USMLE-STEP-1 Online Practice Questions and Answers

Correct Answer: D

Section: Physiology Local hypoxia causes vasoconstriction in vessels of the pulmonary circulation. This is an adaptive response, since it will shunt blood away from poorly ventilated alveoli. This response differentiates the pulmonary circulation from the vasculature of other organs. In heart muscle, skeletal muscle, kidney, and brain (choices A, B, C, and E) vasodilation occurs in response to local hypoxia.

Correct Answer: C

Correct Answer: B

Section: Microbiology/Immunology By definition, the rate of growth of bacteria represents the change in the bacterial cell numbers over the change in time. From the choices given, the maximum rate of growth occurs between 2 p.m. and 3 p.m., where within 1 hour the number of bacteria has increased approximately threefold. Between noon and 1 p.m., 34 p.m., and 35 p.m., there is no increase in the number of cells and the rate of growth is zero.

Correct Answer: C

Section: Microbiology/Immunology Cytomegalovirus (CMV) is an enveloped, double-stranded DNA virus, which causes formation of giant cells with intranuclear inclusion bodies that have an oval owl's eye shape. CMV can cause a generalized infection, which is associated with immunosuppression. This can occur with organ transplantation or AIDS and result in central nervous system involvement, pneumonia, retinitis, colitis, and organ rejection. Adenoviruses (choice A) are also double-stranded DNA viruses but do not have an envelope. Coronaviruses (choice B) contain an RNA genome and do have an envelope. Papillomaviruses (choice D) contain doublestranded DNA and have no envelope. Variola virus (choice E) is a poxvirus, having doublestranded DNA. The largest virus group by size, poxviruses, does contain an "envelope" but it is constructed of multiple membranes closely attached to the virions, unlike lipid envelopes seen in herpes viruses, for example.

Correct Answer: C

Section: Pathology and Path physiology Bacteria are the principle cause of osteomyelitis, infecting bone either by direct penetration (e.g., puncture), extension from a surrounding area (e.g., cellulitis), or via hematogenous spread of an overt infection (e.g., sinusitis, pneumonia) or an occult bacteremia (e.g., mouth, intestinal flora); the leading causative pathogen is S. aureus. Long bone metaphyses are commonly infected in children, whereas long bone epiphyses and vertebrae are more typically affected in adults. Presentation may be limited to pain, with or without fever. The classic x-ray findings include lytic changes caused by necrotic bone (sequestrum) and sclerosis due to the ingrowth of fibrous tissue as new bone growth (involucrum) forms around the devitalized bone. Gout (choice A) is associated with hyperuricemia, leading to acute synovial inflammation and deposition of urate crystals in joint spaces; similarly, rheumatoid arthritis (choice E) is an autoimmune disorder affecting the synovial lining of various joints (chronic synovitis). Osteosarcomas (choice D) are typically large, bulky malignancies most commonly originating in long bone metaphyses, often with secondary spread into epiphyseal regions. Osteochondromas (choice B) are benign tumors arising near the growth plate in endochrondrally derived long bones which form bony, pedunculated, cartilage-capped lesions.

Correct Answer: C

Section: Pathology and Path physiology Primary biliary cirrhosis is an autoimmune disorder. Autoantibodies against mitochondria are usually present. Hyperbilirubinemia, steatorrhea, portal hypertension, and osteomalacia may be seen in the later stages of the disease. Vascular abnormalities (choice A), alcohol abuse (choice B), parasitic infections (choice D), and viral infections (choice E) all may mimic the clinical picture of primary biliary cirrhosis. They are not, however, the usual etiologic agents.

Correct Answer: E

Section: Behavioral Science and Biostatics Wernicke syndrome is caused by thiamine deficiency associated with alcohol withdrawal, and can be treated effectively. Alzheimer's disease (choice A) is the most common primary dementia in the elderly. About 50% of brains of demented patients show evidence of Alzheimer's disease. Creutzfeldt- Jakob (choice B) disease and kuru are slow virus infections that show clinical and histologic features similar to Alzheimer's disease. Multiinfarct dementia (choice C) is secondary to repeated cerebrovascular accidents (CVAs) in patients with underlying atherosclerosis or hypertension. It is more common among men than women. Pick disease (choice D) is a rare cause of cortical dementia. The presence of unilateral cortical atrophy in Pick disease contrasts with the bilateral atrophy evident in Alzheimer's disease. Microscopically, Pick bodies composed of densely packed neurofilaments are seen within diseased neurons.

Correct Answer: A

Section: Physiology Eosinophils normally constitute about 2% of all blood leukocytes. These cells are phagocytic and exhibit chemotaxis. Their primary role is in fighting parasitic infection. In schistosomiasis the eosinophil attaches to the immature parasite and, by releasing various cytotoxic compounds, is able to kill the parasite. Erythrocytes (choice B) are the most numerous blood cells. They are not leukocytes, but function in blood gas transport. Erythrocyte number would not be increased in schistosomiasis. Monocytes (choice C) are leukocytes found in the blood. They are immature cells which migrate to the tissues, where they mature into macrophages. These cells are very active in phagocytosis and play a prominent role in the inflammatory response. They are not, however, particularly important in parasitic infections. Neutrophils (choice D) are another type of leukocyte that, though essential to combat bacterial infections, are not particularly sensitive to parasitic challenge. Platelets (choice E) are not leukocytes. The platelet is a cell fragment that functions in hemostasis.