Physiology Chapter 5: Hemostasis

Questions and Answers

What is the normal range of platelets per microliter of blood?

100,000-200,000

200,000-500,000

150,000-400,000 (correct)

300,000-600,000

What is the purpose of the smooth muscle contraction in the blood vessel spasm stage of hemostasis?

To increase blood flow to the wound site

To reduce blood flow to the wound site (correct)

To release thrombin

To stimulate platelet activation

What is the function of Von Willebrand factor (VWF) in platelet plug formation?

To inhibit platelet secretion

To stimulate platelet activation

To facilitate platelet adhesion (correct)

To release calcium ions

What is the term for the stoppage of bleeding?

Hemostasis Signup and view all the answers

Which of the following is NOT a stage of hemostasis?

Inflammation Signup and view all the answers

What happens when ADP binds to platelets?

They are activated and aggregate Signup and view all the answers

What is the name of the factor released by platelets that stimulates smooth muscle contraction in blood vessels?

Thromboxane A2 Signup and view all the answers

What is the approximate diameter of a platelet?

2-4 µm Signup and view all the answers

What is the result of Stage 3 Blood Coagulation?

Formation of a blood clot Signup and view all the answers

What is the mode of action of Warfarin in decreasing blood clotting?

By blocking an enzyme that reactivates vitamin K1 Signup and view all the answers

What is the function of Streptokinase?

To activate plasminogen Signup and view all the answers

What is the intrinsic pathway also known as?

Contact activation pathway Signup and view all the answers

What activates factor X in the extrinsic pathway?

Tissue thromboplastic Signup and view all the answers

What is the normal range for bleeding time?

2-6 min Signup and view all the answers

What is the normal range for clotting time?

5-11 min Signup and view all the answers

What is the function of platelet-derived growth factor?

Stimulating smooth muscle cells and fibroblasts Signup and view all the answers

What happens to the blood clot after it forms?

It retracts and pulls the edges of a broken blood vessel together Signup and view all the answers

What is the partial thromboplastin time (PTT) used for?

To test the intrinsic and common pathway Signup and view all the answers

What is the difference between serum and plasma?

Serum is the liquid that remains after the blood has clotted, while plasma is the liquid that remains when clotting is prevented Signup and view all the answers

What triggers the clotting cascade?

Cellular damage and blood contact with foreign surfaces Signup and view all the answers

How many separate steps are involved in the clotting cascade?

Seven Signup and view all the answers

What is the function of plasmin in the body?

It digests blood clots Signup and view all the answers

What is the role of fibrin in preventing blood clotting within normal vascular systems?

It absorbs thrombin and prevents the clotting reaction from spreading Signup and view all the answers

What is a thrombus?

An abnormal intravascular clot attached to a vessel wall Signup and view all the answers

What is a common cause of thromboembolism?

Roughened vessel surfaces associated with atherosclerosis Signup and view all the answers

What is the result of vitamin C deficiency in the context of blood clotting?

Lack of stable collagen Signup and view all the answers

What is the function of heparin in the body?

It potentiates antithrombin III Signup and view all the answers

What is the effect of aspirin on platelet activation?

It reduces platelet activation Signup and view all the answers

What is the effect of clopidogrel on platelet activation?

It is an irreversible inhibitor of the ADP receptor on platelet membranes Signup and view all the answers

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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This quiz covers the physiology of hemostasis, focusing on platelets, their formation, structure, and functions.