Platelets

Question 1

how long do platelets circulate in the blood?

Answer 1

5-10 days

Question 2

what do platelets provide?

Answer 2

primary hemostasis: sealing of small vascular defects/leaks

Question 3

what are feline platelets like?

Answer 3

normally vary widely in size

Question 4

what dogs breeds have lower platelet counts?

Answer 4

greyhound
shiba inu
cavalier king charles spaniel

Question 5

when does spontaneous hemorrhage due to thrombocytopenia occur?

Answer 5

platelet count markedly decreased: dogs <30,000/microliter

Question 6

what is pseudothrombocytopenia?

Answer 6

false decrease in platelet count

Question 7

what is pseudothrombocytopenia most commonly caused by?

Answer 7

platelet clumping

Question 8

what can cause decreased production of platelets?

Answer 8

damage to stem cells or microenvironment
suppression of thrombopoiesis or hematopoiesis

Question 9

what are some causes of thrombocytopenia?

Answer 9

pseudothrombocytopenia
decreased production
increased consumption
increased destruction
blood loss (less common)
sequestration

Question 10

what are some general causes of decreased platelet production?

Answer 10

drug-induced/toxic (uncommon)
infectious diseases
bone marrow neoplasia or fibrosis
aplastic anemia

Question 11

what destroys platelets?

Answer 11

macrophage phagocytosis

Question 12

what are some causes of accelerated platelet consumption?

Answer 12

vascular lesions
increased activation of coagulation

Question 13

how can immune thrombocytopenia be diagnosed?

Answer 13

very low platelet counts typically
exclusion of other diseases and/or response to therapy
anti-platelet antibody testing?

Question 14

does hemorrhage always cause thrombocytopenia?

Answer 14

not always
severe hemorrhage can cause marked thrombocytopenia

Question 15

what are the general causes of thrombocytosis?

Answer 15

physiologic
reactive
neoplastic

Question 16

what is physiologic thrombocytosis like?

Answer 16

mild and transient

Question 17

what is physiologic thrombocytosis from?

Answer 17

increased mobilization from splenic and non-splenic pools
stress, exercise, pregnancy

Question 18

how can inflammation cause reactive thrombocytosis?

Answer 18

promotes production of thrombopoietin

Question 19

when are platelet function defects suspected?

Answer 19

when there is evidence of abnormal primary hemostasis with normal platelet numbers

Question 20

what are some platelet function tests?

Answer 20

buccal mucosal bleeding time
thromboelastography
platelet function analyzer

Question 21

what is the most common hereditary platelet disorder in dogs?

Answer 21

von willebrand’s disease

Question 22

what is von willebrand’s disease?

Answer 22

disorder of platelet function caused by a deficiency in functional von willebrand’s factor (abnormal amounts +/- multimer distribution)

Question 23

what are the two categories of acquired platelet dysfunction?

Answer 23

drug-induced
non-drug-induced

Question 24

how do platelets leave circulation?

Answer 24

utilization/consumption
phagocytized by liver

Question 25

what color granules are often seen in mammalian platelets?

Answer 25

reddish-purple

Question 26

what do alpha granules contain?

Answer 26

platelet factor 4 fibrinogen coagulation factors V, VII, XI, XIII P selectin plasminogen activator inhibitor tissue factor pathway inhibitor

Question 27

what do dense granules contain?

Answer 27

nucelotides calcium and magnesium serotonin and histamine

Question 28

when can dense granules be seen?

Answer 28

electron microscopy

Question 29

what tends to happen with platelets with increased regeneration?

Answer 29

larger and more variation in size

Question 30

what species' platelets have a strong tendency to clump in blood tubes?

Answer 30

feline rabbit cattle

Question 31

what do bird and reptile thrombocytes look like?

Answer 31

basophilic nuclei with clear or light blue cytoplasm

Question 32

how do primary hemostatic defects manifest?

Answer 32

petechiae ecchymoses mucosal bleeding excessive post-op bleeding

Question 33

what do cavalier king charles spaniels often have a mutation in?

Answer 33

platelet microtubules

Question 34

what influences platelet count?

Answer 34

production consumption destruction sequestration or release from spleen and lung

Question 35

what can decreased production of platelets cause?

Answer 35

moderately to markedly decreased platelet counts

Question 36

what does consumption of platelets result in?

Answer 36

mildly to moderately decreased platelet numbers

Question 37

what are some vascular lesions that can cause accelerated platelet consumption?

Answer 37

internal trauma vasculitis vascular neoplasia

Question 38

what can cause increased activation of coagulation?

Answer 38

disseminated intravascular coagulation snake envenomation

Question 39

what can cause secondary immune thrombocytopenia?

Answer 39

drugs infectious agents paraneoplastic syndrome

Question 40

what can cause thrombocytopenia in cats?

Answer 40

rule out clumping infectious/viral diseases neoplasia cardiac disease multiple diseases primary ITP uncommon

Question 41

what can cause reactive thrombocytosis?

Answer 41

inflammation neoplasia iron deficiency/hemorrhage rebound thrombopoiesis after thrombocytopenia drug-related post-splenectomy

Question 42

what are some neoplasias of platelets/thrombocytes?

Answer 42

essential thrombocythemia: very rare megakaryocyte leukemia: rare

Question 43

what agonists being exposed lead to platelet activation?

Answer 43

collagen ADP thromboxane A2 serotonin

Question 44

what does intact endothelium secrete to inhibit platelet activation?

Answer 44

prostacyclin

Question 45

what is thromboxane A2 produced by?

Answer 45

platelets with arachidonic acid metabolism

Question 46

what does thromboxane A2 promote?

Answer 46

vasoconstriction platelet activation platelet aggregation

Question 47

what does GPIIb/IIIa bind to?

Answer 47

fibrinogen von willebrand's factor fibronectin

Question 48

what are the functions of von willebrand's factor?

Answer 48

platelet adhesion clotting factor VIII binding

Question 49

in whom is von willebrand's disease uncommon?

Answer 49

horses cattle pigs very rare in cats