Physiology: Application - Haemostasis

Question 1

what is haemostasis

Answer 1

arrest of bleeding and maintenance of vascular patency

Question 2

components of normal haemostatic system (what can happen)

Answer 2

• formation of platelet plug
• formation of fibrin clot
• fibrinolysis
• anti-coagulant defences

Question 3

how and where are platelets formed

Answer 3

formed in bone marrow by budding from megakarocytes

Question 4

describe how a platelet plug is formed

Answer 4

endothelial damage exposes collagen and releases VWF and other proteins, platelets have receptors to these and attach at the site of injury
platelets secrete chemicals leading to platelet aggregation at sit of injury

Question 5

causes of failure of platelet plug formation (4)

Answer 5

• vascular
• low platelet count (thrombocytoenia)
• decreased platlet function
• VWF

Question 6

what are the consequences of failure of platelet plug formation (4)

Answer 6

• spontaneous bruising and purpura
• mucosal bleeding
• intracranial haemorrhage
• retinal haemorrhage

Question 7

what is primary haemostasis

Answer 7

platelet plug formation

Question 8

what is secondary haemostasis

Answer 8

fibrin clot formation

Question 9

describe the process of fribrin clot formation

Answer 9

• TF and VIIa initiate clotting
• V and Xa propagate prothrombin to thrombin
• this changes fibrinogen to fibrin which causes the clot
• thrombin amplifies the pathway via VIII and IXa

Question 10

what are the causes fibrin clot failure (3)

Answer 10

• single clotting factor deficiency (hereditary)
• multiple clotting factor deficiencies (acquired)
• increased fibrinolysis

Question 11

what is fibrinolysis

Answer 11

breakdown of fibrin in blood clot

Question 12

describe fibrinolysis

Answer 12

• tpa activates plasmin from plasminogen

- plasmin changes fibrin to fibrin degredation products

Question 13

what are the consequences of failure of fibrin clot formation

Answer 13

• no characteristic syndrome
• causes bleeding
• primary or secondary haemostatic failure

Question 14

what does the bleeding pattern in fibrin clot failure depend on

Answer 14

• if its single or multiple abnormalities

- clotting factors involved

Question 15

name 2 naturally occuring anto-coagulants

Answer 15

• serine protease inhibitors

- proteins C and S

Question 16

how do serine protease inhibitors work (anti-thrombin III)

Answer 16

• anti-thrombin III inhibits clotting factors TF/VIIa, V/Xa, VIII/IXa and thrombin
• this stops fibrin clot formation

Question 17

how to proteins C and S work

Answer 17

• activated by thrombin and bind to thrombomodulin

- inhibit clotting factors V/Xa and VIII/IXa

Question 18

what is thrombomodulin

Answer 18

thrombin co-factor that decreases coagulation by converting thrombin to and anti-coagulation enzyme

Question 19

describe arterial thrombus and its treatment

Answer 19

• atherosclerosis
• platelet rich
• aspirin and anticoagulants, modify atherosclerotic risk factors

Question 20

describe venous thrombus and its treatment

Answer 20

• plateltes not activated- coagulation cascade activated, fibrin rich clot
• heparin, warfarin or new O anticoagulants

Question 21

what is virchows triad

Answer 21

• factors that contribute to coagulation

- blood stasis, hypercoagulation and endothelial injury

Question 22

what happens with unstable atherosclerotic plaques when they rupture

Answer 22

• platlets are activated causing an actute thrombus

- sudden symptom onset

Question 23

where might and atherosclerotic rupture happen, what are the assoc. disease and what are the consequences of that

Answer 23

• coronary arteries, unstable angina/MI
• cerebral arteries, stroke
• leads to acute organ ischaemia and necrosis

Question 24

describe the symptoms of DVT

Answer 24

• limbs feel swollen, hot or tender

- pitting oedema

Question 25

what can happen as a consequence of PE

Answer 25

• pulmonary infarct, pleuritic chest pain, CV collapse/death
• hypoxia
• R heart strain