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Cells to Tissues > Hemostasis > Flashcards

Hemostasis Flashcards

1
Q

What occurs immediately after blood vessel damage?

A

Myogenic contraction (vasoconstriction)

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2
Q

What occurs after a severe injury to a blood vessel?

A

Neurogenic vasospasm - increased sympathetic nerve firing + vasoconstriction via a spinal (pain) reflex

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3
Q

How long do myogenic and neurogenic contractions last?

A

20-30 min

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4
Q

What types of humoral responses cause vasoconstriction?

A

Serotonin Thromboxane A2 Prostaglandins (PGFs)

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5
Q

How long does humorally-triggered vasoconstriction last?

A

Several hours

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6
Q

What happens when subendothelial connective tissue is exposed to blood during injury?

A

Platelet adhesion to subendothelial collagen

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7
Q

What is Von Willebrand Factor (VWF)?

A

A plasma protein factor synthesized by endothelial cells that promotes platelet adhesion and clotting factor VIII. Missing/non-functioning VWF = Hereditary Von Willebrand disease.

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8
Q

What is platelet release reaction?

A

Alterations in shape and release of granules mediated by binding of VWF or thrombin to platelet membrane receptors. Causes release of calcium, serotonin, and ADP.

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9
Q

What is the relationship between ADP levels and clotting?

A

ADP levels must be above a critical concentration for platelets to maintain clumping. Release of additional ADP from storage sites accelerates clumping.

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10
Q

In addition to ADP, what is another potent aggregating agent?

A

Thromboxane A2

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11
Q

What prevents platelets from spreading?

A

Nearby cells secrete a powerful inhibitor, prostacyclin (PGI3).

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12
Q

What effect does aspirin have on clotting?

A

Reduces clotting by inhibiting cyclo-oxygenase which is needed to form thromboxane A2.

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13
Q

What is primary hemostasis?

A

Vasoconstriction + platelet plug formation

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14
Q

What is secondary hemostasis?

A

Blood coagulation

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15
Q

What is fibrinogen?

A

Circulating precursor to fibrin

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16
Q

What is prothrombin?

A

Circulating precursor to thrombin

17
Q

What is thrombin?

A

Proteolytic enzyme that converts fibrinogen to fibrin.

18
Q

What is thromboplastic activity?

A

Factors released from injured tissue that causes conversion of prothrombin to thrombin (in the presence of calcium)

19
Q

What is the genetic cause of hemophilia?

A

Sex-linked congenital deficiency of factor VIII.

20
Q

What are the proteins of the intrinsic pathway?

A
  1. Prekallikrein 2. HMW kininogen 3. Factor XI
21
Q

What is the first step to activate the intrinsic clotting pathway?

A

Binding of clotting factor XII to the subendothelial connective tissues exposed by blood vessel injury.

22
Q

What other factors convert factor X to factor Xa?

A

VIII, IXa, Ca2+, platelet phospholipid

23
Q

How is prothrombin II activated to IIa?

A

Factor V is cleaved by factor Xa in the presence of calcium.

24
Q

How are fibrin networks formed?

A

Factor XIIIa helps form covalent bonds among fibrin strands

25
Q

What is the first factor in the extrinsic clotting pathway?

A

Exposure of “tissue factor” (factor III/CD142) on the surface of subendothelial cells.

26
Q

Does thrombin act as a positive feedback mechanism on the intrinsic pathway? What does it do to extrinsic?

A

Yes Shuts down extrinsic

27
Q

How quickly does the extrinsic pathway take to activate? Intrinsic?

A

Extrinsic: 10-15 seconds Intrinsic: 1-3 minutes

28
Q

How do many anticoagulants work?

A

Chelate calcium ions to prevent clotting.

29
Q

What clotting factors use calcium?

A

II, VII, IX, X

30
Q

What residues bind calcium and what substance aids their carboxylation/formation?

A

gamma-carboxygltuamic acid residues carboxylated by Vitamin K.

31
Q

What is coumarin?

A

Anticoagulation drug that acts by blocking carboxylation.

32
Q

What causes clot retraction?

A

Platelet actomyosin

33
Q

What circulating plasma protein is the major inhibitor of thrombin? What drug enhances it?

A

Antithrombin III activity increased by heparin

34
Q

Although thrombin has a positive feedback system, it also has a negative feedback system carried out via proteins ____ and ___.

A

C and S Blocks factors VIII and V

35
Q

What proteolytic enzyme digests fibrin and fibrinogen and what activates it?

A

Plasmin made from plasminogen in response to tPA

36
Q

How is tPA used therapeutically?

A

Can be used to restore blood flow to inappropriately ischemic tissues.

37
Q

What effect does serotonin have on blood vessels?

A

Vasoconstriction

38
Q

What effect does histamine have on blood vessels?

A

Increases vessel leakiness after injury to prevent infection.

39
Q

What lesions form in people lacking primary hemostasis?

A

Petechiae (small)

Purpura (medium)

Ecchymoses (large)

Cells to Tissues (23 decks)

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