Hemostasis Flashcards
Hemostasis
the prevention of blood loss and maintenance of blood flow
vascular spasm
why this happen?
the reflex contraction of axial and circular smooth muscle
due to blood pressure loss & the blood flow decreases
What will have more severe vascular spasm (sharp cut vessels or crushing vessels)?
sharp cut vessels
precapillary sphincter
the sphincter that closes down when capillaries pressure drops below critical value
What are the consequences of vascular spasm due to external injuries?
vasoconstriction of blood vessels
retraction of vessel into the surrounding tissue to protect the severe end from exposure to foreign materials
What are the mechanisms of vasoconstriction of blood vessel in vascular spasm?
resulting from myogenic reflexes
local releases of vasoactive agents such as histamin, serotonin & kinin
blood loss into tissue cause local tissue pressure increase
stimulation of sympathetic nervous system
platelets
the cell fragments derived from megakaryocytes in bone marrow
What does platelets do?
maintaining the endothelial lining of blood vessels
repair small breaks
restricting blood flow by forming temporary platelet plug
Process of platelet plug formation
adhesion
aggregation
viscous metamorphosis
adhesion of platelets plug
the positive amino acids on exposed collagen fibers attract platelets to damaged vessel
aggregation of platelets plug
the more attraction of platelets around injuries site
viscous metamorphosis
the adhered platelets undergo morphology change in order to adhere strongly to damaged site and to each other
What kind of morphology changes in platelets during platelets plug formation?
swelling &protruding spinous processes
What are the products released during the
ADP + thromboxane A2
Calcium
beta-integrin
vasoactives amines
thromboplastin
platelet factor 3 (PF3)
What do ADP + thromboxane A2 do?
inducer of platelet aggregation
What does Calcium do in platelet plug formation?
increase the degree of platelets aggregation
plasma coagulation
the formation of blood clots (permanent seal)
beta-integrins
products that glue platelets together
what are the three stages of coagulation?
initiation of coagulation by formation of prothrombin activator
activation prothrombin to thrombin
conversion of fibrinogen to fibrin
What does vasoactive amines do?
release serotonin, kinins, epinephrine to restrict blood vessel (vasoconstriction)
thromboplastin
help in formation of permanent clots
When does the plasma coagulation happen?
when there is more severed damages on blood vessels & platelet plug alone can’t stop the blood loss
platelet factor 3 (PF3)
products released during platelets plug that involved in plasma coagulation
When does the extrinsic pathway of forming prothrombin activator happen?
when there is extract of fluid from tissue into plasma
When does the intrinsic pathway of forming prothrombin activator happen?
when there is trauma to the blood itself or atherosclerosis
clot retraction
the process of blood clot shrink or contract after 3D-fibrin network formed
when does the clot dissolution happen?
when the new fibroblasts arrive at the injury site & repair proces start
during retraction, what also happen to the wound/injuries site?
the edges of wounds are pulled together
the fluids also ooze out of the clot in form of serum
What is the factor III?
thromboplastin
What is the factor IV?
calcium
platelet actomyosin
the protein that help the clot retraction
The steps in forming prothrombin activator of extrinsic pathway?
1) Factor III and tissue phospholipid(TF) are released by damaged cells
2) Factor III + IV act on Factor VII to form complex VIIa
3) Complex VIIa + TF acts on factor X-> complex Xa
4) Complex Xa form with TF & factor V to form prothrombin activator
The steps in forming prothrombin activator in intrinsic pathway?
1) PF3 and Calcium are released
2) Factor XIIa acts on XI -> complex XIa
3) XIa acts on IX -> IXa
4) IXa + VIIIa + PF3 + Calcium -> Xa
5) Xa + PF3 + Va -> prothrombin activator
Where is the prothrombin produced? What vitamin is required for this?
in the liver by endothelial cells
vitamin K
What is the last step of blood clot (or plasma coagulation)?
conversion of fibrinogen into fibrin
What are the two factors in plasma coagulation that are not proteins?
factor IV (calcium)
PF3 (tissue phospholipid)
Lack of factor VIII will cause what disease? What pathway in forming prothrombin activator is affected?
hemophillia
intrinsic pathway
Mechanism of forming thrombin from prothrombin?
prothrombin activator and Ca2+ act on prothrombin to produce thrombin
The steps in conversion of fibrinogen to fibrin
1) thrombin split fibrinogen molecule into fibrin monomer
2) fibrin monomer unites -> fibrin polymers
3) Complex XIIIa acts on fibrin polymers to form strong 3D fibrin network surround the platelet plug
Is it true that factors, once activated adhere to original site of injury and act spreadly?
No, they all act locally
Is it true that extrinsic and intrinsic pathway doesn’t have anything in common?
No, they share the similarites in steps fornming fibrin from prothrombin
NSAIDs
Example of this type of family drug
How long does it take for platelets restores it functions if we stop this drug?
reversible cox 2 inhibitor
ibuprofen, acetaminophen, naproxene
right away
What does thrombin do?
activate factor XIII and I
activate platelet plug to increase aggregation
hemophillia
Example of this disease
inherited disease that lack of factor VIII
uncontrolled bleeding on “Clean” cut vessel while damaged tissue may clot
Mechanism of clot dissolution?
clot produce plasminogen and clot dissolution occur
thrombocytopenia
Cause of this disease?
Consequence of it?
the inadequate number of platelets
dietary deficiency of vitamin B12 & folic acid
prolong bleeding time & impaired clot retraction
Coumadin
How long does it take for this drug to work?
the anticoagulant that inhibit the sysnthesis of vitamin K -> key plasma proteins factors are not produced
36-48 hours
what are the mechanisms to prevent coagulation under normal condition?
the repellence btw negative charge of plasma proteins & of endothelial cells
the circulation of anti-coagulant agents
What are the anti-coagulant agents? Each effect on plasma proteins?
fibrin absorbs most thrombin
antithrombin II binds to excess thrombin
heparin: interferes with activation of factor X
aspirin
What does it do?
the irreversible cox-2 inhibitor
inhibit the production of platelet & thromboxane A2
When should a patient have a surgery if he/she is using aspirin?
in one week after the day stop using aspirin
plasminogen
the enzyme that degrade the fibrin clots
What is the cause of Von Willibrand’s disease?
Consequence?
the deficiency of vWF
poor platelet adherence to injuries site & low lvl of factor VIII
prolong bleeding time
What is chelator used for? Why?
in blood being draw for testing
because it binds with Ca2+ -> inhibit the coagluation pathways
What test is used to measure the deficiency of platelet number?
What does this test also measure?
complete blood count
RBC/ WBC/ hematocrit & hemoglobin
What blood test is used to evaluate the intrinsic pathway?
extrinsic pathway?
partial thromboplastin time (PTT)
prothrombin time (PT)
What blood test is used to evaluate the vW disease?
platelet aggregation test
What blood tests that are used to confirm the heparin contamination?
What do these tests measure in common?
prothrombin & thrombine time test
partial thromboplastin time test
time to clot
What drug that inhibit platelet production & thromboxane A2?
aspirin
What drug is used in blood being drawn to prevent coagulation?
chelator
What drug that will have platelet restored its function right away when it is stoped?
Why?
NSAIDs
because it is reversible cox 2 inhibitor
What drugs that inhibit the vitamin K synthesis so the plasma factors will not be produced?
Coumadin
What drug is use to be anti-coagulant to interfere with activation of factor X?
heparin
What proteins that adhere platelets to collagen fibers?
von WIllibrand’s factor
What blood diseases that have inadequate platelets & is caused due to deficiency of vitamin B12 & folic acid?
thrombocytopenia
