## Core Concept
Endothelial cells line the interior surface of blood vessels and lymphatic vessels, playing a critical role in the regulation of blood pressure, blood clotting, and the formation of new blood vessels. They are involved in various physiological and pathological processes.

## Why the Correct Answer is Right
Endothelial cells are known to have **Weibel-Palade bodies**, which are specific organelles found in these cells. Weibel-Palade bodies contain various proteins, including von Willebrand factor (vWF) and P-selectin, which are crucial for blood clotting and inflammation. The presence of Weibel-Palade bodies is a distinctive feature of endothelial cells.

## Why Each Wrong Option is Incorrect
- **Option A:** This option is incorrect because it does not accurately represent a characteristic specific to endothelial cells.
- **Option B:** This option is incorrect as it does not specify Weibel-Palade bodies, which are unique to endothelial cells.
- **Option C:** This option might mention a feature not exclusive or specific to endothelial cells, making it incorrect in this context.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that **Weibel-Palade bodies** are not only a marker for endothelial cells but also play a significant role in vascular biology, including angiogenesis and response to vascular injury. Damage to endothelial cells can lead to various cardiovascular diseases.

## Correct Answer: D. Weibel-Palade bodies