A & P II Ch. 18

During contraction of heart muscle cells A. the action potential is prevented from spreading from cell to cell by gap junctions B. some calcium enters the cell from the extracellular space and triggers the release of larger amounts of calcium from intracellular stores C. all of the calcium required for contraction comes from storage in the sarcoplasmic reticulum D. calcium is prevented from entering cardiac fibers that have been stimulated

B. some calcium enters the cell from the extracellular space and triggers the release of larger amounts of calcium from intracellular stores

A patient is prescribed a calcium channel blocker to prevent angina (chest pain) by decreasing the demand for oxygen. What is the explanation for this pharmacological effect? A. A drug that inhibits the entry of calcium ions into the cytoplasm of cardiac cells decreases the membrane potential, thereby making the heart beat slower, relieving the chest pain. B. A drug that blocks the calcium channels prevents the cardiac cells from contracting, thereby relieving the chest pain. C. A drug that inhibits the entry of calcium ions into the cytoplasm of cardiac cells decreases the force of myocardial contractility, thereby decreasing the oxygen demand, relieving the chest pain. D. A drug that enhances the entry of calcium ions into the cytoplasm of cardiac cells decreases the force of myocardial contractility, thereby decreasing the oxygen demand, relieving the chest pain. E. A drug that enhances the entry of calcium ions into the cytoplasm of cardiac cells increases the membrane potential, thereby making the heart beat slower, relieving the chest pain.

C. A drug that inhibits the entry of calcium ions into the cytoplasm of cardiac cells decreases the force of myocardial contractility, thereby decreasing the oxygen demand, relieving the chest pain.

Select the correct statement about cardiac output. A. Decreased venous return will result in increased end diastolic volume. B. Stroke volume increases if end diastolic volume decreases. C. A slow heart rate increases end diastolic volume, stroke volume, and force of contraction. D. If a semilunar valve were partially obstructed, the end systolic volume in the affected ventricle would be decreased.

C. A slow heart rate increases end diastolic volume, stroke volume, and force of contraction.

Select the correct statement about the function of myocardial cells. A. The influx of potassium ions from extracellular sources is the initiating event in cardiac muscle contraction. B. The refractory period in skeletal muscle is much longer than that in cardiac muscle. C. The presence of gap junctions reflects the activity of the heart's intrinsic conduction system. D. Each cardiac muscle cell is innervated by a sympathetic nerve ending so that the nervous system can increase heart rate.

C. The presence of gap junctions reflects the activity of the heart's intrinsic conduction system.

Isovolumetric contraction A. occurs while the atrioventricular (AV) valves are open B. occurs immediately after the aortic and pulmonary semilunar valves close C. refers to the short period during ventricular systole when the ventricles are completely closed chambers D. occurs only in people with heart valve defects

C. refers to the short period during ventricular systole when the ventricles are completely closed chambers

The atrioventricular (AV) valves are closed A. while the atria are contracting B. when the ventricles are in diastole C. by the movement of blood from atria to ventricles D. when the ventricles are in systole

D. when the ventricles are in systole

Select the correct statement about the heart valves. The atrioventricular (AV) valves prevent backflow of blood into the atria during ventricular contraction. Aortic and pulmonary semilunar valves control the flow of blood into the heart. The tricuspid valve divides the left atrium from the left ventricle. The mitral (bicuspid) valve separates the right atrium from the right ventricle.

The atrioventricular (AV) valves prevent backflow of blood into the atria during ventricular contraction.

Select the correct statement about the structure of the heart wall. The heart chambers are lined by the endomysium. Connective tissue in the heart wall aids in the conduction of the action potential. The fibrous cardiac skeleton forms the bulk of the heart. The myocardium is the layer of the heart that actually contracts.

The myocardium is the layer of the heart that actually contracts.

Hemorrhage with a large loss of blood causes

a lowering of blood pressure due to change in cardiac output

The P wave of a normal electrocardiogram indicates

atrial depolarization

When viewing a dissected heart, it is easy to visually discern the right and left ventricles by

noticing the thickness of the ventricle walls

If the length of the absolute refractory period in cardiac muscle cells was the same as it is for skeletal muscle cells

tetanic contractions might occur, which would stop the heart's pumping action