Exam 7 L. 4

Question 1

Primary hemostasis

Answer 1

The formation of the platelet plug

-sufficient for small vessel injury

Question 2

Secondary hemostasis

Answer 2

The formation of the fibrin clot through the coagulation cascade
-fibrin clot is needed for medium/large vessels

Question 3

Tertiary hemostasis

Answer 3

Fibrinolysis to reestablish blood flow through vessels

Question 4

Normal vessel

Answer 4

Platelet adhesion prevented by:

• negatively charged endothelium (repels platelets)
• nitric oxide
• prostacyclin
• ADPase

Question 5

Endothelial damage

Answer 5

1) vasoconstriction: platelets are slowed, giving them time to interact with subendothelium
2) subendothelium exposed: vWF visible
3) platelets tether to vWF ==> activates platelets to bind to fibrinogen
- fibrinogen allows platelets to bind together
4) activated platelets attract and activate more platelets (ADP and Thromboxane A2)
5) activated platelets set the stage for secondary hemostasis (provide docking site for clotting factors need)

Question 6

What can go wrong with primary hemostasis?

Answer 6

1) platelet: function and number

2) von Willebrand factor: number and function

Question 7

Primary hemostatic disorders

Answer 7

1) thrombocytopenia
- use, destruction, decreased production
2) acquired
- immune mediated, infectious disease, DIC, drugs
- thrombocytopenia is the most common acquired disorder of primary hemostasis!!

Question 8

Primary hemostatic disorder: von Willebrand’s disease

Answer 8

Inherited: Doberman!

-Most common inherited primary hemostatic disorder is von Willebrand’s disease!**

Question 9

Platelet count

Answer 9

1) estimate from a blood smear
- 1 per 100x field = 20,000 platelets/ul
- check the feathered edge!!
- A normal dog has between 8 to 10 platelets per high-powered field
2) spontaneous bleeding will not occurring last count is under 30,000 platelets/ul

Question 10

How do you test platelet function?

Answer 10

1) Buccal mucosal bleeding time
- a test for a defect in primary hemostasis
- makes an incision of standard depth and width in buccal mucosa
2) will be abnormal (>4 minutes) if:
- thrombocytopenic, thrombopathic, vWF deficient/abnormal, abnormal vasculature

Question 11

Immune-mediated thrombocytopenia (ITP)

Answer 11

1) can be primary or secondary
2) secondary: drugs, infectious agents (especially vectorborne diseases), neoplasia
- for some reason there is antibody versus platelets, and macrophages are gobbling up the platelets

Question 12

Treatment for ITP

Answer 12

1) Vincristine
- a 1 time shot! (It works or it doesn’t)
- prevents microtubule polymerization
- accelerated megakaryocyte fragmentation and platelet release from bone marrow
- no place for vincristine in IMHA treatment

Question 13

When to transfuse platelets?

Answer 13

1) Severe thrombocytopenia
2) suspect pulmonary or CNS hemorrhage
3) acquired or hereditary thrombopathia

Question 14

What products contain viable platelets??

Answer 14

1) fresh whole blood
2) platelet rich plasma
- generated from a soft spin of blood
3) platelet concentrate (fresh or cryopreserved)
- PRP that has been spun hard to concentrate platelets

Question 15

ITP prognosis

Answer 15

1) good!
2) 10-30% mortality rate
3) like IMHA, does require long-term immunosuppressive therapy

Question 16

Inhibitors of primary hemostasis

Answer 16

1) endothelial cells!*
- Physical barrier: separates platelets and vWF unless there is an injury
2) ADPase, prostacyclin, nitric oxide
- inhibit platelet activation

Question 17

Pathological inhibitors of primary hemostasis

Answer 17

1) disease:
- DIC
- metabolites in liver and kidney disease inhibit platelet function

Question 18

Therapeutic inhibitors of primary hemostasis

Answer 18

1) platelet inhibitors
- aspirin, NSAID’s: inhibit TxA2 production ==> platelets don’t activate their neighbors!
- Clopidogrel: inhibit platelets by binding to their ADP receptor (platelets cannot be activated by ADP)

Question 19

Remember

Answer 19

1) platelets do a lot!
- 1st to site of injury, essential for platelet plug formation, and platelet membranes are needed for secondary hemostasis
2) vWF
- the glue for platelet adhesion to the vessel wall: stops bleeding
3) thrombocytopenia is the most common acquired cause of defective primary hemostasis
4) von Willebrand’s disease is the most common cause of inherited defective primary hemostasis