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Blood and Haematology

Platelets and Clotting Disorders Practice Questions

33 free Platelets and Clotting Disorders practice questions for the Physiology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.

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Question 1 of 33 Medium

Platelets are primarily derived from which bone marrow cell?

  1. A Myeloblasts
  2. B Megakaryocytes
  3. C Erythroblasts
  4. D Lymphoblasts

Correct answer: Megakaryocytes

Platelets are cytoplasmic fragments shed from megakaryocytes in the bone marrow. Megakaryocytes are large cells specialized for platelet production.

Question 2 of 33 Medium

The normal platelet count in adult human blood is approximately:

  1. A 50,000–100,000/µL
  2. B 100,000–150,000/µL
  3. C 150,000–400,000/µL
  4. D 400,000–600,000/µL

Correct answer: 150,000–400,000/µL

The normal platelet count ranges from 150,000 to 400,000 per microliter of blood. Values below this range increase bleeding risk.

Question 3 of 33 Medium

Which substance released from platelets promotes vasoconstriction at the site of injury?

  1. A Heparin
  2. B Prostacyclin
  3. C Serotonin
  4. D Plasmin

Correct answer: Serotonin

Serotonin released from platelet granules causes local vasoconstriction. This helps reduce blood loss following vascular injury.

Question 4 of 33 Medium

Platelet adhesion to damaged endothelium is primarily mediated by:

  1. A Circulating fibrinogen
  2. B Von Willebrand factor
  3. C Prothrombin complex
  4. D Antithrombin III cofactor

Correct answer: Von Willebrand factor

Von Willebrand factor bridges platelets to exposed collagen at the injury site. This step is essential for primary hemostasis.

Question 5 of 33 Medium

Which platelet receptor is responsible for binding fibrinogen during platelet aggregation?

  1. A GPIb-IX-V complex
  2. B GPIIb/IIIa
  3. C GPVI collagen receptor
  4. D P-selectin adhesion molecule

Correct answer: GPIIb/IIIa

The GPIIb/IIIa receptor binds fibrinogen, allowing platelets to cross-link with each other. This interaction is crucial for platelet aggregation.

Question 6 of 33 Medium

Which vitamin is essential for the synthesis of several clotting factors?

  1. A Vitamin A
  2. B Vitamin C
  3. C Vitamin K
  4. D Vitamin D

Correct answer: Vitamin K

Vitamin K is required for the gamma-carboxylation of clotting factors II, VII, IX, and X. Deficiency leads to impaired coagulation.

Question 7 of 33 Medium

The intrinsic pathway of coagulation is initiated by activation of:

  1. A Factor VII
  2. B Factor XII
  3. C Factor X
  4. D Factor V

Correct answer: Factor XII

The intrinsic pathway begins with activation of factor XII upon contact with negatively charged surfaces. This pathway is assessed by the aPTT test.

Question 8 of 33 Medium

Which laboratory test primarily evaluates the extrinsic pathway of coagulation?

  1. A Activated partial thromboplastin time
  2. B Bleeding time
  3. C Prothrombin time
  4. D Thrombin time

Correct answer: Prothrombin time

Prothrombin time measures the extrinsic and common pathways of coagulation. It is sensitive to deficiencies of factor VII.

Question 9 of 33 Medium

Hemophilia A is caused by deficiency of which clotting factor?

  1. A Factor VIII
  2. B Christmas factor IX
  3. C Plasma factor XI precursor
  4. D Hageman factor XII

Correct answer: Factor VIII

Hemophilia A results from deficiency of factor VIII. It leads to prolonged bleeding and is inherited as an X-linked disorder.

Question 10 of 33 Medium

Which clotting disorder is characterized by a prolonged bleeding time with a normal platelet count?

  1. A Hemophilia A
  2. B Von Willebrand disease
  3. C Thrombocytopenia
  4. D Disseminated intravascular coagulation

Correct answer: Von Willebrand disease

Von Willebrand disease impairs platelet adhesion despite a normal platelet count. This leads to prolonged bleeding time.

Question 11 of 33 Medium

The primary function of fibrin in hemostasis is to:

  1. A Activate platelets
  2. B Form the initial platelet plug
  3. C Stabilize the blood clot
  4. D Cause vasoconstriction

Correct answer: Stabilize the blood clot

Fibrin forms a stable mesh that reinforces the platelet plug. This stabilizes the clot and prevents further bleeding.

Question 12 of 33 Medium

Which enzyme converts fibrinogen into fibrin?

  1. A Plasmin
  2. B Thrombin
  3. C Prothrombin
  4. D Antithrombin III

Correct answer: Thrombin

Thrombin cleaves fibrinogen to form fibrin strands. This is a key step in the final common pathway of coagulation.

Question 13 of 33 Medium

Thrombocytopenia is defined as:

  1. A Increased platelet aggregation
  2. B Reduced clotting factor synthesis
  3. C Low platelet count
  4. D Abnormal platelet function

Correct answer: Low platelet count

Thrombocytopenia refers to a decrease in platelet count below the normal range. It increases the risk of bleeding.

Question 14 of 33 Medium

Which anticoagulant acts by enhancing the activity of antithrombin III?

  1. A Aspirin
  2. B Warfarin
  3. C Heparin
  4. D Clopidogrel

Correct answer: Heparin

Heparin enhances the inhibitory action of antithrombin III on thrombin and factor Xa. This rapidly reduces clot formation.

Question 15 of 33 Medium

Disseminated intravascular coagulation is characterized by:

  1. A Isolated platelet deficiency only
  2. B Widespread clotting then bleeding
  3. C Congenital absence of clotting factors
  4. D Markedly reduced fibrinolysis

Correct answer: Widespread clotting then bleeding

Disseminated intravascular coagulation involves widespread clotting that consumes platelets and clotting factors. This paradoxically leads to bleeding.

Question 16 of 33 Medium

Which substance released by endothelial cells inhibits platelet aggregation?

  1. A Thromboxane A2
  2. B Serotonin
  3. C Prostacyclin
  4. D ADP

Correct answer: Prostacyclin

Prostacyclin inhibits platelet aggregation and causes vasodilation. It helps maintain blood flow in intact vessels.

Question 17 of 33 Medium

Bleeding time primarily assesses the function of:

  1. A Clotting factors
  2. B Red blood cells
  3. C Platelets
  4. D Fibrinolytic system

Correct answer: Platelets

Bleeding time reflects platelet function and vascular integrity. It is prolonged in platelet disorders.

Question 18 of 33 Medium

Which drug inhibits platelet aggregation by blocking thromboxane A2 synthesis?

  1. A Heparin
  2. B Warfarin
  3. C Aspirin
  4. D Tissue plasminogen activator

Correct answer: Aspirin

Aspirin irreversibly inhibits cyclooxygenase, reducing thromboxane A2 synthesis. This impairs platelet aggregation.

Question 19 of 33 Medium

Which clotting factor links the intrinsic and extrinsic pathways to the common pathway?

  1. A Factor VIII
  2. B Factor IX
  3. C Factor X
  4. D Factor XII

Correct answer: Factor X

Factor X is the point where intrinsic and extrinsic pathways converge. Its activation leads to thrombin formation.

Question 20 of 33 Medium

Which condition is most likely associated with prolonged aPTT but normal prothrombin time?

  1. A Vitamin K deficiency
  2. B Hemophilia A
  3. C Liver disease
  4. D Warfarin therapy

Correct answer: Hemophilia A

Hemophilia A affects the intrinsic pathway, prolonging aPTT while prothrombin time remains normal. This pattern is characteristic of factor VIII deficiency.

Question 21 of 33 Medium

Which clotting disorder is characterized by prolonged bleeding time despite a normal platelet count?

  1. A Hemophilia A
  2. B von Willebrand disease
  3. C Glanzmann thrombasthenia
  4. D Bernard-Soulier syndrome

Correct answer: von Willebrand disease

Von Willebrand disease is caused by a deficiency or dysfunction of von Willebrand factor, which impairs platelet adhesion while the platelet count itself remains normal, producing a prolonged bleeding time. Glanzmann thrombasthenia and Bernard-Soulier syndrome are rarer inherited platelet function disorders that can present similarly but are far less common causes of this pattern.

Question 22 of 33 Medium

Which platelet receptor binds fibrinogen during aggregation?

  1. A GP Ib-IX-V complex
  2. B GP IIb/IIIa
  3. C GP Ia/IIa
  4. D GP VI

Correct answer: GP IIb/IIIa

GP IIb/IIIa (integrin alphaIIb-beta3) is the platelet receptor that binds fibrinogen, cross-linking adjacent platelets to form aggregates. The GP Ib-IX-V complex binds von Willebrand factor for initial adhesion rather than aggregation, while GP Ia/IIa and GP VI mediate platelet binding to collagen.

Question 23 of 33 Medium

Bleeding time primarily assesses:

  1. A Coagulation factors
  2. B Platelet function
  3. C Red blood cell count
  4. D Hemoglobin level

Correct answer: Platelet function

Bleeding time evaluates platelet function and the ability of platelets to form a plug at the site of injury.

Question 24 of 33 Medium

Platelet adhesion to damaged endothelium is mediated by:

  1. A Fibronectin
  2. B Thrombospondin-1
  3. C von Willebrand factor
  4. D Subendothelial collagen

Correct answer: von Willebrand factor

Von Willebrand factor forms a bridge between platelet GP Ib receptors and exposed subendothelial collagen at a site of vascular injury, mediating platelet adhesion to the damaged vessel wall. Fibronectin and thrombospondin-1 support platelet aggregation and stabilization afterward, while collagen itself is the exposed substrate rather than the platelet-binding mediator.

Question 25 of 33 Medium

Which test evaluates the extrinsic pathway of coagulation?

  1. A Bleeding time (BT)
  2. B Activated partial thromboplastin time (aPTT)
  3. C Prothrombin time (PT)
  4. D Platelet count (PLT)

Correct answer: Prothrombin time (PT)

Prothrombin time (PT) evaluates the extrinsic and common coagulation pathways, largely reflecting factor VII activity. Activated partial thromboplastin time (aPTT) instead assesses the intrinsic pathway, while bleeding time and platelet count measure platelet-related hemostasis rather than the coagulation cascade itself.

Question 26 of 33 Medium

Which vitamin is essential for synthesis of several clotting factors?

  1. A Vitamin A
  2. B Vitamin D
  3. C Vitamin K
  4. D Vitamin C

Correct answer: Vitamin K

Vitamin K is required for synthesis of clotting factors II, VII, IX, and X in the liver.

Question 27 of 33 Medium

Which anticoagulant enhances the activity of antithrombin III?

  1. A Warfarin
  2. B Aspirin
  3. C Heparin
  4. D Clopidogrel

Correct answer: Heparin

Heparin enhances antithrombin III activity, inhibiting thrombin and factor Xa.

Question 28 of 33 Medium

Which condition shows prolonged aPTT but normal prothrombin time?

  1. A Vitamin K deficiency
  2. B Hemophilia A
  3. C Liver disease
  4. D DIC

Correct answer: Hemophilia A

Hemophilia A involves deficiency of factor VIII, affecting the intrinsic pathway and prolonging aPTT.

Question 29 of 33 Medium

Hemophilia A is caused by deficiency of:

  1. A Factor IX
  2. B Factor VIII
  3. C Factor VII
  4. D Factor X

Correct answer: Factor VIII

Hemophilia A results from deficiency of factor VIII, impairing the intrinsic coagulation pathway.

Question 30 of 33 Medium

Which factor connects intrinsic and extrinsic pathways to the common pathway?

  1. A Factor XII (Hageman factor)
  2. B Factor VII (Proconvertin)
  3. C Factor X (Stuart-Prower factor)
  4. D Factor VIII (Antihemophilic factor)

Correct answer: Factor X (Stuart-Prower factor)

Factor X (Stuart-Prower factor) sits at the point where the intrinsic and extrinsic pathways converge, initiating the common pathway that generates thrombin and fibrin. Factor XII (Hageman factor) and Factor VIII (Antihemophilic factor) act earlier in the intrinsic pathway, while Factor VII (Proconvertin) initiates the extrinsic pathway.

Question 31 of 33 Medium

The normal platelet count in adults is approximately:

  1. A 50,000–100,000/µL
  2. B 100,000–200,000/µL
  3. C 400,000–600,000/µL
  4. D 150,000–400,000/µL

Correct answer: 150,000–400,000/µL

Normal platelet count ranges from 150,000 to 400,000 per microliter of blood.

Question 32 of 33 Medium

Which substance released from platelets promotes vasoconstriction?

  1. A Prostacyclin
  2. B Serotonin
  3. C Nitric oxide
  4. D Heparin

Correct answer: Serotonin

Serotonin released from platelets causes vasoconstriction, helping reduce blood loss.

Question 33 of 33 Medium

Platelets are derived from which bone marrow cells?

  1. A Erythroblasts
  2. B Lymphocytes
  3. C Monocytes
  4. D Megakaryocytes

Correct answer: Megakaryocytes

Platelets are fragments of megakaryocytes, large bone marrow cells responsible for platelet production.

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