Blood platelets and homeostasis Flashcards
Where is thrombopoietin secreted ?
Liver
What are thrombocytes?
Fragments of megakaryocytes which have broken off.
What are the characteristics of thrombocytes?
Platelet production controlled by
thrombopoietin (increases megakaryocytes)
Platelets contain granules with cytokines and
clotting proteins
Platelets become activated when damage
occurs to the blood vessel walls
Small (2-4 μm)
Lifespan (±10 days)
Normal number: 150‐450 x 103/ μ l blood
What is thrombocytopenia and what effects does it have ?
A decreased amount of thrombocytes in the blood.
Spontaneous bleeding
Skin (purpura, petechiae), mucous membranes of the
nose, mouth, GI tract, uterine cavity
Prolonged bleeding after injury
Outline the heamostatic mechanism of blood and its 3 major steps.
Haemostasis is the process of keeping blood
within the blood vessel by repairing leaks without
compromising the fluidity of blood
- Vasoconstriction: reduces blood loss and makes it easier for platelets to bind to the injury.
- Temporary blockage of the break by a platelet
plug - Blood coagulation/ clot forming that seals the
injury until tissues are repaired
Outline platelet plug formation
Exposed collagen binds and activates platelets.
Release of platelet factors
Factors attract more platelets
Platelets aggregate into platelet plug
Outline platelet plug formation
von Willebrand factor binds platelets to collagen and platelets bind to each other via fibrinogen
what is the role of von Willebrand factor
It binds the vessel wall (collagen) of microfibrils to the glycoprotein 1B of platelet membranes.
What is the role of serotonin in platelet function?
It acts as a vasoconstrictor and is involved in platelet aggregation and is released as a result of platelet activation.
What is the role of PAF in platelet function ?
Increases capillary permeabiltiy to reduce infection.
Role of thromboxane A2 in platelet function
vasoconstrictor and eicosanoid
the roles of PDGF in platelet function
promotes wound healing by attracting fibroblasts and smooth muscle cells
What are the functions of platelets?
Functions of platelets
1. Form platelet plugs that seal off leaks in vessels
2. Release serotonin and thromboxane A2 →
cause local vasoconstriction
3. Release clotting factors
4. Release growth stimulators: stimulate repair of
vascular lesions and bone lesion
What causes blood coagulation ?
Plasma proteins and calcium ions which are released by damaged tissue and activated platelets
What is the order that clotting factors appear in the intrinsic pathway ?
12, 11(Ca), 9(Ca), 8
Which clotting factors require calcium
1,2,9,10,11
why do blood bags contain citrate
prevents coagulation
Which clotting factors require Vitamin K
2,9,10
What is the role of thrombin in coagulation
Stimulates conversion of fibrinogen to fibrin
List the factors involved in coagulation
collagen
Starts intrinsic pathway N/A
von Willebrand
factor (vWF)
Kinonogenand
kallikrein
Tissue factor (tissue
thromboplastin or
Prothrombin and
thrombin (factor II)
Fibrin production N/A
Fibrinogen and
fibrin (factor I)
Fibrin stabilizing
factor (factor XIII)
Ca2+(factor IV) Plasma ions N/A Required for
Vitamin K
Outline anticlotting mechanisms
Intravascular clotting is limited by:
1. Smooth endothelial lining of the cardio‐vascular system
2. Continued circulation of blood
3. Factors counteracting platelet aggregation, i.e.
prostacyclin (released by the intact endothelium)
4. Antithrombin III ‐ a circulating compound (a globulin
produced by the liver) that binds to thrombin and
inactivates it
5. Heparin, a natural occurring anticoagulant (produced by
mast cells
What is fibrinolysis
Conversion of fibrinogen into fibrin and subsequent fibrinolysis
List the factors involved in fibrinolysis and anti-coagulation
Plasmin
Tissue plasminogen activator
antithrombin 3
prostacyclin
Effects of recombinant tPA
acute ischaemic stroke
