In polycythemia the number of red cells increases greatly.This causes adverse effects due to

Options

A. Decreased blood volume
B. Increased circulation time
C. Increased viscosity of blood
D. Increased availability of oxygen

Answer

### Step-by-Step Solution:

1. **Understanding Polycythemia**:
- Polycythemia is a condition characterized by an increased number of red blood cells (RBCs) in the bloodstream. This can occur due to various reasons, including increased production of RBCs or decreased plasma volume.

2. **Effects of Increased RBCs**:
- The primary effect of having a high number of red blood cells is that it increases the overall viscosity (thickness) of the blood. This is because more cells in the same volume of blood make it denser.

3. **Consequences of Increased Blood Viscosity**:
- Increased blood viscosity can lead to several adverse effects. It can slow down blood flow, making circulation less efficient. This can also increase the risk of blood clots, as thicker blood is more prone to coagulation.

4. **Other Factors**:
- While the question mentions decreased blood volume, increased circulation time, and increased availability of oxygen, these are not the primary adverse effects associated with polycythemia. The most significant concern is the increased viscosity of the blood.

5. **Conclusion**:
- Therefore, the adverse effects of polycythemia are primarily due to the increased viscosity of the blood, which can lead to complications such as blood clots and reduced blood flow.

### Final Answer:
The adverse effects in polycythemia are primarily due to **increased viscosity of blood**.

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