The gaps are created through the action of chemical mediators on endothelium. Once through the endothelium the leukocytes may be delayed passing through the basement membrane and pericytes. Initial emigration occurs 30-40 minutes after the inflammatory stimulus, and involves mainly neutrophils. Several hours later, monocyte emigration will occur and progressively increase. Lymphocytes are sluggish and generally will not emigrate until later in the process.
Erythrocytes can move passively to the extravascular space during emigration by diapedesis.
Chemotaxis Chemotaxis is the process by which leukocytes move to the site of an inflammatory focus. It is a directional migration of a cell in response to a chemical attractant. The concentration of attractant is detected as a gradient, and migration is along the gradient. Through a stereotyped set of events, the chemotaxin interacts with the cell membrane of leukocytes, causing activation of the cell locomotor apparatus and ameboid movement towards the inflammatory focus. Cell locomotion is a calcium-dependent phenomenon.