Problem Set 6

Which event does NOT happen during ventricular diastole?

Atrioventricular valves close because of the contracting ventricles.

In the non-exercising heart, which event of the cardiac cycle lasts the longest?

atrial diastole

What effect would compressing the inferior vena cava just below the diaphragm have on cardiac function?

Sympathetic stimulation of the heart would increase.

If the cells of the SA node failed to function, how would the heart rate be affected?

The heart would beat slower because the AV node would be the pacemaker.

Which of the following is greater during left ventricular systole?

the peak pressure in the ventricle

Which of the following can be heard with a stethoscope most easily?

Closing of atrioventricular valves

If the pacemaker cells in the SA node become more permeable to potassium ions,

both heart rate will decrease and membrane will hyperpolarize.

Which of these would cause stroke volume to increase?

both when venous return is increased and when diastolic blood pressure is decreased

The beginning of the QRS complex of the electrocardiogram (ECG) immediately precedes which of the following events?

closing of the atrioventricular valves

What does the circle label "5" indicate on the graph?

peak systolic pressure

List the three stages of an action potential in a cardiac muscle cell.

rapid depolarization, plateau, and repolarization

What occurs at "B" on the graph?

semilunar valve closes

During the cardiac cycle,

the QRS complex of the ECG precedes the increase in ventricular pressure.

Compute Joe's stroke volume if his end-systolic volume (ESV) is 40 mL and his end-diastolic volume (EDV) is 125 mL. (Module 18.16B)

85 mL

Which of the following statements most accurately defines what is happening during the second phase of ventricular systole of the cardiac cycle?

Blood is being ejected from the ventricles through open semilunar valves.

Why does tetany not occur in cardiac muscle?

Cardiac muscle has a long refractory period that continues until relaxation is well under way. As a result, another action potential cannot arrive quickly enough for summation to occur, and thus tetany cannot occur.

Why is it important that cardiac tissue contain many mitochondria and capillaries?

Cardiac tissue is metabolically active and dependent on mitochondrial activity to use aerobic respiration to generate ATP and capillaries provide the oxygen and nutrients for this process.

In cardiac muscle, calcium ions

enter the cell through slow ion channels

Caffeine has effects on conducting cells and contractile cells that are similar to those of NE. What effect would drinking large amounts of caffeinated beverages have on the heart rate?

heart rate would increase

If the connection between the vagus nerve and the heart is cut, which of these changes will occur?

The heart will beat faster.

How would properly functioning valves prevent varicose veins?

Valves prevent backward flow of blood

Veins are more prone to inappropriate stretching and twisting than arteries, because

Veins have thinner walls than arteries

Why is ventricular fibrillation fatal?

Ventricular fibrillation, which causes the condition known as cardiac arrest, is fatal because the ventricles merely quiver and do not pump blood into the systemic circulation.

The mitral valve closing is associated with all of the following except

when the left atrial pressure exceeds the left ventricular pressure.