APPP 17 and 22: Blood-Platelets and Hemostasis Flashcards
What is hemostasis?
series of processes aimed at preventing excessive blood loss after an injury
- cessation of blood loss from a damaged vessel
What does successful hemostasis depend on? (3)
- vessel wall
- circulating platelets
- plasma-coagulation proteins
Briefly describe the process of hemostasis.
- starts with constriction of blood vessels to limit blood loss
- followed by contribution from platelets and coagulation proteins to form a thrombus (blood clot)
What is a thrombus?
clot that adheres to the interior wall of an artery or vein
What is an embolus?
blood clot that has been dislodged and is travelling throughout the bloodstream
Why are both thrombi and emboli dangerous?
may occlude blood vessels, obstruct flow of blood through circulatory system, and deprive tissues of oxygen and nutrients
What is thrombosis?
formation of an unwanted blood clot in the artery or vein
What is arterial thrombosis?
usually a result of adherence of platelets to the arterial wall
- largely a phenomena of platelet activation
- arterial thrombi are pale, granular, and have a lower cell count
What can arterial thrombosis lead to? (5)
- ischemia
- myocardial infarction
- angina
- stroke
- peripheral arterial disease
What is the management strategy for arterial thrombosis?
mainly focused on anti-platelet strategies
What is venous thrombosis?
largely a consequence of activation of the clotting (coagulation) system and hence are made up of RBC and fibrin
- venous thrombi are soft, gelatinous, deep red, and have a higher cell content
- develops in areas of stagnated blood flow (especially in deep leg veins, most commonly femoral vein, near venous valves)
What are the causes of deep vein thrombosis? (4)
- surgery
- injury – ie. broken leg
- sitting or inactivity
- birth control
What would happen if the venous thromboemboli dislodges from the deep veins of the leg?
travels to right side of the heart to reach the lung, where it causes pulmonary embolism (potentially life-threatening)
What is the management strategy for venous thrombosis?
mainly centred on anticoagulation strategies
Arterial Thrombosis
What does clot formation require?
- platelet adhesion, activation, and aggregation
- formation of thrombin
Arterial Thrombosis
What is thrombin and its function?
enzyme that catalyzes the production of fibrin which (when cross-linked) stabilizes the clot
Arterial Thrombosis
What happens in response to an injury to a blood vessel?
- local vasoconstriction occurs due to local spasm of the smooth muscle in the wall of the blood vessel as a result of secretion of vasoconstrictors such as endothelin-1
- immediately after vasoconstriction, primary hemostasis occurs – requires platelets (provides initial plug at sites of vascular injury)
What are platelets?
anucleate, cellular fragments that circulate as inactive, non-binding concave discs
Platelets perform a very important biologic role in the vascular system. Describe this.
- interaction between platelet and vessel wall is important
- platelets normally do not adhere to healthy arterial walls, and are not activated by the vascular endothelium – because platelets have coated glycoproteins which carry negative charges and are therefore repelled by the endothelial cell (EC) which also has a glycoprotein coat of negative charge
- damage to blood vessels exposes collagen and other underlying tissue (sub-endothelium) which have positive charges
- therefore at the site of injury (damaged vessel wall), platelets begin to adhere to the damaged site within seconds, then platelet activation (release of intracellular granules) and platelet aggregation occurs to form a platelet plug
Platelet Adhesion
When does it occur and why?
within seconds of vascular injury, platelets firmly adhere to collagen fibrils in the vascular sub-endothelium via ionic interaction and specific receptors
- this process is provoked by the loss of an intact endothelial lining of the blood vessel, as well as by the exposure of the platelet to activating sub-endothelial structure (ie. collagen)
Platelet Adhesion
How do platelets adhere to collagen in vascular sub-endothelium?
via a specific platelet collagen receptor made up of glycoproteins (Gp)
Platelet Adhesion
What is GPVI?
central receptor that facilitates direct contact with sub-endothelial collagen
Platelet Adhesion
What are the other receptors also suggested to play a role in contacting platelets directly to collagen?
α2β1-integrin and GPIa