Block 2b Hemostasis

Question 1

What are the 4 steps of hemostasis?

Answer 1

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

Question 2

What are the 3 mechanisms for vascular constriction in hemostasis?

Answer 2

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

Question 3

What substances are local vasoconstrictors?

Answer 3

prostaglandins & thromboxane A2

Question 4

What is the myogenic response in vascular constriction?

Answer 4

damage to vasculature –> contraction & spasm

Question 5

What is the half-life of a platelet?

Answer 5

8-12 days

Question 6

Where are platelets cleared?

Answer 6

in spleen by macrophages

Question 7

What are the dimensions of a platelet?

Answer 7

1-4 um discs

Question 8

What substances can platelets secrete?

Answer 8

prostanoids & growth factors

Question 9

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

Answer 9

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

Question 10

What is the result of low platelet counts?

Answer 10

thousands of small hemorrhages in small vessels

Question 11

Where is prothombin produced?

Answer 11

in liver with required Vit. K

Question 12

What is the rate-limiting step in clot formation?

Answer 12

PT –> thrombin activation

Question 13

How is prothombin activator formed?

Answer 13

by endothelium after vessel rupture

Question 14

What are the requirements for PT activation?

Answer 14

PT activator & sufficient Ca++

Question 15

What is the concentration of PT?

Answer 15

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

Question 16

How is a weak clot formed?

Answer 16

spontaneous polymerization of fibrin monomers

Question 17

How is a strong clot formed?

Answer 17

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

Question 18

What are the terminal sequences of fibrin monomers?

Answer 18

Gly-His-Arg or Gly-Pro-Arg

Question 19

What does thrombin do?

Answer 19

causes proteolysis of fibrinogen –> fibrin monomers

Question 20

How are platelets activated?

Answer 20

collagen

Question 21

What substances do platelet granules release?

Answer 21

ADP & TXA2

Question 22

How is a loose plug formed?

Answer 22

more and more platelets are activated to bind sticky granules

Question 23

How are strong/solid plugs formed?

Answer 23

fibrin binds loose plug

Question 24

How does serum differ from plasma?

Answer 24

serums lacks clotting factors

Question 25

What substances catalyze clot contraction?

Answer 25

increased thrombin, increases Ca++

Question 26

How are clots lysed?

Answer 26

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

Question 27

What triggers the extrinsic clotting pathway?

Answer 27

tissue trauma (outside the vessel)

Question 28

What triggers the intrinsic clotting pathway?

Answer 28

blood trauma or contact with collagen

Question 29

What is the result of the intrinsic clotting pathway?

Answer 29

clotting factor cascade

Question 30

What is theresult of the extrinsic clotting pathway?

Answer 30

formation of tissue thromboplastin

Question 31

What pressure range favors clot formation?

Answer 31

< 60 mmHg

Question 32

What factors prevent clots?

Answer 32

1) constant flow 2) endothelium 3) anticoagulants

Question 33

What factors of the endothelium help prevent clotting?

Answer 33

1) smooth glycocalyx coating 2) thrombomodulin

Question 34

How does thrombomodulin prevent clotting?

Answer 34

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

Question 35

What are the physiologic anticoagulants?

Answer 35

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

Question 36

Where are heparin concentrations increased?

Answer 36

mast cells & basophils (lung beds & pericapillary tissues)

Question 37

What issues can cause excessive bleeding?

Answer 37

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

Question 38

What are the most common clotting factor deficiencies?

Answer 38

Factor 8 most common, 15% Factor 9

Question 39

How is hemophilia inherited?

Answer 39

X-linked

Question 40

Where are clotting factors synthesized?

Answer 40

liver

Question 41

What diseases can cause low clotting factor levels?

Answer 41

hepatitis, cirrhosis

Question 42

How are DVTs treated?

Answer 42

anticoagulants, vena cava filter, tPA thrombolysis

Question 43

What is a normal INR?

Answer 43

0.9 - 1.3

Question 44

What is the goal INR during anticoagulant therapy?

Answer 44

3-Feb

Question 45

What is normal PT time?

Answer 45

12 seconds

Question 46

How is clotting time measured

Answer 46

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

Question 47

What is the half-life of heparin?

Answer 47

1.5 - 4 hours

Question 48

Describe the structure of heparin?

Answer 48

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

Question 49

How do coumarins work?

Answer 49

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

Question 50

What is the onset of coumarins?

Answer 50

8-12 hours

Question 51

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

Answer 51

6 mins to >30 minutes

Question 52

Describe the INR equation?

Answer 52

fraction of normal PT raised to tissue factor sensitivity

Question 53

What is the effect of factor 10a?

Answer 53

forms PT activator

Question 54

How are platelets necessary for clot retraction?

Answer 54

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