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4 Hemostasis and Related Disorders > 4.1 Primary hemostasis and related bleeding disorders > Flashcards

4.1 Primary hemostasis and related bleeding disorders Flashcards

1
Q

ITP:

Tx (3)

A
  • Tx:
    1. corticosteroids, reduce immune system
    2. IVIG–“throwing sticks to dog to eat”–give Ab that attach to RBCs–macrophages eat those instead of platelets
    3. Splenectomy–remove Ab source and location of phagocytosis
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2
Q

How do platelets aggregate?

A

Platelet GP2b3a receptors link with each, using fibrinogen as linking molecule.

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2
Q

Petechiae, ecchymoses, purpura

A

skin bleeding: petechiae: 1-2mm purpura: >3mm ecchymoses: >1-2 cm

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3
Q

TXA2, purpose in hemostasis

-how is it made?

A

Released by platelets:

TXA2–induce platelet aggregation via GP2b3a

-made from arachidonic acid via platelet COX

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4
Q

MAHA lab findings:

  1. platelet count
  2. PT/PTT
  3. blood smear
  4. bone marrow biopsy
A
  1. low, increased bleeding time
  2. normal (no change in coag factors)
  3. anemia, schistocytes
  4. increased megakaryocytes
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5
Q

Weibel-Palade bodies, what are they, what do they make?

A
  • found in endothelial cells, secrete:
    1. vWF
    2. P-selectin
    mnemonic: W for vWF, P for P selectin
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5
Q

Qualitative primary hemostasis disorders, list them (4)

A
  • qualitative
    1. . Bernard-Soulier syndrome–GP1b deficiency
    2. Glanzmann thrombasthenia–GP2b3a deficiency
    3. Aspirin–irreversible COX inhibitor, lack of TXA2 impairs aggregation
    4. Uremia–disrupts platelet adhesion and aggregation
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7
Q

Steps in primary hemostasis (4 main ones)

A

Endothelial damage:

  1. Transient vasoconstriction, mediated by endothelin and neural reflexes
  2. Platelet binding
    - vWF binds to subendothelial collagen
    - Platelets bind to vWF via GP1b
  3. Platelet degranulation
    - ADP release, increases expression of GP2b3a
    - TXA2 release, induces aggregation via GP2b3a
  4. Platelet aggregation
    - Fibrinogen is linking molecule, between GP2b3a

Secondary hemostasis stabilizes the fibrinogen by converting it to fibrin, using thrombin

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8
Q

what do platelets release after binding to vessel surface?

A
  1. ADP–increase expression of GP2b3a
  2. TXA2–induce platelet aggregation via GP2b3a
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9
Q

ITP:

  • mech of disease
  • divided into what 2 types
A
  • Immune thrombocytopenic purpura
  • Auto-Ab (IgG) binds to platelet antigens (eg via GP2b3a), making complexes eaten by macrophages in spleen. Ab made in spleen too.
  • acute and chronic
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9
Q

what is most common cause of thrombocytopenia in children and adults?

A

ITP

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9
Q

schistocyte

A
  • split RBC, caused by vessel microthrombi
  • found in MAHA -“helmet cell”
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10
Q

E Coli, why important in hemostasis

A
  • HUS
  • E Coli O157:H7 makes a verotoxin, which damages endothelium
  • this results in microthrombi, leading to HUS (a form of MAHA)
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11
Q

Bernard-Soulier syndrome

A

qualitative platelet disorder:

  • genetic GP1b deficiency, so platelets not able to adhere to vWF.
  • mild thrombocytopenia, enlarged platelets
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13
Q

fibrinogen and fibrin

A

-linking molecule for platelet aggregation -link GP2b3a

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13
Q

Thrombin

A

-final product of secondary hemostasis -converts fibrinogen to fibrin, stabilizing clot

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14
Q

Hemostasis occurs in 2 stages: what are they?

A
  1. primary–formation of platelet plug
  2. secondary–coagulation cascade to stabilize the plug
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15
Q

Pregnant pt with ITP:

what to be concerned about for baby? Why?

A
  • short-lived thrombocytopenia in offspring
  • The IgG Ab from the pt’s ITP can cross placenta, starting from week 20
16
Q

What are the conditions associated with these steps in primary hemostasis, and what are the mechs?

  1. impaired platelet adhesion (3)
  2. impaired platelet aggregation (3)
A
  1. Bernard-Soulier syndrome – GP1b deficiency

Uremia

Von Willebrand disease– low vWF (also needed for Factor 8 stabilization)

  1. Glanzmann thrombasthenia – GP2a3b deficiency

Aspirin – TXA2 deficiency

Uremia

17
Q

ADP, purpose in hemostasis

A

Released by platelets:

ADP–increase expression of GP2b3a

19
Q

ADAMTS13

A
  • enzyme that cleaves vWF multimers into monomers for degradation
  • TTP: decreased ADAMTS13 leads to large, uncleaved multimers of vWF, which leads to abnormal platelet adhesion, resulting in microthrombi (TTP–a form of MAHA)
  • usually caused by autoAb to enzyme
20
Q

Acute vs chronic ITP

A
  • acute:
  • often occurs in children weeks after viral infection/immunization. Self-limited, usu resolves itself in weeks
  • chronic:
  • young women usually, autoimmune. Can be primary or secondary (SLE).
  • can cause temporary thrombocytopenia in newborn since anti-platelet IgG can cross placenta.
21
Q

What is vWF derived from?

A
  1. Weibel-Palade bodies, in endothelial cells
  2. Platelet alpha-granules
22
Q

Pt with kidney disease:

-what to be concern about with platelets?

A

Increased bleeding, b/c uremia disrupts:

  1. platelet adhesion
  2. platelet aggregation
23
Q

TTP

  • mech
  • etiology
A
  • Thrombotic Thrombocytopenic Purpura
  • reduced ADAMTS13 enzyme, which cleaves vWF multimers into monomers for degradation.
  • causes microthrombi, leading to MAHA
  • usually caused by auto-Ab against ADAMTS13, usually young women.
24
Q

MAHA

  • what is it
  • causes (2)
A
  • Microangiopathic hemolytic anemia
  • microthrombi in vessel wall causes RBCs to lyse, forming schistocytes (helmet cells)
  • caused by
    1. TTP–low ADAMTS13 enzyme
    2. HUS–O157:H7 verotoxin
24
Q

Pt with SLE:

What to be concerned about for pt’s platelets?

A

Possible ITP:

autoimmune destruction of platelets by splenic macrophages from production of auto-platelet Ab

26
Q

Role of spleen in ITP

A
  1. site of auto-Ab production from plasma cells
  2. site of phagocytosis of Ab-platelet complex by macrophages
    - splenectomy is tx in severe cases of ITP.
27
Q

HUS, TTP

  • clinical presentation (5)
  • which is more common in HUS, and which is more common in TTP?
A
  1. skin, mucosal bleeding

2, MAHA

  1. Fever
  2. Renal insufficiency (HUS–thrombi involve renal vessels)
  3. CNS abnormalities (TTP–thrombi involve CNS vessels)
27
Q

TTP:

Tx

A
  1. plasmapheresis (remove auto-Ab to platelets)
  2. steroids
28
Q

HUS:

-tx

A

-usu supportive, sometimes with hemodialysis

30
Q

HUS

  • mech
  • etiology
A
  • Hemolytic uremic syndrome
  • Verotoxin of E Coli O157:H7 dysentery causes endothelial damage, leading to microthrombi formation
  • this E Coli comes usually from undercooked beef
32
Q

What symptom is seen in thrombocytopenia but not usu seen in a qualitative hemostatic disorder?

A

petechiae

33
Q

What immediately happens when endothelial cells are damaged?

A

Transient vasoconstriction, mediated by

  1. neural reflexes
  2. endothelin
33
Q

Disorders of primary hemostasis:

  1. divided into what 2 categories?
  2. clinical presentation
    - most feared complication
A
  1. Quantitative, Qualitative
  2. Bleeding:
    - mucosal and skin bleeding (epistaxis is most common)
    - hemoptysis, GI bleeding, hematuria, menorrhagia
    - most feared: intracranial hemmorhage
35
Q

HUS

-most common population

A

-Children, after eating underocoked beef exposed to E Coli O157:H7 verotoxin

36
Q

TTP:

-most commonly seen in what population, why?

A
  • adult female
  • autoimmune–Ab against ADAMTS13 enzyme, which normally cleaves vWF multimers to prevent excessive thrombosis
37
Q

How do platelets adhere to vessel surface?

A
  1. vWF binds to subendothelial collagen
  2. Platelets bind to vWF via GP1b
38
Q

ITP lab values/findings

  • platelet count
  • PT, PTT
  • bone marrow biopsy
A
  • labs:
    1. platelet count low
    2. PT, PTT normal–coag factors not affected
    3. bone marrow–increased # of megakaryocytes trying to replace platelets
40
Q

Endothelin

A
  • vasoconstrictor
  • secreted by endothelial cells in response to injury
41
Q

Quantitative primary hemostasis disorders, list them (3)

A
  1. ITP
  2. TTP (MAHA)
  3. HUS (MAHA)
42
Q

Glanzmann thrombasthenia

A
  • qualitative platelet disorder
  • genetic deficiency in GP2b3a receptors, impairing platelet aggregation through fibrinogen.
43
Q

vWF

  • what are its functions? (2)
  • what disorders are related to it? (2)
A
  1. bind to platelet GP1b receptors for platelet adhesion
  2. needed to stablilize Factor 8 in coagulation
  3. TTP (auto-Ab to ADAMTS13, which normally breaks apart vWF multimers)
  4. Von Willebrand disease (lack of vWF means imparied adhesion and impaired coagulation)
44
Q

When NOT to give platelets to pt with thrombocytopenia? (2)

A
  1. TTP
  2. HIT
    - more platelets may be used to make more thrombi, increase risk of MI or other thrombotic events

4 Hemostasis and Related Disorders (5 decks)

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