Macula densa cells get stimulated by

Options

A. Decreased `Na^(+)`
B. Decreased `K^(+)`
C. Alteration in transmural pressure
D. Hypovolemia

Answer

### Step-by-Step Solution:

1. **Identify Macula Densa Cells**:
- Macula densa cells are specialized cells located in the distal convoluted tubule (DCT) of the nephron.

2. **Location of Macula Densa**:
- These cells are situated adjacent to the Juxtaglomerular Apparatus (JGA), which plays a crucial role in regulating blood pressure and the filtration rate of the glomerulus.

3. **Stimulus for Macula Densa Cells**:
- Macula densa cells are primarily stimulated by a decrease in the concentration of sodium ions (Na+) in the filtrate that flows through the DCT.

4. **Function of Macula Densa Cells**:
- When sodium ion concentration decreases, macula densa cells respond by signaling the JGA to release renin. This process helps in the reabsorption of sodium and ultimately regulates blood pressure.

5. **Conclusion**:
- Therefore, the correct answer to the question is that macula densa cells get stimulated by a decrease in sodium ion concentration.