Blood coagulation vascular system

Platelets play a role in each of the mechanisms of normal hemostasis vasoconstriction, formation of the platelet plug, and blood coagulation. However, they are also involved in pathological processes that lead to atherosclerosis and thrombosis (formation of a blood clot within the vascular system). Antiplatelet drugs interfere with platelet function and are used to prevent the development of atherosclerosis and formation of arterial thrombi. 

Development of the LAL assay was based upon the observation that the presence of Gramnegative bacteria in the vascular system of the American horseshoe crab, Limulus polyphemus, resulted in the clotting of its blood. Tests on fractionated blood showed that the factor responsible for coagulation resided within the crab s circulating blood cells, i.e. the amoebocytes. Further research revealed that the bacterial agent responsible of initiation of clot formation was endotoxin. 

Physiologically, the maintenance of blood circulating freely in the vascular system reflects a meticulous balance between coagulation and fibrinolysis. After microvascular injury subendothelial structures are exposed to which platelets adhere. This is followed by their aggregation and activation of the coagulation cascade with the ultimate conversion of fibrinogen to fibrin. 

The preservation of an intact vascular system requires not only that blood be capable of coagulating but... 

The drugs discus.sed in this chapter arc used for their action on the heart or other parts of the vascular system, to modify the total output of the heart or the distribution of blood to the circulatory system. These drugs are used in the treatment of angina, cardiac arrhythmias, hypertension, hyperlipidemias. and di.sorders of blood coagulation. This chapter also includes a discu.ssion of hypoglycemic agents, thyroid hormones, and antithyroid drugs. 

Normally, newly formed blood clots (fibrin) are dissolved by the actions of the fibrinolytic system, the purpose of which is the removal of unwanted clots without damaging the integrity of the vascular system. This system works via a relatively nonspecific protease enzyme called plasmin, the function of which is to digest fibrin (the very last step of the coagulation cascade) (Fig. 31.1). The lack of substrate specificity of plasmin is illustrated by the fact that it degrades fibrin clots as well as some plasma proteins and coagulation factors. 

The blood clot formed in a test tube is strikingly different from a thrombus deposit formed in vivo in the vascular system. A clot in a test tube consists of a fibrin network in which red cells, white cells, and relatively small numbers of platelets are found. On the other hand, an in vivo thrombus deposit consists of large amorphous masses of platelets, surrounded by white cells with a few red cells. However, it is possible to form deposits closer to thrombi rather than to blood clots in vitro by using circulating plastic loops in which the blood is in motion during coagulation. ... 

The relatively high incidence of thromboembolic phenomena in women on the pill prompted an examination on the effects of the estrogenic and/or progesteronic components in the pill on the surface charge characteristics of the vascular system. Electrophoretic mobilities of erythrocytes and platelets and blood coagulation times were determined with samples of blood drawn from 33 women on the pill and 30 control subjects. The electrophoretic mobilities were reduced thrombin recalcification times were not affected but thrombin times and partial thromboplastin times were shortened. 

Documented effects Effects on the cardio-vascular system and blood coagulability is equal to that of Lagochilus inebrians Bunge (Abdurakhmanov 1962). A tincture of the aboveground parts had low toxicity, hemostatic and sedative properties similar to those of L. inebrians, and hypotensive effects which surpassed those of L inebrians. Clinical tests established the efficacy of the tincture for the treatment of hypertonic illness and as a hemostatic. A tincture of leaves and flowers exhibited hypotensive and sedative effects, and increased the speed of blood coagulation without increase of the prothrombin time (Alimbaeva 1961). 

Inflammation is the first response of any vascularized tissue to tissue damage (surgery trauma or presence of a foreign body). Injury and vascular damage triggers the two branches of the blood coagulation system. The first involves activation of... 

Little intravascular coagulation of blood occurs in normal physiological conditions. Hemostasis involves the interplay of three procoagulant phases vascular, platelet, and coagulation) that promote blood clotting to prevent blood loss (Fig. 22.1). The fibrinolytic system prevents propagation of clotting beyond the site of vascular injury and is involved in clot dissolution, or lysis (Fig. 22.2). 

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