USMLE USMLE-STEP-1 Exam Questions & Answers

Correct Answer: B

Section: Anatomy Obstruction of the portal vein results in an increase in the collateral circulation between veins that normally drain to the portal vein and those that drain to the systemic veins. Choices A, B, D, and E all represent possible collateral venous circulation in case of portal obstruction. Choice Ais rare because the ductus venosus closes after birth. Choice B is correct because varicose veins in this region give rise to esophageal varices. Choice D results in varicose veins in the rectal region. Choice C is incorrect because there is no connection between the right gastric vein and the inferior vena cava. In choice E, enlargement of the epigastric veins results in varicose veins radiating from the umbilicus, the caput medusae.

Correct Answer: E

Section: Microbiology/Immunology Infectious mononucleosis is caused by EBV, which is a member of the herpesviruses. Nucleic acid hybridization assays for EBV DNAare the most sensitive means of diagnosing infectious mononucleosis. Hemagglutinins (choice B) and NAs (choice C) are associated with orthomyxoviruses and paramyxoviruses. The majority of infectious mononucleosis patients develop what is known as an heterophile antibody, antibodies that cross-react with unrelated antigens, such as those found on sheep and horse erythrocytes. The heterophile antibody test (choice D) is used for the diagnosis of infectious mononucleosis, but since it is not a very specific test, it is not as good as the nucleic acid hybridization assays for the presence of Epstein-Barr viral nucleic acid. Important antigens that also may be used, but which are less sensitive for diagnostic purposes, include the viral capsid protein (VCA), the early proteins (EA), and the EBV-associated nuclear antigen (EBNA). Infectious mononucleosis patients develop antibody titers exceeding 1:320 and 1:20 against VCA and EA, respectively, during the acute phase of infectious mononucleosis. Antibodies to EBNA develop 12 months after acute infection (choice A).

Correct Answer: E

Section: Microbiology/Immunology The major event associated with IV hypersensitivity is a helper T-cell reaction with the antigen epitope and class II antigen via Ti and CD4 respectively. IgE reacts with mast cells in type I hypersensitivity (choice C). The major event associated with type IV allergy has nothing to do with the expression of antigen epitopes on B cells (choice B), the reaction of allergen with the nonexistent Ti and CD4 markers of B cells (choice D), or the expression of antigen epitopes on CD8+ of T cells (choice A).