Which has no muscular walls `:-`

Options

A. Artery
B. Vein
C. Arteriole
D. Capillary

Answer

To solve the question "Which has no muscular walls?" we will analyze the given options: artery, vein, arteriole, and capillary.

### Step-by-Step Solution:

1. **Understanding the Structure of Blood Vessels**:
- Blood vessels can be classified into arteries, veins, arterioles, and capillaries, each with distinct structural features.

2. **Analyzing Each Option**:
- **Artery**: Arteries have thick muscular walls that help withstand high pressure from the heart's pumping action.
- **Vein**: Veins have thinner muscular walls compared to arteries, but they still possess some muscle fibers to help in the return of blood to the heart.
- **Arteriole**: Arterioles are smaller branches of arteries and have 1-2 layers of smooth muscle fibers, indicating they also have muscular walls.
- **Capillary**: Capillaries are the smallest blood vessels and have walls that consist only of a single layer of endothelial cells. They do not have muscular walls.

3. **Identifying the Correct Answer**:
- Since capillaries are the only type of blood vessel listed that lacks muscular walls, we conclude that the answer to the question is **capillary**.

4. **Function of Capillaries**:
- Capillaries facilitate the exchange of gases (oxygen and carbon dioxide) and nutrients between blood and surrounding tissues due to their thin walls, which allow for easy diffusion.

### Final Answer:
The correct option is **capillary**, as it has no muscular walls.

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