Lecture 18

Question 1

Thrombosis

Answer 1

inappropriate formation of blood clot within the CVS

Question 2

3 Major mechanisms that predispose to thrombosis

Answer 2

Endothelial injury (most important)
Abnormal hemodynamics (blood stasis or blood turbulence)
hypercoagulability of the blood

Question 3

How does endothelial damage promote thrombosis(2)

Answer 3

Adopt a procoagulant phenotype- promotes local coagulation of the blood and hence thrombosis
-platelet activating factor, vWF, tissue factor

Question 4

Where in the CVS is there a nature tendency for blood turbulence to develop

Answer 4

areas of hydrolic stress- sharp bends, changes in vessel lumen diameter, and branching points

Question 5

How do blood turbulence/stasis predispose to thrombus(3)

Answer 5

blood turbulence-> direct endothelial damage and formation of blood counter currents and local pockets of blood stasis-> inc likelihood of thrombosis

• Blood stasis(dec laminar flow)(venous channels)-> inc blood viscosity->hypercoagulability->hypoxic injury to endothelial cells->procoagulant state
• both may also prevent dilution and removal of activated coag factors

Question 6

Some circumstances that lead to blood hyperocoagulability(3)

Answer 6

inc procoag factors or dec inhibiting factors(like antithrombin 3)
oral contraceptives and pregnancy-inc hepatic synthesis of coag factors and dec hepatic synthesis of antithrombin
snake bite-> release of tissue factor->activation of extrinsic pathway

Question 7

Basic events to thrombus formation(3)

Answer 7

circulating platelets adhere to exposed subendothelial collagen->becoming activated and recruiting more platelets
Aggregate via binding of soluble fibrinogen
Cross linked fibrin polymer:aggregated platelets->coagulum

Question 8

Mural thrombus

Answer 8

non occlusive, protrude only partially into the vessel lumen

Question 9

Occlusive thrombus

Answer 9

completely obstruct the lumen

Question 10

Thrombus propagation

Answer 10

continued flow of blood over a mural thrombus may permit its gradual enlargement (propagation) by allowing repeated layering of platelets and fibrin on its surface and entrapment of RBC and WBC within in

Question 11

What are lines of zahn? signify?

Answer 11

microscopic lamination with altering pale grey white bands of platelets and fibrin with dark red bands containing trapped RBC
Significant because they indicated that the thrombus was initially non-occlusive with continued blood flow over it

Question 12

Expected gross appearance of a thrombus in an artery or within the heart

Answer 12

vegetations, pale or white, dull, dry, rough surface, composed of platelets and fibrin, firmly anchored over a broad zone
initially mural
contains laminations

Question 13

Vegetative valvular endocarditis

Answer 13

involving surface of the heart valves, large thrombotic mass, usually septic

Question 14

Expected gross appearance of thrombus in a vein

Answer 14

develop rapidly, occlusive
form almost perfect cast of the vessel and have smooth shiny surface
Moister than arterial, dark red,
laminations are usually poorly defined or absent
larger, longer tail (easier to break off->thromboemboli)
weak attachments

Question 15

What gross features would allow you to distinguish between ante mortem venous thrombus and a post mortem red currant blood clot?

Answer 15

detection of point of anchorage to the vessel wall
pale grey yellow fibrin on cut surface
evidence of congestion and edema of tissue upstream

Question 16

Thromboembolus

Answer 16

fragments dislodged from an upstream thrombus that travel downstream in the blood to become trapped in distant vessels of smaller calibre

Question 17

Why are venous thrombi more likely to give rise to thromboemboli(2)

Answer 17

weak points of attachment

larger with longer tails

Question 18

septic thrombi

Answer 18

infected with bacteria, softer more friable (more prone to thromboemboli)

Question 19

Bland thrombus

Answer 19

sterile

Question 20

Fibrinolysis

When is it most effective?

Answer 20

enzymatic breakdown of fibrin (by plasmin)
plasminogen(when bound to fibrin)->plasmin by plasmin activators
plasminogen is produced by hepatocytes and circulates in health as a plasma protein
Fibrinolysis is most effective in younger/newer thrombi

Question 21

How do thrombi undergo organization

Answer 21

viable endothelial cells from the margins of the site of thrombus attachment begin to grow over the surface of the thrombus->reducing risk of further propagation

Question 22

Recanalization of a thrombus

Answer 22

endothelial cells grow into the thrombus and form capillaries that provide nutrients for infiltrating leukocytes
capillaries may eventually join from opposite sides and allow longitudinal recanalization to restore some blood flow through the mass