Platelets Flashcards
How are platelets made from megakaryocytes?
via endomitotic synchronous nuclear replicaron where the nucleus divides and the cytoplasm does not until the end
How long do platelets last?
7-10 days normally
What organ has a massive storage of platelets?
the spleen
Describe the membrane of a platelet.
It is intended to increase the surface area available for binding
Where is calcium stored in a platelet?
dense tubular systems (similar to the ER in other cells)
What else do dense tubular systems?
1) half of the nucleotides needed for metabolism- secreted when the platelets are activated
2) serotonin
What are in the larger alpha granules?
1) vMF
2) V and VIII
3) fibrinogen
4) PDGF mitogen
etc.
T or F. Platelets have nuclei
F.
Can GIIb/IIIa bind vMF?
yes, but fibrinogen is the main one
What makes calcium come out of the dense granules?
receptor binding that cleaves IP3 via PIP2 from the membrane. IP3 allows calcium to be released
What role does cAMP play in platelets?
elevating cAMP levels in a platelet turns it off
What does Factor V do once released from alpha granules?
binds directly to the platelet surface
What role does vitamin K play in coag?
it gamma-carboxylates residues on factors (II, VII, IX, and X) and allows those residues to bind calcium which embeds itself into the platelet surface
What other receptors are present on platelets?
- thrombin
- ADP
- epinephrine/serotonin
- TxA2
- fibrinogen
- vMF
What is the main role of TxA2 in platelets?
It is a major proponent of platelet aggregation because once generated (when the receptor that activated PIP2 to IP3 to release calcium, it also releases arachidonic acid and initiates that cycle) it inhibits production go cAMP from ATP
So how does aspirin play in?
blocks cyclooxygenase= no TxA2= elevated cAMP= no platelet aggregation
irreversibly
also blocks PGI2 (made from endothelial cells)- an inhibitor of platelet aggregation so its kind of offset considering you have way more endothelial cells than platelets in the body but SMALL doses (81mg) (baby aspirin) only blocks cyclooxyrgenase so it works great!
What kind of bleeding to people without platelets have?
- bruising
- mucus membrane type bleeding (nose bleed, heavy periods)
- petechiae
What kind of bleeding do hemophilia patients have?
deep tissue and joint bleeding
If a patient is not showing thrombocytopenia but they are bleeding, what should be suspected?
- vMF disease
- qualititative platelet abnormality
What a platelet aggregometer?
can put a cuvette in and keep at 37C and can stir platelet rich (slow spin) and platelet poor plasma (spin hard to bring down platelets) and can measure as a change in optical density as a function of some inhibitor/activator
if its normal, then no qualitative abnormality
What would Glanzman Thrombasthenia (qualitative) look like on platelet aggregometer?
just a straight line at 100% because no platelet aggregation occurs
What would Bernard Soulier (qualitative) look like on platelet aggregometer?
would look normal (risteocetin would be abnormal)
What is a thromboelastogram (TEG)?
draw anti coagulated whole blood and put into machine with probe and cup (two machines- in one the cup rotates and the probe is stationary and vice-versa in the other) and add calcium and a clot forms and the instrument follows it. Takes ~30 minutes
measures resistance of probe to rotation
What is the r time in a TEG?
time it takes the clot to start
What is a good treatment for patients with a platelet antibody?
corticosteroids and splenectomy (where most of the platelet removal occurs)
Can drugs induce antibodies against platelets?
yes, common with heparin-induced thrombocytopenia
What are some causes of thrombophilia/cytosis?
- trauma
- iron deficiency
- splenectomy
- inflammatory disease
- malignancy (Hodgkins, carcinoma)
- MPD
ITS MIM
What kinds of infections could cause thrombocytosis?
osteomyelitis
TB
Why would a splenectomy cause a thrombocytosis?
because all the platelets in the spleen will be released into blood stream
