Flashcards in Hem & Onc - Physiology (Primary Hemostasis & Erythrocyte sedimentation rate) Deck (19):
What are the names of the general steps of platelet plug formation?
(1) Injury (2) Adhesion & Activation (4) Aggregation
What is the first step of platelet plug formation? What key event occurs here?
Injury; vWF binds exposed collagen upon endothelial damage
What is the second step of platelet plug formation? What key events occur here?
Adhesion & Activation; (1) Platelets bind vWF via GpIb receptor at the site of injury (2) Platelets release ADP & Ca2+ (necessary for coagulation cascade) (3) ADP plays two roles: (a) helps platelets adhere to endothelium (b) ACTIVATION: binds to its receptor, inducing GpIIb/IIIa expression at platelet surface
What is the third step of platelet plug formation? What makes this step possible?
Aggregation; Fibrinogen binds GpIIb/IIIa receptors & links platelets
What is the ultimate goal of platelet plug formation?
Temporarily stop bleeding (until secondary hemostasis can stabilize clot)
What are the pro-aggregation versus anti-aggregation factors that must be balanced in order for the third and final step of platelet plug formation to occur (i.e., aggregation)?
PRO-AGGREGATION: (1) TXA2 (released by platelets) (2) Decreased blood flow (3) Increased platelet aggregation; ANTI-AGGREGATION: (1) PGI2 and NO (released by endothelial cells) (2) Increased blood flow (3) Decreased platelet aggregation
What is a deficiency in GpIb called? At what step of platelet plug formation does this interfere?
Bernard-Soulier syndrome; Adhesion
What is a deficiency in GpIIb/IIIa called? At what step of platelet plug formation does this interfere?
Glanzmann's thrombasthenia; Aggregation
What irreversibly blocks the ADP receptor? At what step(s) of platelet plug formation does this interfere?
Clopidogrel & ticlopidine; Adhesion & Activation plus Aggregation
What blocks the GpIIb/IIIa receptor? At what step of platelet plug formation does this interfere?
What is a deficiency in vWF called? At what step of platelet plug formation does this interfere?
von Willebrand's disease; Adhesion
By what mechanism does Aspirin work? What effect does this have on platelet plug formation?
Inhibits cyclooxygenase; Inhibits TXA2 synthesis = impairs aggregation
What activates protein C?
What key players in platelet plug formation are found in endothelial cells?
vWF, thromboplastin, tPA, PGI2, NO
What key players in platelet plug formation are found in platelets?
vWF, fibrinogen, ADP, TXA2
What is an example of acute phase reactant relevant to hemostasis? What effects do such acute phase reactants have on erythrocyte sedimentation rate, and why?
Fibrinogen; Cause RBC aggregation, thereby INCREASING RBC sedimentation rate; RBC aggregates have a higher density than plasma
What are examples of conditions that increase erythrocyte sedimentation rate?
(1) Infections (2) Autoimmune diseases (e.g., SLE, rheumatoid arthritis, temporal arthritis) (3) Malignant neoplasms (4) GI disease (ulcerative colitis) (5) Pregnancy
What are examples of conditions that decrease erythrocyte sedimentation rate?
(1) Polycythemia (2) Sickle Cell anemia (3) Congestive heart failure (4) Microcytosis (5) Hypofibrinogenemia