Haemostasis

Question 1

What are the 5 major steps of haemostasis?

Answer 1

Vascular spasm, formation of a platelet plug, conversion to a clot by reinforcement with fibrin, tissue repair and gradual removal of clot

Question 2

What is the role of ADP in platelet plug formation?

Answer 2

Sticky platelets

Question 3

What is the role of serotonin in plug formation?

Answer 3

Vasoconstrictor

Question 4

What is the role of thromboxane A2 in plug formation?

Answer 4

Vasoconstrictor and activates platelets

Question 5

What is triggered when the platelet plug is formed?

Answer 5

Coagulation cascade

Question 6

What is the intrinsic pathway of the coagulation cascade?

Answer 6

XII–>XIIa
XI–>XIa
IX–>IXa
X-Xa via VIIIa

Question 7

What is the extrinsic cascade? (trauma)

Answer 7

VII–>VIIa
X–>Xa via tissue factor

Question 8

What is the final common pathway?

Answer 8

Xa via Va converts prothrombin to thrombin which converts fibrinogen to fibrin which is acted on by XIII1 to form a cross-linked fibrin clot

Question 9

Where are the 4 calcium/vitamin K dependent sites of the coagulation cascade?

Answer 9

IX–>IXa
VIIIa and tissue factor for X–>Xa
Va for prothrombin to thrombin

Question 10

What is the role of prostacyclin in clotting?

Answer 10

Inhibits adhesion and aggregation

Question 11

What is the role of nitric oxide in clotting?

Answer 11

Inhibits platelet adhesion

Question 12

What is the role of the liver in clotting?

Answer 12

Synthesises bile salts for the absorption of vit K in the GI tract and synthesises clotting factors

Question 13

What enzyme breaks down a clot?

Answer 13

Plasmin

Question 14

How does antithrombin work?

Answer 14

Inactivates thrombin and inactivates factors Xa and IXa, anticoagulant

Question 15

What conditions lead to excessive bleeding?

Answer 15

Clotting defects and platelet deficiency

Question 16

What conditions lead to thrombus formation?

Answer 16

Atherosclerosis, imbalance in clotting mechanism and septicemic shock