Questions and Answers
What is the normal range of platelets per microliter of blood?
What is the purpose of the smooth muscle contraction in the blood vessel spasm stage of hemostasis?
What is the function of Von Willebrand factor (VWF) in platelet plug formation?
What is the term for the stoppage of bleeding?
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Which of the following is NOT a stage of hemostasis?
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What happens when ADP binds to platelets?
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What is the name of the factor released by platelets that stimulates smooth muscle contraction in blood vessels?
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What is the approximate diameter of a platelet?
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What is the result of Stage 3 Blood Coagulation?
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What is the mode of action of Warfarin in decreasing blood clotting?
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What is the function of Streptokinase?
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What is the intrinsic pathway also known as?
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What activates factor X in the extrinsic pathway?
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What is the normal range for bleeding time?
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What is the normal range for clotting time?
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What is the function of platelet-derived growth factor?
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What happens to the blood clot after it forms?
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What is the partial thromboplastin time (PTT) used for?
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What is the difference between serum and plasma?
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What triggers the clotting cascade?
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How many separate steps are involved in the clotting cascade?
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What is the function of plasmin in the body?
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What is the role of fibrin in preventing blood clotting within normal vascular systems?
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What is a thrombus?
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What is a common cause of thromboembolism?
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What is the result of vitamin C deficiency in the context of blood clotting?
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What is the function of heparin in the body?
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What is the effect of aspirin on platelet activation?
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What is the effect of clopidogrel on platelet activation?
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Study Notes
Platelets
- Formed in bone marrow, with a count of 150-400,000/µl
- 30% sequestered in spleen, with a diameter of 2-4 µm and a lifespan of 8-12 days, no nucleus
- Active cytoplasm with enzyme synthesis
- Membrane receptors for thrombin, ADP, and serotonin
- Storage of calcium and adhesion proteins (VWF, fibronectin, collagen, fibrinogen)
- Synthesis of prostaglandins, coat of glycoproteins for adhesion to injured areas
- Granules containing ADP, serotonin, and ATP, phospholipids for activation of intrinsic pathway
- α-granules containing fibrinogen, PDGF, VWF, fibronectin, and fibrin stabilizing factor
Hemostasis
- Refers to the stoppage of bleeding (hemo = blood, stasis = standing)
- Three stages: blood vessel spasm, platelet plug formation, and blood coagulation
Stage 1: Blood Vessel Spasm
- Triggered by pain receptors, local myogenic spasm, and local release of thromboxane A2 and serotonin
- Results in smooth muscle contraction in blood vessels to minimize blood flow from the wound site
Stage 2: Platelet Plug Formation
- Triggered by exposure of platelets to collagen
- Results in platelet adhesion, activation, and aggregation to form a plug
- Steps of platelet plug formation: adhesion, secretion, and aggregation
Stage 3: Blood Coagulation
- Triggered by cellular damage and blood contact with foreign surfaces
- Results in the formation of a blood clot through a series of reactions
- Two pathways: extrinsic (tissue factor pathway) and intrinsic (contact activation pathway)
Coagulation Cascade
- Involves seven separate steps
- Requires contact with tissue factors external to the blood or exposure to collagen
- Intrinsic pathway involves factor XII activation
- Extrinsic pathway involves tissue thromboplastin release from traumatized tissue
Serum and Plasma
- Serum: liquid remaining after blood has clotted
- Plasma: liquid remaining when clotting is prevented with an anticoagulant
Fate of Blood Clots
- Plasmin digests blood clots
- Platelet-derived growth factor stimulates smooth muscle cells and fibroblasts to repair damaged blood vessel walls
Prevention of Blood Clotting
- Smooth lining of blood vessels discourages platelet accumulation and clotting factors
- Fibrin absorbs thrombin and prevents clotting reaction from spreading
- Cells like basophils and mast cells secrete heparin (an anticoagulant)
- Dynamic blood flow
Abnormal Blood Clotting
- Thrombus: abnormal intravascular clot attached to a vessel wall
- Emboli: freely floating clots
- Factors causing thromboembolism include roughened vessel surfaces, imbalances in clotting-anticlotting systems, slow-moving blood, and release of tissue thromboplastin
Coagulation Defects
- Vitamin C deficiency: lack of stable collagen (in elderly, alcoholics)
- Hepatic failure: most clotting factors are made in the liver
- Vitamin K deficiency: required for prothrombin, VII, IX, and X
- Hemophilia: excessive bleeding due to deficiency of clotting factors
- Thrombocytopenia: bleeding from small capillaries and blood vessels due to low platelet count
Anti-Hemostatic Drugs
- Heparin: potentiates antithrombin III
- Aspirin: inhibits thromboxane A2 production and platelet activation
- Clopidogrel: irreversible inhibitor of ADP receptor on platelet membranes
- Warfarin: decreases blood clotting by blocking vitamin K epoxide reductase
- Streptokinase: plasminogen activator
Tests for Hemostasis
- Platelet disorder tests: bleeding time (increased in thrombocytopenia)
- Coagulation disorder tests: clotting time, partial thromboplastin time (PTT), and prothrombin time (PT)
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Description
This quiz covers the physiology of hemostasis, focusing on platelets, their formation, structure, and functions.