Self-test questions: Chapter 28

. Which of the following statements regarding the conduction system of the heart is true?

Between action potentials, the cells of the sino-atrial node have a steady resting potential.

The cardiac action potential is conducted through the atria via Purkinje fibres.

The Purkinje fibres are specialized cardiac myocytes linked by gap junctions.

The spread of cardiac excitation speeds up at the atrio-ventricular node.

. Regarding the cardiac cycle of a healthy young adult. Which of the following statements is true?

During ventricular diastole the pressure in the left ventricle is close to 80 mm Hg (10.6 kPa).

During ventricular systole, the pressure in the left ventricle reaches a maximum of about 25 mm Hg (3.3 kPa).

During the initial stage of ventricular contraction the volume of the ventricle does not change.

During ventricular systole, one third of the blood in the ventricles is ejected.

. Which of the following statements concerning the normal heart sounds is true?

The first heart sound corresponds with the closure of the mitral and tricuspid valves.

The first heart sound occurs just before the R wave of the ECG.

The first heart sound is split into two components during inspiration.

The second heart sound occurs during the T-wave.

. Is it true that the action potentials of the heart muscle are about 100 times longer than those of skeletal muscle?

True

False

. The cardiac action potential is conducted through the atria via specialized conducting fibres.

True

False

. The spread of cardiac excitation is delayed by about 0.1 s at the atrio-ventricular node.

True

False

. The second heart sound is due to closure of the aortic and pulmonary valves.

True

False

. Which of the following statements concerning the cardiac output are correct?

Is increased by aldosterone released from the adrenal medulla.

Is decreased by stimulation of the vagus nerve

Can be measured by dividing the oxygen consumption by the difference in PO2 of the venous and arterial blood.

Is largely determined by the end-diastolic volume

. The stroke volume is decreased during strong sympathetic stimulation.

True

False

. Stimulation of the vagus nerve increases heart rate.

True

False

. Cardiac output is increased by circulating adrenaline.

True

False

. A subject has an oxygen consumption of 250 ml min^-1. A sample of arterial blood shows it to contain 20.1 ml O₂ dl^-1 and a sample of mixed venous blood contains 13.5 ml O₂ dl^-1. What is the subject's cardiac output?

4.25 l min^-1

5.0 l min^-1

3.78 l min^-1

37.8 l min^-1

. A subject has a left-right shunt (i.e. blood from the right side of the heart mixes with that from the left). A sample of blood from the pulmonary vein shows it to contain 20 ml O2 dl^-1 while the oxygen content of blood in the radial artery was only 18 ml O2 dl^-1. If the mixed venous blood has an oxygen content of 13 ml dl^-1 what fraction of the cardiac output passes through the shunt?

0.286

0.355

0.50

0.252

. A 45 year old man feels increasingly tired and has a pan-systolic murmur which is loudest at the lower left sternal edge. He has a prominent v wave in the jugular pulse. What is the most likely explanation for the pansystolic murmur?

Aortic stenosis

Tricuspid regurgitation

Mitral valve incompetence

Mitral stenosis

. A 45 year old woman has had chest palpitations and is short of breath. On examination an ejection murmur is heard which is clearest at the upper right sternal edge. What is the most likely cause of the murmur?

Aortic valve incompetence

Mitral stenosis

Aortic stenosis

Mitral regurgitation

Self-test questions: Chapter 28

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