Objective 1 pt 2 Flashcards
cytoplasmic fragments of extraordinarily large cells
megakaryocytes
blue-staining outer region, purple granules
granules contain serotonin, Ca2+, enzymes, ADP, and platelet-derived growth factor
platelets
what is the function of platelets?
form temporary platelet plug that helps seal breaks in blood vessels
platelet formation is regulated by hormone …
thrombopoietin
plateleets are formed in myeloid line from…
megakaryoblast
sends cytoplasmic projections into lumen of capillary
projections break off into platelet fragments
stage IV megakaryocyte
fast series of reactions for stoppage of bleeding
requires clotting factors and substances released by platelets and injured tissues
hemostasis
what are the 3 steps involved in hemostasis?
vascular spasm
platelet plug formation
coagulation
damaged vessel constricts through _________
most effective in smaller blood vessels
can significantly reduce flow until other mechanisms can kick in
step 1: vascular spasm
what are vascular spasms triggered by?
direct injury to vascular smooth muscle
chemical released by endothelial cells and platelets
pain reflexes
platelets stick to collagen fibers that are exposed when vessel is damaged
the plasma protein von Willebrand factor helps to stabilize platelet-collagen adhesion
platelets become activated and swell, become spiked and sticky and release chemical messengers
postitive feedback cycle occurs
platelet plugs are fine for small vessel tears
step 2: platelet plug formation
as more platelets stick, they release more chemicals, which cause more platelets to stick and release more chemicals
positive feedback cycle
reinforces platelet plug with fibrin threads that act as a glue
blood is transformed from liquid to gel
series of reactions use clotting factors, mostly plasma proteins
step 3: coagulation
what are the 3 phases of coagulation?
Phases 1: two pathways to prothrombin activator
Phase 2: pathway to thrombin
phase 3: common pathway to the fibrin mesh
initiated by either intrinsic or extrinsic pathway
triggered by tissue-damaging events
involves a series of clotting factors
the intermediate steps of each pathway cascade toward a common intermediate, factor X
once factor X is activated, it complexes with Ca2+, PF3, and factor V to form prothrombin activator
Phase 1: two pathways to prothrombin activator
because clotting factors are present within the blood
triggered by negatively charged surfaces such as activated platelets, collagen, or even glass of a test tube
slow process
intrinsic pathway
because factors needed for clotting are located outside blood
triggered by exposure to tissue factor, also called factor III
bypasses several steps of intrinsic pathway, so faster pathway
extrinsic pathway
prothrombin activator speeds up the transformation of prothrombin to activate enzyme thrombin
phase 2: pathway to thrombin
thrombin converts soluble fibrinogen to fibrin
fibrin strands form structural basis of clot
fibrin causes plasma to become a gel-like trap catching formed elements
thrombin activates factor XIII, which:
cross-links fibrin
strengthens and stabilizes clot
Phase 3: common pathway to the fibrin mesh
factors that normally dominate in blood to prevent coagulation
anticoagulants
actin and myosin in platelets contact within 30-60 mins
contraction pulls on fibrin strands, squeezing serum from clot
draws ruptured blood vessel edges together
clot retraction
released by platelets
stimulates division of smooth muscle cells and fibroblasts to rebuild blood vessel wall
platelet-derived growth factor
stimulates endothelial cells to multiply and restore endothelial lining
vascular endothelial growth factor
process whereby clots are removed after repair is completed
begins within 2 days and continues for several days until clot is dissolved
fibrinolysis
