MLT GlobePhysiology: Cardiovascular physiology – page 2
40 Physiology MCQs on Cardiovascular physiology with answers and explanations.
A normal cardiac output of about 5 L/min refers to blood ejected by:
Cardiac output is stroke volume × heart rate for a single ventricle. The two ventricles have equal outputs; output per beat is the stroke volume.
A sudden threat triggers a sympathetic "fight or flight" response. Which change is expected?
Sympathetic activation raises heart rate, blood pressure and metabolic rate, dilates pupils and slows digestion. Pupil constriction and increased motility are parasympathetic effects.
According to Poiseuille's law, which change most increases resistance to blood flow in a vessel?
Resistance is inversely proportional to the fourth power of radius, so small reductions in radius sharply increase resistance. Lower viscosity and shorter length decrease it.
Which vessels hold the largest share of circulating blood volume and act as a reservoir?
Veins are highly compliant capacitance vessels holding about 60–65% of blood volume. Arterioles are the main resistance vessels.
Tracing blood leaving the left ventricle, which sequence of vessels is correct?
Blood passes from large arteries to arterioles, exchanges across capillaries, then collects in venules and veins returning to the heart.
The first heart sound ("lub") heard at the start of ventricular systole is caused by:
S1 coincides with atrioventricular valve closure as ventricular pressure rises. Semilunar valve closure causes S2; valve opening is normally silent.
The second heart sound ("dub") at the end of ventricular systole results from:
S2 is produced by semilunar valve closure when ventricular pressure falls below arterial pressure. Rapid ventricular filling produces the third sound (S3) when audible.
Blood leaving which chamber of the heart is under the greatest pressure?
The left ventricle pumps into the high-resistance systemic circuit, generating about 120 mmHg systolic, far above right ventricular (~25 mmHg) or atrial pressures.
A reading of 120/80 mmHg is recorded. How is this blood pressure value conventionally written?
Blood pressure is written as systolic/diastolic, here 120 systolic and 80 diastolic. Pulse pressure is their difference (40 mmHg).
Which statement about the myocardium is correct?
Myocardium is the thick muscular layer of branched cells joined by intercalated discs, working as a functional syncytium. Stretched atrial myocytes release atrial natriuretic peptide.
Which statement about the atrioventricular (mitral and tricuspid) valves is correct?
Chordae tendineae stop the AV cusps inverting in systole. The mitral valve has two cusps, and the valves are open during atrial depolarisation and contraction (P wave).
A 25-year-old runs hard for 10 minutes. Which parameter is expected to decrease?
Sympathetic activation during exercise raises heart rate, breathing and heat production, while diverting blood away from the gut and reducing motility.
Coronary arteries arise from the aortic root. At rest, about what share of the left ventricle's output flows through them?
Resting coronary flow is roughly 225-250 mL/min, about 4-5% of cardiac output, despite the heart's high oxygen demand.
At a heart rate of 75 beats/min, which phase takes up the largest share of each 0.8 s cycle?
Atrial systole lasts about 0.1 s and ventricular systole about 0.3 s, leaving about 0.4 s of complete cardiac diastole for filling and coronary flow.
In a resting adult, cerebral blood flow (about 15% of cardiac output) is closest to:
The brain receives roughly 50-55 mL/100 g/min, around 750 mL/min in total, which is about 15% of a 5 L/min resting cardiac output.
After leaving the atrioventricular node, the cardiac impulse travels in which sequence to reach the ventricular myocardium?
The impulse passes from the AV node into the bundle of His, down the right and left bundle branches, then spreads through Purkinje fibres into ventricular muscle.
Which statement about carotid sinus and aortic arch baroreceptors is correct?
Baroreceptors respond to wall stretch; rising pressure increases firing, which reduces sympathetic output and heart rate. Oxygen is sensed by chemoreceptors. They adapt within days, so they mainly buffer short-term changes.
Which feature distinguishes the ventricular muscle action potential from that of skeletal muscle?
Both action potentials are all-or-none with a sodium-driven upstroke. Cardiac muscle alone has a plateau from L-type calcium channels, lengthening the refractory period and preventing tetany.
Which statement about total cerebral blood flow at rest is correct?
The brain receives ~750 mL/min (~15% of output). Raised pCO2 dilates cerebral vessels, autoregulation keeps flow constant between ~60–140 mmHg, and sympathetic control is minor.
Epinephrine raises SA node firing via beta-1 receptors, Gs protein, adenylyl cyclase and cAMP. In this pathway, the first messenger is:
The extracellular signal molecule (hormone) is the first messenger; cAMP generated inside the cell is the second messenger. Receptor and enzyme are transducers.