Basic and Clinical Sciences (BCSE) Practice Exam 2025 - Free BCSE Practice Questions and Study Guide

The delayed depolarization of cardiac cells in hypokalaemia is primarily a result of potassium ions (K+) not leaving the cell. In a state of hypokalaemia, where there is a lower-than-normal concentration of potassium in the extracellular fluid, the concentration gradient for potassium across the cell membrane becomes less favorable. Normally, potassium ions, which are more concentrated inside the cell, move out during the repolarization phase of the cardiac action potential. This efflux of potassium is critical for returning the membrane potential back to its resting state after depolarization.

When there is inadequate potassium available outside the cell due to hypokalaemia, the ability of potassium to leave the cell is reduced. This impairment in potassium efflux leads to a slower return to the resting membrane potential and delays depolarization, which can affect the overall excitability of cardiac tissues and may result in arrhythmias.

The other options do not directly cause the delayed depolarization in hypokalaemia. While increased sodium influx (as seen in option B) could theoretically contribute to depolarization, it is not the primary factor in the context of potassium deficiency. Decreased calcium levels (option C) and altered chloride permeability (option D) do not have

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