Chapter 18 The Cardiovascular System: The Heart
Fill-in-the-Blank/Short Answer Questions
1) The enlarged coronary vessel outside the heart that empties blood into the right atrium is the
Answer: coronary sinus
Page Ref: 669
2) What structure in the fetal heart allows blood to flow from the right atrium directly to the left
Answer: foramen ovale
Page Ref: 688
3) The ECG T wave interval represents ________.
Answer: ventricular repolarization
Page Ref: 679; Fig. 18.16
4) CO = ________ × SV.
Answer: HR or heart rate
Page Ref: 683
5) The ________ membrane covers the heart.
Answer: visceral layer of the serous pericardium
Page Ref: 663
6) The ________ valve of the heart has three valves with chordae tendineae.
Page Ref: 670
7) The ________ and ________ valves of the heart have no chordae tendineae attached.
Answer: aortic; pulmonary
Page Ref: 670; Fig. 18.9
8) Define systole and diastole. Which heart chambers are usually referenced when these terms
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
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.
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.
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
Page Ref: 668-670
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.
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.
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.
Page Ref: 675
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.
Page Ref: 673
16) What is bradycardia?
Answer: Bradycardia is a heart rate slower than 60 beats per minute.
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.
Page Ref: 689
1) A 14-year-old 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.
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 stressinduced
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.
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
Answer: The suggested treatment is surgery to implant an artificial pacemaker.
Page Ref: 678-679
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
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.
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
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
Page Ref: 682, 684
7) A 55-year-old 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 left-sided heart failure and which reflect right-sided 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).
Page Ref: 687
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.
Page Ref: 678-679
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.
Page Ref: 676, 687
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