Week 5 Flashcards
von Willebrand Factor
Multimeric glycoprotein that is stored in platelets. binds to subendothelial collagen at sites of vascular injury, and binds to glycoprotein IB at the platelet surface. Also binds to and stabilizes coag. factor VIII
Phospholipase A2
after plateets adhere to collagen, and increased intracellular Ca2+, phospholipase A2 is released which hydrolyzes membrane phospholipids liberating arachadonic acid
TXA2
is a potent vasoconstrictor and inducer of platelet aggregation that functions by binding to receptors
Myosin Light Chain Kinase
Activated by released Ca2+ stores, phosphorylates the light chain of myosin which interacts with actin leading to platelet shape change.
GPIIb-GPIIIa
Is a receptor for vonWildebrands factor and fibrinogen leading to fibrinogen induced platelet aggregation. It is inhibited by abciximab.
Fibrinogen
Protein which circulates in the blood, also found in platelet granules. Is composed of 3 pairs of polypeptide chains linked by disulfide bonds. Binds platelets helping them bind together.
Thrombin
Cleaves fibrinogen to fibrin which polymerize and form a soft clot with platelets. Also activates platelts by binding to specific receptors leading to phospholipase C leading to IP3 (Ca2+ release) and DAG (activates protein kinase C)
Extrinsic Pathway
Initiated at the site of injury in response to tissue factor release which is a cofactor in the factor VIIa catalyzed activation of factor X
Tissue Factor
is an integral membrane protein that is expressed on surface of activated monocytes, and endothelial cells exposed to cytokines. Not found in plasma
Extrinsic pathway steps
Tissue injury leads to tissue factor which binds to and activates factor VII->VIIa. TF-VIIa can activate IX-> IXa. Factors IXa and Xa assemble with their non-enzymatic protein cofactors on the surface of aggregated platelets leading to large amounts of Xa and thrombin(IIa). and conversion of fibrinogen to fibrin… common pathway
Intrinsic Pathway
also called the contact activation pathway, much less significant to hemostasis under normal physiological conditions than is the extrinsic. Hyperlipidemia or sepsis can lead to activation of thrombosis via the intrinsic clotting cascade.
Intrinsic pathway steps
Factor XII is converted to XIIa by HMWK collagen. Factor XIIa converts XI to XIa. XIa converts IX to IXa which binds VIIIa (which was activated by thrombin). IXa-VIIIa convert X->Xa. common pathway
Common Pathway
IXa and VIIIa convert X to Xa in presence of Ca2+. Xa converts prothrombin(II) to thrombin using prothrombinase and factor Va(activated in minute amounts by increasing thrombin). Thrombin(IIa) converts fibrinogen to fibrin. Fibrin is cross linked by XIIIa (also activated by thrombin).
Antithrombin III
Most important thrombin inhibitor. inhibits activities of factors IXa, Xa, XIa and XIIa, plasmin, and kallikrein leading to clot dissolution. Activity is potentiated by heparin
Heparin Sulfate
Is on the surface of vessel endothelial cells, and regulates antithrombin III.
Protein C
Is a trypsin like serine protease It uses Protein S as a cofactor. It, along with activated protein C degrade Va and VIIIa via proteolysis, decreasing thrombin production. Protein S anchors the activated Protein C complex to the clot. Activated protein C also stimulates endothelial cells to increase secretion of prostaglandin I2 which reduces platelet aggregation.
Fibrinolysis
Involves the degradation of fibrin in a clot by plasminin.
Plasmin
is a serine protease that is formed by plasminogen. It degrades fibrin in a clot.
Plasminogen
has a high affinity for fibrin, promoting the incorporation of plaminogen in the developing clot. it is mediated by activators which turn it to plasmin.
Tissue Plasminogen activator
Clears up clots especially in central lines.
Vitamin K
is required in many factors for blood coagulation. It is needed for gamma carboxylation which occurs in the hepatocyte before clotting factor release.
Warfarin
is slow and long acting bloodanticoag. It competes with vitamin K and prevents gamma-carboxylation of glutamate residues in factors II, VII,IX,X, proteinsC and S. The factors cannot bind Ca2+or form the complexes necessary for the coagulation cascade to be initiated. IT DROPS PROTEIN C AND S LEVELS FIRST LEADING TO INCREASED CLOTTING AT FIRST. must bridge with heparin.
Heparin
Binds to annd activates ATIII which leads to thrombin inactivation, blocks the activity of factors VIIIa, Ixa, Xa, and Xia by potentiating antithrombin 3 preventing a clot.
IL-2
Released from T cells after binding with APC, supports growth and expansion of T, B and NK cell populations, can self activate