What is diapedesis?

Options

A. a kind of amoeboid movement
B. the process of filtration of urea in kidney
C. a type of locomotion found in Hydra
D. migration of WBCs into the tissue spaces from blood capillaries

Explanation

### Step-by-Step Solution:

1. **Understanding Diapedesis**: Diapedesis refers to the process through which white blood cells (WBCs) move out of the bloodstream and into the surrounding tissues. This movement is crucial for the immune response.

2. **Identifying the Context**: Diapedesis is particularly important during an inflammatory response, which occurs when the body detects foreign pathogens, such as bacteria or viruses.

3. **Mechanism of Diapedesis**: The WBCs, which are part of the immune system, squeeze through the walls of the capillaries. This process is facilitated by the amoeboid movement of the WBCs, allowing them to navigate through the narrow spaces between the endothelial cells of the blood vessels.

4. **Purpose of Diapedesis**: The primary goal of diapedesis is to enable WBCs to reach the site of infection or injury, where they can attack and eliminate pathogens, thus protecting the body from disease.

5. **Conclusion**: Based on the definitions and context provided, the correct answer to the question "What is diapedesis?" is the migration of WBCs into the tissue spaces from blood capillaries.

### Final Answer:
Diapedesis is the migration of WBCs into the tissue spaces from blood capillaries.