haemostasis

Question 1

describe the actions of haemostasis after an artery is severed

Answer 1

1. artery contracts and pressure decreases downstream
2. primary haemostat plug forms out of platelets= v fragile and temporary (1min)
3. secondary haemostat plug forms and firkin stabilises it (30 mins)

Question 2

components that platelets are activated by

Answer 2

collagen surfaces
ADP (released by platelets and damaged RBC)
thromboxane (aggregates platelets)
thrombin (informs which clotting factors are activated)

Question 3

action of platelets once activated

Answer 3

1. stick to vWF on endothelial membrane
2. aggregate other platelets to form a plug and bound by fibrinogen to form secondary plug
3. change shape to stick spiny spheres
4. factors excreted which aid growth of platelet plug e.g ADP or thomboxne

Question 4

action of aspirin

Answer 4

it irreversibly acetylates an enzyme of prostogladin synthesis meaning platelets can’t produce thromboxane reducing coagulation

Question 5

what does the intrinsic pathway of the clotting cascade involve

Answer 5

triggered by damaged blood vessel. contained in the blood. involves factors I, II, IX, X, XI, and XII

Question 6

what des extrinsic pathway involve

Answer 6

trauma to extravascular cells. triggered by thromboplastin outside blood. involves factors I, II, VII, and X

Question 7

learn clotting cascade

Answer 7

:)

Question 8

cofactors needed by the clotting cascade

Answer 8

ca2+ and phospholipids act as cofactors for enzymes in these reaction
ALSO vit k required for synthesis of protein S and C (anticoagulants)

Question 9

role of vascular wall in coagulation

Answer 9

contracts when vessel damage 
sub endothelium traps platelets 
also balances coagulation by secreting 
protein C=  anticoagulant 
plasminogen activator = fibrinolysis  
vWF= clotting

Question 10

factors opposing clot

Answer 10

antithrombin III
protein C
protein S
also oppose it by dilution of clotting factors

if missing any of these leads to thrombosis

Question 11

describe clot retraction

Answer 11

platelets die = cling to fibrin and pull on actin and myosin filaments together.

Question 12

describe fibrinolysis

Answer 12

1. plasminogen (inactive precursor circulating blood made in liver) is activated by tea (tissue plasminogen activator)
   = PLASMIN
2. plasmin is an enzyme used by macrophages to break down fibrin
3. increase in FDP (breakdown product of fibrin which is found very high in thrombosis
4. eventually clot is replaced by granulation tissue and leaves a scar

Question 13

how is fibrinolysis activated

Answer 13

activated by clotting cascade. fibrin increases activity of plasminogen activators. fibrinolytic activity drops after surgery increasing risk of DVT

Question 14

what are streptokinase and urokinase and side effects

Answer 14

streptokinase (from streptococcus) and urokinase (from urea) are also plasminogen activators.
side effects of these drugs = bleeding e.g nose bleeds.
used to break down clots

Question 15

what is haemophilia and effects

Answer 15

have platelets but lack clotting factors so can’t produce fibrin
easy bruising, haemorrhage after surgery and trauma.
may develop harm-arthritis from minor injuries
petechiae is also seen

Question 16

what is haemophilia A

Answer 16

factor VIII deficiency - X linked and therefore affects males. treated by infusion of engineered factor VIII

Question 17

what is haemophilia B

Answer 17

reduction in factor IX = prolonged APTT. treated by infusion of engineered factor IX

Question 18

what is vonwillerbrands disease

Answer 18

reduced FVIII- leads to bleeding e.g nose bleeds, bruising,prlonged bleeding after trauma.
skin and mucosal associated bleeding - gums, bruising and epistaxis

Question 19

what is DIC

Answer 19

disseminated intravascular coagluation - activator of clotting which gets into blood forming clots. no disease in itself always occurs as a complication e.g sepsis or trauma

Question 20

treatment of DIC

Answer 20

treat underlying cause of DIC
if lots of bleeding because factors/ platelets have been consumed require transfusion
sometimes anticoagulant e.g herapin is needed

Question 21

causes of DIC

Answer 21

gangrene, renal failure, respiratory distress, haemorrhage

Question 22

signs of DIC

Answer 22

increased FDP’s e.g Ddimers in the blood as the fibrinolytic system is activated and damage to RBC as the move past thrombi

Question 23

screening tests

Answer 23

PT- measure extrinsic pathway (time to make prothrombin)
APPT- measures intrinsic common pathway - time to make partial thromboplastin
thrombin time
fibrinogen