Blood Plasma Plasma –Liquid part of blood –Clear, straw-colored fluid –90% water and 10% solutes –Solutes 6% to 8% of solutes are proteins –Albumins—helps maintain osmotic balance of the blood –Globulins—essential component of the immunity mechanism –Fibrinogen—key role in blood clotting

Blood Clotting (Coagulation) Mechanism of blood clotting –Goal of coagulation is to stop bleeding and prevent loss of vital body fluid in a swift and sure method –“Classic theory” of coagulation advanced in 1905 Identified four components critical to coagulation –Prothrombin –Thrombin –Fibrinogen –Fibrin

Blood Clotting (Coagulation) Mechanism of blood clotting (cont.) –Current explanation of coagulation involves three stages Stage I –Production of thromboplastin activator by one or the other of the following: »chemicals released from damaged tissues (extrinsic pathway) »chemicals present in the blood (intrinsic pathway) Stage II –Conversion of prothrombin to thrombin Stage III –Conversion of fibrinogen to fibrin and production of fibrin clot

Blood Clotting (Coagulation) Conditions that oppose clotting –Clot formation in intact vessels is opposed –Several factors oppose clotting Smooth surface of the normal endothelial lining of blood vessels Antithrombins –Substances in the blood that oppose or inactivate thrombin –Prevent thrombin from converting fibrinogen to fibrin; e.g., heparin

Blood Clotting (Coagulation) Conditions that hasten clotting –Rough spot in the endothelium –Abnormally slow blood flow Clot dissolution –Fibrinolysis Physiological mechanism that dissolves fibrin –Fibrinolysin Enzyme in the blood that catalyzes the hydrolysis of fibrin –Additional factors are presumed to aid clot dissolution; e.g., substances that activate profibrinolysin

The Big Picture: Blood and the Whole Body Blood plasma transports substances, including heat, around the body, linking all body tissues together –Substances can be transported between almost any two points in the body Blood tissue contains formed elements—blood cells and platelets –RBCs assist in the transport of oxygen and carbon dioxide –WBCs assist in the defense mechanisms of the whole body –Platelets prevent loss of the fluid that constitutes the internal environment

The Big Picture: Blood and the Whole Body No organ or system of the body can maintain proper levels of nutrients, gases, or water without direct or indirect help from blood –Other systems assist the blood Blood is useless unless it continues to transport, defend, and maintain balance