Which of the following structure is not made up of a single layer of flattened cell with irregular boundaries?

Options

A. Alveoli
B. Endothelium
C. Bowman's capsule
D. Skin

Answer

To solve the question "Which of the following structure is not made up of a single layer of flattened cell with irregular boundaries?", we will analyze each option provided in the context of their cellular structure.

### Step-by-Step Solution:

1. **Understanding the Question**:
- The question asks us to identify a structure that is NOT made up of a single layer of flattened cells with irregular boundaries. This means we are looking for a structure that either has multiple layers or is not composed of flattened cells.

2. **Analyzing Alveoli**:
- Alveoli are tiny air sacs in the lungs where gas exchange occurs. They are made up of a single layer of flattened epithelial cells (simple squamous epithelium). Therefore, alveoli fit the description of a structure made up of a single layer of flattened cells.

3. **Analyzing Endothelium**:
- The endothelium is the thin layer of cells lining the blood vessels. It is also composed of a single layer of flattened cells. Thus, endothelium fits the criteria of a single layer of flattened cells.

4. **Analyzing Bowman's Capsule**:
- Bowman's capsule is part of the nephron in the kidney and is involved in the filtration of blood. It consists of a single layer of flattened cells (podocytes) that form the outer layer of the capsule. Hence, Bowman's capsule also meets the criteria of a single layer of flattened cells.

5. **Analyzing Skin**:
- The skin is composed of multiple layers, primarily the epidermis and dermis. The epidermis itself is made up of several layers of cells (stratified squamous epithelium), which do not fit the description of a single layer of flattened cells. Therefore, skin is the structure that does NOT consist of a single layer of flattened cells with irregular boundaries.

6. **Conclusion**:
- Based on the analysis, the correct answer is **skin**, as it is not made up of a single layer of flattened cells.

### Final Answer:
The structure that is not made up of a single layer of flattened cells with irregular boundaries is **skin**.