NTA Cardiovascular Anatomy and Physiology 3

Question 1

Which electrolyte is most critical for maintaining the cardiac action potential and myocardial contractility?

Accepted Answer

Calcium

Answer

Calcium influx during phase 2 (plateau) of the action potential couples electrical excitation to myocardial contraction.

Question 2

The sympathetic nervous system affects the heart primarily by:

Accepted Answer

Increasing heart rate and contractility

Answer

Sympathetic stimulation releases norepinephrine, which binds beta-1 receptors to increase heart rate (chronotropy) and contractility (inotropy).

Question 3

What is the primary function of the Purkinje fibers?

Accepted Answer

Rapidly distribute the electrical impulse throughout the ventricles

Answer

Purkinje fibers conduct impulses very rapidly through the ventricular walls, ensuring near-simultaneous contraction of both ventricles.

Question 4

Hypokalemia (low potassium) is most likely to cause which ECG change?

Accepted Answer

Prominent U waves

Answer

Hypokalemia characteristically produces prominent U waves (often larger than the T wave) and may predispose to dysrhythmias.

Question 5

Which vessel carries oxygenated blood from the lungs to the heart?

Accepted Answer

Pulmonary vein

Answer

The four pulmonary veins return oxygenated blood from the lungs to the left atrium, completing the pulmonary circuit.

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