MoD S5 - Haemostasis and thrombosis

Question 1

What is haemostasis and what does it depend on?

Answer 1

• Process that stops bleeding

- Vessel walls, platelets, fibrinolytic and coagulation system

Question 2

How do platelets contribute to haemostasis?

Answer 2

• Adhere to the site of damage and to each other
• Form a platelet plug
• Platelet release reaction

Question 3

Platelet release reaction

Answer 3

• Platelets activated by adhesion
• Extend projections to make contact with each other
• Release thromboxane A2 & ADP activating other platelet
• Serotonin & thromboxane A2 are vasoconstrictors decreasing blood flow through the injured vessel

Question 4

Outline the process of the platelet release reaction

Answer 4

• ATP is converted to ADP
• ADP and thromboxane A2 aggregate platelets
• 5-HT and factor III are also release
• Factor III is required for the extrinsic coagulation pathway
• Platelets coalesce after aggregation

Question 5

Why must the coagulation cascade be tightly regulated?

Answer 5

1ml of blood contains enough thrombin to convert all fibrinogen in the body to fibrin

Question 6

Give an example of one specific and non-specific thrombin inhibitor

Answer 6

Specific - anti-thrombin III, protein C and S

Non-specific - alpha 1 anti-trypsin, alpha 2 macroglobulin

Question 7

Define thrombosis

Answer 7

Formation of a solid mass within the circulatory system during life

Question 8

What is responsible for the conversion of plasmin to plasminogen?

Answer 8

Streptokinase and tPA

Question 9

What is Virchow’s triad?

Answer 9

Causes of thrombosis‐ due to either abnormal vessel wall, abnormal blood flow or abnormal cell components of the blood

Question 10

List the possible outcomes of thrombosis

Answer 10

Lysis, Propagation, Organisation, Recanalization and Embolism

Question 11

In which outcomes of a thrombosis would blood flow be re-estalished?

Answer 11

Lysis, recanalisation

Question 12

Outline the differences in appearance between an atrial and a venous thromboembolism

Answer 12

Arterial‐ pale, granular, lines of Zahn, low number of cells

Venous‐ soft, gelatinous, deep red, high number of cells

Question 13

How could a venous thromboembolism result in ischemia and infarction?

Answer 13

If venous pressure increases to match arterial pressure then blood flow will stop causing ischaemia

Question 14

What are the possible outcomes of a venous thrombi?

Answer 14

Congestion and oedema (specific to venous thrombi)

Ischaemia and infarction

Question 15

Where could a thromboembolism in the renal or mesenteric arteries originate from?

Answer 15

The heart, travels via aorta to other arteries

Question 16

List the types of pulmonary embolism and their consequences

Answer 16

Massive‐ block blood flow above 60%, rapidly fatal

Major‐ block medium vessel, shortness of breath, blood in sputum and coughing

Minor‐ small vessel, may be asymptomatic or have shortness of breath

Question 17

Why is pregnancy a risk factor for DVT?

Answer 17

Adaptation of pregnancy in preparation for labour is increased coagulative ability

Head of baby may get stuck in pelvic region during labour which blocks veins travelling from lower limb back up to the heart

Question 18

Why is post‐operation a risk factor for DVT?

Answer 18

Time under anaesthetic followed by bed rest results in stasis

Acute phase response involved after operation

Question 19

How can DVT be prevented?

Answer 19

Heparin administered sub‐cutaneously

Leg compression in surgery

TED stockings

Question 20

How can DVT be treated?

Answer 20

Oral warfarin, intravenous heparin

Question 21

List some other risk factors for DVT

Answer 21

Oral contraceptives, immobility, disseminated cancer, severe burns, cardiac failure

Question 22

What is DIC?

Answer 22

Activation of both coagulative and fibrinolytic systems simultaneously which depletes clotting factors and platelets, increasing the likelihood of haemorrhage

Question 23

List some potential causes of DIC

Answer 23

Infection, liver disease, cancer, obstetric complications, burns

Question 24

Could haemophilia A and B be distinguished between on a blood test?

Answer 24

No, requires an assay

Haemophilia A - Factor VIII would be lower than 50%

Haemophilia B - Low factor IX

Question 25

What are some clinical symptoms of thrombocytopenia purpura?

Answer 25

Purpura, Frequent nose bleeds

Question 26

List some potential causes of thrombocytopenia

Answer 26

Lack of platelet production by bone marrow e.g. in leukaemia

Break down of platelets e.g. autoimmune disease

Platelets sequestered by spleen e.g. when spleen enlarged due to cirrhosis