MLT GlobePhysiology: Cardiovascular physiology
40 Physiology MCQs on Cardiovascular physiology with answers and explanations.
According to the Frank-Starling mechanism, what happens when venous return to the heart rises?
More venous return stretches the ventricular fibres (greater preload), which strengthens contraction and increases stroke volume. This matches output to input.
In which situation would heart rate normally fall rather than rise?
During sleep, parasympathetic (vagal) tone dominates and slows the heart. Exercise and emotional arousal increase sympathetic drive.
Echocardiography shows that the mitral valve cannot open fully, obstructing flow. This narrowing is termed:
Stenosis is narrowing of a valve orifice that impedes forward flow. Incompetence (regurgitation) means the valve fails to close and blood leaks backwards.
Exchange of gases, nutrients and wastes between blood and tissues takes place mainly across the walls of:
Capillaries have walls one endothelial cell thick and a huge total surface area, so they are the exchange vessels. Arterioles are resistance vessels.
The sinoatrial node, the heart's pacemaker, is in the:
The SA node lies in the upper right atrial wall where the superior vena cava enters. The AV node is near the septum above the tricuspid valve.
Which pathway describes the route of the pulmonary circuit?
Pulmonary arteries carry deoxygenated blood to the lungs, and pulmonary veins return oxygenated blood to the left atrium. The systemic circulation supplies the other tissues.
A transplanted heart has no nerve supply yet keeps beating. Which property is NOT true of cardiac muscle?
Cardiac muscle is autorhythmic; nerves only modify rate and force. A denervated heart beats at the intrinsic SA node rate.
To calculate heart rate from an ECG strip, you measure the time for one complete cardiac cycle. Which interval is used?
The interval between successive R waves equals one beat; rate = 60 / R-R (s). The QT covers ventricular depolarisation and repolarisation only.
If the sinoatrial node fails, which structure usually takes over as pacemaker at about 40-60 beats per minute?
The AV node is the secondary pacemaker, firing slower than the SA node (60-100/min). Purkinje fibres give an even slower ventricular escape rhythm.
Which cardiac event produces the first heart sound (S1)?
S1 marks the start of ventricular systole, when the atrioventricular (mitral and tricuspid) valves close. Closure of the semilunar valves produces S2.
The mitral (bicuspid) valve is positioned between which two structures?
The mitral valve guards the left atrioventricular opening. The tricuspid valve guards the right side; the aortic and pulmonary valves guard the ventricular outflow tracts.
Which structure normally generates impulses at the fastest intrinsic rate and so sets the heart rate?
The SA node depolarises spontaneously at about 60-100 per minute, faster than the AV node (40-60) or Purkinje fibres (20-40), so it acts as the pacemaker.
On an ECG, which deflection reflects depolarisation of the ventricles?
The QRS complex records ventricular depolarisation. The P wave is atrial depolarisation, the T wave ventricular repolarisation, and the PR interval AV conduction time.
A blood pressure reading of 120/80 mmHg is recorded. The value 120 represents pressure during:
The upper figure is systolic pressure, the peak during ventricular contraction. The lower is diastolic; their difference is pulse pressure, and the time-weighted average is mean arterial pressure.
Stroke volume is best defined as:
Stroke volume equals end-diastolic volume minus end-systolic volume, about 70 mL at rest. End-diastolic volume is the pre-contraction volume; systolic minus diastolic is pulse pressure.
The arterial baroreceptors that regulate blood pressure are located in the:
Baroreceptors in the carotid sinus and aortic arch send signals via the glossopharyngeal and vagus nerves to the medulla, which processes them but does not sense stretch itself.
Long-standing systemic hypertension most directly overloads which chamber, making it likely to fail first?
The left ventricle pumps against systemic arterial pressure, so hypertension causes left ventricular hypertrophy and eventually left-sided failure. Pulmonary hypertension strains the right ventricle.
After passing through the left atrium, blood next enters the:
Oxygenated blood flows from the pulmonary veins into the left atrium, through the mitral valve to the left ventricle, then out into the aorta.
Oxygenated blood leaving the lungs reaches the left atrium through the:
Four pulmonary veins carry oxygenated blood to the left atrium. Pulmonary arteries carry deoxygenated blood to the lungs; the vena cava enters the right atrium.
Ventricular ejection into the aorta and pulmonary trunk occurs while which valves are open?
During ejection the semilunar (aortic and pulmonary) valves open while the atrioventricular valves are closed, preventing backflow into the atria.