What is the process called when leukocytes pass through the walls of small capillary blood vessels to reach infected tissues?

• A. Leukocyte migration
• B. Emigration
• C. Diapedesis
• D. Extravasation

Answer: (D)

The process in which leukocytes pass through the walls of small capillary blood vessels to reach infected tissues is called diapedesis. During diapedesis, leukocytes change shape and squeeze through the endothelial cells of the capillaries, allowing them to exit the bloodstream and migrate toward areas of infection or inflammation. This mechanism is essential for the immune response, as it enables white blood cells to reach the sites where they are needed to combat pathogens.

Though "extravasation" often refers to the leakage of fluids or substances out of blood vessels, in the context of leukocytes, diapedesis is the more precise term describing their movement through the capillary walls. The terms "leukocyte migration" and "emigration" also relate to leukocytes moving towards infection sites but do not specifically focus on the passage through the capillary walls like diapedesis does. Therefore, understanding diapedesis is crucial in grasping how the immune system functions in response to infection.