186 Anatomy, Histology, and Cell Biology
There are several stages in extravasation:rolling, firm adhesion, and diapedesis.Cytokines,
such as tumor necrosis factor-alpha (TNF-α), are released during inflammation and
stimulate the endothelium of veins to express the surface adhesion molecule P-selectin
(also E-selectin). E and P-selectins bind reversibly to glycoproteins on leukocytes
causing them to rollalong the endothelial surface. Intercellular adhesion molecules (e.g.
ICAM-1) are up-regulated and bind to the leukocyte integrins LFA-1 and CR3.Adhesion
of leukocytes results in arrest of leukocyte motion, allowing secreted proteases to
disrupt endothelial tight junctions and the basement membrane, subsequently resulting
indiapedesis. L-selectins expressed by leukocytes are also involved in the process.
95.The answer is b.(Alberts, pp 1113–1118.)A mutation resulting in loss
of integrin function would prevent leukocytes from extravasting from the
blood to the lymph nodes (see figure below) and sites of inflammation result-
ing in increased lymphocytes in the blood (leukocytosis), not leukopenia