19.5 hemostasis Flashcards
define hemostasis
arresting or stopping of bleeding
in hemostasis a series of events helps prevent
excessive blood loss
what is the immediate response in a damaged blood vessel?
vascular spasm
describe vascular spasm
the immediate but temporary response to vascular damage, due to smooth muscle cntx in the wall
what type of stimulus will create a vascular spasm
upon tissue damage:
reflex
thromboxane released by platelets
endothelin released by endothelial cells
what are thromboxanes?
prostaglandin derived chemical released by platelets that trigger vascular spasm
what is endothelin?
a chemical released by endothelial cells that triggers vascular spasm
what is a platelet plug?
an accumulation of platelets that seals up small holes in vessels
what are the 3 steps of platelet plug formation
platelet adhesion
platelet release rxn
platelet aggregation
how does platelet adhesion occur in a platelet plug?
von Willebrand factor (a protein) is produced and secreted by the damaged endothelial cells and connects the exposed collagen to the platelets
what is vWF (von Willebrand factor)?
a protein secreted by the endothelial cells that connects the exposed collagen to the platelets
describe the positive feedback mechanism of platelet release rxn
adhered platelets release ADP, thromboxanes and other chemicals that activate more platelets to join the plug, which in turn release the same chemicals to recruit even more platelets
in which step of platelet plug formation is vWF released by endothelial cells?
step 1, platelet adhesion
in which step of platelet plug formation do platelets release ADP, thromboxanes and other chemicals?
step 2, platelet release rxn
describe platelet aggregation in platelet plug formation
activated platelets express surface receptors to which fibrinogen can bind
fibrinogen binds to these surface receptors and forms a bridge between other activated platelets and a platelet plug is formed
what chemicals do platelets release once a plug is formed?
phospholipids (platelet factor III)
coagulation factor V
both important in clot formation
what factors in coagulation are already in the blood stream?
prothrombin
fibrinogen
what enzyme is used to change prothrombin to thrombin?
prothrobinase
what does thrombin do?
changes fibrinogen to fibrin
what is fibrinogen?
a soluble plasma protein
what does fibrin do?
forms the fibrous network of a clot
what are the coagulation factors?
proteins found in plasma that circulate in their inactive state until the tissues are injured
what produces changes that begin activation of the coagulation factors?
damaged tissues and platelets
what are the 2 pathways to clot formation?
extrinsic and intrinsic
what is a blood clot?
network of threadlike fibrin fibers, trapped blood cells, platelets and fluid
define anticoagulants
they prevent coagulation factors from initiating clot formation
or
inhibit the processes that contribute to clote formation
when does coagulation occur?
when coagulation factor concentrations exceed a certain threshold at the site of injury
what are 3 anticoagulants?
antithrombin
heparin
prostacyclin
what does antithrombin do and where is it produced?
produced by liver
slowly inactivates thrombin
what does heparin do and where is it produced?
produced by basophils and endothelial cells
increases effectiveness of antithrombin
what does prostacyclin do and where is it produced?
prostaglandin derivative from endothelial cells
causes vasodilation
inhibits release of coagulating factors from platelets?
what inhibits release of coagulating factors from platelets?
prostacyclin
what inactivates thrombin?
antithrombin
what increases the effectiveness of antithrombin?
heparin
what is clot retraction?
the condensing of the blood clot to become a denser, compact structure
how does clot retration work?
platelets contain actin and myosin and attach to fibrin through processes
actin and myosin pull on the fibrinogen leading to clot retraction
how is a clot dissolved?
plasmin (an enzyme that hydrolyzes fibrin)
