Human urine is usually acidic because :

Options

A. Excreted plasma proteins are acidic
B. Potassioum and sodium exchange generates actively
C. Hydrogen ions are actively secreted into filtirate
D. The sodium transporter exchanges one hydrogen each sodium ion , in peritubular capillaries .

Answer

**Step-by-Step Solution:**

1. **Understanding Urine Composition**: Human urine is primarily composed of water, urea, creatinine, uric acid, and various ions. The composition can influence the pH level of urine.

2. **Normal pH of Urine**: The typical pH of human urine ranges from about 4.5 to 8, but it is usually slightly acidic, with an average pH around 6.0.

3. **Role of Hydrogen Ions**: The acidity of urine is largely due to the presence of hydrogen ions (H+). These ions are actively secreted into the urine during the filtration process in the kidneys.

4. **Mechanism of Acid Secretion**: In the renal tubules, particularly in the proximal convoluted tubule, hydrogen ions are exchanged for sodium ions. This process helps to maintain the acid-base balance in the body.

5. **Conclusion**: Therefore, the primary reason why human urine is usually acidic is that hydrogen ions are actively secreted into the filtrate during urine formation. This makes option C the correct answer.

**Final Answer**: Human urine is usually acidic because hydrogen ions are actively secreted in the filtrate.

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