Physiological Thrombosis

Question 1

lumen is found in

Answer 1

artery

Question 2

Platelets are not normally exposed to

Answer 2

interstitial collagen fibres around vessel

Question 3

Plasma consists of

Answer 3

water and numerous proteins and other molecules

Question 4

Plasma contains

Answer 4

clotting factors (serum is plasma without clotting factors)

Question 5

Clotting factors

Answer 5

Many are mainly produced in the liver (but also by endothelial cells)
Many clotting factors are named with a Roman numeral eg Factor VIII

They are an amplification system, resulting in thrombin production
Thrombin, in turn converts soluble fibrinogen into insoluble fibrin
Fibrin forms a mesh of strands

Question 6

The clotting cascade is

Answer 6

an amplification system so many more molecules of fibrin are produced compared to, for instance, Tissue Factor

Question 7

What is meant by initial damage

Answer 7

One obvious way is trauma
Trauma leads to
- Exposure of interstitial collagens (collagens in connective tissue between structures)
- Exposure of a molecule called Tissue Factor (=TF)

Question 8

Trauma results in

Answer 8

defects in vessels.
Blood leaks out and serum comes into contact with interstitial collagen fibres
Plasma clotting factors can now be activated as they contact interstitial collagens
(Tissue factor is released from smooth muscle cells)
Tissue factor can now bind a particular clotting factor and initiate the clotting cascade

Question 9

How does a clotting factor(s) become activated?

Answer 9

Many clotting factors are serine proteases - that is they have a serine amino acid in them and they cleave other clotting factors to form the active molecule

Question 10

Clotting cascade leads to

Answer 10

production of thrombin from prothrombin
Thrombin converts soluble fibrinogen to insoluble fibrin
Endpoint of clotting cascade is production of insoluble fibrin strands that form a meshwork

Question 11

Platelets are produced in

Answer 11

bone marrow from cell called a megakaryocyte

Megakaryocyte = Large cell with many nuclei

Question 12

Megakaryocyte in bone marrow

Answer 12

Undergoes nuclear division but not cell division so get huge cell with many nuclei

Question 13

Platelets bud off as fragments from

Answer 13

cytoplasmic extensions

Question 14

How do platelets work?

Answer 14

Trauma to vessel leads to exposure of platelets to interstitial collagen.
Platelets adhere together try to form bridge to close gap

Question 15

Coagulation =

Answer 15

‘solidification of blood’

2 types:

- Thrombus formation
- Clot formation

Question 16

Thrombus formation Occurs in

Answer 16

flowing blood.
A pure thrombus is pale cream coloured
A thrombus consists of platelets and a mesh like network of fibrin strands

Question 17

Why does a thrombus of platelets and fibrin occur in flowing blood?

Answer 17

Platelets have molecules on their surfaces which allow adherence to interstitial collagen, even when blood is flowing past them – the clotting cascade deposits Factor VIII which enhances this further

Question 18

Clot formation =

Answer 18

blood leaks out off a vessel and becomes stationary (or stagnant)
Within the stagnant blood, sitting next to interstitial collagen, the clotting cascade is activated

Question 19

A clot consists of

Answer 19

a network of fibrin strands and red blood cells

Question 20

When trauma to skin disrupts one side of vessel

Answer 20

Blood, including RBC’s, leaks out
The clotting system is activated by collagen and by the stagnant blood, forming a clot
- But this may not work perfectly and the wound may
continue to bleed
The vessel vasoconstricts to decrease blood loss

Question 21

A platelet and fibrin thrombus forms to

Answer 21

bridge the gap between the ends of the vessel adjacent to flowing blood

Question 22

In any wound due to trauma there may be bleeding and these mechanisms occur

Answer 22

Vasoconstriction helps reduce bleeding
Clot formation occurs in space around vessel and may fill void of wounded tissue
Thrombus forms in flowing blood and stops bleeding from gaps in vessels

Question 23

New vessels can grow into

Answer 23

area of wound.

These new vessels are called granulation tissue

Question 24

The capillaries that grow in (granulation tissue) can

Answer 24

oxygenate the area of the wound and keep it alive

Question 25

How to remove thrombus?

Answer 25

A blood protein called Plasminogen converts to plasmin, and plasmin cuts up fibrin into smaller fragments, as a way of removing fibrin (in both clots and thrombi). In a thrombus this is sometimes called thrombolysis

Question 26

How is the excess thrombus or clot removed?

Answer 26

In blood there is a fibrinolytic system which removes fibrin and stops thrombi from propagating

Question 27

Fibrinolytic system depends on:

Answer 27

Plasma protein called plasminogen being converted to plasmin

Plasmin cuts up fibrin into fibrin degradation products

Question 28

Fibrinolytic system is normally in balance with

Answer 28

clotting system.

Plasmin generation, at the site of injury, limits the extent of the evolving thrombus

Question 29

Thrombosis and clotting are ‘normal’ in:

Answer 29

Wound healing

Stopping bleeding during menstruation

Question 30

Thrombosis: 3 main causes

Answer 30

Changes in the intimal surface of a vessel (when trauma occurs)
Changes in the pattern of blood flow
Changes in the blood constituents

Question 31

The 3 predisposing situations that may result in thrombus formation are known as

Answer 31

Virchow’s triad