Exam 1 Review:  Chapter 17:  Hemostasis II:  Coagulation

coagulation = thrombosis - The formation of a fibrin-based blood clot = thrombus; two complex enzyme pathways lead to the formation of a fibrin clot:  the intrinsic and extrinsic pathways, which are initiated by distinct mechanisms; the two pathways converge on a common pathway which leads to the completion of clot formation; the biochemical components of these pathways are called clotting factors.  [Note:  Coagulation is usually preceded by platelet plug formation.]  See details of the components to coagulation below and follow the link above for a diagram.

clot = thrombus - The major component of hemostasis, the mass of fibrin, formed by the enzyme cascade known as the coagulation pathway, which traps platelets and red blood cells to limit the flow of blood following a hemorrhage of any degree.

clotting factors - A group of soluble plasma proteins, most synthesized by the liver, which interact with one another, various additional chemical regulators, and calcium ions, to initiate the process of coagulation which ultimately produces a fibrin blood clot = thrombus; the classic clotting factors are numbered with Roman numerals from I to XIII.

prothrombinase - Coagulation factor X, the activation of which is the common point uniting the intrinsic and extrinsic pathways to coagulation; activated factor Xa (a signifies active) complexes with calcium ions, platelet phospholipid PF₃, and factor V to form the prothrombin activator complex which converts prothrombin = factor II into active thrombin = factor IIa (a signifies active).

extrinsic pathway (to coagulation) - The response to hemorrhagic injury to the body tissues (of any degree); the faster enzyme cascade which triggers the initiation of coagulation when the primary stimulus is exposure of the soluble clotting factor VII in the blood to tissue factor (TF) = factor III = tissue thromboplastin (which is released when tissue cells have ruptured to any degree); this pathway leads to the conversion of factor X (inactive) to factor Xa (a signifies active); it requires the clotting factors III, VII, and X and it also requires calcium ions. 

intrinsic pathway (to coagulation) - The response to minor injury to the endothelial lining of blood vessels; the slower more complex enzyme cascade which triggers the initiation of coagulation when the primary stimulus is exposure of certain soluble clotting factors in the blood to collagen (which is found immediately external to the vessel endothelium, i.e., when an endothelial cell membrane has ruptured to any degree -- this is termed the contact phase); this pathway leads to the conversion of factor X (inactive) to factor Xa (a signifies active); it requires the clotting factors VIII, IX, X, XI, and XII as well as the proteins prekallikrein and high-molecular-weight kininogen, as well as calcium ions and phospholipid PF₃ provided from platelets. 

common pathway (to coagulation) - The common conclusion to coagulation with the final formation of fibrin from the inactive precursor fibrinogen (clotting factor I); it begins when activation of either the extrinsic or intrinsic pathways (to coagulation) have produced factor Xa (a signifies active); factor Xa activates prothrombin = factor II into active thrombin = factor IIa (a signifies active) which occurs on the surface of platelets; thrombin = factor IIa (a signifies active) converts inactive fibrinogen (clotting factor I) into fibrin; these fibrin strands form a meshwork which traps additional platelets and usually red blood cells to form the clot = thrombus; it requires the clotting factors I, II, V, VIII, and X, as well as calcium ions and phospholipid PF₃ provided from platelets.

fibrin - An elastic, insoluble, whitish fibrous protein produced by the proteolytic action of thrombin on fibrinogen and forming an interlacing fibrous network in the coagulation of blood; this fibrous network traps red cells and platelets.

vitamin K - A fat-soluble vitamin, occurring in leafy green vegetables, tomatoes, and egg yolks, which promotes blood clotting and prevents hemorrhaging; it exists in several related forms, such as K₁ (from plants) and K₂ (from bacteria including human intestinal normal flora); vitamin K-dependent clotting factors include prothrombin (II) and factors VII, IX, and X, and Protein C.

clot retraction - A platelet function in which platelets, containing the contractile protein thrombosthenin, activate contraction of platelet pseudopods attached to fibrin after coagulation is completed, which causes the platelets and the fibrin network to contract; this reduces the size of the entire blood clot, pulling the torn edges of the vessel or injured tissue closer together, reducing the size of the damaged area, and making repairs easier.

hemophilia - A term for two hereditary bleeding disorders which are X-linked (sex-linked) and, therefore, seen almost exclusively in males:  hemophilia A and hemophilia B; individuals with these clotting factor deficiencies suffer joint and muscle hemorrhage, easy bruising and prolonged bleeding from wounds; treatment of either hemophilia is accomplished by infusion of the missing clotting factor in concentrates prepared from either human plasma or by recombinant DNA technology.  [(A)  Hemophilia A is classic hemophilia which results from a deficiency in factor VIII, a key component of the coagulation cascade; there are severe, moderate and mild forms of hemophilia A which reflect the level of active factor VIII in the plasma.  (B)  Hemophilia B ("Christmas disease") results from deficiencies in factor IX; the prevalence of hemophilia B is approximately one-tenth that of hemophilia A; like hemophilia A, there are severe, moderate and mild forms of hemophilia B which reflect the factor IX activity in plasma.]

For more information, visit The Blood Clot Center.

List:

5. The three basic mechanisms of hemostasis.

     vascular spasm → platelet plug formation → coagulation

6. The stages or events that occur from the point of an injury that ruptures a blood vessel to the completion of repair of the injury.

     vascular spasm → platelet plug formation → coagulation (extrinsic pathway → common pathway) →  clot retraction → fibrinolysis →  repair (either parenchymal repair or scar tissue formation depending on scope of injury)

Describe:

5. The three pathways of blot clotting (coagulation)