W1 LECT 4: platelets Flashcards
where are platelets formed?
megakaryocytes in the bone marrow
how does megakaryocytes differentiate?
hematopoietic stem cell- megakaryocyte progenitor cells - mature megakaryocyte
what helps with facilitating fragmentation of
proplatelets into 1 to 2 μm
platelets?
-shear and turbulent blood flow
how many platelets does each megakaryote give rise to?
2000- 3000 platelets
what is the T1/2 of platelets?
9-10 days
what clears the platelets?
liver and spleen
what is thrombopiotein?
primary regulator of platelet production
what regulates the circulating levels of TPO?
clearance of TPO after it
binds to c-mpl receptors on
circulating platelets
what is thrombocytopenia?
Thrombocytopenia is a medical condition characterized by a lower than normal number of platelets in the bloodstream.
what is the treatment for thrombocytopenia?
TPO receptor agonist
outline the structure of platelets?
Extremely small
(3um by 0.5um)
* High level in
circulation-range
150-400x109
platelets/l
* discoid
* anucleate cells
but have distinct
mitochondria
what maintains the discoid shape of platelets?
cytoskeleton
* protects the cell from getting sheared in the blood stream
what are the 3 types of platelet storage granules?
- alpha granules
- dense granules
- lysosomes
how does platelet promote hemostasis?
-Adhesion to sites of vascular injury
* Granule release
* Aggregation to form a platelet plug, and
* providing a procoagulant surface for activated CF on their phospholipid surfacemembrane
what makes platelets active following damage to the vessel wall?
thrombin
what is the initial step in platelet activation?
platelet adhesion to subendothelium (collagen, VWF)
what mediates adhesion
membrane GP receptors
* expressed by platelets
where do vwf bind to on platelet?
glycoprotein Ib/ IX/ V at high shear rates
when do platelets release their content?
upon activation
what are the examples of alpha granules?
- coagulation factors: fibrinogen, vwf, factor v
- growth factors
- membrane proteins
what are the e.g. of dense granules?
ATP, ADP, Ca, serotonin
