A 50-year-old male who had frequent infections of his upper respiratory tract manifested with subcutaneous petechiae over his arms and legs. Investigations revealed low hemoglobin and a dry tap marrow. The most likely condition the patient is suffering from

Correct Answer: D

Rationale: The correct answer is D: Aplastic anemia. This condition is characterized by pancytopenia, which includes low hemoglobin (anemia), low platelets (manifested as petechiae), and low white blood cells (frequent infections). Dry tap marrow is a classic finding in aplastic anemia due to bone marrow failure. Iron deficiency anemia (choice A) typically presents with microcytic hypochromic anemia without pancytopenia. Megaloblastic anemia (choice B) is characterized by macrocytic anemia with hypersegmented neutrophils and is usually caused by deficiencies in vitamin B12 or folate. Hemolytic anemia (choice C) presents with anemia due to increased destruction of red blood cells, which does not explain the low platelets and white blood cells seen in this patient.

Correct Answer: C

Rationale: Platelets change their shape during platelet aggregation to form a plug at the site of vascular injury. This process involves platelets adhering to the injured blood vessel wall, becoming activated, and then changing shape to form a clot. Vasodilation is not an initial response, as vasoconstriction occurs to reduce blood loss. Clotting factors are essential for clot formation and play a significant role. Serotonin is released from platelets during aggregation but does not directly stimulate aggregation. The correct choice, C, directly correlates with the physiological process of platelet aggregation in response to vascular injury.

Correct Answer: B

Rationale: The correct answer is B because the Aedes mosquito, the vector for dengue fever, remains infective for life once it is infected with the dengue virus. This is due to the virus establishing a lifelong infection in the mosquito's salivary glands. The other choices are incorrect because: A) Dengue is caused by an RNA virus, not a DNA virus. C) The Aedes mosquito prefers clean, stagnant water for breeding, not polluted water. D) Joint symptoms are commoner in chikungunya, not dengue fever.

Correct Answer: C

Rationale: Virchow's node is a left supraclavicular lymph node that typically receives lymphatics from abdominal organs. The correct answer is C: prostate because the prostate is not an abdominal organ and does not drain into Virchow's node. The other choices, A: testes, B: stomach, and D: breast, all drain into the abdominal lymphatic system, making them potential sources of lymphatic drainage to Virchow's node.

Correct Answer: D

Rationale: In thrombasthenia, there is a deficiency or dysfunction of the glycoprotein IIb/IIIa receptor complex on platelets, leading to impaired platelet aggregation. This results in prolonged bleeding time due to ineffective platelet plug formation (choice A). Platelet count is typically normal (choice B). Platelet aggregation is defective (choice C). However, clotting time is not affected in thrombasthenia as it primarily involves platelet function, not the clotting factors involved in coagulation (choice D). Therefore, the correct answer is D.