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Drew 921 > Block 2b Hemostasis > Flashcards

Block 2b Hemostasis Flashcards

1
Q

What are the 4 steps of hemostasis?

A

1) vascular constriction 2) platelet plug formation 3) clot formation 4) fibrous tissue repair

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2
Q

What are the 3 mechanisms for vascular constriction in hemostasis?

A

1) myogenic response of vascular smooth muscle 2) local vasoconstrictors 3) CNS ischemic response

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3
Q

What substances are local vasoconstrictors?

A

prostaglandins & thromboxane A2

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4
Q

What is the myogenic response in vascular constriction?

A

damage to vasculature –> contraction & spasm

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5
Q

What is the half-life of a platelet?

A

8-12 days

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6
Q

Where are platelets cleared?

A

in spleen by macrophages

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7
Q

What are the dimensions of a platelet?

A

1-4 um discs

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8
Q

What substances can platelets secrete?

A

prostanoids & growth factors

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9
Q

Where are platelets produced, and what cellular elements do they have?

A

produced in spleen – no nucleus, but they do have ER & Golgi

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10
Q

What is the result of low platelet counts?

A

thousands of small hemorrhages in small vessels

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11
Q

Where is prothombin produced?

A

in liver with required Vit. K

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12
Q

What is the rate-limiting step in clot formation?

A

PT –> thrombin activation

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13
Q

How is prothombin activator formed?

A

by endothelium after vessel rupture

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14
Q

What are the requirements for PT activation?

A

PT activator & sufficient Ca++

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15
Q

What is the concentration of PT?

A

15 mg/dL (abundant & unstable –> thrombin)

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16
Q

How is a weak clot formed?

A

spontaneous polymerization of fibrin monomers

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17
Q

How is a strong clot formed?

A

thrombin activates transglutaminase (13a) to cause amid polymerization of fibrinogen monomers

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18
Q

What are the terminal sequences of fibrin monomers?

A

Gly-His-Arg or Gly-Pro-Arg

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19
Q

What does thrombin do?

A

causes proteolysis of fibrinogen –> fibrin monomers

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20
Q

How are platelets activated?

A

collagen

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21
Q

What substances do platelet granules release?

A

ADP & TXA2

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22
Q

How is a loose plug formed?

A

more and more platelets are activated to bind sticky granules

23
Q

How are strong/solid plugs formed?

A

fibrin binds loose plug

24
Q

How does serum differ from plasma?

A

serums lacks clotting factors

25
Q

What substances catalyze clot contraction?

A

increased thrombin, increases Ca++

26
Q

How are clots lysed?

A

plasminogen –> plasmin (activated by tPA, which is released by tissues)

27
Q

What triggers the extrinsic clotting pathway?

A

tissue trauma (outside the vessel)

28
Q

What triggers the intrinsic clotting pathway?

A

blood trauma or contact with collagen

29
Q

What is the result of the intrinsic clotting pathway?

A

clotting factor cascade

30
Q

What is theresult of the extrinsic clotting pathway?

A

formation of tissue thromboplastin

31
Q

What pressure range favors clot formation?

A

< 60 mmHg

32
Q

What factors prevent clots?

A

1) constant flow 2) endothelium 3) anticoagulants

33
Q

What factors of the endothelium help prevent clotting?

A

1) smooth glycocalyx coating 2) thrombomodulin

34
Q

How does thrombomodulin prevent clotting?

A

binds & inhibits thrombin; activates plasma protein C (another thrombin inhibitor)

35
Q

What are the physiologic anticoagulants?

A

1) fibrin adsorbs & inhibits thrombin for the major effect 2) antithrombin III inhibits thrombin 3) heparin binds & increases antithrombin III activity

36
Q

Where are heparin concentrations increased?

A

mast cells & basophils (lung beds & pericapillary tissues)

37
Q

What issues can cause excessive bleeding?

A

1) low [clotting factors] 2) Vit. K deficiency 3) hemophilia (clotting factor deficiency) 4) thrombocytopenia

38
Q

What are the most common clotting factor deficiencies?

A

Factor 8 most common, 15% Factor 9

39
Q

How is hemophilia inherited?

A

X-linked

40
Q

Where are clotting factors synthesized?

A

liver

41
Q

What diseases can cause low clotting factor levels?

A

hepatitis, cirrhosis

42
Q

How are DVTs treated?

A

anticoagulants, vena cava filter, tPA thrombolysis

43
Q

What is a normal INR?

A

0.9 - 1.3

44
Q

What is the goal INR during anticoagulant therapy?

A

3-Feb

45
Q

What is normal PT time?

A

12 seconds

46
Q

How is clotting time measured

A

1) drawn blood is oxalated to inhibit PT 2) excess Ca & tissue factor added 3) PT time measured

47
Q

What is the half-life of heparin?

A

1.5 - 4 hours

48
Q

Describe the structure of heparin?

A

heterogenous polysaccharide of various molecular weights (LMWH is commonly used)

49
Q

How do coumarins work?

A

decrease PT & decrease factor 2/7/9/10 synthesis in liver

50
Q

What is the onset of coumarins?

A

8-12 hours

51
Q

What is the increase in clotting time when heparin is used?

A

6 mins to >30 minutes

52
Q

Describe the INR equation?

A

fraction of normal PT raised to tissue factor sensitivity

53
Q

What is the effect of factor 10a?

A

forms PT activator

54
Q

How are platelets necessary for clot retraction?

A

links fibrin via actin-myosin skeleton to cause contraction & serum expression

Drew 921 (33 decks)

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