1.7 Thrombopoeisis & Platelet Function

Front 1

Thrombopoeisis is better known as _________________.

Back 1

Megakaryopoiesis

Megakaryocytopoeisis

Front 2

Are megakaryocytes typically found in peripheral blood?

Back 2

No

Front 3

Megakaryocyte mature by the process of _______________.

Back 3

Endoreduplication (endomitosis)

Front 4

What happens in endoreduplication?

Back 4

Everything reduplicates (nucleus, cytoplasm, granules), but nothing actually divides.

Front 5

Megakaryocytes have a ___________ nucleus.

Back 5

Polyploid nucleus

Front 6

What are the stages of megakaryocyte maturation?

Back 6

1. Megakaryoblast

2. Promegakaryocyte

3. Megakaryocyte

Front 7

What are the distinguishing features of a megakaryoblast?

Back 7

- Very large

- Single round nucleus with 1-2 nucleoli

- "Hairy" basophilic protrusions

- Scant cytoplasm, no granules

Front 8

What are the distinguishing features of a promegakaryocyte?

Back 8

- Increased nuclear and cytoplasmic material

- Nucleus becomes lobed

- Reddish granules

- Membrane demarcation around individual platelets

Front 9

What are the distinguishing features of a megakaryocyte?

Back 9

- Gigantic

- 8 nuclear lobes with coarse, linear chromatin

- Lots of reddish-blue granules

- Uniform demarcation system

Front 10

What is the normal number of megakaryocytes in bone marrow?

Back 10

1-4 megas per 1000 nucleated cells

Front 11

Platelets are also known as ___________________.

Back 11

Thrombocytes

Front 12

What is the major regulating factor of megakaryopoiesis?

Back 12

Thrombopoietin (TPO)

Front 13

Where is thrombopoietin (TPO) produced?

Back 13

Liver, kidneys, spleen

Front 14

What happens to megakaryocytes in the absence of TPO?

Back 14

Apoptosis

Front 15

How do platelet levels affect TPO regulation?

Back 15

TPO binds to megas and circulating platelets, so more platelet means less TPO is available to stimulate mega maturation. If platelets are low, more TPO is able to stimulate the production of platelets.

Front 16

How long do platelets last in circulation?

Back 16

9-12 days

Front 17

What is the distribution of platelets in the body?

Back 17

70% are in peripheral blood

30% are in the spleen

Front 18

What could be considered an abnormally low platelet count?

Back 18

< 20,000

Front 19

What granules are present in platelets?

Back 19

1. Alpha granules

2. Dense granules

3. Lysosomes

4. Glycogen

Front 20

What is contained in alpha granules?

Back 20

1. Beta thromboglobulin

2. Platelet Factor 4 (PF4)

3. Platelet-derived Growth factor (PDGF)

4. Thrombospondin

Front 21

Which proteins in alpha granules inhibit heparin?

Back 21

Beta-thromboglobulin, PF4

Front 22

What protein in alpha granules promotes interaction between platelets?

Back 22

Thrombospondin

Front 23

True/False:

Normal platelets will interact with each other and endothelium.

Back 23

False

Front 24

What activates the coagulation pathway?

Back 24

a) Vascular damage exposing subendothelial collagen (basement membrane)

b) Release of tissue factors from damaged epithelial cells

Front 25

What are the 4 functional steps of platelet coagulation?

Back 25

1. Adhesion

2. Aggregation

3. Plug formation

4. Clot stabilization

Front 26

What happens during adhesion?

Back 26

Platelets bind to collage in subepithelial layers via vonWillebrand Factor (vWF) bridge.

Platelets are "activated" by factors that alter their levels of cytosolic Ca, changing their shape into a spiculated sphere.

Front 27

What happens during aggregation?

Back 27

GPIIb/IIIa receptors on platelets become active and available for vWF and Fibrinogen binding. Fibrinogen pulls platelets together like glue.

Front 28

What happens during plug formation?

Back 28

Platelets degranulate, which recruits more platelets for more aggregation.

Clotting cascade creates fibrin to stabilize the mass. Thrombin, plasminogen, tPA, and antiplasmin get trapped in the clot.

Front 29

What happens during clot stabilization?

Back 29

Trapped thrombin activates cross-linking of fibrin, everything consolidates and stabilizes at injury site.

Front 30

GPIb binds to _________________.

Back 30

vonWillebrand Factor (vWF)

Front 31

GPIIb/IIIa binds to ____________________.

Back 31

Fibrinogen

Front 32

Besides coagulation, what other functions do platelets have?

Back 32

Maintain vascular integrity by

1) Nurturing endothelial lining by incorporating into wall and releasing PDGF (platelet derived growth factor)

2) Promotes healing of damaged endothelium

Front 33

What is a clinical symptom of low/absent platelets?

Back 33

Petechiae or purpura -- RBCs break through vessels and enter lymphatics

Front 34

What is considered a normal "bleeding time" test of platelet function?

Back 34

2.5 - 9.5 minutes

Front 35

What are potential causes of platelet clumping in a specimen?

Back 35

1. Improper mixing of blood with anticoagulant

2. Improper ratio of blood/anticoagulant

3. (rare) Antibody to EDTA

Front 36

How should platelet count be reported if clumping is seen on the feathered edge of a smear?

Back 36

Platelet count is NOT reported

Front 37

What should be done if platelet clumping is seen on the feathered edge of a specimen's smear?

Back 37

Redraw a new sample in a sodium citrate (blue top) tube