A stillborn male newborn is delivered to a 32-year-old prnmigravid woman at 36 weeks' gestation. A photograph of the newborn is shown. Histologic examination of the sacrococcygeal tumor shows a haphazard arrangement of somatic tissues representing denvatives of ectoderm, mesoderm, and endoderm. The pathogenesis of this congenital neoplasm is most ikely related to a defect arising dunng which of the following developmental processes?

A 19.year-old woman comes to the emergency department because of nght lower abdominal pain for 10 hours. Her temperature is 39°C (102 2°F). Abdominal examination shows rebound tendemess of the right lower quadrant. She is admitted to the hospital, and an emergency exploratory operation is done. A photograph of the removed appendix is shown. Which of the following best describes the process involved in her condition?

A 6 year-old boy with congenital HIV infection comes to the physician because of fatigue for 3 weeks. Laboratory studies show:

Hemoglobin  → 46 g/dL (N=12 1-149)
Hematocrit  → 14% (N=37-44)
Leukocyte count  → 6500/mm³ (N=4000-11 600)
Reticulocyte count  → 0.5% of red cells (N=0.5-15)
Platelet count  → 200,000/mm ³ (N=140,000-440,000)

A bone marrow aspirate smear is shown. Which of the following is the most likely causal organism of the patient's anemia?

A 57-year old man with asthma comes to the emergency department 30 minutes after the onset of severe shortness of breath and left-sided chest discomfort while cross-country Skiing. He has no history of similar symptoms. He also has major depressive disorder and hypertension Current medications include albuterol, fluticasone inhaler, fluoxetine, and lisinopril His temperature is 37°C (98.6°F), pulse is 110/min, respirations are 30/min, and blood pressure is 130/70 mm Hg. On auscultation, wheezes are heard that are more prominent on the right side than on the left. Cardiac examination shows normal heart sounds with no murmurs. A chest x-ray is shown. Which of the following conditions is the most likely cause of this patient's acute dyspnea?

A male newborn delivered at 32 weeks' gestation dies of respiratory failure at the age of 2 days. A photomicrograph of lung tissue obtained at autopsy is shown. This patient most likely had a deficiency of which of the following substances?

A 45-year-old man with a long history of severe rheumatoid arthritis is being treated aggressively with gold salts. Over the past 6 weeks, he has gained 6.8 kg (15 lb) and has had progressive ankle swelling that has made it difficult to put on his shoes in the morning. He has generalized edema. Serum creatinine concentration is 1.0 g/dL. Urinalysis shows 4+ protein, numerous hyaline casts, and oval fat bodies, but no red cell casts. Urinary protein excretion is 8.4 g/24 h. The electron micrograph shows a glomerular capillary loop obtained on biopsy. Which of the following is the most likely diagnosis?

A 20-year-old man comes to the physician because of a 2-month history of persistent pain in his right knee. He is a college football player Physical examination shows a stable right knee with tendemess to palpation. An x-ray of the right knee is shown the arrow indicates an abnormality. The most likely cause of this patient's pain is ossification of which of the following structures?