Basic Biomedical Sciences One Case Two: "This Oozing Makes Me Woozy"

Basic Biomedical Sciences One Case Two: "This Oozing Makes Me Woozy"

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MECHANISMS INVOLVED IN HEMOSTASIS VASCULAR CONSTRICTION

· Immediately after a blood vessel has been cut or ruptured, the trauma to the vessel wall itself causes the vessel to contract; this instantaneously reduces the flow of blood from the vessel rupture.

· The contraction results from nervous reflexes, local myogenic spasm, and local humoral factors (e.g. endothelin - a potent endothelium-derived vasoconstrictor) from the traumatized tissues and blood platelets.

· The nervous reflexes are initiated by pain nerve impulses or other impulses that originate from traumatized vessel or from nearby tissues.

· However, most of the vasoconstriction probably results from local direct damage to the vascular wall. For the smaller vessels, the platelets are responsible for much of the vasoconstriction by releasing the vasoconstrictor substance thromboxane A Two.

· The more a vessel is traumatized, the greater the degree of spasm; this means that a sharply cut blood vessel usually bleeds much more than does a vessel ruptured by crushing. The local vascular spasm can last for many minutes or even hours, during which time the processes of platelet plugging and blood coagulation can take place.