Haemostasis Intro

Question 1

what is haemostasis

Answer 1

the arrest of bleeding and the maintenance of vascular patency

Question 2

what does haemostasis need to be

Answer 2

always ready
prompt response to reduce blood loss
localised response
protection against unwanted thrombosis

Question 3

what constitutes primary homeostasis

Answer 3

the formation of a platelet plug

Question 4

what is secondary homeostasis

Answer 4

the formation of a fibrin clot (more stable meshwork)

Question 5

what happens after secondary haemostasis

Answer 5

fibrinolysis and anticoagulant defences to re-establish blood flow in the vessel

Question 6

how are platelets made

Answer 6

bud of megakaryocytes in the bone marrow

Question 7

what is the lifespan of platelets

Answer 7

7-10 days in the circulation (as have no nucleus)

Question 8

what is the structure of platelets

Answer 8

small anucleate discs

Question 9

how are platelets directed to a site of injury

Answer 9

endothelial (vessel wall) damage exposes collagen and releases von willebrand factor (+other proteins) to which platelets have receptors= bind to site of injury

platelets then secrete chemicals which auses aggregation at this site

Question 10

what might cause a failure of platelet plug formation (primary haemostasis)

Answer 10

vascular (e.g. if collagen deficient)
platelets (reduced number- thrombocytopenia, or reduced function- e.g. on aspirin or NSAIDs)
von willebrand factor (e.g. inherited deficiency)

Question 11

what can cause a collagen deficiency resulting in primary haemostasis problems

Answer 11

old age

scurvy (vit c needed to make collagen)

Question 12

what are the potential consequences of platelet plug formation failure

Answer 12

spontaneous bruising and purpura
mucosal bleeding (epistaxes, GI, blood blisters in mouth, conjunctival haemorrhages, menorrhagia)
intracranial haemorrhage
retinal haemorrhages

Question 13

where does purpura usually affect

Answer 13

lower limbs (as gravity big influence, pulls blood out of vessels)

Question 14

does purpura blanch

Answer 14

no

Question 15

why do more women with VWF deficiency present

Answer 15

affects men and women equally but women more likely to present with menorrhagia

Question 16

what screening test for primary haemostasis

Answer 16

platelet count

Question 17

where does the fibrin clot form

Answer 17

on the platelet plug surface

Question 18

how does the fibrin clot form

Answer 18

platelets full of phospholipids which are negatively charged
platelets release calcium which is positively charged and sits on the cell surface
this attracts the clotting factors

tissue factor (CF7) attracted first which starts haemostasis and activates CF 5 and 10 (initiation phase) 
prothrombin activated into thrombin (by factors 5 and 10) (propagation stage)
thrombin cleaves fibrinogen into fibrin 

thrombin also activates CF 8 and 9 (amplification stage) which activate CF 5 and 10 creating positive feedback mechanism allowing fast clot formation

Question 19

what can cause failure of fibrin clot formation (secondary haemostasis)

Answer 19

single clotting factor deficiency (usually hereditary e.g. haemophilia)
multiple clotting factor deficiency (usually acquired e.g. DIC) 
increased fibrinolysis (usually part of complex coaguloplathy e.g. DIC)

Question 20

which single clotting deficiencies are more common

Answer 20

haemophilia A (CF 8) most common 
haemophilia B (CF 9) less common

Question 21

why do you have multiple CF deficiency in DIC

Answer 21

as making so many and then breaking down so many clots

Question 22

how does fibrinolysis happen

Answer 22

plasminogen converted to plasmin by tissue plasminogen activator (tPA)

fibrin then broken down into fibrin degradation products by plasmin

Question 23

what test can measure fibrin degradation products

Answer 23

D dimers

Question 24

what are the consequences of fibrin clot formation failure (problems with secondary haemostasis)

Answer 24

no classic clinical syndrome
can be combined with primary haemostasis failure

pattern of bleeding depends on:

• single/ multiple factors affected (single e.g. haemophilia, affects joints in certain pattern. multiple e.g. DIC)
• the clotting factors involved

Question 25

what happens to clotting factors in DIC

Answer 25

all used up

Question 26

what screening tests for fibrin clot formation (secondary haemostasis)

Answer 26

prothrombin time (uses citrate to analyse factors 7, 5, 10 and thrombin) 
activated partial thromboplastin time (analyses factors 8 and 9 (which in turn activate 5 and 10) 

e.g. if missing factor 8/0 then APTT will be increased by PT normal

Question 27

how do NSAIDs affect haemostasis

Answer 27

interfere with platelet function affecting primary haemostasis

Question 28

how do warfarin and NOAC affect haemostasis

Answer 28

affect secondary hameostasis

Question 29

what does anti-thrombin do

Answer 29

neutralises thombin, tissue factor (CF 7), CF 5, 10, 8 and 9

Question 30

how can you assess previous haemostasis from Hx

Answer 30

bleeding/ bruising 
duration (if lifelong)
previous surgery/ dental procedure, how long were you nleeding for afterwards 
Drug Hx
FHx
exam

Question 31

what is serine protease inhibitor

Answer 31

antithrombin- naturally occurring anti coagulant

Question 32

what are protein C and protein S

Answer 32

naturally occurring anticoagulants

switch off CF 8 and 8

Question 33

what does thrombomodulin do

Answer 33

modulates the function of thrombin to increase protein C and protein S which in turn deactivate CF 5 and 8, cause anti coagulation

Question 34

what is thrombophilia

Answer 34

increased tendency to develop venous thrombosis (e.g. DVT, PE)

Question 35

what can cause thrombophilia

Answer 35

deficiency of naturally occurring anticoagulants (serine protease inhibitors (anti thrombin), protein C and protein S (thombomodulin)