Platelets - Siegel

Question 1

What leads to platelet release from the megakaryocyte

Answer 1

fragmentation of megakaryocyte cytoplasm

Question 2

Do platelets have a DNA or nucleus?

Answer 2

NO

Question 3

What sorts of proteins are found in platelets?

Answer 3

structural, granule, glycoproteins, enzymes

Question 4

How do platelets join together?

Answer 4

form fibrillar bridges between platelet membranes

Question 5

What sort of coat do platelets have?

Answer 5

thick proteoglycan coat

Question 6

What are the dense granules in the platelet?

Answer 6

the energy source

- store ATP, ADP, Ca, serotonin, Mg

Question 7

What do the alpha granules of platelets contain

Answer 7

vWF, factor V, VWF

Question 8

What proteins serve to keep the vessel walls dilated? (4)

Answer 8

prostacycline, nitric acid, ADPase, plaminogen activator

Question 9

what do endothelial cells secrete with vessel wall injury?

Answer 9

procoagulants

• selectins
• integrins
• vWF
• promote platelet adhesion and vasoconstriction

Question 10

What are subendothelial substances that are released with vessel wall injury

Answer 10

collagen, glycoprotein IIb/IIIa on platelet surface, thrombospondin, fibronectin, tissue factor

Question 11

What are strong platelet agonists

Answer 11

thrombin and collagen

Question 12

What are weak agonists for platelets

Answer 12

ADP and epinephrine

Question 13

What does an elevated bleeding time mean

Answer 13

platelets aren’t function properly or thrombocytopenia

Question 14

Mucosal bleeding

Answer 14

platelet defects

• easy bruising
• heavy menstrual periods
• abnormal period times

Question 15

What does von Willebrands disease affect

Answer 15

platelet function and coagulopathy

Question 16

What are causes of hypoproliferation in thrombocytopenia

Answer 16

radiation, drugs, chemicals, infections, bone marrow dysfunction

Question 17

What are causes of increased desctruction in thrombocytopenia

Answer 17

drug induced, DIC

Question 18

What is TPO

Answer 18

mediator of platelet production, produced in liver

Question 19

What is the effect of TPO on megakaryocytes

Answer 19

more platelet production due to increased maturation

Question 20

What is the effect of TPO on platelets circulating

Answer 20

platelets just absorb the TPO and they are degraded

Question 21

What are drugs that lead to a decreased production of platelets

Answer 21

alcohol, thiazide diuretics, cimetidine, chemotherapy

Question 22

What are three mechanisms that lead to a decreased survival of platelets

Answer 22

autosensitization of platelets

• hapten penicillin type
• immune complex deposition

Question 23

Heparin induced thrombocytopenia

Answer 23

UFG can lead to platelets dropping to very low levels

• can lead to bleeding and thrombotic complications - low platelets but they’re bound together
• need direct thrombin inhibitors

Question 24

Immune thrombocytopenia purpura

Answer 24

• low platelet count
• menorrhagia
• cutaneous bleeding
• intracranial hemmorhage
• no viral infection, no drugs, no congenital

Question 25

What causes ITP

Answer 25

autoantibodies to platelet membrane antigens

Question 26

What is the biggest risk of ITP

Answer 26

intracranial hemmorhage

Question 27

What is the pathophysiology of ITP

Answer 27

rapid destruction of the spleen and liver - suppression of TPO - platelets are barely lasting

Question 28

What are the autoantibodies targeting in ITP

Answer 28

GP IIb/IIIa and GP Ib/IX

Question 29

What age group is acute ITP found in?

Answer 29

2-6 yo, usually after a viral infection

Question 30

Thrombocytopenic purpura

Answer 30

thrombocytopenia, CNS symptoms, renal failure

Question 31

What is the mechanism of action for thrombocytopenic purpura

Answer 31

antibody blocks the function of VWF cleaving | - no cleaving = increased platelet adhesion without activating coagulation cascade

Question 32

What is therapy for TTP

Answer 32

removal of antibody and clearance of multimers - plasma exchange - steroids

Question 33

What is the lifespan of a platelet

Answer 33

8 days

Question 34

What holds the platelet plug together

Answer 34

fibrin wraps around to hold the platelet plug

Question 35

What promotes platelet adhesion?

Answer 35

VWF - protein that plays an important role in clotting cascade and physiological adhesion of platelets to subendothelial membrane

Question 36

What does prostacycline do

Answer 36

leads to vasodilation to make clotting less likely

Question 37

What is the role of collagen with platelets?

Answer 37

strong platelet agonist that causes dense granule release

Question 38

what is glycoprotein IIb/IIIa

Answer 38

antigens expressed on the platelet surface that helps platelets bind together

Question 39

What is the role of thrombospondin and fibronectin

Answer 39

help activate platelets

Question 40

What are examples of mucosal bleeding due to decreased platelet numbers

Answer 40

nose bleeds, easy bruising, heavy menstrual bleeding

Question 41

A 25 yo woman presents to office complaining of easy bruising and petechiae but feels well otherwise. platelet count is 10,000 but her Hgb is 12.8 and Hct is 39 and WBC is 5.5

Answer 41

normal HgB, Hct, and WBC but LOW platelet count | - most likely diagnosis is immune thrombocytopenia

Question 42

What is happening with TTP

Answer 42

not associated with clotting time - collection of large VWF multimers, platelets are coming together forming platelet only clots - using up platelets faster than the bone marrow can use them

Question 43

A 45 yo woman presents with profound fatigue, fevers, and confusion. A CBC reveals a markedly diminished platelet count and the lab test saw schiztocytes. What would you want to check?

Answer 43

- check the peripheral smear - check PT/PTT - checking intrinsic and extrinsic system - draw blood cultures - check LDH (hemolysis)

Question 44

What are the common symptoms of TTP

Answer 44

low platelets, fever, don't feel well, renal failure, CNS symptoms

Question 45

What is the mechanism of TTP

Answer 45

- Ab blocks function of vWF cleaving protein ADAMTS-13 - increased level of high molecular vWF multimers - increased platelet adhesion without activating coagulation cascade

Question 46

What is the role of ADAMTS-13?

Answer 46

it cleaves Vwf and if you have antibodies against it then you can have TTP

Question 47

What is the therapy for TTP?

Answer 47

removal of antibody and clearance of multimers | - plasma exchange

Question 48

When would an in-vitro platelet aggregation study be helpful?

Answer 48

A patient has normal platelet count and bleeds excessively after a biopsy - figure out what the problem is if you have a normal platelet count

Question 49

How is a bleeding time study conducted?

Answer 49

pumping BP cuff to 40 mm, making a 1 cm cut 1 mm in depth, blotting q 30 sec until bleeding stops

Question 50

What is a normal bleeding time?

Answer 50

less than equal to 8 minutes

Question 51

Where is TPO produced

Answer 51

liver

Question 52

What does TPO affect

Answer 52

platelets and megakaryocytes and promegakaryoctes in the bone marrow

Question 53

What happens when TPO binds to progenitor cells?

Answer 53

expansion and maintenance of progenitor cells which leads to more megakaryocytes production

Question 54

What happens when TPO binds magakaryocytes

Answer 54

enhancement of megakaryocyte maturation which leads to increased platelet production

Question 55

What happens when TPO binds to platelets

Answer 55

- internalized and degraded within the cytoplasm - doesn't affect function or activity - platelet numbers determine available TPO level

Question 56

What do storage pool diseases result in

Answer 56

inherited causes of platelet dysfunction | - decrease or absence of dense granules

Question 57

heparin inducted thrombocytopenia

Answer 57

- antibody reaction that leads to reduced platelet count - platelets start clotting - Elisa test to determine the Ab test

Question 58

What type of heparin is more likely to cause HIT

Answer 58

unfractionated heparin

Question 59

preeclampasia

Answer 59

- hypertension - platelet levels can drop - especially after 30 weeks

Question 60

HELLP syndrome

Answer 60

- hemolysis - elevated bilirubin - elevated liver enzymes - low platelets

Question 61

Neonatal alloimmune thrombocytopenia

Answer 61

- fetal inheritance of platelet isoantigens not present in the mother - comes from the dad - well infant with very low platelet count - intracranial bleeding of the baby

Question 62

What is the treatment for neonatal alloimmune thrombocytopenia

Answer 62

infusion of washed maternal platelets