Platelets Flashcards
What are platelets(Thrombocytes)?
- They are cytoplasmic fragments of bizarre multi-nucleated cells called MEGAKANYOCYTES.
- They are derived from the cytoplasm of megakanyocytes.
Note: -They are cells in the strict sense.
-They contain granules.
What does the granules of platelets consists of?
- Serotine
- Calcium
- Platelet factors 3 and 4
What is the function of platelets?
They are essential for coagulation(clotting) of blood when blood vessels are ruptured or their lining is
injured.
Note: By sticking to the damaged site, platelets form a temporary plug that helps seal the break.
What is the lifespan of platelets in the circulation?
About 8-11 days.
Where are platelets stored?
Spleen
Give the order of formation of platelets?
Hemocytoblast/Myeloid stem cell/Megakaryoblast/Promegakaryocyte/Megakaryocyte/Platelets
Why does platelets age quickly?
Because they are anucleate.
Which hormone regulates the formation of platelets?
Thrombopoietin
Where are thrombopoietin produced?
By the liver and kidney.
What is the stimulus that kick-start thrombopoietin production?
A fall in platelet count.
What is the normal platelet count?
150,000- 300,000/μL.
Note: Thrombocytopenia is the term for a low platelet count.
What is hemostasis?
It is a sequence of responses that stops bleeding.
What are the three mechanisms that contribute to
hemostasis?
(1) Vascular spasm
(2) Platelet plug formation
(3) Blood clotting (coagulation)
Describe the vascular spasm mechanism?
It is the immediate response to blood vessels injury which causes the blood vessel to go into spasms (constriction) thus narrowing the blood vessel, decreasing blood loss until clotting can occur.
What causes the spasm effect when there is blood vessel injury?
- Serotin( released by platelets).
- Reflexes initiated by pain receptors.
Describe the platelet plug formation mechanism?
It is the mechanical blockage of the hole by a platelet plug that temporally seals the damage in the blood vessel wall. The platelets clump to each other and attracts more platelets to the site to form plug.
During the coagulation phase, what happens to the blood?
Blood is transformed from a liquid to a gel.
When does the coagulation phase start?
~30 sec after the vessel has been damaged.
Describe the blood clotting(coagulation) mechanism?
The coagulation phase involves a complex sequence of steps causing the extrinsic and intrinsic pathways to respond leading to formation of fibrin network.
The fibrin network grows, covering the surface of the platelet plug.
