Platelets

Question 1

What are platelets(Thrombocytes)?

Answer 1

• 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.

Question 2

What does the granules of platelets consists of?

Answer 2

• Serotine
• Calcium
• Platelet factors 3 and 4

Question 3

What is the function of platelets?

Answer 3

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.

Question 4

What is the lifespan of platelets in the circulation?

Answer 4

About 8-11 days.

Question 5

Where are platelets stored?

Answer 5

Spleen

Question 6

Give the order of formation of platelets?

Answer 6

Hemocytoblast/Myeloid stem cell/Megakaryoblast/Promegakaryocyte/Megakaryocyte/Platelets

Question 7

Why does platelets age quickly?

Answer 7

Because they are anucleate.

Question 8

Which hormone regulates the formation of platelets?

Answer 8

Thrombopoietin

Question 9

Where are thrombopoietin produced?

Answer 9

By the liver and kidney.

Question 10

What is the stimulus that kick-start thrombopoietin production?

Answer 10

A fall in platelet count.

Question 11

What is the normal platelet count?

Answer 11

150,000- 300,000/μL.

Note: Thrombocytopenia is the term for a low platelet count.

Question 12

What is hemostasis?

Answer 12

It is a sequence of responses that stops bleeding.

Question 13

What are the three mechanisms that contribute to

hemostasis?

Answer 13

(1) Vascular spasm
(2) Platelet plug formation
(3) Blood clotting (coagulation)

Question 14

Describe the vascular spasm mechanism?

Answer 14

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.

Question 15

What causes the spasm effect when there is blood vessel injury?

Answer 15

• Serotin( released by platelets).

- Reflexes initiated by pain receptors.

Question 16

Describe the platelet plug formation mechanism?

Answer 16

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.

Question 17

During the coagulation phase, what happens to the blood?

Answer 17

Blood is transformed from a liquid to a gel.

Question 18

When does the coagulation phase start?

Answer 18

~30 sec after the vessel has been damaged.

Question 19

Describe the blood clotting(coagulation) mechanism?

Answer 19

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.