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. **Understanding Macula Densa Cells**:
- The macula densa cells are specialized cells located in the kidney. They are found in the distal convoluted tubule (DCT) at the point where the loop of Henle meets the DCT.

2. **Location and Structure**:
- These cells form a thickening in the wall of the distal tubule, which is adjacent to the glomerulus. This positioning allows them to monitor the composition of the filtrate.

3. **Sensitivity to Sodium Chloride**:
- Macula densa cells are particularly sensitive to the concentration of sodium chloride (NaCl) in the distal convoluted tubule. They play a crucial role in regulating kidney function.

4. **Response to Decreased Sodium Concentration**:
- When the concentration of sodium ions (Na+) decreases, the macula densa cells detect this change. This decrease in sodium concentration triggers two main responses:
- **First Response**: It reduces the resistance to blood flow, which helps to restore the glomerular filtration rate (GFR) towards normal levels.
- **Second Response**: It stimulates the release of renin from the juxtaglomerular cells located in the afferent and efferent arterioles. Renin is an important enzyme that helps regulate blood pressure and fluid balance.

5. **Conclusion**:
- Therefore, macula densa cells get stimulated by a decrease in sodium ion concentration (Na+).

**Final Answer**: Macula densa cells get stimulated by decreased Na+ ion concentration.

---