Haemostasis Flashcards
What is the average blood volume?
4-6 litres
What is the name given to when you lose more than 20% of your blood?
Hypovolaemic shock
Define haemostasis
The cessation of blood loss from damaged vessels
What does haemostasis require?
Cell-cell communication
How many cells per mm3 of peripheral blood do Erythrocytes make up?
5 million cells per cm^3
What is the lifespan of an erythrocyte? What is the significance that they are anucleate when they are damaged?
- 120 days
- They cannot repair themselves as they have no nucleus for transcription
What are the 3 phases of haemostasis?
- Vascular phase
- Platelet phase
- Coagulation phase
What occurs during the vascular phase?
Vasoconstriction
Endothelial cells contract
Endothelial adhesion increases
In the vascular phase of haemostasis, what does the contraction of endothelial cells result in?
- Exposes basal lamina to blood
- Releases factors; ADP, tissue factor, endothelins
In the vascular phase of haemostasis, what does the release of ADP result in?
ADP - platelet aggregation
What are endothelins?
Peptide hormones which stimulate contraction of smooth muscle and promote mitosis of damaged tissue in vessels
During the vascular phase of Haemostasis, what are 4 examples of factors that endothelial cells release? What do each of these factors contribute to?
- ADP - platelet aggregation
- Prostacyclin - reduces spread of platelet aggregation 3. Tissue Factor - involved in extrinsic pathway of coagulation
- Endothelins - stimulate contraction of smooth muscle
In smaller vessels how can endothelial adhesion help haemostasis?
- Endothelial cells can stick together to cover damaged vessels
- Can also provide attachments for platelets
How and where are platelets formed? How long is the life span of a platelet?
- Megakaryocytes have structures that project into marrow sinuses in the bone marrow - These pockets of cytoplasm them pinch off to form platelets -
Life span of a platelet is 10 days
What are the 3 stages of the platelet phase?
- Adhesion
- Activation
- Aggregation
What is the platelet phase dependent on?
Temperature
During platelet adhesion, what do the platelets adhere to? What factor is important for this?
- They adhere to the endothelium and basal lamina
- von Willebrand factor (for activation and aggregation of platelets)
What occurs during the activation stage in the platelet phase?
- They swell and form spike extensions
- Granulolysis
During platelet activation, what are 5 examples of substances released by granulolysis? What do they each do?
- ADP - platelet aggregation
- Serotonin - stimulates smooth muscle contraction
- Thrombaxane A2 - stimulates smooth muscle contraction
- Clotting factors - promote clot formation
- Ca2+ - platelet aggregation and coagulation
What is the aggregation stage of the platelet phase stimulated by?
ADP, thromboxane A2 and calcium ions
What are 3 examples of substances that inhibit platelet activation?
- Prostacyclin
- Nitrous Oxide (produced by intact endothelial cells)
- Aspirin
What does prostacyclin do?
Inhibit platelet activation and vasodilator
What are the 2 pathways involved in the coagulation phase of haemostasis?
- Intrinsic Pathway
2. Extrinsic Pathway
Which vitamin is essential for formation of clotting factors in the liver?
Vitamin K
What is essential for the formation of clotting factors in the liver?
Vitamin K
As well as catalysing the conversion of fibrinogen into fibrin, what is another function of thrombin?
It causes release of more tissue factor and clotting factors
Why is clot restriction important?
Prevents the formation of a thrombus
What are 3 substances that inhibit coagulation?
- Thrombin stimulates anti-thrombin III to slow down coagulation
- Natural anticoagulants e.g. heparin and prostacyclin
- Thrombolytics e.g. warfarin and aspirin
Describe the pathway for fibrinolysis of a clot
Clot removal by plasmin
Plasminogen activated by thrombin and t-PA (tissue plasminogen activator)
Plasminogen is converted to plasmin which digests the fibrin strands in the clot
Give 4 examples of disorders related to abnormal haemostasis
- Haemophilia
- Deep vein thrombosis
- Liver function
- von Willebrand’s disease
What are the 3 types of haemophilia? What clotting factors are absent in each type?
- A - factor VIII, X-linked recessive
- B - factor IV, X-linked recessive
- C, factor VI, autosomal recessive
Haemophilia B is associated with which clotting factor?
Factor IV
Clotting factor VIII is associated with which type of haemophilia?
Haemophlia A
Clotting factor VI is associated with which type of haemophilia?
Haemophilia C
What kind of disease is acquired haemophilia?
An autoimmune disease
What is the cause of deep vein thrombosis?
Clotting factor accumulation
What is von Willebrand’s disease?
vWF deficiency
vWF factor links platelets to endothelium by activating and aggregating them
