Page 85 - Veterinary Immunology, 10th Edition

vessels. This leakage occurs in two stages. First, there is an
VetBooks.ir immediate increase caused by vasoactive molecules produced by

sentinel cells, damaged tissues, and nerves (Table 3.2). The second
phase of leakage occurs several hours after the onset of

inflammation, at a time when the leukocytes are beginning to
emigrate. Endothelial and perivascular cells contract so that they
pull apart and allow fluid and cells to escape through the
intercellular spaces. After the invaders are eliminated, the

inflammation is terminated, and blood flow returns to normal.

TABLE 3.2

Some Vasoactive Molecules Produced During Acute
Inflammation

Mediator Major Source Function
Histamine Mast cells and basophils, platelets Increased vascular permeability, pain
Serotonin Platelets, mast cells, basophils Increased vascular permeability
Kinins Plasma kininogens and tissues Vasodilation
Increased vascular permeability, pain
Prostaglandins Arachidonic acid Vasodilation
Increased vascular permeability
Thromboxanes Arachidonic acid Increased platelet aggregation
Leukotriene B Arachidonic acid Neutrophil chemotaxis
4
Increased vascular permeability
Leukotrienes C, D, E Arachidonic acid Smooth muscle contraction
Increased vascular permeability
Platelet-activating factor Phagocytic cells Platelet secretion
Neutrophil secretion
Increased vascular permeability
Fibrinogen breakdown products Clotted blood Smooth muscle contraction
Neutrophil chemotaxis
Increased vascular permeability
C3a and C5a Serum complement Mast cell degranulation
Smooth muscle contraction
Neutrophil chemotaxis (C5a)

Vasoactive molecules come from multiple sources. Some are
derived from inactive precursors in plasma. Others are derived
from sentinel cells such as macrophages and mast cells; from
leukocytes such as neutrophils, basophils, and platelets; or from

damaged tissue cells. Stimulated sensory nerves may also produce
neurotransmitters that cause vasodilation and increased
permeability.

Vasoactive Amines

One of the most important of the vasoactive molecules released by
mast cells is histamine (Fig. 3.6). Histamine receptors are expressed

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