Thrombosis

Question 1

Describe the typical structure of an artery or arteriole

Answer 1

Endothelial cells lining the lumen

Surrounded by basal lamina (made by endothelial cells)

Smooth muscle cells surround basal lamina

Interstitial collagen fibres (collagen in connective tissue between structures) surrounds this

Question 2

What is the difference between serum and plasma?

Answer 2

Plasma contains clotting factors

Serum is plasma without clotting factors

Question 3

Where are clotting factors mainly produced?

Answer 3

Liver
or
Endothelial cells

Question 4

Describe the clotting cascade (amplification sequence) when there is damage to a tissue

Answer 4

1) Damage exposes interstitial collagen fibres and tissue factor
2) TF reacts with various clotting factors, finally producing Xa-Va
3) Promthrombin is converted to thrombin
3) Thrombin causes soluble fibrinogen to to polymerise to form insoluble fibrin
4) Fibrin cross links leading to coagulation

Question 5

How is the clotting cascade (amplification sequence) initiated?

Answer 5

1) Trauma ∴ blood leaks out of blood vessel
2) Clotting factors in contact with interstitial collagen fibres ∴ activated
3) Tissue factor is released from smooth muscle cells
4) TF binds to clotting factor ∴ initiates clotting cascade

Question 6

Describe the structure of most clotting factors and how most are activated

Answer 6

Many CF are serine proteases

They have serine Amino Acid section and enzyme section

• CF cleaves next CF in cascade
• Producing active CF and redundant fragment

Question 7

How are platelets produced?

Answer 7

Produced in bone marrow

From cell called a megakaryocyte

(large cell with many nuclei)

Platelets synthesised in the cell and bud off as fragments from cytoplasmic extensions

Question 8

Describe how platelets work as coagulants

Answer 8

1) Trauma ∴ exposure of platelets to interstitial collagen

2) Platelets clump together and try to form a bridge to close gap in the blood vessel

Question 9

What is coagulation?

Answer 9

Solidification of blood

Two types:

1) Thrombus formation
2) Clot formation

Question 10

What is the difference in the composition of a thrombus and a clot?

Answer 10

Thrombus - Mesh network of fibrin strands + platelets

Clot - Mesh of fibrin strands + RBCs

Question 11

What are the conditions for the formation of a clot and a thrombus? How are the different?

Answer 11

Thrombus occurs when there is flowing blood

Clots occur when the blood flows out and become stationary

Question 12

What feature of platelets allow thrombus formation in flowing blood?

Answer 12

They have molecules on their surface that allow adherence to interstitial collagen

Question 13

What is the function of coagulants?

Answer 13

Haemostasis - stopping bleeding

Question 14

What ways does the body try to minimise/stop bleeding?

Answer 14

• Clot/thrombus formation

- Vessel vasoconstriction of damaged vessel

Question 15

Describe how clot and thrombus formation are used together to achieve homeostasis

Answer 15

Clots form in the space around the vessel to fill the void of the wounded tissue

Thrombus forms to seal the gaps in the blood vessel

Question 16

After a wound is successfully plugged, what will happen?

Answer 16

Angiogenesis - capillaries grow into clot

It becomes granulation tissue

Blood supply provides oxygen/nutrients etc and keeps GT alive

Question 17

What is ischaemia?

Answer 17

Lack of blood flow to tissues

Can happen if thrombus blocks blood flow

Will lead to hypoxia (lack of oxygen)

Question 18

Aside from ischaemia & hypoxia, what negative effect cam thrombus formation have?

Answer 18

Blocks blood flow ∴ stagnant blood behind it ∴ clotting

Lead to a mixture of clot and thrombus

Question 19

Under normal circumstances, once a blood vessel is repaired, then the clot and thrombus are removed.

How is excess thrombus and clot removed?

Answer 19

Fibrinolytic system present in blood

Fibrinolytic = breaks down fibrin

This stops thrombi from propagating

Question 20

How does the fibrinolytic system work?

Answer 20

Consists of a plasma protein called plasminogen

This is converted to plasmin

Plasmin breaks down fibrin strands

Question 21

What does Virchow’s triad describe?

Answer 21

Factors that cause abnormal clotting/thrombosis which can lead to many diseases

Question 22

What is Virchow’s triad?

Answer 22

Abnormalities of vessel wall

Abnormalities of components of the blood

Abnormalities of vessel flow

Question 23

Why is Virchow’s triad useful?

Answer 23

It defines the 3 abnormalities that lead to thrombosis/clotting in disease