4.1-PRIMARY HOMEOSTASIS Flashcards
1
Q
What is the process that rapidly stops bleeding by forming a platelet plug after vascular injury?
A
Primary hemostasis
2
Q
What forms the initial barrier to blood loss in small vessel injury?
A
Platelet plug
3
Q
What is the first step in primary hemostasis following endothelial injury?
A
Vasoconstriction
4
Q
What is the main purpose of vasoconstriction in hemostasis?
A
Reduce blood flow and blood loss at the injury site
5
Q
What is exposed after endothelial injury that triggers platelet adhesion?
A
Subendothelial matrix (collagen
6
Q
What protein mediates platelet capture and slows platelets at high shear rates?
A
von Willebrand factor (vWF)
7
Q
What glycoprotein on platelets binds vWF for initial adhesion?
A
GpIb
8
Q
What is the process where platelets stick to exposed subendothelial collagen?
A
Platelet adhesion
9
Q
What is the process where platelets change shape and release granule contents after adhesion?
A
Platelet activation
10
Q
What is the process where platelets stick to each other to form a plug?
A
Platelet aggregation
11
Q
What glycoprotein complex on platelets is essential for aggregation via fibrinogen binding?
A
GpIIb/IIIa
12
Q
What is the main agonist released from dense granules that recruits additional platelets?
A
ADP
13
Q
What is the main product of arachidonic acid metabolism in platelets that promotes aggregation?
A
Thromboxane A2 (TXA2)
14
Q
What type of granules in platelets contain vWF
A
fibrinogen
15
Q
What type of granules in platelets contain ADP
A
ATP
16
Q
What is the average lifespan of circulating platelets?
A
7-10 days
17
Q
Where are platelets produced?
A
Bone marrow (by megakaryocytes)
18
Q
What hormone stimulates platelet production?
A
Thrombopoietin
19
Q
What is the normal platelet count range in adults?
A
150
20
Q
What term describes a decreased platelet count?
A
Thrombocytopenia
21
Q
What term describes an increased platelet count?
A
Thrombocytosis
22
Q
What is the minimum platelet count below which spontaneous bleeding may occur?
A
<50
23
Q
What is the minimum platelet count required for major surgery?
A
> 50
24
Q
What is the minimum platelet count required for minor procedures?
A
> 20
25
What is the minimum platelet count required to prevent spontaneous bleeding?
>10
26
What is the test that measures the time for a standardized skin wound to stop bleeding?
Bleeding time
27
What is the normal range for bleeding time?
2–8 minutes
28
What test method uses a blood pressure cuff and a forearm incision to measure bleeding time?
Ivy method
29
What test method uses a spring-loaded device for standardized incision in bleeding time measurement?
Simplate/Surgicutt method
30
What does a prolonged bleeding time indicate?
Platelet function defect or vascular disorder
31
What is the main protein required for platelet adhesion to subendothelium?
von Willebrand factor (vWF)
32
What is the main protein required for platelet aggregation?
Fibrinogen
33
What is the main receptor for fibrinogen on platelets?
GpIIb/IIIa
34
What is the main receptor for vWF on platelets?
GpIb
35
What is the main function of prostacyclin (PGI2) produced by endothelium?
Inhibit platelet aggregation and promote vasodilation
36
What is the main function of nitric oxide (NO) produced by endothelium?
Inhibit platelet aggregation and promote vasodilation
37
What is the main function of ADP released from platelet dense granules?
Recruit and activate additional platelets
38
What is the main function of serotonin released from platelet dense granules?
Vasoconstriction
39
What is the main function of calcium in platelet granules?
Required for platelet activation and coagulation
40
What is the main function of thromboxane A2 (TXA2)?
Promote vasoconstriction and platelet aggregation
41
What is the main function of platelet-derived growth factor (PDGF)?
Promote smooth muscle proliferation and vascular repair
42
What is the main function of platelet factor 4 (PF4)?
Promote platelet aggregation and neutralize heparin
43
What is the main function of platelet factor 3 (PF3)?
Provide phospholipid surface for coagulation factor complexes
44
What is the main function of the platelet glycocalyx?
Provide binding sites for coagulation factors and mediate adhesion
45
What is the main function of GpIa/IIa on platelets?
Collagen binding for adhesion
46
What is the main function of GpVI on platelets?
Collagen binding for activation
47
What is the main function of the dense tubular system in platelets?
Calcium storage and release during activation
48
What is the main function of the open canalicular system in platelets?
Facilitate granule release and increase surface area
49
What is the main function of the cytoskeletal (sol-gel) zone in platelets?
Maintain shape and facilitate shape change during activation
50
What is the main function of the organelle zone in platelets?
Storage of granules (alpha
51
What is the main function of lysosomes in platelets?
Degrade internalized material and participate in clot retraction
52
What is the main function of the peripheral zone in platelets?
Adhesion and aggregation (contains glycocalyx and membrane glycoproteins)
53
What is the main function of the membrane system in platelets?
Granule release and calcium mobilization
54
What is the main function of the alpha granule protein thrombospondin?
Promote platelet aggregation
55
What is the main function of beta-thromboglobulin in platelets?
Promote fibroblast chemotaxis and wound healing
56
What is the main function of factor V in platelets?
Cofactor in prothrombinase complex (coagulation)
57
What is the main function of factor XIII in platelets?
Cross-link fibrin in clot stabilization
58
What is the main function of protein S in platelets?
Cofactor for protein C (anticoagulant pathway)
59
What is the main function of plasminogen activator in platelets?
Promote fibrinolysis
60
What is the main function of inhibitor 1 in platelets?
Inhibit fibrinolysis
61
What is the main function of fibronectin in platelets?
Promote cell adhesion and wound healing
62
What is the main function of the GpIb-IX-V complex?
vWF binding for adhesion
63
What is the main function of the GpIIb/IIIa complex?
Fibrinogen binding for aggregation
64
What is the main function of the GpIV complex?
Thrombospondin binding
65
What is the main function of the GpVa complex?
Thrombin binding for aggregation
66
What is the main function of the GpIX complex?
Adhesion (part of Ib-IX-V complex)
67
What test is used to estimate platelet count from a blood smear?
Indirect platelet count (smear estimation)
68
What is the normal number of platelets seen per oil immersion field in a blood smear?
7–25 platelets/field
69
What is the approximate ratio of platelets to RBCs in a normal smear?
1 platelet per 10–40 RBCs
70
What is the formula for estimating platelet count from a smear?
Platelets in 10 fields × 2000 or average per field × 20
71
What is the term for increased platelet count due to disease?
Thrombocytosis
72
What is the term for increased platelet count of unknown cause?
Thrombocythemia
73
What is the term for decreased platelet count?
Thrombocytopenia
74
What are common causes of increased platelet count?
Polycythemia vera; essential thrombocythemia; post-splenectomy; tuberculosis; secondary anemia
75
What are common causes of decreased platelet count?
Pernicious anemia; aplastic anemia; acute leukemia; bone marrow lesions
76
What is the test that measures capillary resistance to pressure and is used for vitamin C deficiency?
Capillary fragility test
77
What grade does few petechiae on anterior forearm indicate in the capillary fragility test?
Grade 1+
78
What grade does many petechiae on anterior forearm indicate in the capillary fragility test?
Grade 2+
79
What grade does multiple petechiae over whole arm and back of hand indicate in the capillary fragility test?
Grade 3+
80
What is the test that measures the effect of aspirin on bleeding time?
Aspirin tolerance test
81
What is the effect of aspirin on bleeding time in platelet abnormalities?
2 tablets prolong bleeding time
82
What is the effect of aspirin on bleeding time in normal individuals?
4 tablets prolong bleeding time
83
What is the critical value for bleeding time that indicates abnormal hemostasis?
>15 minutes
84
What should be done if bleeding persists beyond 15 minutes during bleeding time test?
Discontinue test and apply pressure
85
What is the test where a punctured fingertip is immersed in saline at 37°C to measure bleeding?
Copley-Lalitch immersion test
86
What is the normal range for the Copley-Lalitch immersion test?
3–6 minutes
87
What is the main receptor for collagen on platelets?
GpIa/IIa and GpVI
88
What is the role of GpVI in platelet activation?
Signaling receptor for collagen (triggers release of ADP and TXA2)
89
What is the role of calcium released from dense granules?
Activate phospholipase A2 and support coagulation enzyme complexes
90
What is the role of magnesium released from dense granules?
Cofactor for platelet enzymes (e.g.
91
What is the role of serotonin in platelet function?
Vasoconstriction and amplification of platelet activation
92
What is the role of epinephrine in platelet function?
Enhance platelet activation via α2-adrenergic receptors
93
What is the role of ATP released from dense granules?
Provide energy for platelet activation and aggregation
94
What is the role of fibronectin in wound healing?
Promote cell adhesion and tissue repair
95
What is the role of beta-thromboglobulin in wound healing?
Chemotaxis for fibroblasts and endothelial cells
96
What is the role of platelet factor 4 (PF4) in heparin neutralization?
Bind and neutralize heparin to prevent anticoagulation
97
What is the role of factor V in coagulation?
Cofactor for factor Xa in prothrombinase complex
98
What is the role of factor XIII in clot stabilization?
Cross-link fibrin polymers to strengthen clot
99
What is the role of protein S in anticoagulation?
Cofactor for activated protein C (inactivates factors Va/VIIIa)
100
What is the role of plasminogen activator in fibrinolysis?
Convert plasminogen to plasmin to dissolve clots
101
What is the role of inhibitor 1 in fibrinolysis?
Neutralize plasminogen activators to limit clot breakdown
102
What is the role of thrombospondin in aggregation?
Bridge between platelets via GpIV and fibrinogen
103
What is the role of the glycocalyx in coagulation?
Bind factors IXa
104
What is the role of the open canalicular system in granule release?
Channel for secretion of alpha/dense granule contents
105
What is the role of the dense tubular system in calcium storage?
Store and release calcium during activation
106
What is the role of the cytoskeleton in platelet shape change?
Reorganize actin filaments to form pseudopods
107
What is the role of pseudopods in platelet aggregation?
Increase surface area for cell-cell interactions
108
What is the role of thrombin in platelet activation?
Protease that cleaves PAR receptors to trigger activation
109
What is the role of PAR receptors on platelets?
Mediate thrombin-induced activation (PAR1/PAR4)
110
What is the role of cyclooxygenase-1 (COX-1) in platelets?
Convert arachidonic acid to TXA2
111
What is the role of aspirin in platelet inhibition?
Irreversibly inhibit COX-1 to block TXA2 synthesis
112
What is the role of ADP receptors (P2Y1/P2Y12) on platelets?
Mediate ADP-induced activation and aggregation
113
What is the role of P2Y12 inhibitors (e.g.
clopidogrel)?
114
What is the role of GpIIb/IIIa inhibitors (e.g.
abciximab)?
115
What is the role of nitric oxide (NO) in hemostasis?
Inhibit platelet activation and promote vasodilation
116
What is the role of prostacyclin (PGI2) in hemostasis?
Inhibit platelet activation and promote vasodilation
117
What is the role of endothelial cells in preventing platelet adhesion?
Secrete NO and PGI2 to maintain non-thrombogenic surface
118
What is the role of thrombomodulin on endothelial cells?
Bind thrombin to activate protein C (anticoagulant)
119
What is the role of tissue factor pathway inhibitor (TFPI)?
Inhibit tissue factor-factor VIIa complex (anticoagulant)
120
What is the role of heparan sulfate on endothelial cells?
Enhance antithrombin activity (anticoagulant)
121
What is the role of tissue plasminogen activator (tPA)?
Convert plasminogen to plasmin to lyse clots
122
What is the role of plasminogen activator inhibitor-1 (PAI-1)?
Inhibit tPA to prevent excessive fibrinolysis
123
What is the role of α2-antiplasmin?
Inhibit plasmin to prevent premature clot breakdown
124
What is the role of factor VIII in coagulation?
Cofactor for factor IXa in tenase complex
125
What is the role of factor IX in coagulation?
Activate factor X in tenase complex
126
What is the role of factor X in coagulation?
Convert prothrombin to thrombin in prothrombinase complex
127
What is the role of factor XI in coagulation?
Activate factor IX in intrinsic pathway
128
What is the role of factor XII in coagulation?
Initiate intrinsic pathway (contact activation)
129
What is the role of prekallikrein in coagulation?
Activate factor XII in intrinsic pathway
130
What is the role of high-molecular-weight kininogen (HMWK)?
Cofactor for factor XII activation
131
What is the role of factor XIII in clot stabilization?
Cross-link fibrin to strengthen clot
132
What is the role of fibrinogen in coagulation?
Converted to fibrin by thrombin to form clot matrix
133
What is the role of thrombin in coagulation?
Convert fibrinogen to fibrin and activate platelets
134
What is the role of antithrombin in coagulation?
Inhibit thrombin and factors Xa/IXa (heparan sulfate enhances)
135
What is the role of protein C in coagulation?
Inactivate factors Va/VIIIa (thrombomodulin-thrombin activates)
136
What is the role of protein S in coagulation?
Cofactor for activated protein C
137
What is the role of tissue factor (factor III) in coagulation?
Initiate extrinsic pathway (binds factor VIIa)
138
What is the role of factor VII in coagulation?
Bind tissue factor to activate factors IX/X
139
What is the role of factor V in coagulation?
Cofactor for factor Xa in prothrombinase complex
140
What is the role of calcium in coagulation?
Cofactor for coagulation enzyme complexes
141
What is the role of phospholipids in coagulation?
Provide surface for tenase/prothrombinase complexes
142
What is the role of vitamin K in coagulation?
Carboxylate factors II/VII/IX/X for calcium binding
143
What is the role of warfarin in anticoagulation?
Inhibit vitamin K reductase to block coagulation factors
144
What is the role of heparin in anticoagulation?
Enhance antithrombin to inhibit thrombin/factor Xa
145
What is the role of direct oral anticoagulants (DOACs)?
Directly inhibit thrombin or factor Xa
146
What is the role of fibrinolytic agents (e.g.
alteplase)?
147
What is the role of tranexamic acid in hemostasis?
Inhibit plasminogen activation to reduce fibrinolysis
148
What is the role of desmopressin (DDAVP) in hemostasis?
Release vWF from endothelial stores to improve platelet adhesion
149
What is the role of cryoprecipitate in hemostasis?
Provide fibrinogen
150
What is the role of platelet transfusions in hemostasis?
Increase platelet count to prevent/treat bleeding
151
What is the role of von Willebrand disease (vWD) in hemostasis?
Impaired platelet adhesion due to vWF deficiency/defect
152
What is the role of Bernard-Soulier syndrome in hemostasis?
Defective GpIb causing impaired platelet adhesion
153
What is the role of Glanzmann thrombasthenia in hemostasis?
Defective GpIIb/IIIa causing impaired aggregation
154
What is the role of storage pool disorders in hemostasis?
Defective granule release (e.g.
155
What is the role of aspirin-like defects in hemostasis?
Impaired TXA2 synthesis (COX-1 deficiency)
156
What is the role of thrombotic thrombocytopenic purpura (TTP)?
ADAMTS13 deficiency causing microvascular thrombosis
157
What is the role of hemolytic uremic syndrome (HUS)?
Shiga toxin-induced endothelial damage and microangiopathy
158
What is the role of disseminated intravascular coagulation (DIC)?
Widespread thrombosis and consumption of coagulation factors
159
What is the role of immune thrombocytopenia (ITP)?
Antibody-mediated platelet destruction
160
What is the role of heparin-induced thrombocytopenia (HIT)?
Antibody-mediated platelet activation and thrombosis
161
What is the role of acquired platelet function defects?
Caused by uremia
162
What is the role of congenital platelet function defects?
Genetic disorders (e.g.
163
What is the role of ADAMTS13 in von Willebrand factor (vWF) regulation?
Cleaves ultra-large vWF multimers to prevent spontaneous platelet aggregation
164
What is the consequence of ADAMTS13 deficiency?
Thrombotic thrombocytopenic purpura (TTP) due to unchecked vWF-platelet microthrombi
165
What is the role of Shiga toxin in hemolytic uremic syndrome (HUS)?
Damages endothelial cells
166
What is the role of P-selectin in platelet activation?
Surface exposure during granule release; mediates platelet-leukocyte interactions
167
What is the role of CD40 ligand (CD40L) in platelets?
Promotes inflammation and stabilizes thrombi via leukocyte interactions
168
What is the role of microparticles in hemostasis?
Procoagulant vesicles released by activated platelets/endothelium
169
What is the role of phosphatidylserine (PS) in coagulation?
Exposed on activated platelets to anchor coagulation factor complexes (e.g.
170
What is the role of tissue factor-bearing microparticles?
Initiate coagulation in pathologic states (e.g.
171
What is the role of platelet endothelial cell adhesion molecule-1 (PECAM-1)?
Inhibits excessive platelet activation via ITIM signaling
172
What is the role of glycoprotein VI (GpVI) signaling?
Activates phospholipase Cγ2 (PLCγ2) to trigger calcium release and TXA2 synthesis
173
What is the role of phosphoinositide 3-kinase (PI3K) in platelets?
Amplifies activation signals downstream of GpIIb/IIIa and PAR receptors
174
What is the role of RhoA/ROCK in platelet shape change?
Regulates actin cytoskeleton reorganization during pseudopod formation
175
What is the role of calpain in platelet activation?
Cleaves cytoskeletal proteins to facilitate granule release and aggregation
176
What is the role of nitric oxide synthase (NOS) in endothelial cells?
Produces NO to maintain vasodilation and inhibit platelet adhesion
177
What is the role of endothelial protein C receptor (EPCR)?
Enhances protein C activation by thrombin-thrombomodulin complex
178
What is the role of annexin V in laboratory testing?
Binds phosphatidylserine to detect procoagulant platelet membranes
179
What is the role of flow cytometry in platelet disorders?
Detects deficiencies in GpIb
180
What is the role of thromboelastography (TEG)?
Measures clot formation
181
What is the role of platelet function analyzer (PFA-100)?
Simulates high-shear conditions to assess platelet adhesion/aggregation
182
What is the role of light transmission aggregometry (LTA)?
Gold standard for diagnosing platelet function defects using agonists (e.g.
183
What is the role of genotyping in inherited platelet disorders?
Identifies mutations in genes like ITGA2B (Glanzmann) or GP1BA (Bernard-Soulier)
184
What is the role of desmopressin (DDAVP) in von Willebrand disease?
Releases vWF from Weibel-Palade bodies to improve platelet adhesion
185
What is the role of recombinant factor VIIa in platelet disorders?
Bypasses coagulation defects by directly activating factor X
186
What is the role of cold storage platelets in transfusion medicine?
Extend shelf life to 14 days but may reduce post-transfusion recovery
187
What is the role of pathogen-reduced platelets?
Mitigate transfusion-transmitted infections using UV light/chemical treatment
188
What is the role of thrombopoietin receptor agonists (e.g.
romiplostim)?
189
What is the role of complement in atypical HUS?
Uncontrolled complement activation (C5b-9) causes endothelial injury and microthrombi
190
What is the role of fondaparinux in heparin-induced thrombocytopenia (HIT)?
Indirect factor Xa inhibitor that avoids platelet activation
191
What is the role of direct thrombin inhibitors (e.g.
argatroban) in HIT?
192
What is the role of rituximab in immune thrombocytopenia (ITP)?
Depletes B cells to reduce anti-platelet antibody production
193
What is the role of splenectomy in chronic ITP?
Removes site of platelet destruction and autoantibody production
194
What is the role of neonatal Fc receptor (FcRn) blockade in ITP?
Prevents IgG antibody recycling (e.g.
195
What is the role of Bruton tyrosine kinase (BTK) inhibitors in ITP?
Target B cell and macrophage signaling to reduce platelet destruction
196
What is the role of glycoprotein Ibα inhibitors in arterial thrombosis?
Block vWF binding (e.g.
197
What is the role of PAR-1 antagonists (e.g.
vorapaxar)?
198
What is the role of shear stress in arterial thrombosis?
Unmasks vWF binding sites on collagen
199
What is the role of hypoxia in platelet production?
Stimulates thrombopoietin (TPO) synthesis in the liver
200
What is the role of JAK2 mutations in myeloproliferative neoplasms?
Constitutively activate TPO signaling
201
What is the role of CALR mutations in essential thrombocythemia?
Activate TPO receptor (MPL) to drive platelet overproduction
202
What is the role of clonal hematopoiesis in aging-related thrombosis?
Mutant clones (e.g.
203
What is the role of NETosis in thrombosis?
Neutrophil extracellular traps (NETs) provide scaffold for platelet adhesion
204
What is the role of podoplanin in cancer-associated thrombosis?
Activates platelet CLEC-2 receptors to promote metastasis
205
What is the role of heparinase in laboratory testing?
Neutralizes heparin to distinguish HIT from other thrombocytopenias
206
What is the role of serotonin release assay (SRA) in HIT?
Detects heparin-dependent platelet-activating antibodies
207
What is the role of PF4/heparin ELISA in HIT?
Detects antibodies against PF4/heparin complexes
208
What is the role of 14C-serotonin in platelet survival studies?
Tracks platelet lifespan in disorders like ITP or thrombocytosis
209
What is the role of thromboxane metabolites (e.g.
11-dehydro-TXB2) in testing?
210
What is the role of microRNA-223 in platelet production?
Regulates megakaryocyte maturation by targeting NFIA
211
What is the role of tubulin β1 in platelet shape change?
Forms microtubule coils that maintain discoid shape
212
What is the role of mitochondrial apoptosis in platelet lifespan?
Intrinsic pathway limits platelet survival to ~7–10 days
213
What is the role of Bcl-xL in platelet survival?
Anti-apoptotic protein that extends platelet lifespan
214
What is the role of caspase inhibitors in platelet storage?
Prevent apoptosis to improve transfusion efficacy
215
What is the role of cold-induced platelet clearance?
Liver macrophages (Kupffer cells) phagocytose chilled platelets via Ashwell-Morell receptor
216
What is the role of GPIbα shedding in platelet aging?
ADAM17-mediated cleavage reduces platelet lifespan
217
What is the role of necroptosis in platelet death?
RIPK1/RIPK3/MLKL pathway triggers procoagulant platelet formation
218
What is the role of gasdermin D in pyroptosis?
Forms pores in procoagulant platelets
219
What is the role of platelet RNA in thrombosis?
Spliced mRNA and microRNAs regulate clot structure and stability
220
What is the role of platelet mitochondria in energy production?
Generate ATP for activation and aggregation via oxidative phosphorylation
221
What is the role of hexokinase deficiency in platelet disorders?
Impairs glycolysis
222
What is the role of glutathione peroxidase in platelets?
Protects against oxidative stress during storage or inflammation
223
What is the role of cyclooxygenase-2 (COX-2) in aspirin resistance?
Inducible enzyme that restores TXA2 synthesis despite COX-1 inhibition
224
What is the role of P2Y12 gene polymorphisms?
Affect clopidogrel metabolism (e.g.
225
What is the role of platelet glycoprotein polymorphisms?
Modify bleeding/thrombosis risk (e.g.
226
What is the role of platelet transfusion refractoriness?
Caused by HLA/HPA antibodies; requires HLA-matched or crossmatched platelets
227
What is the role of ABO antigens in platelet transfusion?
ABO-mismatched platelets have reduced survival due to isoagglutinin clearance
228
What is the role of platelet additive solutions (PAS)?
Replace plasma in stored platelets to reduce allergic reactions
229
What is the role of pathogen inactivation in platelet storage?
Uses amotosalen/UV-A to inactivate viruses
230
What is the role of cold-stored platelets in trauma?
Enhance clot stability for acute bleeding
231
What is the role of lyophilized platelets in emergencies?
Reconstituted freeze-dried platelets for rapid hemostasis in field settings
232
What is the role of platelet-derived extracellular vesicles (PEVs)?
Amplify coagulation and inflammation via TF
