Primary Hemostasis: Normal physiology, disorders, and clinical findings
Authors: Mina Mina Reviewers: Parker Lieb Mao Ding Kareem Jamani* *MD at time of publication
Normal physiology:
Injury to blood vessels from trauma (blunt or penetrating injury)
Disorders of primary hemostasis:
Collagen and microfibrils (subendothelial elements
that are normally protected) are exposed to circulating blood due to vessel injury
Storage granules in endothelial cells release large multimers of clotting factor von Willebrand (vWF) when damaged
Acquired or inherited reduction in vWF quantity or quality (see vWF deficiency slide)
von Willebrand Disease
Defect in expression of GpIb interferes with platelet ability to bind to vWF
Bernard-Soulier syndrome
Defect in platelet membrane glycoproteins IIb and IIIa
Glanzmann’s Thrombasthenia
Insufficient platelets to form a platelet plug
Thrombocytopenia
(low platelet count)
Disorders of primary hemostasis: problems with formation of a platelet plug
Platelet adhesion: vWF binds to collagen and interacts with the platelet surface receptor glycoprotein Ib (GpIb) allowing platelet adhesion
Platelet activation: mediated by agonists like ADP, thrombin and collagen
Mucocutaneous bleeding (bleeding of the skin and mucous membrane)
↑ Closure time, ↑ bleeding time
Platelets change shape and release substances from their granules
Conformational changes in platelet cell surface glycoprotein IIb/IIIa
↑Affinity for fibrinogen through GpIIb/IIIa
ADP
Fibrinogen, vWF, and other substances
Thromboxane A2 (see note)
Induces aggregation
Epistaxis
Menorrhagia Note:
Petechiae
Platelet aggregation: fibrinogen forms bridges between adjacent platelets by binding to activated glycoprotein IIb/IIIa
Interaction with coagulation factors: platelets provide a scaffold that allows the activation of phospholipid-dependent coagulation factors
Primary hemostasis
(formation of a platelet plug)
Secondary hemostasis (see slide for normal physiology)
Drugs like Aspirin and NSAIDs inhibit Thromboxane A2 synthesis (by inhibiting cyclooxygenase) and thereby inhibit platelet aggregation
Legend:
Pathophysiology
Mechanism
Sign/Symptom/Lab Finding
Complications
Published March 30, 2023 on www.thecalgaryguide.com