Question

What does diapedesis refer to?

• A. Attachment of neutrophils to blood vessel
• B. Escape of neutrophils from capillaries through the capillary endothelium
• C. Stimulation of cytokine secretion by inflammatory cells
• D. Response of mediator cells to cytokine secretion

Hint:

Diapedesis is the physical step where neutrophils cross the capillary endothelium into tissue, after adhesion.

Answer 1

The Correct Option is B

Step 1: Place diapedesis in the sequence of leukocyte extravasation.
When tissue is injured or infected, leukocytes must travel from the blood inside a vessel to the site of injury in the tissue. This journey happens in an ordered sequence: margination, rolling, firm adhesion, and then transmigration.

Step 2: Define diapedesis precisely.
Diapedesis, also called transmigration, is the step where the neutrophil squeezes itself between adjacent endothelial cells and escapes out of the capillary, moving from inside the vessel lumen into the surrounding tissue.

Step 3: Separate this from the earlier steps.
Attachment of neutrophils to the vessel wall is an earlier step, called adhesion, mediated by integrins on the neutrophil binding to ICAM-1 on the endothelium. Diapedesis happens only after this firm attachment, when the neutrophil actively crosses the endothelial barrier.

Step 4: Rule out the cytokine based options.
Stimulation of cytokine secretion by inflammatory cells and the response of mediator cells to cytokines describe chemical signalling between cells, which drives and coordinates inflammation, but neither one is the physical act of a neutrophil crossing the vessel wall. Diapedesis is specifically that physical escape.

Final Answer:
Diapedesis is the escape of neutrophils from the capillary lumen across the capillary endothelium into the tissue. \[ \boxed{\text{Escape of neutrophils across the capillary endothelium}} \]