PH of blood is maintained at 7.4 due to  

Options

A. buffering activity of plasma proteins
B. lipo proteins of cell membrane
C. fibrin
D. none

Answer

To answer the question about how the pH of blood is maintained at 7.4, we can break down the explanation into several key steps:

### Step-by-Step Solution:

1. **Understanding Blood pH**:
- The normal pH of blood is slightly alkaline, specifically around 7.4. This pH level is crucial for various biochemical processes in the body.

2. **Role of Buffers**:
- The pH of blood is maintained through buffering systems. Buffers are substances that help resist changes in pH by neutralizing acids or bases.

3. **Key Compounds in Blood Buffering**:
- The primary buffering system in blood involves two key compounds: carbonic acid (H2CO3) and bicarbonate ion (HCO3-).
- Carbonic acid acts as a weak acid, while bicarbonate serves as its conjugate base.

4. **Formation of Bicarbonate**:
- Bicarbonate ions are formed from carbon dioxide (CO2) that is produced in the body. CO2 can combine with water to form carbonic acid, which then dissociates to release bicarbonate ions.

5. **Role of Hemoglobin**:
- Hemoglobin, a protein found in red blood cells, plays a crucial role in this buffering system. It binds to carbon dioxide, facilitating the formation of bicarbonate.
- Hemoglobin also helps buffer excess hydrogen ions (H+) that are produced during metabolic processes, thus preventing significant changes in blood pH.

6. **Conclusion**:
- The buffering activity of plasma proteins, particularly hemoglobin, is essential in maintaining the pH of blood at 7.4. Therefore, the correct answer to the question is that the pH of blood is maintained due to the buffering action of plasma proteins.

### Final Answer:
The pH of blood is maintained at 7.4 due to the buffering activity of plasma proteins, specifically hemoglobin.

---