Compared to an artery, the wall of a vein differs in which of the following ways?

Options

A. It consists of three coats called tunics.
B. It is lined by a thin layer of endothelium.
C. It contains smooth muscle.
D. The middle tunic is thin.

Answer

To answer the question "Compared to an artery, the wall of a vein differs in which of the following ways?", we can analyze the structural differences between arteries and veins step by step.

### Step-by-Step Solution:

1. **Understanding the Structure**: Both arteries and veins have three layers in their walls: the tunica intima (inner layer), tunica media (middle layer), and tunica externa (outer layer).

2. **Tunica Intima**: The inner lining of both arteries and veins is made up of a thin layer of endothelial cells. This layer is present in both types of blood vessels.

3. **Tunica Media**: This is the middle layer that consists primarily of smooth muscle and elastic fibers. In arteries, the tunica media is thick, which helps maintain blood pressure and allows arteries to withstand the high pressure of blood being pumped from the heart. In contrast, the tunica media in veins is much thinner, which means veins have less smooth muscle and fewer elastic fibers.

4. **Lumen Size**: Due to the thickness of the tunica media in arteries, the lumen (the inner open space through which blood flows) is narrower in arteries compared to veins. Veins have a larger lumen, which allows them to hold more blood.

5. **Tunica Externa**: The outer layer, or tunica externa, is also present in both arteries and veins, but it is generally thicker in veins than in arteries.

6. **Conclusion**: The primary difference between the walls of arteries and veins is that the tunica media in veins is thinner compared to that in arteries. This structural difference is crucial for the different functions of arteries and veins in the circulatory system.

### Final Answer:
Compared to an artery, the wall of a vein differs primarily in that the tunica media is thinner.

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