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MEDSCI 203 Second half > Lecture 21 > Flashcards

Lecture 21 Flashcards

1
Q

What is haemostasis?

A

A physiological response to the injury of blood vessels where ‘plug’ is formed to prevent loss of plasma

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2
Q

What is the role of haemostasis in normal, healthy conditions?

A

It is normally inhibited by endothelial cells as they produce Nitric Oxide, prostacyclin and antithrombin (which binds and inactivates the thrombin coagulation enzyme)

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3
Q

What is the role of endothelial cells after injury?

A

They promote haemostasis through production of von Willebrand factor and tissue factor
They also express endothelin which vasoconstriction

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4
Q

What are the roles of von Willebrand factor and tissue factor?

A

von Willebrand factor which promotes platelet adhesion to ECM proteins which become exposed in vessel injury
Tissue factor or thromboplastin activates the coagulation cascade

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5
Q

What is the role of platelets in haemostasis?

A

Become activated by the exposed ECM proteins and begin secretion of thromboxane A2, vasoactive amines and ADP promoting vasoconstriction and platelet aggregation

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6
Q

What is purpura?

A

Bleeding from skin capillaries

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7
Q

What is the role of the coagulation cascade in haemostasis?

A

A cascade of proteolytic reactions leading to the activation of several zymogens.
This cascade is activated by tissue factor, and ultimately results in the activation of thrombin causing the conversion of fibrinogen and fibrin which act as fibres to form a meshwork

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8
Q

What is the method used to break down the haemostatic plug when it is no longer needed?

A

The fibrinolytic system

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9
Q

What are the stages of haemostasis?

A

Brief period of vasoconstriction
Endothelial injury exposes highly thrombogenic ECM
Platelets secrete granules to form primary haemostasis
Tissue factor activates the coagulation cascade
Thrombin causes further platelet aggregation causing secondary haemostasis
Fibrin and platelet aggregations form a solid permanent plug
Counter-regulatory mechanisms are activated

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10
Q

What is thrombosis?

A

When the haemostasis mechanisms are inappropriately activated

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11
Q

What is a thrombus?

A

A mass formed from blood constituents within the circulation during life, these are composed of fibrin, platelets and red and white blood cells

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12
Q

Where can thrombi form?

A

In cardiac chambers or blood vessels, they may cause damage where they occur through obstruction of the lumen
Alternatively they can break off forming an embolus and travel to cause damage in another distant part of the cardiovascular system

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13
Q

What is the difference between a blood clot and a thrombus?

A

Blood clots occur as a result of static blood flow, as a result of the coagulation system

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14
Q

What is Virchow’s Triad?

A

The three things that can result in thrombosis:
Changes in the vessel wall
Changes in blood flow
changes in constituents of blood

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15
Q

What is hypercoagulability?

A

Changes in the blood constituents

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16
Q

What are the changes in the vessel wall causing thrombosis?

A

Changes due to endothelial cells through injury and activation these can come from circumstances such as
Myocardial infarction
atherosclerotic plaques
vasculitis

17
Q

What are the changes in blood flow which can lead to thrombosis?

A

Turbulence caused by atherosclerosis, aneurisms, infarcted myocardium can cause clotting
Alternatively stasis in veins can cause thrombosis this typically occurs in pelvic vaines and superficial leg veins. This stasis cans arise due to a failure of the heart, immobilization or compressed veins

18
Q

What are the changes in the constituents of blood that lead to thrombosis?

A 
The two potential genetic causes are: Deficiency in protein C
Deficiency in antithrombinin III
The acquired causes are:
Tissue damage
Post-Operative
Malignancy
Cigarette Smoke
Elevated Blood Lipids
Oral Contraceptives
19
Q

What methods exist to limit coagulation?

A

Antithrombins
Proteins C and S which require vitamin K
Tissue Factor pathway inhibitor
Fibrinolytic cascade

20
Q

What are the potential fates of thrombi?

A

Dissolution (Breakdown via fibrinolytic system)
Propagation (Moves in a long tail along the vein towards the heart)
Stenosis (narrowing or occlusion of a blood vessel)
Organisation and Recanalisation where the thrombi becomes incorporated into the vessel wall and new blood vessels are formed
Formation of Emboli

21
Q

What is an emboli?

A

Intravascular mass carried by blood flow from its point of origin to a distant site

22
Q

What are the typical effects of emboli?

A

Typically effects due to stenosis this often occurs in legs or pelvis veins as emboli travel and often lodge in pulmonary veins causing pulmnary infarction
Can also occur in the systemic circulation

23
Q

What are the different types of emboli?

A 
Thrombus
Fat
Air
Atheromatous Debris
Bone Marrow
Amniotic Fluid

MEDSCI 203 Second half (13 decks)

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