Platelet Structure and Function

Question 1

Primary hemostasis

Answer 1

Platelets-adhesion, activation, aggregation (AAA)

Question 2

Secondary hemostasis

Answer 2

Coagulation cascase-3D network of fibrin, platelets, and RBCs to form fibrin clot

Question 3

Clot removal, vessel wall restored

Answer 3

Fibrinolysis

Question 4

Platelets form by fragmentation at the end of cytoplasmic processes extending from these cells

Answer 4

Megakaryocytes

Question 5

Where are platelets produced?

Answer 5

In bone marrow

Question 6

Normal platelet life span

Answer 6

10 days

Question 7

At any one time, 1/3 of platelets are resting in this organ

Answer 7

Spleen (also a little in liver)

Question 8

Normal platelet count

Answer 8

145,000-450,000 / ul

Question 9

Like RBC, platelets do not contain?

Unlike RBCs, platelets contain?

Answer 9

no nucleus, mitochondria in cytoplasm

Question 10

How and where are old platelets removed?

Answer 10

In spleen and by kupffer cells in the liver

Question 11

Platelets contain many important glycoprotein surface receptors. List the 4 important ones:

Answer 11

1. VWF receptor
2. Thrombin receptor
3. Fibrinogen receptor
4. ADP receptor

Question 12

GP1b/IX/V

Answer 12

Von Willebrand receptor

Question 13

This ligand facilitates adhesion, the “glue” between platelets and subendothelium

Answer 13

Von Willebrand Factor

Question 14

G-coupled protein platelet receptor

Answer 14

ADP receptor

Question 15

ligand responsible for initial platelet shape change, binds ADP receptor

Answer 15

P2Y1

Question 16

ligand responsible for completion of platelet aggregation, binds ADP receptor

Answer 16

P2Y12

Question 17

Activates platelets through a family of unique protease-activated receptors (PAR)

Answer 17

Thrombin, binds to thrombin receptor

Question 18

When does Thromboxane A2 (TxA2) synthesis occur?

Answer 18

platelet activation. promotes aggregation

Question 19

In addition to glycogen stores, the central area of platelet cytoskeleton contains what two types of granules?

Answer 19

Dense and alpha granules

Question 20

Platelet cytoskeleton contains what type of tubular system?

Answer 20

Dense. Contain microtubules (maintain shape) and actin filaments (maintain shape and platelet contraction)

Question 21

Platelet cytoskeleton contains what type of canalicular system?

Answer 21

Open, vesicles continuous with outer plasma membrane

Question 22

Main function of platelets (3)

Answer 22

Blood clotting, repair blood vessels, prevent blood loss

Question 23

In addition to serving as a cofactor in platelet adhesion, VWF is also a carrier for what?

Answer 23

Factor VIII, has other functions

Question 24

What type of granule ca you not see under conventional light microscopy (requires EM)

Answer 24

Dense granules

Question 25

Specific receptor exposure, glycoprotein IIb/IIIa, occurs during this phase

Answer 25

Activation

Question 26

What are glycoprotein IIb/IIIa's primary ligands?

Answer 26

Von Willebrand factor and fibrinogen This receptor is present on platelet surface but inaccessible to ligands, needs to be activated.

Question 27

ADP, ATP, serotonin, and calcium are in this granule

Answer 27

Dense granules

Question 28

Growth factors, proteoglycans, coagulation proteins, adhesive glycoproteins, and P-selectin are in this granule

Answer 28

Alpha granules

Question 29

Can see these granules under conventional light microscopy

Answer 29

Alpha granules

Question 30

Platelet shape change occurs during this phase

Answer 30

Activation

Question 31

Granule release occurs during this phase

Answer 31

Activation

Question 32

TxA2 synthesis occurs during this phase

Answer 32

Activation

Question 33

Phospholipid exposure occurs during this phase

Answer 33

Activation

Question 34

What do Phosphatidylserine and Phosphatidylethanolamine provide during phospholipid exposure?

Answer 34

The negative charge for a catalytic surface for fibrin clot formation

Question 35

These activating complexes require calcium ions for binding of coagulation factors

Answer 35

Tenase and prothrombinase complexes

Question 36

TxA2 is involved in activating other platelets. What pathway produces TxA2? What initiates the pathway?

Answer 36

The arachidonic acid pathway produces TxA2. Platelet activation initiates the arachidonic acid pathway.

Question 37

COX inhibitors

Answer 37

Inhibit TxA2 formation, an example is aspirin. This is why older people take baby aspirin to decrease risk of stroke. Essentially keep platelets quiet

Question 38

Formation of platelet cluster

Answer 38

Aggregation

Question 39

What is the glue during aggregation?

Answer 39

Fibrinogen

Question 40

What is the role of thrombin in platelet pro-coagulant activity?

Answer 40

Recruits additional activated platelets to clot and stimulates conversion of fibrinogen to fibrin (helps stabilize fibrin clot)

Question 41

How do platelets promote vessel repair?

Answer 41

Release growth factors

Question 42

These two growth factors play a major role in connective tissue repair and regeneration.

Answer 42

PDGF (platelet derived growth factor) | TGF-beta (transforming growth factor)

Question 43

Thrombocytopenia

Answer 43

Decreased platelet count (bleeding)

Question 44

Thrombocytosis

Answer 44

Increased platelet count

Question 45

What is the thrombocytosis paradox?

Answer 45

Increased platelet count usually implies clotting, but sometimes thrombocytosis is due to bleeding. If you have disfunctional platelets, they either don't adhere, activate, aggregate etc. properly. This is an example of mixed quantitative and qualitative.

Question 46

In a platelet aggregation test, epinephrine, ADP, Collagen, Arachidonic Acid, and Ristocetin are all examples

Answer 46

Agonists (platelets are exposed to these ligands, and if they aggregate, ere is an increase in light transmission)

Question 47

During platelet aggregation test, you can see a biphasic pattern. What are the primary and secondary wave due to?

Answer 47

Primary wave: activation of GPIIb/IIIa integrin | Secondary wave: platelet granule release

Question 48

What is TxA2 involved in?

Answer 48

activating other platelets