This epithelium is made up of a single thin layer of flattened cells and is involved in forming a diffusion boundary. It is found in :

Options

A. Walls of blood vessels
B. Ducts of glands
C. Tubular parts of nephrons
D. All of these

Answer

To answer the question regarding the type of epithelium made up of a single thin layer of flattened cells involved in forming a diffusion boundary, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Characteristics of the Epithelium**:
- The question describes an epithelium that is composed of a single layer of flattened cells. This type of epithelium is known as **simple squamous epithelium**.

2. **Understand the Function of Simple Squamous Epithelium**:
- Simple squamous epithelium is primarily involved in processes that require diffusion. It facilitates the exchange of gases and other substances due to its thinness, allowing for easy passage.

3. **Determine Where Simple Squamous Epithelium is Found**:
- This type of epithelium is commonly found in areas where diffusion and filtration occur. Key locations include:
- **Alveoli of the lungs**: where gas exchange occurs.
- **Endothelium of blood vessels**: which allows for the diffusion of substances between blood and surrounding tissues.
- **Serous membranes**: lining body cavities.

4. **Evaluate the Options Given**:
- The question suggests that this epithelium is found in specific locations. Based on the characteristics and functions identified, the most relevant location is the **endothelium of blood vessels**.

5. **Conclude the Answer**:
- Therefore, the correct answer is that this epithelium is found in the **walls of blood vessels**.

### Final Answer:
The epithelium made up of a single thin layer of flattened cells involved in forming a diffusion boundary is found in the **walls of blood vessels**.

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