Anatomy and Physiology / Unit 8: The Cardiovascular and Lymphatic Systems
8.3 Hemostasis and Blood Types
Notes
Hemostasis is the stopping of bleeding in three steps: (1) vascular spasm (vessel constricts); (2) platelet plug forms; (3) coagulation (clotting): a cascade converts prothrombin to thrombin, which converts fibrinogen to fibrin that forms a mesh. Calcium and vitamin K are needed. Hemophilia is inherited lack of a clotting factor. A thrombus is a clot in an unbroken vessel; an embolus is a clot that travels.
- ABO blood groups depend on antigens on red blood cells: type A has A antigens (anti-B antibodies in plasma), type B has B antigens (anti-A), type AB has both (no anti-A or anti-B), type O has neither (both anti-A and anti-B).
- Rh factor: Rh-positive cells have the D antigen. Mismatched transfusion causes agglutination and hemolysis.
- Type O negative is the universal red cell donor; type AB positive is the universal recipient.
- Example: a person with type A blood can safely receive type A or type O red cells.
Practice
Smooth muscle constricts immediately, followed by the platelet plug and then coagulation.
Type B plasma has anti-A antibodies, so type A and AB cells would agglutinate. Type O cells lack A and B antigens.
Type AB has both antigens on its cells, so it does not form either antibody.
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