Heparin is an anticoagulant produced by the basophils. The most likely mechanism heparin prevents blood clotting is by

Correct Answer: D

Rationale: The correct answer is D because heparin binds to antithrombin III, enhancing its ability to inactivate thrombin. This prevents the conversion of fibrinogen to fibrin, thereby inhibiting blood clot formation. Choices A and B are incorrect because heparin does not affect vitamin K-dependent clotting factors or platelet activation. Choice C is incorrect because heparin does not directly prevent platelet aggregation.

Correct Answer: C

Rationale: The correct answer is C, pernicious anemia. Pernicious anemia is a macrocytic anemia caused by vitamin B12 deficiency affecting red blood cell production. Sideroblastic anemia (A), thalassemia (B), and lead poisoning (D) can all lead to microcytic anemia due to different mechanisms such as impaired hemoglobin synthesis or red blood cell destruction. Pernicious anemia, on the other hand, is not associated with microcytosis.

Correct Answer: C

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

Correct Answer: B

Rationale: The correct answer is B: gum bleeding. In Immune Thrombocytopenic Purpura (ITP), the hallmark feature is thrombocytopenia leading to mucocutaneous bleeding, including gum bleeding. Fever (choice A) is not a typical feature of ITP. Splenomegaly (choice C) can be present in chronic ITP but is not a defining feature. Sterna tenderness (choice D) is not specific to ITP and is not considered a characteristic feature. Thus, gum bleeding is the outstanding feature of ITP due to the primary pathophysiology of decreased platelet count leading to bleeding manifestations.

Correct Answer: C

Rationale: The correct answer is C: Optic neuritis. Busulfan therapy is known to cause adverse effects like hyperpigmentation, pulmonary fibrosis, and bone marrow suppression due to its cytotoxic nature. However, optic neuritis is not a common side effect associated with busulfan. Optic neuritis typically occurs due to inflammation of the optic nerve and is more commonly linked to conditions like multiple sclerosis. Therefore, in the context of busulfan therapy, optic neuritis is not a expected side effect, making it the correct answer.