Page 132 - Textbook of Pathology, 6th Edition

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SECTION I

General Pathology and Basic Techniques
Figure 5.20 Schematic representation of pathways of coagulation mechanism and fibrinolytic system.

Regulation of coagulation system. The blood is kept in fluid down, the blood cells including platelets marginate to the
state normally and coagulation system kept in check by periphery and form a kind of pavement close to endothelium
controlling mechanisms. These are as under: (margination and pavementing) (Fig. 5.21,B). While stasis
a) Protease inhibitors. These act on coagulation factors so as allows a higher release of oxygen from the blood, turbulence
to oppose the formation of thrombin e.g. antithrombin III, may actually injure the endothelium resulting in deposition
protein C, C inactivator, α1-antitrypsin, α2-macroglobulin. of platelets and fibrin. Formation of arterial and cardiac
1
b) Fibrinolytic system. Plasmin, a potent fibrinolytic enzyme,
is formed by the action of plasminogen activator on
plasminogen present in the normal plasma. Two types of
plasminogen activators (PA) are identified:
Tissue-type PA derived from endothelial cells and
leucocytes.
Urokinase-like PA present in the plasma.
Plasmin so formed acts on fibrin to destroy the clot and
produces fibrin split products (FSP).
4. ALTERATION OF BLOOD FLOW. Turbulence means
unequal flow while stasis means slowing.
i) Normally, there is axial flow of blood in which the most
rapidly-moving central stream consists of leucocytes and red
cells. The platelets are present in the slow-moving laminar
stream adjacent to the central stream while the peripheral
stream consists of most slow-moving cell-free plasma close
to endothelial layer (Fig. 5.21,A).
ii) Turbulence and stasis occur in thrombosis in which the
normal axial flow of blood is disturbed. When blood slows Figure 5.21 Alterations in flow of blood.