MoD S5 - Haemostasis and thrombosis Flashcards
(26 cards)
What is haemostasis and what does it depend on?
- Process that stops bleeding
- Vessel walls, platelets, fibrinolytic and coagulation system
How do platelets contribute to haemostasis?
- Adhere to the site of damage and to each other
- Form a platelet plug
- Platelet release reaction
Platelet release reaction
- 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
Outline the process of the platelet release reaction
- 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
Why must the coagulation cascade be tightly regulated?
1ml of blood contains enough thrombin to convert all fibrinogen in the body to fibrin
Give an example of one specific and non-specific thrombin inhibitor
Specific - anti-thrombin III, protein C and S
Non-specific - alpha 1 anti-trypsin, alpha 2 macroglobulin
Define thrombosis
Formation of a solid mass within the circulatory system during life
What is responsible for the conversion of plasmin to plasminogen?
Streptokinase and tPA
What is Virchow’s triad?
Causes of thrombosis‐ due to either abnormal vessel wall, abnormal blood flow or abnormal cell components of the blood
List the possible outcomes of thrombosis
Lysis, Propagation, Organisation, Recanalization and Embolism
In which outcomes of a thrombosis would blood flow be re-estalished?
Lysis, recanalisation
Outline the differences in appearance between an atrial and a venous thromboembolism
Arterial‐ pale, granular, lines of Zahn, low number of cells
Venous‐ soft, gelatinous, deep red, high number of cells
How could a venous thromboembolism result in ischemia and infarction?
If venous pressure increases to match arterial pressure then blood flow will stop causing ischaemia
What are the possible outcomes of a venous thrombi?
Congestion and oedema (specific to venous thrombi)
Ischaemia and infarction
Where could a thromboembolism in the renal or mesenteric arteries originate from?
The heart, travels via aorta to other arteries
List the types of pulmonary embolism and their consequences
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
Why is pregnancy a risk factor for DVT?
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
Why is post‐operation a risk factor for DVT?
Time under anaesthetic followed by bed rest results in stasis
Acute phase response involved after operation
How can DVT be prevented?
Heparin administered sub‐cutaneously
Leg compression in surgery
TED stockings
How can DVT be treated?
Oral warfarin, intravenous heparin
List some other risk factors for DVT
Oral contraceptives, immobility, disseminated cancer, severe burns, cardiac failure
What is DIC?
Activation of both coagulative and fibrinolytic systems simultaneously which depletes clotting factors and platelets, increasing the likelihood of haemorrhage
List some potential causes of DIC
Infection, liver disease, cancer, obstetric complications, burns
Could haemophilia A and B be distinguished between on a blood test?
No, requires an assay
Haemophilia A - Factor VIII would be lower than 50%
Haemophilia B - Low factor IX
