Flashcards in Hemostasis: Approach to a Patient Deck (41)
What cell is described as small anuclear discoid or 2-3 microns and is derived from megakaryocytes?
How long does it take for a platelet to mature?
How long is the lifespan of a platelet?
What percentage of platelets are found in circulation?
In the spleen?
80% in circulation
20% in spleen
What are megathrombocytes?
Newly formed platelets that are large in size
Platelets contain ____________ but do not contain ____________
What are the three kinds of functional granules found in a platelet?
What do dense granules contain?
What do alpha-granules contain?
A number of proteins essential for platelet funciton including procoagulant proteins, plaelet-specific factors for platelet activation, and growth favtors
What do lysosomal granules contain?
What is the function of surface-connected canalicular systems?
These extensive systems of internal membrane tunnels are tunnels through which the contents of the platelet granules are extruded during platelet aggregation and secretion
What are the main functions of platelets?
Adhesion to the vascular subendothelium at sites of injury
Activation of intracellular signaling pathways leading to cytoskeletal changes and release of intracellular gransules
Aggregation to form the platelet plug
Support thrombin generation
Intact endothelial cells can produce what two compounds that act as inhibitors of platelet activation?
Nitric oxide and prostacyclin
What factor do platelets bind in order to adhere to injured endothelium?
von Willebrand's Factor
What protein is used to link vWF to platelets?
What is the role of GPIIb-IIIa in platelet and vWF adhesion?
The enzyme increases its affinity
What happens after platelets adhere to the injured vessel wall?
They undergo a shape change through cytoskeletal activation, becoming more spherical with extended pseudpods and spread over the exposed subendothelium
Then they release the granules
Platelets adhere to each other through which protein?
Fibrinogen is a cross-linker between GPIIb-IIIa
What converts fibrinogen to fibrin to form a stabilized plaatelet plug?
What two tests are commonly used to evaluate platelet function?
Platelet count as a part of a CBC
Bleeding time which will be prolonged if
This type of QUALITATIVE platelet disorder is characterized by as a disorder in adhesion. It is the most common congenital bleeding disorder. It leads to a primary and secondary bleeding disorder. What is it?
Von Willebrands disease.
What test can you use to test the activity of vWF?
Ristocetin cofactor activity test
What drug can you use to treat type I vWD?
DDAVP because it enhances the release of vWF from endothelial stores
What is Bernard-Soulier syndrome?
A rare autosomal recessive disorder where expression of GP1b on the platelet surface is reduced
Abnormal ristocetin test
What is gray platelet syndrome?
Deficiency in dense granules or alpha-granules
Afibrogenemia is a rare inherited defect that results in a decreased amount of what protein?
What rare autosomal recessive bleeding disorder is characterized by the absence of defective GPIIb-IIIa?
What is the normal platelet range?
At what platelet count could you expect patients to spontaneously hemorrhage?
At what platelet count could you expect patients to spontaneously hemorrhage intracranially?