CVS Practice Test

The Na+/Ca++ exchange pump, which operates on a ratio of three sodium ions (Na+) in exchange for one calcium ion (Ca++), does not operate solely in one direction. Instead, this pump can function bidirectionally depending on the electrochemical gradients of sodium and calcium ions across the cell membrane.

Under normal physiological conditions, the pump primarily removes calcium ions from the cell while bringing sodium ions in, which is crucial in muscle contractions and neuronal signaling. However, if the conditions change—such as altered ion concentrations or membrane potential—the pump can also work in reverse, allowing calcium ions to enter the cell while expelling sodium ions. This flexibility allows the cell to respond to various signals and maintain homeostasis of ion concentrations.

The other choices suggest specific conditions (like hypoxia or hypercalcemic states) that would limit the function of the pump to one direction. However, the pump's ability to operate in both directions is a fundamental aspect of its role in cellular ion regulation. Therefore, the answer is accurately identified as false since the Na+/Ca++ exchange pump can indeed function in both directions under different physiological circumstances.