decrease the force of cardiac contractions. It achieves this by releasing acetylcholine, which binds to muscarinic receptors in the heart. However, the parasympathetic nervous system has minimal direct effect on arterioles and veins. Its main function in the cardiovascular system is to counterbalance the actions of the sympathetic nervous system, returning the body to a resting state after a stressor is removed. c. Autonomic control of the heart only: While the autonomic nervous system does control the heart, it also plays a significant role in controlling the diameter of arterioles and veins. As mentioned earlier, sympathetic stimulation causes vasoconstriction of these vessels, while the parasympathetic system has minimal direct effects on them. Hence, saying that the ANS controls only the heart is incomplete and doesn't capture the full scope of its effects on the cardiovascular system. d. Somatic
Match the description with the corresponding terms. _____ A. Relationship among blood flow, pressure, and resistance _____ B. Increased heart rate from increased volume _____ C. Relationship of wall tension, intraventricular pressure, internal radius, and wall thickness _____ D. Cycles of attachment, movement, and dissociation of thin filaments during the attachments of actin to myosin _____ E. Length-tension relationship of cardiac muscle Poiseuille law
ANS: A Poiseuille law for resistance to fluid flow through a tube takes into account the length of the tube, the viscosity of the fluid, and the radius of the tube's lumen.
Match the description with the corresponding terms. _____ A. Relationship among blood flow, pressure, and resistance _____ B. Increased heart rate from increased volume _____ C. Relationship of wall tension, intraventricular pressure, internal radius, and wall thickness _____ D. Cycles of attachment, movement, and dissociation of thin filaments during the attachments of actin to myosin _____ E. Length-tension relationship of cardiac muscle Bainbridge reflex
ANS: B The Bainbridge reflex causes changes in the heart rate after intravenous infusions of blood or other fluid.
Match the description with the corresponding terms. _____ A. Relationship among blood flow, pressure, and resistance _____ B. Increased heart rate from increased volume _____ C. Relationship of wall tension, intraventricular pressure, internal radius, and wall thickness _____ D. Cycles of attachment, movement, and dissociation of thin filaments during the attachments of actin to myosin _____ E. Length-tension relationship of cardiac muscle Laplace's law
ANS: C In Laplace's law, wall tension is directly related to the product of intraventricular pressure and internal radius and inversely to the wall thickness.
Match the description with the corresponding terms. _____ A. Relationship among blood flow, pressure, and resistance _____ B. Increased heart rate from increased volume _____ C. Relationship of wall tension, intraventricular pressure, internal radius, and wall thickness _____ D. Cycles of attachment, movement, and dissociation of thin filaments during the attachments of actin to myosin _____ E. Length-tension relationship of cardiac muscle Cross-bridge theory
ANS: D With the attachment of actin to myosin at the cross-bridge, the myosin head molecule undergoes a position change, exerting traction on the rest of the myosin bridge, causing the thin filaments to slide past the thick filaments. During contraction, each cross-bridge undergoes cycles of attachment, movement, and dissociation from the thin filaments.
Match the description with the corresponding terms. _____ A. Relationship among blood flow, pressure, and resistance _____ B. Increased heart rate from increased volume _____ C. Relationship of wall tension, intraventricular pressure, internal radius, and wall thickness _____ D. Cycles of attachment, movement, and dissociation of thin filaments during the attachments of actin to myosin _____ E. Length-tension relationship of cardiac muscle Frank-Starling law
ANS: E The Frank-Starling law states that the cardiac muscle, like other muscles, increases its strength of contraction when it is stretched.
What is the ratio of coronary capillaries to cardiac muscle cells? a. 1:1 (one capillary per one muscle cell) 1:2 (one capillary per two muscle cells) 1:4 (one capillary per four muscle cells) 1:10 (one capillary per ten muscle cells)
Correct Answer: a. 1:1 (one capillary per one muscle cell) Why it's correct: The heart has an extraordinarily high metabolic demand and thus requires a very efficient and extensive capillary network for nutrient and oxygen exchange. The 1:1 ratio of capillaries to cardiac muscle cells is indicative of this need. Why others are wrong: 1:2 (one capillary per two muscle cells): A ratio less than 1:1 would indicate a less-than-optimal nutrient and oxygen supply, insufficient for the heart's high metabolic demand. 1:4 (one capillary per four muscle cells): Again, such a ratio would be insufficient to meet the metabolic needs of the cardiac muscle cells. 1:10 (one capillary per ten muscle cells): This ratio would be vastly insufficient to meet the metabolic demands of cardiac muscle cells.
What is an expected change in the cardiovascular system that occurs with aging? a. Arterial stiffening b. Decreased left ventricular wall tension c. Decreased aortic wall thickness d. Arteriosclerosis
Correct Answer: a. Arterial stiffening Why it's correct: Arterial stiffening is a well-documented change that occurs with aging. This phenomenon is due to a variety of factors including changes in collagen and elastin content in arterial walls, as well as increased wall thickness. This results in a decreased ability for arteries to expand and contract efficiently, contributing to elevated systolic blood pressure levels and increased cardiac workload. Why others are wrong: b. Decreased left ventricular wall tension: Aging is more likely to result in increased ventricular wall tension due to factors like hypertrophy and increased afterload, not a decrease. c. Decreased aortic wall thickness: In general, arterial walls, including the aorta, tend to thicken and not thin with age. d. Arteriosclerosis: Although arteriosclerosis is often seen in older individuals, it is not an inevitable consequence of aging itself but is more related to other factors like diet, exercise, and genetic predisposition.
The Bainbridge reflex is thought to be initiated by sensory neurons in which cardiac location? a. Atria b. Aorta c. Sinoatrial (SA) node d. Ventricles
Correct Answer: a. Atria Why it's correct: The Bainbridge reflex is initiated by stretch receptors in the atria. These receptors sense an increase in atrial pressure, which usually occurs when there is increased venous return. This reflex is mediated by the vagus nerve and serves to increase heart rate to match the increased volume, thereby helping to prevent atrial and pulmonary congestion. Why others are wrong: b. Aorta: The aorta is not the location of the stretch receptors involved in the Bainbridge reflex. c. Sinoatrial (SA) node: The SA node is the primary pacemaker of the heart but is not the site of stretch receptors that initiate the Bainbridge reflex. d. Ventricles: The ventricles do have some stretch receptors, but they are not involved in the Bainbridge reflex.
Within a physiologic range, what does an increase in left ventricular end-diastolic volume (preload) result in? a. Increase in force of contraction b. Decrease in refractory time c. Increase in afterload d. Decrease in repolarization
Correct Answer: a. Increase in force of contraction Why it's correct: This phenomenon is explained by the Frank-Starling law, which states that an increase in the end-diastolic volume, or preload, results in increased force of contraction during the next cardiac cycle. Essentially, as the myocardial fibers are stretched due to higher volumes of blood, they produce a more forceful contraction to expel that blood. This helps to maintain cardiac output in a variety of physiological conditions. Why others are wrong: b. Decrease in refractory time: Refractory time is related to the responsiveness of cardiac cells to a second stimulus. Preload does not affect the refractory period of cardiac cells. c. Increase in afterload: Afterload refers to the resistance the heart has to overcome to eject blood. It is not directly affected by preload, although a sustained increase in preload could indirectly affect afterload through various compensatory mechanisms. d. Decrease in repolarization: Preload does not affect the repolarization phase of the cardiac action potential, which is a cellular electrical event.
Occlusion of the left anterior descending artery during a myocardial infarction would interrupt blood supply to which structures? a. Left and right ventricles and much of the interventricular septum b. Left atrium and the lateral wall of the left ventricle c. Upper right ventricle, right marginal branch, and right ventricle to the apex d. Posterior interventricular sulcus and the smaller branches of both ventricles
Correct Answer: a. Left and right ventricles and much of the interventricular septum Why it's correct: The left anterior descending (LAD) artery is a major coronary artery that supplies a significant portion of the myocardium. Blockage here affects both ventricles and the interventricular septum, potentially leading to significant loss of cardiac function. Why others are wrong: b. Left atrium and the lateral wall of the left ventricle: The left atrium is typically not supplied by the LAD, and while the LAD does supply part of the left ventricle, it doesn't limit itself to just the lateral wall. c. Upper right ventricle, right marginal branch, and right ventricle to the apex: These areas are generally supplied by the right coronary artery, not the LAD. d. Posterior interventricular sulcus and the smaller branches of both ventricles: This is typically the domain of the posterior descending artery, not the LAD.
What period follows depolarization of the myocardium and represents a period during which no new cardiac potential can be propagated? a. Refractory b. Hyperpolarization c. Threshold d. Sinoatrial (SA)
Correct Answer: a. Refractory Why it's correct: Following depolarization, the myocardium enters a refractory period, during which it is unable to respond to further stimulation. This is crucial for allowing the cardiac muscle cells sufficient time to reset their ion channels in preparation for the next action potential. The refractory period also prevents the occurrence of tetanic contractions in the heart, which would be fatal. Why others are wrong: b. Hyperpolarization: This term refers to a state where the membrane potential becomes more negative than the resting potential, and it is not what follows depolarization in myocardial cells. c. Threshold: This refers to the membrane potential at which an action potential is initiated, not the period that follows depolarization. d. Sinoatrial (SA): This refers to the SA node, not a period following myocardial depolarization.
The coronary sinus empties into which cardiac structure? a. Right atrium b. Left atrium c. Superior vena cava d. Aorta
Correct Answer: a. Right atrium Why it's correct: The coronary sinus is a venous structure that collects deoxygenated blood from the myocardium and empties it into the right atrium. This allows for the recirculation of blood back to the lungs for reoxygenation. Why others are wrong: b. Left atrium: The coronary sinus does not empty into the left atrium; it specifically drains into the right atrium. c. Superior vena cava: This vessel also empties into the right atrium but is not where the coronary sinus drains. d. Aorta: The coronary sinus is a venous structure and therefore does not empty into the arterial system, represented by the aorta.
Which cardiac chamber has the thinnest wall and why? a. The right and left atria; they are low-pressure chambers that serve as storage units and conduits for blood. b. The right and left atria; they are not directly involved in the preload, contractility, or afterload of the heart. c. The left ventricle; the mean pressure of blood coming into this ventricle is from the lung, which has a low pressure. d. The right ventricle; it pumps blood into the pulmonary capillaries, which have a lower pressure compared with the systemic circulation.
Correct Answer: a. The right and left atria; they are low-pressure chambers that serve as storage units and conduits for blood. Why it's correct: The atria are indeed the chambers with the thinnest walls because they don't need to generate much pressure. They simply receive blood from the veins and push it into the ventricles. Because they function in this low-pressure system, there's no need for thick muscular walls. Why others are wrong: b. The right and left atria; they are not directly involved in the preload, contractility, or afterload of the heart: While it's true that atria are not directly involved in these factors, the primary reason they have thin walls is their role as low-pressure chambers, not this reason. c. The left ventricle; the mean pressure of blood coming into this ventricle is from the lung, which has a low pressure: This is incorrect because the left ventricle actually has the thickest wall to pump blood into the systemic circulation, which requires high pressure. d. The right ventricle; it pumps blood into the pulmonary capillaries, which have a lower pressure compared with the systemic circulation: Although the right ventricle does operate under lower pressure than the left ventricle, its wall is thicker than that of the atria.
If the sinoatrial (SA) node fails, then at what rate (depolarizations per minute) can the atrioventricular (AV) node depolarize? a. 60 to 70 b. 40 to 60 c. 30 to 40 d. 10 to 20
Correct Answer: b. 40 to 60 Why it's correct: If the SA node fails, the AV node can serve as a backup pacemaker for the heart, typically at a rate of 40 to 60 beats per minute. This is slower than the typical SA node rate but sufficient to maintain some level of cardiac output. Why others are wrong: a. 60 to 70: This rate is more typical of the SA node when it is functioning normally, not the AV node. c. 30 to 40: While some secondary pacemaker cells can fire at this rate, it is slower than the typical rate for the AV node. d. 10 to 20: This rate would be dangerously slow and is not characteristic of the AV node.
Pressure in the left ventricle must exceed pressure in which structure before the left ventricle can eject blood? a. Superior vena cava b. Aorta c. Inferior vena cava d. Pulmonary veins
Correct Answer: b. Aorta Why it's correct: For blood to be ejected from the left ventricle into the systemic circulation, the intraventricular pressure must exceed the pressure in the aorta, which is the immediate outlet for the ventricular blood. This is a fundamental principle governing the mechanics of ventricular ejection. Why others are wrong: a. Superior vena cava: This is not relevant to left ventricular ejection as it is a structure that returns deoxygenated blood to the right atrium. c. Inferior vena cava: Similar to the superior vena cava, this structure is not related to left ventricular ejection. d. Pulmonary veins: These bring oxygenated blood into the left atrium, not the left ventricle. The left ventricle does not have to overcome pressure in the pulmonary veins to eject blood.
What can shorten the conduction time of action potential through the atrioventricular (AV) node? a. Parasympathetic nervous system b. Catecholamines c. Vagal stimulation d. Sinoatrial node (SA)
Correct Answer: b. Catecholamines Why it's correct: Catecholamines, such as epinephrine and norepinephrine, increase heart rate and shorten the conduction time through the AV node. They do so by binding to β-adrenergic receptors, leading to a cascade of intracellular events that result in increased calcium ion influx. This accelerates the pace at which the AV node depolarizes, consequently quickening the electrical conduction through it. Why others are wrong: a. Parasympathetic nervous system: Activation of the parasympathetic system, primarily via the vagus nerve, would actually slow down conduction through the AV node, not speed it up. c. Vagal stimulation: Vagal stimulation is a function of the parasympathetic nervous system and, like in answer "a," would slow down conduction, not speed it up. d. Sinoatrial node (SA): The SA node sets the pace for the heart but doesn't directly influence the speed of conduction through the AV node.
What is the process that ensures mitral and tricuspid valve closure after the ventricles are filled with blood? a. Chordae tendineae relax, which allows the valves to close. b. Increased pressure in the ventricles pushes the valves to close. c. Trabeculae carneae contract, which pulls the valves closed. d. Reduced pressure in the atria creates a negative pressure that pulls the valves closed.
Correct Answer: b. Increased pressure in the ventricles pushes the valves to close. Why it's correct: As the ventricles contract, the pressure within them rises, forcing the atrioventricular valves (mitral and tricuspid) to close. This prevents backflow of blood into the atria. Why others are wrong: a. Chordae tendineae relax, which allows the valves to close: The chordae tendineae actually maintain tension and prevent the valves from prolapsing; they don't relax to close the valves. c. Trabeculae carneae contract, which pulls the valves closed: Trabeculae carneae are muscular ridges inside the ventricles but they don't directly pull the valves closed. d. Reduced pressure in the atria creates a negative pressure that pulls the valves closed: This isn't what causes the valves to close. It's the increased pressure in the ventricles that pushes them closed.
What enables electrical impulses to travel in a continuous cell-to-cell fashion in myocardial cells? a. Sarcolemma sclerotic plaques b. Intercalated disks c. Trabeculae carneae d. Bachmann bundles
Correct Answer: b. Intercalated disks Why it's correct: Intercalated disks are specialized structures found in the myocardium that provide a strong mechanical and electrical coupling between adjacent myocardial cells. These disks contain gap junctions that allow for rapid ion exchange and communication between cells. This enables electrical impulses to propagate in a fast and coordinated fashion across the heart muscle, allowing for synchronous contraction of the ventricles or atria. They are essential for the functioning of the heart as a functional syncytium where cells work as a unified tissue. Why others are wrong: a. Sarcolemma sclerotic plaques: Sarcolemma refers to the cell membrane of a muscle cell, and sclerotic plaques are related to atherosclerotic processes. Neither of these structures play a role in the continuous, cell-to-cell electrical communication in myocardial cells. c. Trabeculae carneae: These are muscular columns and bands inside the ventricles of the heart. They are involved in the structural aspect of the ventricles and do not specifically enable cell-to-cell electrical propagation. d. Bachmann bundles: These are specialized fibers that facilitate electrical communication between the right and left atria, but they do not play a direct role in cell-to-cell electrical impulse propagation within myocardial cells.
Which statement does not accurately describe the pericardium? a. The pericardium is a double-walled membranous sac that encloses the heart. b. It is made up of connective tissue and a surface layer of squamous cells. c. The pericardium protects the heart against infection and inflammation from the lungs and pleural space. d. It contains pain and mechanoreceptors that can elicit reflex changes in blood pressure and heart rate.
Correct Answer: b. It is made up of connective tissue and a surface layer of squamous cells. Why it's correct: The pericardium is actually made up of a fibrous layer and a serous layer, which itself is divided into the parietal and visceral layers. The serous layer is made of mesothelial cells, not squamous cells. While there is connective tissue involved, describing it as having a "surface layer of squamous cells" is incorrect. Why others are wrong: a. The pericardium is a double-walled membranous sac that encloses the heart: This statement is accurate. The pericardium does consist of two layers: the fibrous pericardium and the serous pericardium. c. The pericardium protects the heart against infection and inflammation from the lungs and pleural space: This statement is also accurate. The pericardium serves as a physical barrier that isolates the heart from potential pathogens and inflammatory processes originating from adjacent structures like the lungs and pleural space. d. It contains pain and mechanoreceptors that can elicit reflex changes in blood pressure and heart rate: This is also true. The pericardium has sensory innervation that can affect cardiovascular function.
The resting heart rate in a healthy person is primarily under the control of which nervous system? a. Sympathetic b. Parasympathetic c. Somatic d. Spinal
Correct Answer: b. Parasympathetic Why it's correct:The parasympathetic nervous system, through the vagus nerve, exerts a dominant influence on the heart rate at rest. The neurotransmitter involved is acetylcholine, which acts on muscarinic receptors in the heart to decrease heart rate. This is the "rest and digest" system that predominates in conditions of rest and calm. Why others are wrong: a. Sympathetic: The sympathetic nervous system increases heart rate and contractility but is not the dominant controller at rest. It kicks in during stress or exercise ("fight or flight"). c. Somatic: The somatic nervous system controls voluntary muscles and has no direct role in controlling heart rate. d. Spinal: Spinal nerves are part of the central nervous system and don't directly control heart rate. They are more involved in reflex arcs and transmitting signals to and from the peripheral nervous system.
Oxygenated blood flows through which vessel? a. Superior vena cava b. Pulmonary veins c. Pulmonary artery d. Coronary veins
Correct Answer: b. Pulmonary veins Why it's correct: Pulmonary veins carry oxygenated blood from the lungs back to the left atrium of the heart. This is unique, as veins typically carry deoxygenated blood. Why others are wrong: a. Superior vena cava: This vein carries deoxygenated blood from the upper part of the body to the right atrium. c. Pulmonary artery: Despite the name, this vessel carries deoxygenated blood from the right ventricle to the lungs for oxygenation. d. Coronary veins: These carry deoxygenated blood from the myocardium back into the coronary sinus, which empties into the right atrium.
Which complex (wave) represents the sum of all ventricular muscle cell depolarizations? a. PRS b. QRS c. QT interval d. P
Correct Answer: b. QRS Why it's correct: The QRS complex on an electrocardiogram (ECG) represents the sum of all ventricular muscle cell depolarizations. This is the electrical event that leads to the mechanical contraction of the ventricles and subsequent ejection of blood into the pulmonary artery and aorta. It is a quick and coordinated event that involves the entire ventricular myocardium. Why others are wrong: a. PRS: This is not a standard complex or wave recognized in the field of cardiology or electrocardiography. The PR segment is separate from the QRS complex, and the S wave is part of the QRS complex. c. QT interval: The QT interval includes not just ventricular depolarization but also repolarization (QRS and T wave). Therefore, it does not solely represent the sum of all ventricular muscle cell depolarizations. d. P: The P wave represents atrial depolarization and has nothing to do with ventricular depolarization.
What causes depolarization of a cardiac muscle cell to occur? a. Decrease in the permeability of the cell membrane to potassium b. Rapid movement of sodium into the cell c. Decrease in the movement of sodium out of the cell d. Rapid movement of calcium out of the cell
Correct Answer: b. Rapid movement of sodium into the cell Why it's correct: Depolarization of cardiac muscle cells, like many other excitable cells, is caused by the rapid influx of sodium ions into the cell. This changes the cell's membrane potential and leads to an action potential that triggers muscle contraction. Why others are wrong: a. Decrease in the permeability of the cell membrane to potassium: Decreasing potassium permeability would actually make the cell less likely to depolarize. c. Decrease in the movement of sodium out of the cell: Decreasing sodium efflux alone wouldn't cause depolarization; it's the rapid influx of sodium that does. d. Rapid movement of calcium out of the cell: Moving calcium out of the cell would not contribute to depolarization; it's the inward movement of sodium ions that does.
Regarding the heart's valves, what is a function of the papillary muscles? a. The papillary muscles close the semilunar valve. b. These muscles prevent backward expulsion of the atrioventricular valve. c. They close the atrioventricular valve. d. The papillary muscles open the semilunar valve.
Correct Answer: b. These muscles prevent backward expulsion of the atrioventricular valve. Why it's correct: Papillary muscles are attached to the chordae tendineae and atrioventricular valves. When the ventricles contract, these muscles also contract, pulling on the chordae tendineae to prevent the valves from inverting or prolapsing into the atria, thus preventing regurgitation of blood. Why others are wrong: a. The papillary muscles close the semilunar valve: The semilunar valves (pulmonary and aortic valves) are not connected to papillary muscles. c. They close the atrioventricular valve: Papillary muscles do not actively close these valves; they prevent them from opening in the wrong direction. d. The papillary muscles open the semilunar valve: Again, the semilunar valves are not connected to papillary muscles. They open and close passively due to pressure changes.
As stated in the Frank-Starling law, a direct relationship exists between the _____ of the blood in the heart at the end of diastole and the _____ of contraction during the next systole. a. Pressure; force b. Volume; strength c. Viscosity; force d. Viscosity; strength
Correct Answer: b. Volume; strength Why it's correct: The Frank-Starling law directly correlates the volume of blood present in the heart at the end of diastole to the strength of the contraction in the subsequent systole. The greater the volume, the stronger the contraction, all else being equal. Why others are wrong: a. Pressure; force: While it may seem related, the Frank-Starling law specifically talks about volume, not pressure. Pressure is a result of volume and other factors like wall tension and compliance. c. Viscosity; force: Viscosity of the blood is not directly related to the strength of contraction. It's more related to the rheological properties of the blood and doesn't determine myocardial contractility. d. Viscosity; strength: Again, viscosity does not determine the strength of myocardial contraction and is not part of the Frank-Starling relationship.
What is the most important negative inotropic agent? a. Norepinephrine b. Epinephrine c. Acetylcholine d. Dopamine
Correct Answer: c. Acetylcholine Why it's correct: Inotropic agents are substances that affect myocardial contractility. A negative inotropic agent decreases the force of cardiac muscle contraction. Acetylcholine, which is released from the vagus nerve, is a principal neurotransmitter that exerts negative inotropic effects on the heart by binding to muscarinic receptors, primarily M2 receptors, on cardiac myocytes. This activation leads to hyperpolarization and a decreased rate of spontaneous action potential generation at the sinoatrial (SA) node, thereby lowering heart rate and reducing force of contraction. Why others are wrong: a. Norepinephrine: Norepinephrine is actually a positive inotropic agent. It is released by sympathetic nerve endings and binds to beta-1 adrenergic receptors on cardiac myocytes. This results in increased intracellular calcium concentrations, enhancing the force of cardiac muscle contraction. b. Epinephrine: Like norepinephrine, epinephrine is a positive inotropic agent. It is released from the adrenal medulla and also stimulates beta-1 adrenergic receptors, leading to increased cardiac contractility. d. Dopamine: Dopamine is another positive inotropic agent. It is often used in clinical settings to improve hemodynamic parameters, including cardiac output. Dopamine activates dopaminergic and beta-1 adrenergic receptors, leading to increased contractility.
In the normal electrocardiogram, what does the PR interval represent? a. Atrial depolarization b. Ventricular depolarization c. Atrial activation to onset of ventricular activity d. Electrical systole of the ventricles
Correct Answer: c. Atrial activation to onset of ventricular activity Why it's correct: The PR interval on an ECG represents the time it takes for an electrical impulse to travel from the onset of atrial activation (P wave) to the onset of ventricular activation (QRS complex). It encompasses atrial depolarization as well as the conduction delay that occurs at the AV node, allowing time for ventricular filling. Why others are wrong: a. Atrial depolarization: This is represented only by the P wave and not the entire PR interval. b. Ventricular depolarization: This is actually represented by the QRS complex, not the PR interval. d. Electrical systole of the ventricles: This would relate more to the QRS complex and the ST segment, not the PR interval.
Where is the major cardiovascular center in the central nervous system? a. Frontal lobe b. Thalamus c. Brainstem d. Hypothalamus
Correct Answer: c. Brainstem Why it's correct: The major cardiovascular control center is located in the medulla oblongata within the brainstem. It receives and integrates sensory inputs related to blood pressure, blood volume, and other factors, and sends autonomic signals to regulate heart rate, contractility, and blood vessel tone. Why others are wrong: a. Frontal lobe: The frontal lobe is primarily associated with higher cognitive functions like decision-making and planning, not with autonomic control of cardiovascular function. b. Thalamus: The thalamus is an important relay station for sensory and motor signals but does not house the major cardiovascular control center. d. Hypothalamus: While the hypothalamus does play a role in autonomic control and interacts with the medulla, it is not the primary cardiovascular control center.
After the baroreceptor reflex is stimulated, the resulting impulse is transmitted from the carotid artery by which sequence of events? a. Vagus nerve to the medulla to increase parasympathetic activity and to decrease sympathetic activity b. Glossopharyngeal cranial nerve through the vagus nerve to the medulla to increase sympathetic activity and to decrease parasympathetic c. Glossopharyngeal cranial nerve through the vagus nerve to the medulla to increase parasympathetic activity and to decrease sympathetic activity d. Glossopharyngeal cranial nerve through the vagus nerve to the hypothalamus to increase parasympathetic activity and to decrease sympathetic activity
Correct Answer: c. Glossopharyngeal cranial nerve through the vagus nerve to the medulla to increase parasympathetic activity and to decrease sympathetic activity Why it's correct: Baroreceptors in the carotid sinus sense changes in blood pressure and send impulses via the glossopharyngeal nerve (ninth cranial nerve) to the medulla oblongata. The medulla integrates this input and modulates autonomic output, increasing parasympathetic activity via the vagus nerve to reduce heart rate and decreasing sympathetic activity to reduce cardiac output and vascular resistance. Why others are wrong: a. Vagus nerve to the medulla to increase parasympathetic activity and to decrease sympathetic activity: The vagus nerve is not the primary afferent pathway for baroreceptor signals; the glossopharyngeal nerve is. b. Glossopharyngeal cranial nerve through the vagus nerve to the medulla to increase sympathetic activity and to decrease parasympathetic: *d. Glossopharyngeal cranial: The baroreceptor reflex actually decreases sympathetic activity and increases parasympathetic activity in response to increased blood pressure.
The significance of the atrial kick is that it affects the contraction of the: a. Right atria, which is necessary to open the tricuspid valve. b. Right atria, which is necessary to increase the blood volume from the vena cava. c. Left atria, which increases the blood volume into the ventricle. d. Left atria, that is necessary to open the mitral valve.
Correct Answer: c. Left atria, which increases the blood volume into the ventricle. Why it's correct: The atrial kick refers to the final phase of diastolic filling, where the atria contract to push additional blood into the ventricles. This enhances ventricular filling and thus cardiac output. It's particularly relevant for the left atrium and ventricle, as it can contribute to around 20-30% of ventricular filling. Why others are wrong: a. Right atria, which is necessary to open the tricuspid valve: The atrial kick is not required to open the tricuspid valve; it opens due to pressure differences between the atria and ventricles. b. Right atria, which is necessary to increase the blood volume from the vena cava: The atrial kick does help to increase ventricular volume, but the question specifically asks about contraction, making this answer less accurate. d. Left atria, that is necessary to open the mitral valve: Like the tricuspid valve, the mitral valve doesn't require the atrial kick to open. It opens passively when the left atrial pressure exceeds that of the left ventricle.
Which chamber of the heart endures the highest pressures? a. Right atrium b. Left atrium c. Left ventricle d. Right ventricle
Correct Answer: c. Left ventricle Why it's correct: The left ventricle endures the highest pressures because it is responsible for pumping blood into the systemic circulation. This requires overcoming the resistance of the entire systemic vasculature, necessitating high pressure. Why others are wrong: a. Right atrium: This chamber receives venous blood at low pressure and is not involved in high-pressure pumping. b. Left atrium: Although it receives oxygenated blood from the lungs, it does not endure the high pressures seen in the ventricles. d. Right ventricle: It pumps blood into the lower resistance pulmonary circulation, and thus does not experience the high pressures that the left ventricle does.
What is the major determinant of the resistance that blood encounters as it flows through the systemic circulation? a. Volume of blood in the systemic circulation b. Muscle layer of the metarterioles c. Muscle layer of the arterioles d. Force of ventricular contraction
Correct Answer: c. Muscle layer of the arterioles Why it's correct: Arterioles are the primary sites of vascular resistance in the systemic circulation. The thick smooth muscle layer of arterioles allows for contraction and relaxation, thereby regulating the internal diameter of the blood vessel. This diameter directly affects resistance according to Poiseuille's law. By adjusting the diameter, arterioles control the rate of blood flow to various tissues and organs. Why others are wrong: a. Volume of blood in the systemic circulation: While the volume of blood can influence cardiac output and venous return, it is not the primary determinant of systemic vascular resistance. b. Muscle layer of the metarterioles: Metarterioles are transitional vessels between arterioles and capillaries. While they do contribute to vascular resistance, their impact is far less compared to that of arterioles. d. Force of ventricular contraction: Although the force of ventricular contraction (or inotropy) influences cardiac output, it is not the primary determinant of resistance in the systemic circulation.
Where in the heart are the receptors for neurotransmitters located? a. Semilunar and atrioventricular (AV) valves b. Endocardium and sinoatrial (SA) node c. Myocardium and coronary vessels d. Epicardium and AV node
Correct Answer: c. Myocardium and coronary vessels Why it's correct: Sympathetic and parasympathetic neurotransmitters act on specific receptors located in the myocardium and coronary vessels. These receptors, including adrenergic and cholinergic types, regulate heart rate, contractility, and vascular tone. Why others are wrong: a. Semilunar and atrioventricular (AV) valves: Neurotransmitter receptors are not typically found in the valves of the heart. b. Endocardium and sinoatrial (SA) node: While the SA node does have neurotransmitter receptors that influence its rate of firing, the endocardium is not a primary site for these receptors. d. Epicardium and AV node: The AV node does contain neurotransmitter receptors, but the epicardium is not a primary site for these receptors.
Continuous increases in left ventricular filing pressures result in which disorder? a. Mitral regurgitation b. Mitral stenosis c. Pulmonary edema d. Jugular vein distention
Correct Answer: c. Pulmonary edema Why it's correct: Increased left ventricular filling pressures cause a backlog of blood and pressure in the pulmonary circulation. This heightened pressure forces plasma to leak out of the pulmonary capillaries and into the alveolar and interstitial spaces, leading to pulmonary edema. This condition manifests as respiratory distress and is a serious medical emergency. Why others are wrong: a. Mitral regurgitation: While mitral regurgitation can lead to elevated left ventricular filling pressures, it is not a direct result of the increase in these pressures. b. Mitral stenosis: Similar to mitral regurgitation, mitral stenosis could be a cause of elevated pressures but is not a direct consequence of increased left ventricular filling pressures. d. Jugular vein distention: This is usually a sign of right-sided heart failure or elevated central venous pressure and is not directly related to left ventricular filling pressures.
During the cardiac cycle, which structure directly delivers action potential to the ventricular myocardium? a. Sinoatrial (SA) node b. Atrioventricular (AV) node c. Purkinje fibers d. Bundle branches
Correct Answer: c. Purkinje fibers Why it's correct: Purkinje fibers are specialized conductive fibers located within the heart tissue and are responsible for rapidly transmitting the action potential to the ventricular myocardium. This allows for the synchronized and effective contraction of the ventricles. Why others are wrong: a. Sinoatrial (SA) node: Although it is the primary pacemaker of the heart, the SA node does not directly deliver action potentials to the ventricular myocardium. Its impulses are initially localized to the atria. b. Atrioventricular (AV) node: The AV node is a crucial relay point but is not the structure directly responsible for delivering action potentials to the ventricular myocardium. d. Bundle branches: While these play a role in transmitting the action potential, they are not the terminal structures that directly pass it to the ventricular myocardium. That role is played by the Purkinje fibers.
The right lymphatic duct drains into which structure? a. Right subclavian artery b. Right atrium c. Right subclavian vein d. Superior vena cava
Correct Answer: c. Right subclavian vein Why it's correct: The right lymphatic duct collects lymph from the right side of the head, neck, thorax, and arm, and drains it into the right subclavian vein. This vein is part of the systemic venous system and eventually drains into the superior vena cava and right atrium of the heart. Why others are wrong: a. Right subclavian artery: The right subclavian artery is a blood vessel that carries oxygenated blood away from the heart. Lymphatic ducts do not drain into arteries. b. Right atrium: The right atrium is a chamber of the heart that receives deoxygenated blood from systemic circulation. It is not directly connected to the lymphatic system. d. Superior vena cava: While the superior vena cava is the ultimate destination for the blood returning from the upper part of the body, the right lymphatic duct directly drains into the right subclavian vein, not the superior vena cava.
The coronary ostia are located in the: a. Left ventricle b. Aortic valve c. Coronary sinus d. Aorta
Correct Answer: d. Aorta Why it's correct: The coronary ostia are the openings in the aorta through which blood flows into the coronary arteries. These openings are located just above the aortic valve leaflets and are the initial points from where the coronary circulation begins. When the left ventricle contracts, blood is ejected into the aorta, and some of this blood flows into the coronary arteries to nourish the heart muscle itself. Why others are wrong: a. Left ventricle: The coronary ostia are not located in the left ventricle. The left ventricle pumps blood into the aorta, from where the coronary arteries take their supply. b. Aortic valve: Although close to the aortic valve, the coronary ostia are not part of the valve itself. They are located in the wall of the ascending aorta just above the aortic valve leaflets. c. Coronary sinus: The coronary sinus is a vein that collects deoxygenated blood from the myocardium, not an area where coronary ostia are located.
During the cardiac cycle, why do the aortic and pulmonic valves close after the ventricles relax? a. Papillary muscles relax, which allows the valves to close. b. Chordae tendineae contract, which pulls the valves closed. c. Reduced pressure in the ventricles creates a negative pressure, which pulls the valves closed. d. Blood fills the cusps of the valves and causes the edges to merge, closing the valves.
Correct Answer: d. Blood fills the cusps of the valves and causes the edges to merge, closing the valves. Why it's correct: The aortic and pulmonic valves are semilunar valves that function to prevent backflow of blood into the ventricles after they have contracted to push blood into the aorta and pulmonary artery, respectively. When the ventricles relax, the pressure within them drops below that in the aorta and pulmonary artery. This differential pressure causes blood to start backflowing toward the ventricles, but as it does, it fills the cusps of the semilunar valves, forcing them to close. This is a passive mechanism driven by hemodynamic forces, rather than muscular activity. Why others are wrong: a. Papillary muscles relax, which allows the valves to close: Papillary muscles are not involved in the function of the semilunar valves; they are relevant to the atrioventricular valves (mitral and tricuspid). b. Chordae tendineae contract, which pulls the valves closed: Again, the chordae tendineae are structures associated with the atrioventricular valves and do not have a role in the function of the semilunar valves. c. Reduced pressure in the ventricles creates a negative pressure, which pulls the valves closed: This is misleading because it suggests an active "pulling" mechanism. The closing of the semilunar valves is a passive process triggered by the flow of blood back toward the ventricles.
The cardiac electrical impulse normally begins spontaneously in the sinoatrial (SA) node because it: a. Has a superior location in the right atrium. b. Is the only area of the heart capable of spontaneous depolarization. c. Has rich sympathetic innervation via the vagus nerve. d. Depolarizes more rapidly than other automatic cells of the heart.
Correct Answer: d. Depolarizes more rapidly than other automatic cells of the heart Why it's correct: The SA node has the highest rate of automaticity among all the pacemaker cells in the heart, meaning it depolarizes more rapidly. This is why it usually sets the pace for heart rate, serving as the natural pacemaker of the heart. Why others are wrong: a. Has a superior location in the right atrium: While its location is optimal for initiating the heartbeat, this is not why it serves as the heart's primary pacemaker. b. Is the only area of the heart capable of spontaneous depolarization: Other areas can also depolarize spontaneously but at a slower rate. c. Has rich sympathetic innervation via the vagus nerve: The vagus nerve actually provides parasympathetic, not sympathetic, innervation, and this slows down heart rate. This is not why the SA node initiates the heartbeat.
Which event occurs during phase 1 of the normal myocardial cell depolarization and repolarization? a. Repolarization when potassium moves out of the cells b. Repolarization when sodium rapidly enters into the cells c. Early repolarization when sodium slowly enters the cells d. Early repolarization when calcium slowly enters the cells
Correct Answer: d. Early repolarization when calcium slowly enters the cells Why it's correct: Phase 1 of the myocardial cell action potential represents the initial phase of repolarization, often termed "early repolarization." During this phase, there is a decrease in sodium conductance and an increase in potassium conductance, but importantly, calcium ions also slowly enter the cells. This calcium influx contributes to the plateau phase that follows (Phase 2) and is essential for the contractility of the cardiac muscle. Why others are wrong: a. Repolarization when potassium moves out of the cells: This statement is not accurate for Phase 1. While it's true that potassium moves out during repolarization, this is more characteristic of Phase 3 of the action potential, not Phase 1. In Phase 3, potassium outflow is the primary ion movement responsible for full repolarization of the cell. b. Repolarization when sodium rapidly enters into the cells: Sodium rapidly enters the cells during Phase 0, which is the phase of rapid depolarization. It doesn't describe events in Phase 1. c. Early repolarization when sodium slowly enters the cells: Sodium influx is primarily a feature of Phase 0, not of Phase 1. In Phase 1, the sodium channels are mostly inactivated, leading to the cessation of the rapid sodium influx that characterizes Phase 0.
When the volume of blood in the ventricle at the end of diastole increases, the force of the myocardial contraction during the next systole will also increase, which is an example of which law or theory about the heart? a. Laplace's law b. Poiseuille law c. Cross-bridge theory d. Frank-Starling law
Correct Answer: d. Frank-Starling law Why it's correct: The Frank-Starling law is a fundamental principle in cardiac physiology that describes the relationship between the end-diastolic volume (EDV) of the heart and the force of the subsequent contraction (systole). Specifically, the law states that the stroke volume (and force of contraction) of the heart increases in response to an increase in the volume of blood filling the heart when all other variables are constant. This relationship exists because the increased EDV results in greater stretching of the cardiac muscle fibers, leading to enhanced force generation during the contraction. Why others are wrong: a. Laplace's law: Laplace's law is more about the relationship between the tension in a wall of a sphere (or cylinder), the pressure inside the sphere, and its radius. While it is applied in the context of cardiac physiology to explain wall stress, it does not specifically address the relationship between end-diastolic volume and the force of myocardial contraction. b. Poiseuille law: Poiseuille's law relates to fluid flow in a tube and is often applied to blood flow in vessels. It describes how flow is related to pressure, radius, length, and viscosity of the fluid. It has nothing to do with the relationship between ventricular filling and myocardial contractile force. c. Cross-bridge theory: The Cross-bridge theory explains the molecular mechanisms by which muscle contraction occurs, particularly how actin and myosin interact to produce force. While it describes the mechanics at a cellular level, it doesn't discuss the relationship between end-diastolic volume and force of contraction.
Occlusion of the circumflex artery during a myocardial infarction would interrupt blood supply to which area? a. Left and right ventricles and much of the interventricular septum b. Posterior interventricular sulcus and the smaller branches of both ventricles c. Upper right ventricle, right marginal branch, and right ventricle to the apex d. Left atrium and the lateral wall of the left ventricle
Correct Answer: d. Left atrium and the lateral wall of the left ventricle Why it's correct: The circumflex artery branches off the left coronary artery and supplies the left atrium and the lateral and posterior walls of the left ventricle. An occlusion here would compromise blood supply to these areas. Why others are wrong: a. Left and right ventricles and much of the interventricular septum: This is more characteristic of an LAD blockage. b. Posterior interventricular sulcus and the smaller branches of both ventricles: This would more likely be affected by an occlusion of the posterior descending artery. c. Upper right ventricle, right marginal branch, and right ventricle to the apex: These areas are generally supplied by the right coronary artery, not the circumflex artery.
Which phase of the normal myocardial cell depolarization and repolarization correlates with diastole? a. Phase 1 b. Phase 2 c. Phase 3 d. Phase 4
Correct Answer: d. Phase 4 Why it's correct: Phase 4 of the cardiac action potential correlates with diastole, the period of cardiac muscle relaxation and ventricular filling. During this phase, the membrane potential of the myocardial cell is stable, and the cell is in a polarized, or resting, state. This phase allows for cardiac filling and readies the myocardial cells for the next action potential. Why others are wrong: a. Phase 1: This phase is associated with early repolarization and is not indicative of diastole. b. Phase 2: This is the plateau phase, mainly associated with systole and effective ejection of blood from the ventricles. c. Phase 3: This is the phase of rapid repolarization, also more closely associated with systole than with diastole.
What is the effect of epinephrine on B3 receptors on the heart? a. Decreases coronary blood flow. b. Supplements the effects of both B1 and B2 receptors. c. Increases the strength of myocardial contraction. d. Prevents overstimulation of the heart by the sympathetic nervous system.
Correct Answer: d. Prevents overstimulation of the heart by the sympathetic nervous system Why it's correct: B3 receptors in the heart, when stimulated, act as a counterbalance to the effects of B1 and B2 receptors. They essentially provide a negative feedback loop to prevent overstimulation by the sympathetic nervous system. They are thought to have a negative inotropic effect, reducing myocardial contractility. Why others are wrong: a. Decreases coronary blood flow: This would be counterproductive during sympathetic activation, which usually aims to increase cardiac performance. b. Supplements the effects of both B1 and B2 receptors: B3 receptors have the opposite effect; they mitigate the actions of B1 and B2 receptors. c. Increases the strength of myocardial contraction: B3 receptors are generally thought to decrease, not increase, the strength of myocardial contraction.