Anatomy & Physiology ch 18
Anatomy & Physiology ch 18 Biol 2301
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Human Anatomy & Physiology, 8e (Marieb/Hoehn) Chapter 18 The Cardiovascular System: The Heart Matching Questions Figure 18.1 Using Figure 18.1, match the following: 1) Purkinje fibers. Answer: E Diff: 1 Page Ref: 677; Fig. 18.14 2) SA node. Answer: A Diff: 1 Page Ref: 677; Fig. 18.14 3) AV bundle. Answer: C Diff: 1 Page Ref: 677; Fig. 18.14 4) AV node. Answer: B Diff: 1 Page Ref: 677; Fig. 18.14 5) Bundle branches. Answer: D 1 Copyright © 2010 Pearson Education, Inc. Diff: 1 Page Ref: 677; Fig. 18.14 Figure 18.2 Using Figure 18.2, match the following: 6) Atrial depolarization. Answer: A Diff: 1 Page Ref: 679; Fig. 18.16 7) Point after which pressure begins to rise in the aorta. Answer: D Diff: 2 Page Ref: 679; Fig. 18.16 8) Ventricular repolarization. Answer: E Diff: 2 Page Ref: 679; Fig. 18.16 9) Point that represents the "dup" sound made by the heart. Answer: E Diff: 3 Page Ref: 679; Fig. 18.16 2 Copyright © 2010 Pearson Education, Inc. Figure 18.3 Using Figure 18.3, match the following: 10) Ventricular fibrillation. Answer: D Diff: 2 Page Ref: 681; Fig. 18.18 11) Seconddegree heart block. Answer: C Diff: 3 Page Ref: 681; Fig. 18.18 12) Junctional rhythm. Answer: B Diff: 3 Page Ref: 681; Fig. 18.18 13) Normal sinus rhythm. Answer: A Diff: 3 Page Ref: 681; Fig. 18.18 3 Copyright © 2010 Pearson Education, Inc. Match the following: A) Epicardium B) Parietal layer C) Myocardium D) Endocardium 14) The inner lining of the heart. Diff: 1 Page Ref: 664 15) Heart muscle. Diff: 1 Page Ref: 663 16) Serous layer covering the heart muscle. Diff: 1 Page Ref: 663 17) The outermost layer of the serous pericardium. Diff: 2 Page Ref: 663 Answers: 14) D 15) C 16) A 17) B Match the following: A) Purkinje fibers B) AV bundle C) SA node D) AV node 18) The pacemaker of the heart. Diff: 1 Page Ref: 677; Fig. 18.14 19) Found in the interventricular septum. Diff: 1 Page Ref: 677 20) Network found in the ventricular myocardium. Diff: 2 Page Ref: 677 21) The point in the conduction system of the heart where the impulse is temporarily delayed. Diff: 2 Page Ref: 677 Answers: 18) C 19) B 20) A 21) D 4 Copyright © 2010 Pearson Education, Inc. Match the following: A) Pulmonary valves B) Aortic valve C) Mitral valve D) Tricuspid valve 22) Prevents backflow into the left ventricle. Diff: 1 Page Ref: 670 23) Prevents backflow into the right atrium. Diff: 1 Page Ref: 670 24) Prevents backflow into the left atrium. Diff: 1 Page Ref: 670 25) Prevents backflow into the right ventricle. Diff: 1 Page Ref: 670 26) AV valve with two flaps. Diff: 1 Page Ref: 670 27) AV valve with three flaps. Diff: 1 Page Ref: 670 Answers: 22) B 23) D 24) C 25) A 26) C 27) D 5 Copyright © 2010 Pearson Education, Inc. Figure 18.4 Using Figure 18.4, match the following: 28) Tricuspid valve. Answer: B Diff: 1 Page Ref: 667; Fig. 18.4e 29) Mitral valve. Answer: D Diff: 1 Page Ref: 667; Fig. 18.4e 30) Right atrium. Answer: A Diff: 1 Page Ref: 667; Fig. 18.4e 31) Left ventricle. Answer: E Diff: 1 Page Ref: 667; Fig. 18.4e 32) Pulmonary veins. Answer: C Diff: 1 Page Ref: 667; Fig. 18.4e 6 Copyright © 2010 Pearson Education, Inc. Match the following: A) Ischemia B) Ectopic focus C) Quiescent period D) Infarction E) Fibrillation 33) Heart muscle is deprived of oxygen. Diff: 1 Page Ref: 675 34) Death of heart muscle cells. Diff: 1 Page Ref: 670 35) A condition of rapid and irregular or outofphase contraction of heart muscle cells. Diff: 1 Page Ref: 678 36) An abnormal pacemaker. Diff: 1 Page Ref: 679 37) Total heart relaxation. Diff: 1 Page Ref: 682 Answers: 33) A 34) D 35) E 36) B 37) C True/False Questions 1) The myocardium receives its blood supply from the coronary arteries. Answer: TRUE Diff: 1 Page Ref: 670 2) Cardiac muscle has more mitochondria and depends less on a continual supply of oxygen than does skeletal muscle. Answer: FALSE Diff: 1 Page Ref: 673 3) Anastomoses among coronary arterial branches provide collateral routes for blood delivery to the heart muscle. Answer: TRUE Diff: 2 Page Ref: 669 4) Congestive heart failure means that the pumping efficiency of the heart is depressed so that there is inadequate delivery of blood to body tissues. Answer: TRUE Diff: 1 Page Ref: 687 7 Copyright © 2010 Pearson Education, Inc. 8 Copyright © 2010 Pearson Education, Inc. 5) Tissues damaged by myocardial infarction are replaced by connective tissue. Answer: TRUE Diff: 1 Page Ref: 670, 687 6) The left side of the heart pumps the same volume of blood as the right. Answer: TRUE Diff: 1 Page Ref: 668 7) Chronic release of excess thyroxine can cause a sustained increase in heart rate and a weakened heart. Answer: TRUE Diff: 1 Page Ref: 686 8) Arterial blood supply to heart muscle is continuous whether the heart is in systole or diastole. Answer: FALSE Diff: 2 Page Ref: 669670 9) Trabeculae carneae are found in the ventricles and never the atria. Answer: TRUE Diff: 1 Page Ref: 668 10) The "lub" sounds of the heart are valuable in diagnosis because they provide information about the function of the heart's pulmonary and aortic valves. Answer: FALSE Diff: 2 Page Ref: 681 11) Autonomic regulation of heart rate is via two reflex centers found in the pons. Answer: FALSE Diff: 2 Page Ref: 685 12) The papillary muscles contract after the other ventricular muscles so that they can take up the slack on the chordae tendineae before the full force of ventricular contractions sends blood against the AV valve flaps. Answer: FALSE Diff: 2 Page Ref: 670 13) An ECG provides direct information about valve function. Answer: FALSE Diff: 3 Page Ref: 679 14) As pressure in the aorta rises due to atherosclerosis, more ventricular pressure is required to open the aortic valve. Answer: TRUE Diff: 3 Page Ref: 687 9 Copyright © 2010 Pearson Education, Inc. 15) Proxysmal atrial tachycardia is characterized by bursts of atrial contractions with little pause between them. Answer: TRUE Diff: 2 Page Ref: 690 MultipleChoice Questions 1) Normal heart sounds are caused by which of the following events? A) excitation of the SA node B) closure of the heart valves C) friction of blood against the chamber walls D) opening and closing of the heart valves Answer: B Diff: 1 Page Ref: 681 2) Which of the events below does not occur when the semilunar valves are open? A) Ventricles are in diastole. B) Blood enters pulmonary arteries and the aorta. C) AV valves are closed. D) Ventricles are in systole. Answer: A Diff: 2 Page Ref: 670 3) Hemorrhage with a large loss of blood causes ________. A) a lowering of blood pressure due to change in cardiac output B) a rise in blood pressure due to change in cardiac output C) no change in blood pressure but a slower heart rate D) no change in blood pressure but a change in respiration Answer: A Diff: 1 Page Ref: 682684 4) The left ventricular wall of the heart is thicker than the right wall in order to ________. A) accommodate a greater volume of blood B) expand the thoracic cage during diastole C) pump blood with greater pressure D) pump blood through a smaller valve Answer: C Diff: 2 Page Ref: 668 5) Damage to the ________ is referred to as heart block. A) SA node B) AV valves C) AV bundle D) AV node Answer: D 10 Copyright © 2010 Pearson Education, Inc. Diff: 1 Page Ref: 679 11 Copyright © 2010 Pearson Education, Inc. 6) The P wave of a normal electrocardiogram indicates ________. A) ventricular repolarization B) ventricular depolarization C) atrial repolarization D) atrial depolarization Answer: D Diff: 1 Page Ref: 679 7) Blood within the pulmonary veins returns to the ________. A) right atrium B) left atrium C) right ventricle D) left ventricle Answer: B Diff: 1 Page Ref: 668 8) Small muscle masses attached to the chordae tendineae are the ________. A) trabeculae carneae B) pectinate muscles C) papillary muscles D) venae cavae Answer: C Diff: 1 Page Ref: 670 9) The term for pain associated with deficient blood delivery to the heart that may be caused by the transient spasm of coronary arteries is ________. A) ischemia B) pericarditis C) myocardial infarct D) angina pectoris Answer: D Diff: 1 Page Ref: 670 10) To auscultate the aortic semilunar valve, you would place your stethoscope in the ________. A) second intercostal space to the right of the sternum B) second intercostal space to the left of the sternum C) fifth intercostal space inferior to the left nipple D) fifth right intercostal space Answer: A Diff: 1 Page Ref: 681; Fig. 18.19 12 Copyright © 2010 Pearson Education, Inc. 11) The source of blood carried to capillaries in the myocardium would be the ________. A) coronary sinus B) fossa ovalis C) coronary arteries D) coronary veins Answer: C Diff: 1 Page Ref: 669 12) The fact that the left ventricle of the heart is thicker than the right ventricle reveals that it ________. A) pumps a greater volume of blood B) pumps blood against a greater resistance C) expands the thoracic cage D) sends blood through a smaller valve Answer: B Diff: 1 Page Ref: 668 13) Which of the following factors does not influence heart rate? A) skin color B) age C) gender D) body temperature Answer: A Diff: 1 Page Ref: 685687 14) Which of the following is not an agerelated change affecting the heart? A) atherosclerosis B) decline in cardiac reserve C) fibrosis of cardiac muscle D) thinning of the valve flaps Answer: D Diff: 2 Page Ref: 686687 15) If cardiac muscle is deprived of its normal blood supply, damage would primarily result from ________. A) decreased delivery of oxygen B) a decrease in the number of available mitochondria for energy production C) a lack of nutrients to feed into metabolic pathways D) an inadequate supply of lactic acid Answer: A Diff: 1 Page Ref: 675 13 Copyright © 2010 Pearson Education, Inc. 16) If the length of the absolute refractory period in cardiac muscle cells was the same as it is for skeletal muscle cells ________. A) it would be much longer before cardiac cells could respond to a second stimulation B) contractions would last as long as the refractory period C) tetanic contractions might occur, which would stop the heart's pumping action D) it would be less than 12 ms Answer: C Diff: 2 Page Ref: 673 17) Norepinephrine acts on the heart by ________. A) decreasing heart contractility B) causing a decrease in stroke volume C) blocking the action of calcium D) causing threshold to be reached more quickly Answer: D Diff: 2 Page Ref: 685686 18) If the vagal nerves to the heart were cut, the result would be that ________. A) the heart would stop, since the vagal nerves trigger the heart to contract B) the heart rate would increase by about 25 beats per minute C) the AV node would become the pacemaker of the heart D) parasympathetic stimulation would increase, causing a decrease in heart rate Answer: B Diff: 2 Page Ref: 686 19) Foramen ovale ________. A) connects the two atria in the fetal heart B) is a condition in which the heart valves do not completely close C) is a shallow depression in the interventricular septum D) is a connection between the pulmonary trunk and the aorta in the fetus Answer: A Diff: 1 Page Ref: 688 20) Which vessel of the heart receives blood during right ventricular systole? A) venae cavae B) pulmonary trunk C) aorta D) pulmonary veins Answer: B Diff: 1 Page Ref: 668, 682 14 Copyright © 2010 Pearson Education, Inc. 21) Which of these vessels receives blood during ventricular systole? A) aorta only B) pulmonary arteries only C) pulmonary veins only D) both the aorta and pulmonary trunk Answer: D Diff: 1 Page Ref: 682 22) Which of the following is not part of the conduction system of the heart? A) AV node B) bundle of His C) AV valve D) SA node Answer: C Diff: 1 Page Ref: 677; Fig. 18.14 23) The tricuspid valve is closed ________. A) while the ventricle is in diastole B) when the ventricle is in systole C) while the atrium is contracting D) by the movement of blood from atrium to ventricle Answer: B Diff: 2 Page Ref: 682; Fig. 18.20 24) When viewing a dissected heart, it is easy to visually discern the right and left ventricles by ________. A) tracing out where the auricles connect B) noticing the thickness of the ventricle walls C) locating the apex D) finding the papillary muscles Answer: B Diff: 1 Page Ref: 668 25) Select the correct statement about the heart valves. A) The mitral valve separates the right atrium from the right ventricle. B) The tricuspid valve divides the left atrium from the left ventricle. C) Aortic and pulmonary valves control the flow of blood into the heart. D) The AV valves are supported by chordae tendineae so that regurgitation of blood into the atria during ventricular contraction does not occur. Answer: D Diff: 2 Page Ref: 670 15 Copyright © 2010 Pearson Education, Inc. 26) Select the correct statement about the function of myocardial cells. A) The entire heart contracts as a unit or it does not contract at all. B) Each cardiac muscle cell is innervated by a sympathetic nerve ending so that the nervous system can increase heart rate. C) The refractory period in skeletal muscle is much longer than that in cardiac muscle. D) The influx of potassium ions from extracellular sources is the initiating event in cardiac muscle contraction. Answer: A Diff: 3 Page Ref: 673675 27) Select the correct statement about the structure of the heart wall. A) The fibrous skeleton forms the bulk of the heart. B) Connective tissue in the heart wall aids in the conduction of the action potential. C) The heart chambers are lined by the endomysium. D) The myocardium is the layer of the heart that actually contracts. Answer: D Diff: 2 Page Ref: 663664 28) Compared to skeletal muscle, cardiac muscle ________. A) has gap junctions that allow it to act as a functional syncytium B) lacks striations C) has more nuclei per cell D) cells are larger than skeletal muscle cells Answer: A Diff: 2 Page Ref: 672673 29) During the period of ventricular filling ________. A) pressure in the heart is at its peak B) blood flows passively through the atria and the open AV valves into the ventricles C) the atria remain in diastole D) it is represented by the P wave on the ECG Answer: B Diff: 2 Page Ref: 682 30) The second heart sound is heard during which phase of the cardiac cycle? A) isovolumetric relaxation B) isovolumetric contraction C) ventricular ejection D) ventricular filling Answer: A Diff: 3 Page Ref: 682; Fig. 18.20 16 Copyright © 2010 Pearson Education, Inc. 31) The time of day most hazardous for heart attacks is ________. A) morning B) noontime C) evening D) during sleep Answer: A Diff: 3 Page Ref: 685686 32) If we were able to artificially alter the membrane permeability of pacemaker cells so that sodium influx is more rapid, ________. A) threshold is reached more quickly and heart rate would increase B) potassium channels compensate and no change in heart rate would occur C) heart rate would decrease, but blood pressure would rise due to the excess sodium present D) tetanic contraction would occur due to the short absolute refractory period of cardiac muscle Answer: A Diff: 3 Page Ref: 676677 33) Select the correct statement about cardiac output. A) A slow heart rate increases end diastolic volume, stroke volume, and force of contraction. B) Decreased venous return will result in increased end diastolic volume. C) If a semilunar valve were partially obstructed, the end systolic volume in the affected ventricle would be decreased. D) Stroke volume increases if end diastolic volume decreases. Answer: A Diff: 3 Page Ref: 682684 34) During contraction of heart muscle cells ________. A) the action potential is initiated by voltagegated slow calcium channels B) some calcium enters the cell from the extracellular space and triggers the release of larger amounts of calcium from intracellular stores C) the action potential is prevented from spreading from cell to cell by gap junctions D) calcium is prevented from entering cardiac fibers that have been stimulated Answer: B Diff: 2 Page Ref: 673675 35) Isovolumetric contraction ________. A) refers to the short period during ventricular systole when the ventricles are completely closed chambers B) occurs while the AV valves are open C) occurs immediately after the aortic and pulmonary valves close D) occurs only in people with heart valve defects Answer: A Diff: 3 Page Ref: 682; Fig. 18.20 17 Copyright © 2010 Pearson Education, Inc. 36) Commotio cordis is heart failure due to a ________. A) mild electrical shock to the heart itself B) severe electrical shock to the body C) relatively mild blow to the chest that occurs during a vulnerable interval (2 ms) when the heart is repolarizing D) loss of blood from an artery Answer: C Diff: 3 Page Ref: 690 FillintheBlank/Short Answer Questions 1) The enlarged coronary vessel outside the heart that empties blood into the right atrium is the ________. Answer: coronary sinus Diff: 1 Page Ref: 669 2) What structure in the fetal heart allows blood to flow from the right atrium directly to the left atrium? Answer: foramen ovale Diff: 1 Page Ref: 688 3) The ECG T wave interval represents ________. Answer: ventricular repolarization Diff: 1 Page Ref: 679; Fig. 18.16 4) CO = ________ × SV. Answer: HR or heart rate Diff: 1 Page Ref: 683 5) The ________ membrane covers the heart. Answer: visceral layer of the serous pericardium Diff: 1 Page Ref: 663 6) The ________ valve of the heart has three valves with chordae tendineae. Answer: tricuspid Diff: 1 Page Ref: 670 7) The ________ and ________ valves of the heart have no chordae tendineae attached. Answer: aortic; pulmonary Diff: 1 Page Ref: 670; Fig. 18.9 8) Define systole and diastole. Which heart chambers are usually referenced when these terms are used? Answer: Systole is contraction of the muscle. Diastole is relaxation of the muscle. The contraction and relaxation of the ventricles are normally described with the terms systole and 18 Copyright © 2010 Pearson Education, Inc. diastole. Diff: 1 Page Ref: 682 9) Define the terms end diastolic volume (EDV) and end systolic volume (ESV) and relate them to the calculation of stroke volume. Answer: EDV is the amount of blood that collects in a ventricle during diastole. ESV is the volume of blood remaining in a ventricle after it has contracted. Stroke volume (ml/beat) equals EDV ESV. Diff: 1 Page Ref: 684 10) What is the difference between the auricles and the atria? Answer: Auricles are the flaplike appendages attached to the atria that increase the atrial volume. The atria are receiving chambers for blood returning to the heart from the pulmonary and systemic circulation. Diff: 1 Page Ref: 664 11) The heart is called a "double pump" because there are two functionally separate circulations. Trace the pathway of each of these circulations and include the following information: heart chambers involved, major blood vessels involved, and general areas through which the blood flows. Begin with the right atrium. Answer: Right atrium to right ventricle to pulmonary arteries to lungs (pulmonary circuit pump); pulmonary veins to left atrium to left ventricle to aorta to body tissues to venae cavae (systemic circuit pump). Diff: 2 Page Ref: 668670 12) What two important functions does the cardiac conduction system perform? Answer: The important functions of the cardiac conduction system are to initiate impulses (pacemaker) and to distribute impulses throughout the heart so that it depolarizes and contracts in an orderly, sequential manner. Diff: 2 Page Ref: 676 13) Explain autorhythmicity in cardiac muscle cells. Answer: Autorhythmic cells do not maintain a stable resting membrane potential. Instead, they have an unstable resting potential that continuously depolarizes, drifting toward threshold for firing. These spontaneously changing membrane potentials, called pacemaker potentials, initiate the action potentials that trigger the heart’s rhythmic contractions. Diff: 3 Page Ref: 676 14) Why is oxygen so much more critical to the heart muscle than to skeletal muscles? Answer: Cardiac muscle cells are highly dependent on oxygen and rely almost exclusively on aerobic respiration. Thus, they cannot incur much oxygen debt. When there is a forced switch to anaerobic respiration, lactic acid and rising H levels impair heart function. Diff: 3 Page Ref: 675 19 Copyright © 2010 Pearson Education, Inc. 15) What is the functional importance of the intercalated discs of cardiac muscle? What is the functional importance of the fibrous skeleton of the heart? Answer: Intercalated discs contain anchoring desmosomes that prevent cell separation, and gap junctions that allow ions to travel from cell to cell, transmitting current across the entire heart. The fibrous skeleton acts both as a tendon and an insertion, giving the cardiac cells something to pull or exert their force on. Diff: 2 Page Ref: 673 16) What is bradycardia? Answer: Bradycardia is a heart rate slower than 60 beats per minute. Diff: 1 Page Ref: 687 17) Why is fibrosis of the cardiac muscle serious? Answer: With fibrosis the heart muscle stiffens and is unable to fill the atria as it once did; therefore, less blood is pumped. Further, as the muscle stiffens it takes more energy to expel the bolus of blood from the heart, which will eventually weaken the heart. Diff: 2 Page Ref: 689 Clinical Questions 1) A 14yearold girl undergoing a physical examination prior to being admitted to summer camp was found to have a loud heart diastolic murmur at the second intercostal space to the left side of the sternum. Explain the reason for the loud heart murmur associated with this girl's condition. Answer: The heart murmur is due to incomplete closing of the pulmonary valve. Diff: 2 Page Ref: 681 2) A man enters the hospital complaining of chest pain. His history includes smoking, a stressful job, a diet heavy in saturated fats, lack of exercise, and high blood pressure. Although he is not suffering from a heart attack, his doctor explains to him that a heart attack is quite possible. What did the chest pain indicate? Why is this man a prime candidate for a heart attack? Answer: His symptoms indicate angina pectoris, possibly due to either atherosclerosis or stress induced spasms of the coronary arteries. If the arteries are occluded (atherosclerosis), the heart muscle could be deprived of blood, and therefore oxygen. A heart attack could occur if the coronary vessels experience further (or progressive) occlusion. Diff: 3 Page Ref: 670 3) An older woman complains of shortness of breath and intermittent fainting spells. Her doctor runs various tests and finds that the AV node is not functioning properly. What is the suggested treatment? Answer: The suggested treatment is surgery to implant an artificial pacemaker. Diff: 2 Page Ref: 678679 20 Copyright © 2010 Pearson Education, Inc. 4) An angiocardiogram was performed on an infant who had symptoms of breathlessness and it was found that he had a patent ductus arteriosus. Discuss the location and function of the ductus arteriosus in the fetus and relate it to the reason for the infant's breathlessness. Answer: The ductus arteriosus is a shunt between the pulmonary trunk and the aorta in the fetus, which normally closes at birth. Breathlessness is due to the mixing of oxygenated and deoxygenated blood because the connection between the aorta and the pulmonary trunk remains slightly open. Diff: 2 Page Ref: 689 5) A patient takes a nitroglycerin tablet sublingually for chest pain. Nitroglycerin acts directly on smooth muscle, producing relaxation and vessel dilation. How would this relieve chest pain? Answer: Angina pectoris is thoracic pain caused by a fleeting deficiency in blood delivery to the myocardium, with resulting decreased oxygen being delivered to the cells. Because nitroglycerin acts as a vasodilator, blood flow is increased, promoting the delivery of oxygen to the cells. Diff: 3 Page Ref: 670 6) A patient was admitted to the hospital with chest pains. On admission, his pulse was 110 and blood pressure was 96/64. According to his history, his normal pulse rate is usually between 80 and 88 and his blood pressure runs from 120/70 to 130/80. Explain why these changes in BP and HR occur. Answer: Increased heart rate (measured by taking his pulse) without maintaining his normal blood pressure is suggestive of reduced stroke volume. Both a drop in blood volume and a weakened heart could cause this, but the chest pains suggest heart damage. Failure of compensating mechanisms to maintain blood pressure suggest a serious decline in cardiac output. Diff: 3 Page Ref: 682, 684 7) A 55yearold male was admitted to the hospital with heart failure. He complains of increasing shortness of breath on exertion and needing to sleep on three pillows at night. On physical assessment, the nurse determines that his ankles and feet are very swollen. Which of these symptoms reflect leftsided heart failure and which reflect rightsided heart failure? Answer: Because the heart is a double pump, each side can initially fail independently of the other. If the left side fails, pulmonary congestion occurs. The right side of the heart continues to propel blood to the lungs, but the left side does not adequately eject the returning blood into the systemic circulation. Thus, blood vessels in the lungs become engorged with blood, pressure within them increases, and fluid leaks from the circulation into the lung tissue, causing pulmonary edema. Shortness of breath and difficulty breathing in a prone position may occur. If the right side of the heart fails, peripheral congestion occurs. Blood stagnates within body organs, and pooled fluids in the tissue spaces impair the ability of body cells to obtain adequate nutrients and oxygen and to rid themselves of wastes. Edema is most noticeable in the extremities (feet, ankles, and fingers). Diff: 3 Page Ref: 687 21 Copyright © 2010 Pearson Education, Inc. 8) Asystole is the total absence of ventricular electrical activity. Explain why defibrillation would not be effective in this situation. Answer: Defibrillation is accomplished by electrically shocking the heart, which interrupts its chaotic twitching by depolarizing the entire myocardium. In this case, the ventricles are at a total standstill and defibrillation would not be effective. Diff: 3 Page Ref: 678679 9) A patient is prescribed a calcium channel blocker to prevent angina (chest pain), by decreasing the demand for oxygen. Explain why. Answer: By preventing the influx of calcium ions into myocardial and vascular smooth muscle cells, calcium channel blockers inhibit the intracellular release of additional stores of calcium ions. A drug that inhibits the release of intracellular calcium ions decreases the force of myocardial contractility, thereby decreasing the oxygen demand. Diff: 3 Page Ref: 676, 687 22 Copyright © 2010 Pearson Education, Inc.
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