also known as diapedesis, refers to the exit from the bloodstream of neutrophils and other circulating leukocytes.

Extravasation

Explanation:

Neutrophils and other circulating leukocytes, present in blood circulation, need to cross the walls of capillaries within the tissues to reach the site of infection. These cells exhibit a change in shape and squeeze through the endothelial layer of walls of blood capillaries and enter the interstitial tissue fluid.

Once in the tissue fluid, these immune cells reach the site of infection to kill pathogens or the other causative agents of injury. After this, these cells again enter the blood circulation via lymph vessels.

This process of movement of leukocytes from blood circulation into the interstitial space, and from interstitial space to the lymph vessels and finally back to the blood circulation is called extravasation or diapedesis.