Intramural Fibrinoid of Uteroplacental Arteries and Veins

Fibrinoid of the uteroplacental arteries is very likely to be composed mainly of fibrin-type fibrinoid. At present, there is no evidence for the secretion of matrix-type fibrinoid by endovascular trophoblast cells. Rather, Sheppard and Bonnar (1974b, 1988) and Bonnar and Sheppard (1977) described typical fibrin with a 200-A cross-striation in all layers of these vessel walls. They observed intraluminal fibrin thrombi attached to the intimal lining and noted that muscular and elastic components of the vessel walls may be replaced by fibrin.

Whether the deposition is caused by increased fibrin polymerization or by decreased fibrinolytic activity is a matter of dispute. Endothelium is well known to have fibrinolytic activity. The endothelium of the uteroplacental arteries, however, becomes largely replaced by tro-phoblast during pregnancy. According to Sheppard and Bonnar (1974a), also trophoblast is discussed as being a potent source of antifibrinolytic activity. The latter is said to prevent the enzymatic digestion of fibrin (Kawano et al., 1968).

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  • Category: Pregnancy and childbirth