Applied Physiology Lecture 2

Front 1

How many stages of Haemostasis is there? And what are they?

Back 1

5:

1. Vascular phase
2. Platelets phase
3. Coagulation phase
4. Fibrinolysis
5. Repair

Front 2

What is primary haemostasis?

Back 2

The formation of the primary platelet plug

Front 3

What does the primary platelet plug serve?

Back 3

To plug off small injuries especially in microvessels (<100 micrometers) in mucosal tissues.

Front 4

What is the pathway of primary haemostasis?

Back 4

Adhesion -> Activation -> Aggregation

Front 5

What is secondary haemostasis?

Back 5

The formation of insoluble, cross-linked fibrin by activated coagulation factors, specifically thrombin

Front 6

What does fibrin do?

Back 6

Stabilizes the primary platelet plug, particularly in larger blood vessels where the platelet plug is insufficient alone to stop haemorrhage

Front 7

What pathways are involved in secondary haemostasis?

Back 7

The intrinsic, extrinsic and common pathway

Front 8

What is fibrinolysis?

Back 8

The breakdown of fibrin clot, dependent on the protease plasmin

Front 9

What is a thrombus?

Back 9

An aggregation of platelets, fibrin, and red blood cells that attaches to the interior wall of a vein or artery, sometimes occluding the lumen of the vessel

Front 10

List the appearance of arterial thrombus

Back 10

• Occurs in arteries
  
• Growth in retrograde fashion (back towards the heart)
• Forms at site of endothelial injury
• Pale white in colour composed of platelets, fibrin, RBC's and WBC's (forming the lines of Zahn)
• Firmly attached to vessel wall
• Can cause infarction in lower extremities (75%), heart, brain, kidneys and spleen etc.

Front 11

List the appearance of venous thrombus

Back 11

• Arise in deep veins
• Antigrade (in same direction as blood flow)
• Forms at site of stasis (lower extremities)
• Red/dark in colour (more RBC's in clot due to slower blood blow). So there are no lines of Zahn
• Loosely attached to vessel wall
• Can cause DVT and PE

Front 12

What is the name of the system that combines all the predisposing factors that resulted in thrombosis?

Back 12

Virchow's Triad

Front 13

What are the fundamental predisposing factors named in Virchow's Triad?

Back 13

• Endothelial injury
  
• Stasis
• Hyper coagulopathy

Front 14

What does endothelial injury usually lead to?

Back 14

Platelet aggregation and activation of extrinsic clotting pathway

Front 15

What steps bring about platelet aggregation and activation of extrinsic clotting pathway from endothelial injury?

Back 15

• Release of tissue factor
  
• Exposure of subendothelial collagen and other platelet activators
• Increases in pro-coagulant factors and decreases in anti-coagulant effectors

Front 16

Describe the normal blood flow

Back 16

Laminar. Characterised by concentric layers of blood moving in parallel down the length of a blood vessel. Normally platelets flow centrally in the lumen, separated from the endothelium by a slow moving zone of plasma.

Front 17

Name the types of abnormal blood flow. What can they lead to?

Back 17

Stasis and Turbulence. They can lead to thrombus formation

Front 18

How can Stasis and Turbulence lead to Thrombus formation?

Back 18

The abnormal blood flow can lead to:

• Disruption of laminar blood flow; bringing the platelets into contact w the endothelium
• Promotes endothelial cell activation
• Prevents the dilution of the activated clotting factors that fresh flowing blood usually does
• Retard the inflow, clotting factors inhibitors

Front 19

List some main features of Deep Vein Thrombosis

Back 19

DVT:

• Deep, dull pain in the calf
• Violet or red colour in the leg
• Tense swollen leg

Front 20

Describe the main presentation of Deep Vein Thrombosis

Back 20

Acute right lower extremity with deep vein thrombosis. With presentation of swelling, erythema and pitting oedema

Front 21

List the symptoms of DVT

Back 21

• Swelling in one or both legs
  
• Pain or tenderness in one of both legs
• Warm skin on our leg
• Red or discoloured skin on your legs
• Veins you can see
• Tired legs

Front 22

Treatment of DVT?

Back 22

• Anticoagulant medicines
  
• Compression stockings
• Exercise
• Inferior vena cava filters

Front 23

What do the anticoagulant medicines do and name one?

Back 23

They prevent blood clots getting bigger. They can also help stop part of the blood clot breaking off and becoming lodged in another part of your blood stream (an embolism)

Front 24

Name the two types of Heparin

Back 24

Un-fractioned heparin and Low Molecular Weight heparin (LMWH)

Front 25

How can compression stockings help with treating DVT?

Back 25

They help prevent calf pain and swelling and lower the risk of ulcers developing after having DVT.

They can also help prevent post-thrombotic syndrome (damage to leg tissue caused by the increase in venous pressure that occurs when a vein is blocked by a clot and blood is diverted to the outer veins)

Front 26

When should inferior vena cava filters be used as treatment?

Back 26

When anticoagulant treatment needs to be stopped, isn't suitable, or isn't working

Front 27

What are IVC filters?

Back 27

Small mesh devices that can be placed in a vein. They trap large fragments of a blood clot and stop it travelling to the heart and lungs

Front 28

What can happen after a thrombus

Back 28

Some combination of the following four events:

1. Propagation
2. Dissolution
3. Organisation and recanalization
4. Embolization

Front 29

What is propagation?

Back 29

When a small thrombus becomes a larger thrombus because more platelets, erythrocytes and fibrin are accumulating. This can lead to complete obstruction of the vessel or extension of the thrombus into additional vessels

Front 30

Why can a venous thrombus lead to obstruction of the next largest vessel?

Back 30

It has a tail that extends toward the heart (in the direction of blood flow), and propagation along this tail can lead to obstruction of the next largest vessel. While an arterial thrombus has a tail that builds up against the flow of blood (again, propagating towards the heart)

Front 31

What is Dissolution?

Back 31

The most favourable outcome for a thrombi and the fibrinolytic system is responsible for this process.

Front 32

How does the fibrinolytic system lead to dissolution of a thrombi?

Back 32

Cleavage of plasminogen to plasmin by tissue plasminogen activator (t-PA) begins the fibrinolytic pathway resulting in removal of the thrombus.

Front 33

Describe how normal blood flow can be achieved in dissolution

Back 33

Sometimes the central portion of the thrombus undergoes fibrinolysis (central softening) and the periphery organizes resulting in a return of blood flow through a slightly narrowed lumen.

Alternatively the thrombus may retract (retraction is mediated by actin-myosin proteins from platelets).

A combination of fibrinolysis and retraction can result in a return to normal blood flow.

Front 34

Continue from slide 26

Back 34

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