AEMCA Practice Exam

How do loop diuretics primarily function in the body?

1. By enhancing water retention

2. By inhibiting sodium and potassium re-absorption at the thick ascending limb of Henle

3. By blocking aldosterone

4. By obstructing the distal convoluted tubule

The correct answer is: By inhibiting sodium and potassium re-absorption at the thick ascending limb of Henle

Loop diuretics primarily function by inhibiting sodium and potassium re-absorption at the thick ascending limb of the loop of Henle in the nephron. This action leads to a significant increase in the excretion of sodium, chloride, and water, which ultimately results in diuresis, or increased urine production. In the thick ascending limb, loop diuretics target a specific transporter known as the Na-K-2Cl cotransporter. By blocking this transporter, loop diuretics prevent the reabsorption of these electrolytes back into the bloodstream. Consequently, the osmotic gradient in the tubule is altered, leading to decreased reabsorption of water and an overall increase in urine output. The other options describe different mechanisms that do not accurately reflect the primary action of loop diuretics. For instance, enhancing water retention goes against the fundamental function of diuretics, which is to promote fluid elimination. Although aldosterone antagonists do block aldosterone, this is not the main mechanism of action for loop diuretics. Lastly, obstruction at the distal convoluted tubule is not related to the specific action of loop diuretics; rather, it pertains to the action of thiazide diuretics. Thus,