Hemostasis Flashcards
Primary hemostasis
Platelets and platelet function
- vessels
Secondary
Coagulation
- coagulation factors
- vessel
Tertiary
Fibrinolysis
- fibrinolytic molecules
- vessel
_____ plays a role in all 3 parts of hemostasis
Vessel
- no test to assess vessel function/viability
- look for morphological presence via biopsy
If endothelial cells are quiescent, they will _____ primary and secondary and _____ tertiary
Inhibit; enhance
- once activated, they enhance primary and secondary and inhibit tertiary
Platelet - structure
Small fragments of megakaryocyte cytoplasm
- phospholipid membrane w/ glycoproteins
- open canalicular system of membrane invaginations
- cytoskeleton
Platelet - granules
- tubular system of ER: stores Ca (platelet activation and TBX production)
- alpha granules: hemostasis and angiogenesis
- dense granules: Ca, Mg, ADP, ATP
- glycogen and mitochondria
Megakaryopoiesis and thrombopoiesis
Thrombopoietin and other cytokines
- BM, spleen, lung (most important site of production)
- platelets released directly into the blood
Thrombopoietin
- hepatocytes (dogs), renal tubular epithelium, BM stromal cells
- constitutively expressed
- plasma concentration dependent on MPL receptor numbers (present in platelets and megakaryocytes)
- inflammation: IL-6 –> TPO expression in BM
Reticulated platelets
- young platelets
- increased RNA
- less than 24 hours in dogs
Platelet concentration
- production
- consumption
- destruction
- shift/sequestration
- dilution
Blood smear
- platelet estimation
- morphologic abnormalities
Platelet sample
- EDTA
- citrate, theopylline, dipyridamole, and adenosine (CTAD tubes) may be useful for cats
- 8 hr at RT and 48 hr at 4C
- check for platelet clumping
Platelet count
- impedance counters
- optical or laser flow cytometers
- CBC
- hemocytometer
Mean platelet volume
Varies between analyzer, anticoagulant and storage time
- presence of cell fragments and large platelets
Thrombocytopenia
Concentration is lower than the LRL
- common in Greyhounds and Shiba Inus (lower than other dogs)
- reflects a pathologic process (not a diagnosis)
Thrombocytopenia less than 30,000/uL
- petechiae and ecchymosis
- mucosal bleeding (epistaxis, hematochezia, melena), hematuria, hyphema
Pseudo-thrombocytopenia
- not all platelets were counted
- in vitro platelet activation or aggregation
- presence of large platelets (cats or CKCS) in impedance counters
- cold agglutinins, or anticoagulant induced, antibody-mediated agglutination
Thrombocytopenia - shift/sequestration
- reversibly distributed in vascular systems (spleen)
- mild or moderate thrombocytopenia
- splenomegaly
- severe hypothermia (20 C, spleen and liver in dogs)
- endotoxemia: lung pooling in dogs (may see increased consumption)
Thrombocytopenia - decreased production
- generalized BM dz or MK specific process
- idiopathic thrombocytopenia of CKCS –> maybe due to lack of production
Thrombocytopenia - decreased production due to drugs
- predictable, dose-dependent –> antineoplastic chemotherapeutic agents
- idiosyncratic (sporadic)
Thrombocytopenia - decreased production due to infection
Multifactorial, often include decreased production
- direct infection of MK (BVD, canine distemper)
- myelosuppressive cytokines (EIA)
- unclear (canine parvo, canine monocytic ehrlichiosis)
- FeLV (due to neoplasia)
Thrombocytopenia - decreased production due to marrow replacement
Myelophthisis
- bone marrow neoplasia: primary or metastatic, physical replacement, lysis of marrow cells, competition for nutrients, secretion of inhibitors, obstruction of blood supply
- myelonecrosis: infections, neoplasia, toxicants
Thrombocytopenia - destruction
Immune mediated thrombocytopenia
- platelet surface associated Ig (PSAIg)
- Ab binds directly or indirectly
- destruction by mononuclear phagocytic system
- defective immune system –> defective platelets
- absorbed antigens from neoplasm, drugs, infectious agents