platelets

demarcation membrane system

• composed of extensive network of cisternae and tubules continious with the plasma membrane

  • acts as a reservoir for the development of platelets

what is the principal regulator of megakaryocyte and platelet production

• thrombopoietin by thrombopoietin receptors

what are the two membrane systems of a resting platelet

• open canicular system - necessary for substance transport between platelets and plasma

• closed dense tubular system - regulates platelet activation through release of calcium

what does the glycocalyx contain

membrane binding proteoglycans, TFPI and thrombomodulin

function of the glycocalyx 

• allows adhesion of platelet to collagen and damaged vessels 

platelet production

• produced in bone marrow

• fragmentation of megakaryocyte cytoplasm

  • endomitotic synchronous nuclear replication

  • cytoplasmic volume inc as number of nuclear lobes in in multiples of 2

  • cytoplasmic granulation

  • platelets released

• 9-10 days lifespan

• destroyed in spleen and in liver by kupffer cells

what is platelet production controlled by

• neg feedback - number of circulating platelets

• stimulated by thrombopoeitin (produced in liver)

• IL-3 and GM-CSF stimulate precursor cells

dense tubular system

• site of prostaglandin and thromboxane A2 synthesis

function of platelet contractile proteins

• makes aggregation irreversible

• committing to the stable fibrin clot 

what are the two types of granules of platelets

alpha and delta

delta granules contain

Ca2+, ADP, ATP and serotonin

alpha granules

inc platelet derived growth factor, platelet factor, fibrinogen, vWF, factors V and VIII

which system allows the release of granules

• canalicular