A 34-year-old woman is admitted to the hospital for treatment of pulmonary tuberculosis. Infliximab therapy was initiated 6 months ago for severe Crohn disease. This pharmacotherapy most likely inhibited which of the following immunologic functions in this patient?

A female newborn delivered at 38 weeks’ gestation to a 28-year-old woman, gravida 1, para 1, develops respiratory distress. Pregnancy and delivery were uncomplicated; amniotic fluid was clear, and the placenta was normal. Fetal ultrasonography and MRI at 34 weeks’ gestation showed a congenital diaphragmatic hernia, with evidence of small bowel and stomach herniation into left hemithorax. She is 52 cm (20.4 in) long and weighs 3500 g (7 lb 11 oz). Her temperature is 37.5°C (99.5°F), pulse is 138/min, respirations are 50/min, and blood pressure is 70/55 mm Hg. Physical examination shows peripheral cyanosis that improves after administration of oxygen via endotracheal intubation. Breath sounds are decreased on the left. Cardiac examination shows normal heart sounds without murmurs. Which of the following complications of the described pathology is most likely to be life threatening to this newborn?

A 5-year-old boy is brought to the emergency department after ingesting 10 oz of a household cleaning solvent. He is treated for acute hepatic and renal failure for 1 week and then discharged. During the next month, regeneration of this boy’s mature hepatocytes and renal tubular epithelial cells will be accomplished mostly by which of the following mechanisms?

A cohort study assessing risk factors for acquisition of infection with a newly identified agent is performed. Only newly diagnosed subjects are eligible, and controls are selected on the basis of age. The results of this study are shown:

Which of the following is the relative risk for the exposure variable?

A 67-year-old woman comes to the physician for a health maintenance examination. Her brother and mother have a history of colon cancer. The physician recommends colonoscopy, but the patient says that she would prefer only for her stool to be tested for blood. The physician explains that testing the stool for occult blood is not appropriate in this case. The physician is most likely concerned about which of the following regarding this test?

A 48-year-old woman comes to the office because of a 4-month history of headaches, itchy skin, difficulty swallowing, heartburn, chest tightness, pain in her arms and legs, and a burning sensation with urination. She has a history of similar symptoms since the age of 14 years, but previous examinations showed no abnormalities. Her vital signs are within normal limits. Physical examination and laboratory studies today show no abnormalities. Which of the following is the most likely diagnosis?

A 5-year-old girl with premature sexual development is diagnosed with precocious puberty. Pelvic examination shows a mass consistent with an ovarian tumor. Laboratory studies show decreased serum concentrations of gonadotropins and a marked increase in circulating estrogens. The ovarian tumor is most likely derived from which of the following cell types?

A 5-year-old girl is brought to the physician because of listlessness, fatigue, and dull pain in the right upper quadrant of the abdomen. Her height and weight are below the 25th percentile. Laboratory findings indicate that the content of her (3-globin chain is 15% to 20% of normal. Sequencing of the (3-globin gene shows a point mutation in a sequence 3′ to the coding region in which AATAAA is converted to AACAAA. Consequently, the amount of mRNA for (β-globin is decreased to 10% of normal. Which of the following functions in mRNA synthesis and processing is most likely encoded by the sequence AATAAA?

The graph shows changes in serum estradiol concentration during a normal menstrual cycle. Which of the following ovarian cells is primarily responsible for the aromatization of androstenedione to estradiol at the time indicated by the arrow?

A 20-year-old woman comes to the emergency department 30 minutes after slipping on ice and extending her hand to break her fall. Palpation of the anatomic snuff-box produces pain. A wrist x-ray is most likely to show a fracture of which of the following carpal bones?

An investigator is studying the effects of triiodothyronine (T3) and thyroxine (T4) in hepatocytes in an experimental animal model. Which of the following best describes the action of these thyroid hormones on this target tissue?

A 36-year-old woman with type 2 diabetes mellitus comes to the physician for a follow-up examination. Current medications include a sulfonylurea. She is 173 cm (5 ft 8 in) tall and weighs 95 kg (210 lb); BMI is 32 kg/m2. Physical examination shows acanthosis nigricans. Treatment with metformin is most likely to produce which of the following effects in this patient?

A 14-year-old girl is brought to the physician by her parents because of a 1-month history of a rash that appears with sun exposure. Her parents tell the physician that she has been eating little food. Physical examination shows a pruritic rash on the exposed areas of the body. Her serum tryptophan concentration is decreased. Urine studies show increased excretion of amino acids, predominantly alanine, isoleucine, leucine, phenylalanine, tryptophan, and valine. Production of which of the following vitamins is most likely impaired in this patient?

The synthesis of the enzymes necessary for the replication of the genome occurs during which of the following phases of the cell cycle?

A 76-year-old man undergoes laparotomy for resection of an abdominal aortic aneurysm. During the procedure, an incidental finding of acquired colonic diverticula is made. The diverticula in this patient are most likely present in which of the following?

A 17-year-old boy is brought to the physician by his mother because she is concerned that his puberty is delayed. The mother states, “He is so short. His father is 6 feet 5 inches tall. I don’t understand why he has not had his growth spurt.” When the mother leaves the room, the patient states, “I’m fine. I don’t know what’s the matter with her. She wants me to be tall like my dad.” The patient is 175 cm (5 ft 9 in) tall and weighs 70 kg (155 lb); BMI is 23 kg/m2. Sexual development is Tanner stage 4. In addition to reassuring the mother that her son is fine, which of the following is the most appropriate initial statement by the physician to the mother?

Which of the following types of sensory information is compromised by lesions of the structure at site X in the photograph shown?

A 25-year-old woman comes to the physician after her blood pressure was found to be 180/105 mm Hg at a health fair. She takes no medications. There is no family history of hypertension. Her last menstrual period was 1 week ago. Her blood pressure today is 180/110 mm Hg. Bilateral abdominal bruits are heard. Treatment with an angiotensin¬converting enzyme (ACE) inhibitor will most likely have which of the following acute effects on this patient’s renal function?

A previously healthy 21-year-old woman comes to the office because of a 2-month history of shortness of breath and fatigue. Her most recent menstrual period was 3 months ago. Menses previously had occurred at regular 28-day intervals. She tells the physician that she thinks she may be pregnant. She takes no medications and has not seen a physician for several years. She appears healthy. She is 160 cm (5 ft 3 in) tall and weighs 54 kg (120 lb); BMI is 21 kg/m2. Vital signs are within normal limits. The lungs are clear. Cardiac examination shows a normal S1, a widely split S2 that does not change with respiration, and a grade 3/6 holosystolic murmur that is loudest at the lower left sternal border and radiates to the upper left sternal border. ECG is shown. The most likely cause of these findings is dysfunction of which of the following structures?

Lesch-Nyhan syndrome, an X-linked recessive disease, is seen in approximately 1/100,000 males. Which of the following is the expected prevalence of heterozygous females?

A 25-year-old man is brought to the emergency department because of severe abdominal pain, nausea, and vomiting for 1 hour. The pain originates in the left flank and radiates to his groin. His pulse is 100/min, respirations are 18/min, and blood pressure is 150/100 mm Hg. Physical examination shows tenderness of the left flank and the left lower quadrant of the abdomen. Bowel sounds are mildly hypoactive. Test of the stool for occult blood is negative. Which of the following best explains these findings?

A 53-year-old man has had progressive difficulty swallowing for the past 3 months. He has a 10-year history of heartburn with esophageal regurgitation of gastric contents. Tissue obtained on biopsy of the lower third of the esophagus is shown. Which of the following best describes the nature of this lesion?

A 55-year-old man comes to the physician because of a 2-month history of increasing difficulty swallowing and regurgitation of undigested food. He also has noticed unusual rumbling sounds in his voice that he feels originate in his neck. Physical examination shows halitosis. A videofluoroscopic swallowing study shows a 4-cm, posterior midline pouch protruding between the thyropharyngeus and cricopharyngeus portions of the inferior pharyngeal constrictor muscle. These muscles are most likely innervated by which of the following nerves?

During a period of 36 hours, an 80-year-old woman has increasingly severe abdominal pain followed by fever, chills, tachycardia, hypotension, and, finally, shock. Blood cultures grow Escherichia coli. Her condition worsens and, despite supportive therapy and antibiotics, she dies 4 days after the onset of the illness. Which of the following is the most likely cause of the initial hypotension?

The diagram shows the major factors that determine blood pressure. Which of the following labeled factors is affected most by an α1 adrenergic antagonist?

Aminoglycoside antibiotics are used for their synergistic action against bacteria, in combination with other agents. These antibiotics demonstrate in vitro synergy for several bacterial species when combined with which of the following classes of antibiotics?

A 35-year-old man is admitted to the hospital because of a 5-day history of fever and dyspnea. He underwent a bone marrow transplantation 6 months ago; the procedure was complicated by severe graft-versus-host disease. His temperature is 38°C (100.4°F), and respirations are 30/min. Scattered crackles are heard on auscultation of the chest. A chest x-ray shows patchy infiltrates. A transbronchial biopsy specimen shows findings consistent with cytomegalovirus infection. Intravenous administration of ganciclovir is begun. This drug interferes with the function of which of the following enzymes?

An 8-year-old boy continues to bleed excessively after tooth extraction. Prothrombin time, bleeding time, and platelet count are within the reference range. Partial thromboplastin time is prolonged but corrects after addition to the assay chamber of plasma from a patient with hemophilia A. Which of the following is the most likely diagnosis?

A 25-year-old man comes to the physician because of a 3-day history of pain and swelling of his right leg. He has no history of major medical illness or recent trauma. Examination of the right lower extremity shows edema and tenderness. Duplex ultrasonography of the right lower extremity shows a thrombus extending into the superficial femoral vein. Further studies show protein C deficiency. Inactivation of which of the following coagulation factors is most likely as a result of this deficiency in this patient?

A 16-year-old boy with moderate intellectual disability is brought to the physician for a routine examination. There is a family history of mild and moderate intellectual disability in his mother and brother, respectively. Physical examination shows a long face, prominent ears, and moderately enlarged testicles. Which of the following best describes the genetic mechanism of this patient’s disorder?

Which of the following is most directly responsible for concentrating testosterone in the lumen of the seminiferous tubules?

A 23-year-old man in the emergency department has apnea and pinpoint pupils. Needle tracks are present on his arms. Activation of which of the following opioid receptors in the central nervous system is most likely to be responsible for the apnea?

A 16-year-old boy is brought to the physician because of a 3-month history of shortness of breath while playing sports. He has no shortness of breath at rest. He says, “Whenever I run around I cough, so I don’t want to be on the basketball team anymore.” He takes no medications and has no known allergies. There is a family history of hypertension and asthma. He is 165 cm (5 ft 5 in) tall and weighs 68 kg (150 lb); BMI is 25 kg/m2. His respirations are 12/min, and blood pressure is 115/75 mm Hg. Cardiac examination shows no abnormalities except for a midsystolic click at the apex. The lungs are clear to auscultation of the chest. Which of the following best explains this patient’s symptoms?

A 41-year-old woman is evaluated because of increasingly severe headaches for 6 weeks. Her blood pressure is 160/100 mm Hg while standing and supine. A bruit is heard over the left costovertebral angle. Urinalysis shows no abnormalities. An angiogram of the left renal artery shows alternating areas of stenosis and aneurysmal dilatation (“string of beads” sign). Which of the following conditions of the renal artery is the most likely diagnosis?

A 22-year-old woman is brought to the emergency department in a semicomatose condition after collapsing near the end of running a marathon. Her prerace weight was 47 kg (103 lb). She now weighs 50 kg (110 lb). Her pulse is 115/min, respirations are 15/min, and blood pressure is 90/50 mm Hg. Physical examination shows cool, dry skin. She is responsive to painful stimuli. Laboratory studies show:

This patient’s condition is most likely due to which of the following?

Moving the forearm against resistance from palm-down to palm-up (supination) position requires the use of which of the following muscles?

A 75-year-old woman comes to the physician because of a 3-month history of an enlarging lesion on her face. Physical examination shows a 1.5-cm, brown-black, mottled, scaly lesion with irregular borders. Microscopic examination of a biopsy specimen of the lesion shows atypical melanocytes spread along the basilar layer of the epidermis. Which of the following is the most likely cause of these findings?

Failure of normal differentiation of the endoderm in the embryonic lung bud is most likely to affect the development of which of the following?

A 22-year-old woman comes to the physician because of a 6-month history of difficulty swallowing. She says that she feels like she is choking on both solids and liquids. She has no pain with swallowing. She has had a 4.5-kg (10- lb) weight loss during this time. There is no history of fever or chills. She is not sexually active. She does not smoke cigarettes or use illicit drugs. She is 170 cm (5 ft 7 in) tall and weighs 59 kg (130 lb); BMI is 20 kg/m2. Her vital signs are within normal limits. Physical examination shows no abnormalities. An x-ray of the esophagus is shown. Which of the following is the most likely explanation for this patient’s symptoms?

A 67-year-old man with poorly controlled unstable angina is about to undergo coronary angiography with stent placement. Prior to the procedure, treatment is initiated with aspirin and a drug that inhibits platelet interaction with fibrinogen. This drug is most likely which of the following?

Based on the graph of p-aminohippurate (PAH) concentration versus PAH secretion, which of the following is lower at point Y than at point X?

The specimen shown is from a 65-year-old man. Which of the following is the most likely diagnosis?

A 23-year-old woman has had the lesions shown in her mouth for 3 days. She has had frequent similar episodes over the past 15 years. The lesions are exacerbated by spicy, salty, and acidic food and drinks. They last approximately 1 week and resolve spontaneously. Visits to the dentist seem to trigger the development of the sores. Which of the following is the most likely diagnosis?

A 76-year-old man comes to the physician for a follow-up examination. He has hypertension treated with a [3-adrenergic antagonist. He lives on a farm in central California and says he has always distilled his own liquor. Before retiring 10 years ago, he worked in a hat factory and subsequently in a textile factory. He has smoked 2 packs of cigarettes daily for the past 55 years. He tells the physician that he has had several episodes of painful swelling of his right great toe. Physical examination shows several lesions consistent with gouty tophi over the elbows bilaterally. Laboratory studies show:

The most likely cause of this patient’s condition is which of the following?

A 50-year-old man comes to the emergency department because of a 2-week history of progressive shortness of breath. His pulse is 90/min, respirations are 26/min, and blood pressure is 120/80 mm Hg. Physical examination shows no other abnormalities. Laboratory studies show:

Which of the following is the most likely explanation for these findings?

An 18-hour-old male newborn is 61 cm (24 in) long and weighs 5443 g (12 lb). His mother has type 1 diabetes mellitus. His serum glucose concentration is 20 mg/dL. Which of the following fetal conditions immediately prior to birth most likely precipitated the newborn’s postnatal hypoglycemia?

A 45-year-old man who is able to bicycle 4 5 minutes a day has switched to a rowing machine. After 5 minutes on the machine, he experiences vertigo, lightheadedness, and fatigue of the left upper extremity. Within a few minutes of stopping the rowing exercise, all symptoms resolve. Which of the following findings is most likely on physical examination?

A 65-year-old woman comes to the physician because of a 3-month history of headache, weakness of her arms, and left flank pain; she also has had a 14-kg (31-lb) weight loss during this period. Physical examination shows weakness of the proximal upper and lower extremity muscles. There is augmentation of strength with repetitive testing of the deltoid muscles. An MRI of the brain shows a single well-demarcated mass surrounded by edema in the right frontal lobe. A stereotactic biopsy specimen of the lesion shows a malignant, small blue cell neoplasm that expresses cytokeratin, chromogranin, and synaptophysin. Which of the following is the most likely diagnosis?

A healthy 22-year-old woman undergoes testing to determine whether she is a suitable kidney donor for her 25-year-old brother with end-stage renal disease caused by type 1 diabetes mellitus. Immunologic studies show that she is human leukocyte antigen (HLA)-DR3/DR6 positive, and her brother is HLA-DR3/DR4 positive. To determine the extent of alloreactivity, a mixed lymphocyte reaction is done using irradiated stimulator cells isolated from the donor and responder cells isolated from the recipient. The T lymphocytes that proliferate in these cultures will most likely react with which of the following HLA types?

A physician wishes to determine the proportion of newborns delivered at a local hospital who had a diagnosis of congenital heart disease within the past year. Which of the following statistical measurements best describes these data?