If a thiazide diuretic is administered for hypertension, the response seen within 24 hrs on the excretion of different electrolytes are:
## Core Concept
Thiazide diuretics act on the distal convoluted tubule of the nephron, inhibiting the **sodium-chloride cotransporter (NCC)**, which is responsible for the reabsorption of sodium and chloride ions. This action leads to increased excretion of sodium and chloride in the urine.
## Why the Correct Answer is Right
The correct answer shows an increase in the excretion of sodium (Na+), chloride (Cl-), and potassium (K+) ions, along with a mild increase in calcium (Ca2+) reabsorption (or decrease in excretion). Thiazides increase sodium and chloride excretion by inhibiting the **NCC**. The increased delivery of sodium to the collecting duct enhances potassium secretion by the **principal cells** (or intercalated cells to some extent), leading to increased potassium excretion. The effect on calcium is unique to thiazides; they decrease calcium excretion by increasing its reabsorption in the **proximal convoluted tubule**, likely due to increased sodium reabsorption.
## Why Each Wrong Option is Incorrect
- **Option A:** Incorrect because it does not accurately reflect the changes in electrolyte excretion seen with thiazide diuretics. Thiazides do increase sodium and chloride excretion but the effect on other electrolytes needs to match the known mechanism.
- **Option B:** Incorrect because, although it shows increased sodium and chloride excretion, the effects on potassium and calcium need to align with thiazide action.
- **Option D:** Incorrect because it inaccurately represents the changes in electrolyte excretion; specifically, thiazides do not cause a significant decrease in potassium excretion.
## Clinical Pearl / High-Yield Fact
A key point to remember is that thiazide diuretics can cause **hypokalemia** due to increased potassium excretion. This side effect is significant because it can lead to cardiac arrhythmias and muscle weakness. Monitoring potassium levels and possibly supplementing potassium or using potassium-sparing diuretics is a common clinical practice.
## Correct Answer: C.