"Methemoglobin" refers to

Options

A. A colourless respiratory pigment
B. Oxidized haemoglobin
C. Oxygenated haemoglobin
D. Deoxygenated haemoglobin

Answer

**Step-by-Step Solution:**

1. **Understanding Hemoglobin:**
- Hemoglobin is a respiratory pigment found in red blood cells that is responsible for transporting oxygen throughout the body. It contains iron, which is crucial for its function.

2. **States of Hemoglobin:**
- Hemoglobin exists in two main states:
- **Oxyhemoglobin:** This is the form of hemoglobin when it is bound to oxygen.
- **Deoxyhemoglobin:** This is the form of hemoglobin when it is not bound to oxygen.

3. **Oxidation of Iron:**
- In normal hemoglobin, the iron is in the ferrous (Fe²⁺) state. However, if the iron gets oxidized, it changes from the ferrous state to the ferric (Fe³⁺) state.

4. **Formation of Methemoglobin:**
- When the iron in hemoglobin is oxidized to the ferric state, hemoglobin is converted into methemoglobin.

5. **Characteristics of Methemoglobin:**
- Methemoglobin is a brown pigment and is incapable of carrying oxygen. This means it cannot perform the primary function of hemoglobin, which is to transport oxygen to tissues.

6. **Conclusion:**
- Therefore, "methemoglobin" refers to the oxidized form of hemoglobin that cannot transport oxygen.

**Final Answer:**
Methemoglobin refers to the oxidized form of hemoglobin that is incapable of carrying oxygen.

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