FINAL EXAM Flashcards
where are platelets derived from?
megakaryocytes in bone marrow
how long do platelets last?
8-9 days in circulation
where is platelts stored and how much
1/3 stored in the spleen and released when needed
what stimulates platelet production
thrombopoietin
where are platelets made
liver, kidney, smooth muscle, bone marrow
do platelets have a nucleus?
no
what do a-granules contain?
fibronogen, coagulation factors, plasminogen, PAF and PDGFs
what do δ-granules contain?
ADP, ATP, Ca2+, serotonin and histamine
All but which of the following are true about platelets?
A. An enzyme called erythropoietin stimulates their
production. B. They are made from megakaryocytes. C. They originate from the bone marrow. D. They are stored in the spleen
A
what do plasma proteins circulate as
inactive procoagulation factors
where are plasma proteins synthesised
most are by the liver
when is ca2+ (factor IV) required?
in all but the first two clotting steps
steps of clot dissolution
Antithrombin III, proteins C & S, plasminogen –> plasmin
(digests fibrin strands)
The endothelial surface prevents?
platelets & plasma
coagulation factors from interacting with the underlying
thrombogenic subendothelial ECM
Healthy, intact endothelial cells normally produce several
substances that prevent platelet adhesion & aggregation
- PGI2
– NO
– ADPase
– tPA
stages of hemostasis
1) Vessel spasm
2) Formation of the platelet plug
3) Blood coagulation or development of an insoluble fibrin
clot
4) Clot retraction
5) Clot dissolution
stage 1 of hemostasis
- MOI: Local and
humoral
mechanisms * Transient (<1 min) - Vascular smooth
muscle contracts
to decrease blood flow - Local neural
reflexes & humoral
factors (TXA2
from
platelets)
contribute to
vasoconstriction
stage 2 of hemostasis
- vWF (from endothelium)
causes adhesion of
platelets to exposed
collagen of vessel wall - Platelets become
activated & release ADP
& TXA
2
which causes
platelet aggregation &
formation of a plug
(therefore aspirin acts as a platelet aggregation inhibitor)
stage 2 hemostasis
- Insoluble fibrin threads hold the clot together
- Anticoagulants such as heparin (mast cells) act to prevent
excessive fibrin formation (ie. decrease clotting)
stage 4 hemostasis
- Within 20-60 mins
- Actin & myosin in
platelets contract to
squeeze serum from
the clot & join the
edges of the broken
vessel - Failure of clot
retraction indicative
of a low platelet
count
stage 5 hemostasis
- “Fibrinolysis”: Allows
blood flow to be re-
established & tissue
repair to take place;
strands of the clot are
dissolved - Plasminogen activators
such as tPA & uPA
cause formation of
plasmin, which digests
the fibrin strands of the
clot
what is fibrinolysis
- “Fibrinolysis”: Allows
blood flow to be re-
established & tissue
repair to take place;
strands of the clot are
dissolved
hypercoagulability
Conditions that predispose to thrombosis & blood vessel
occlusion
two forms of hypercoagulability
- increase platelet function
- increase clotting acitivity