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A premature infant develops progressive difficulty breathing over the first few days of life. Deficient surfactant synthesis by which of the following cell types may have contributed to the baby's respiratory problems?

During development, the formation of the kidney is induced by which of the following structures?

A 40-year-old woman presents to the emergency department because of hematuria. Laboratory analyses show significant proteinuria, bacteria and white cells in the urine, and a blood urea nitrogen (BUN) of 40 mg/dL with a creatinine of 4.0 mg/dL. Ultrasonography reveals enlarged kidneys, and she is given a provisional diagnosis of polycystic renal disease. Which of the following is likely to be decreased in this patient?

A 30-year-old pregnant woman of Jewish descent presents to a physician with painful oral ulcers. Physical examination demonstrates widespread erosions of her mucous membranes. Close examination reveals a friable mucosa, but no well-defined aphthous ulcers. Biopsy of perilesional mucosa demonstrates acantholysis; direct immunofluorescence demonstrates an intraepidermal band of IgG and C3. Which of the following is the most likely diagnosis?

An experimental serologic test is developed to detect the presence of HIV antibody. Epidemiological analysis reveals the results shown below. What is the sensitivity of this test?

A 60-year-old alcoholic smoker abruptly develops high fever, shakes, a severe headache, and muscle pain. He initially has a dry, insignificant cough, but over the next few days he develops marked shortness of breath requiring assisted ventilation. Chest x-ray demonstrates homogeneous radiographic shadowing that initially involves the left lower lobe but continues to spread until both lungs are extensively involved. Culture of bronchoalveolar lavage fluid on buffered charcoal yeast extract (BCYE) demonstrates a coccobacillary pathogen. Which of the following is the most likely causative organism?

A 43-year-old man presents complaining of pain in the groin. On examination, his physician palpates a bulge in the region of the superficial inguinal ring, which he diagnoses as a direct inguinal hernia. The hernial sac most likely

A 25-year-old woman develops extensive pruritic wheals following ingestion of seafood to which she was allergic. While these lesions are usually not biopsied, a biopsy would probably show which of the following features?

A 4-year-old child living in a slum is bitten by a rat while sleeping. Two days later, the child develops a rash characterized by discrete erythematous 1-4 mm macules on the extremities and face, most obvious on the palms and soles. Which of the following organisms is the most likely cause of this child's disease?

A patient develops a swollen and tender lymph node in his popliteal fossa. An infected skin lesion in which of the following sites would most likely induce lymphadenopathy in this region?