A 57-year-old man undergoes coronary artery bypass grafting. The stress of the operation results in increased secretion of cortisol from the adrenal gland postoperatively. Which of the following cells is the most likely origin of the stimulus of this cortisol secretion?

A 32-year-old woman comes to the physician because of a 1 -year history of palpitations and intermittent headaches. She has a 10-year history of poorly controlled hypertension treated with hydrochlorothiazide and metoprolol. Her blood pressure is 180/105 mm Hg. Physical examination shows no other abnormalities. CT scans of the abdomen are shown; the arrows indicate an abnormality. An abnormality of which of the following structures is the most likely cause of these findings?

A 30-year-old woman comes to the physician for evaluation of recurrent postprandial retrosternal burning occurring three times weekly during the past 6 months. The symptoms occur only during the day and are noticeably more severe after large meals, especially if she eats fried foods. Initially, the symptoms responded well to over-the-counter antacids, but in the past 2 months, the antacids have failed to control her symptoms. She had similar symptoms 5 years ago during pregnancy that also responded well to antacids and then resolved after the delivery of her child. She has had no difficulty swallowing, weight loss, or gastrointestinal bleeding. She is sleeping well. She takes no other medications and does not smoke cigarettes or drink alcohol. Physical examination shows no abnormalities. Which of the following is the most likely cause of her condition?

A 6-day-old female newborn is brought to the physician by her parents because of a 3-day history of difficulty feeding, vomiting, and progressive lethargy. Her parents have noticed that her urine has a burnt-sugar odor. Physical examination shows lethargy and hypotonia. Deficiency of which of the following is the most likely cause of these findings in this patient?

A 24-year-old woman, gravida 1, para 1, comes to the physician because of nervousness and tremor since delivering a healthy female newborn 6 weeks ago. She also has had a 5-kg (11-lb) weight loss during this period. She has a history of panic disorder and carpal tunnel syndrome. Her temperature is 37°C (98.6°F), pulse is 100/min, and blood pressure is 140/80 mm Hg. Physical examination shows a firm thyroid gland that is twice the normal size. Serum studies show a free thyroxine (FT4) concentration of 2.4 ng/dL (N=0.8-2.4), thyroid-stimulating hormone concentration of less than 0.03 pU/mL, and 24-hour thyroid radioactive iodine uptake of 1% (N=8-25%). Which of the following is the most likely explanation for this patient’s symptoms?

A healthy 20-year-old man comes to the physician with his wife for genetic counseling prior to conception. His sister died of cystinosis, an autosomal recessive disorder affecting cystine transport across lysosomal membranes. The incidence of this disorder in the general population is approximately 1/40,000. The wife’s history is noncontributory. The wife’s risk for being a carrier of this disorder is closest to which of the following?

A 25-year-old man is admitted to the hospital after he sustained second-degree burns over 70% of his body while fighting a fire. Administration of fluid and antibiotics is started. Two days later, he develops dyspnea, tachypnea, and hypoxemia. Diffuse crackles are heard on auscultation of the chest. A chest x-ray shows fluffy alveolar infiltrates. Despite appropriate intervention, he dies. Autopsy shows diffusely firm and hyperemic lungs. Microscopic examination of the lung tissue shows widening of the alveolar septa and eosinophilic hyaline membranes lining the alveolar spaces. Which of the following pathologic mechanisms is the most likely cause of the pulmonary disorder in this patient?

A 39-year-old woman, gravida 5, para 5, with type 2 diabetes mellitus and a history of gallstones comes to the physician because of a 4-day history of nausea, vomiting, and midabdominal pain radiating to her back. She is 165 cm (5 ft 5 in) tall and weighs 82 kg (180 lb); BMI is 30 kg/m2. Physical examination shows bluish discoloration of both flanks and epigastric tenderness. Which of the following is the most likely diagnosis?

A 2-month-old male infant has jaundice and pale stools caused by congenital biliary atresia. Deficiency of which of the following is most likely in this patient?

A 45-year-old man with type 1 diabetes mellitus comes to the physician because of a 6-week history of swelling of his face, legs, and left testicle. He says that his blood pressure has been higher than normal (>170/100 mm Hg) during the past 2 months. At his last visit 1 year ago, his serum creatinine concentration was 2.1 mg/dL. He is 180 cm (5 ft 11 in) tall and weighs 100 kg (220 lb); BMI is 31 kg/m2. His blood pressure is 172/93 mm Hg. Physical examination shows marked edema around the eyes and of the lower extremities to the level of the thighs. The left side of the scrotum is 114 times the size of the right side and enlarges further when the patient bears down. Palpation shows a lumpy mass just superior to the normal-sized left testis. Which of the following is the most likely cause of these scrotal findings?

An investigator is studying the effects of several different drugs on human brain activity. During the study, positron emission tomography is used to measure real-time brain activity in human participants after administration of various drugs with abuse potential. Results show a common pattern of neurologic effects for drugs such as cocaine, amphetamines, opioids, sedative-hypnotics, alcohol, and nicotine. Activation of which of the following neurotransmitter pathways best explains the rewarding or positive reinforcing effects of using these drugs?

An 80-year-old woman undergoes a brain biopsy of a cerebral mass. Immunofluorescence studies of a biopsy specimen show that the tumor cells contain intermediate filaments of the cytokeratin type. This patient’s cancer cells most likely arose from which of the following cell types?

A 44-year-old woman with a history of breast cancer comes to the physician for an initial examination. She says, “I’m concerned about my future. Can you give me any advice?” She recently moved to the city because her husband changed jobs. She underwent a mastectomy for inflammatory breast cancer, and she completed a course of chemotherapy 2 months ago. Physical examination shows an absent left breast and a well-healed scar on the left side of the chest. There are no palpable lymph nodes. Which of the following initial responses by the physician is most appropriate?

A 41-year-old woman comes to the physician for a follow-up examination 6 weeks after the diagnosis of hypertension was made. Her blood pressure today is 162/104 mm Hg. A right abdominal bruit is heard. Physical examination shows no other abnormalities. Serum studies show:

On renal arteriography, sampling shows a left renal vein renin activity of 5 pU/mL (N=5-97) and right renal vein renin activity of 176 pU/mL (N=5-97). The systemic hypertension in this patient is directly mediated by a vasoconstrictor that emerges from which of the following?

A 2-year-old boy has had recurrent sinopulmonary infections since 8 months of age. Flow cytometric analysis of his peripheral blood lymphoid cells with anti-CD3 and anti-IgM (with blockade of Fc receptor-mediated binding of IgG) is shown. Which of the following is the most likely diagnosis?

A 17-year-old boy has septic shock that is unresponsive to intravenous ADH (vasopressin) therapy. This treatment is discontinued, and high-dose dopamine therapy is initiated. Stimulation of which of the following receptors is most likely to be of benefit to this patient?

An investigator is conducting a study of natural killer cells and their role in destroying malignant tumors in experimental animals. This study is most likely to show that natural killer cells are particularly effective in destroying malignant tumors with which of the following characteristics?

A 5-year-old boy is stung on his foot by a bee. Within 30 minutes the local area is edematous. The extravascular accumulation of fluid is most directly related to which of the following?

A previously healthy 55-year-old man comes to the physician 2 months after he noticed a lump in his neck. His vital signs are within normal limits. Physical examination shows a 2.5-cm, firm, cervical lymph node on the lower right. A photomicrograph of a biopsy specimen of the node stained with hematoxylin and eosin is shown. Flow cytometry of lymphoid cells from the node yields the following phenotype:

Which of the following is the most likely diagnosis?

An 18-year-old woman comes to the physician because of irregular menstrual periods since menarche at the age of 13 years. Menses occur at 60- to 120-day intervals. She takes no medications. She does not smoke cigarettes, drink alcohol, or use illicit drugs. She is sexually active with one partner, and they use condoms consistently. She is 157 cm (5 ft 2 in) tall and weighs 75 kg (165 lb); BMI is 30 kg/m2. Physical examination shows facial hirsutism. Pelvic examination shows no cervical motion tenderness or masses. Which of the following is the most likely diagnosis?

A 58-year-old woman comes to the physician because of a 6-month history of shortness of breath and chronic nonproductive cough. She has a 2-year history of difficulty swallowing, joint stiffness, and diffuse tightening of the skin of the face, neck, shoulders, arms, and fingers. She has had significant sensitivity to cold weather for 20 years, and she says that her hands turn white when they are exposed to the cold. Current medications include a histamine (H2) blocking agent for a long-standing history of esophageal reflux. Biopsy specimens of the skin from 1 year ago are shown in the photomicrographs. Examination of the hands shows cutaneous ulceration, clawlike flexion deformity, and decreased joint mobility. An autoimmune disorder is suspected. Which of the following pulmonary disorders is most likely in this patient?

A 20-year-old woman comes to the emergency department because of pain in the right lower quadrant of the abdomen and vaginal bleeding for 2 days. Her last menstrual period was 8 weeks ago. Which of the following historic findings further increases the likelihood of an ectopic pregnancy in this patient?

A 65-year-old man with hypertension volunteers to participate in a clinical trial of a newly developed loop diuretic. As part of the study, his acid-base/volume status is monitored. After 3 days of treatment, which of the following sets of findings is most likely in this patient?

A 40-year-old man with alcoholism is admitted to the hospital because of a 2-day history of confusion. Serum studies show a sodium concentration of 99 mEq/L. He is treated with 0.9% saline. Four days later, he develops slurred speech. Physical examination shows mild-to-moderate muscle weakness of all extremities and dysarthria. Sensation is intact. Babinski sign is present bilaterally. These findings are most likely caused by a lesion in which of the following locations?

A 53-year-old woman is diagnosed with gastric carcinoma and receives a chemotherapeutic regimen including doxorubicin. Six months later, she develops cardiomyopathy. Dose- limiting toxicity of doxorubicin, resulting in cardiomyopathy, is produced by which of the following mechanisms?

A 65-year-old woman with type 1 diabetes mellitus suddenly develops continuous involuntary ballistic movements of her right arm and leg. She is alert, and neurologic examination shows no other abnormalities. The most likely cause of this patient’s movement disorder is infarction involving which of the following areas of the brain on the contralateral side?

The kinetics of a regulatory enzyme are shown in the figure as curve A. The kinetics in the presence of an allosteric modifier are represented by curve B. Which of the following best describes the effect of the modifier on the activity of this enzyme?

A randomized, double-blind, clinical trial of a new medication for acute stroke was just completed. The results are summarized as follows:

Compared with the placebo group, which of the following sets best summarizes the relative risks in the active drug group?

Patients with a history of deep venous thrombosis are recruited as part of a research study on chronic venous insufficiency. The patients are evaluated at the beginning of the study and reevaluated 2 years later. At the second visit, they are asked if they wore compression stockings since the study began. The prevalence of venous insufficiency in those who wore the stockings is compared to those who did not. Which of the following best describes this type of study?

A mildly obese 42-year-old woman comes to the physician 2 days after the sudden onset of chest pain and intermittent cough while she was doing laundry. Medications include oral contraceptives. She has smoked 114 packs of cigarettes daily for 24 years. She appears somewhat anxious. An x-ray of the chest shows normal findings, and an ECG shows sinus tachycardia. Ventilation-perfusion lung scans show a defect in the anterior inferior segment of the right upper lobe. Collateral arterial flow is provided to this area by which of the following arteries?

A 35-year-old woman who is being examined because of infertility receives an injection of contrast material into her cervix to visualize the reproductive tract before undergoing radiographic tests. On the hysterosalpingogram shown, the contrast material (as indicated by the arrows) is also seen in the peritoneal cavity. Which of the following best explains this finding?

A 67-year-old woman is brought to the emergency department 30 minutes after she fainted while grocery shopping. On arrival, she is conscious. Her blood pressure is 115/85 mm Hg. Physical examination shows carotid pulses with small amplitude and a delayed upstroke. A grade 4/6, crescendo systolic murmur that is heard throughout the precordium is loudest at the upper right sternal border and radiates to the carotid arteries. There is a loud S4. A chest x-ray shows no cardiomegaly. This patient most likely has which of the following cardiac valve abnormalities?

A 45-year-old man develops multiple punctate, erythematous, nonblanching, 1-mm lesions on the upper and lower extremities and the belt line. A defect in which of the following is the most likely cause of the patient’s symptoms?

A 16-year-old girl comes to the physician because of worsening acne over her forehead for the past month. She began a vegetarian diet 6 months ago; she also has been craving and eating large amounts of chocolate. She currently works outdoors as a flag person for a local road construction company and is required to wear a helmet. Her brother received a chinchilla for a pet 2 months ago. Physical examination shows erythematous papules and pustules on the forehead. Which of the following is the most likely cause of the exacerbation of this patient’s condition?

A 65-year-old woman with rheumatoid arthritis comes to the physician for a follow-up examination. In addition to methotrexate therapy, a course of rituximab is initiated. Approximately 45 minutes after the first infusion of rituximab, the patient’s temperature is 38.5°C (101.3° F), and she develops diffuse muscle pain. She does not have any difficulty breathing or swallowing, and there are no signs of urticaria or angioedema. Which of the following is the most likely cause of this patient’s symptoms?

A 19-year-old woman comes to the physician because of a 2-day history of pain in her left index finger. She injured it during a softball game when catching a ball. Physical examination shows erythema of the left index finger. The patient is unable to flex the distal phalanx when the proximal interphalangeal joint and metacarpophalangeal joints are restrained. Laboratory studies and x-rays of the left hand show no abnormalities. Which of the following structures is most likely injured in this patient?

Cytogenetic analysis of 20 metaphases from the peripheral lymphocytes of a 15-year-old girl with gonadal dysgenesis (Turner syndrome) shows the karyotype 45,X in 11 metaphases and 46,XX in 9 metaphases. Which of the following is the most likely explanation for this result?

A full-term newborn has respiratory distress. Imaging studies show herniation of abdominal contents into the left pleural cavity. Maldevelopment of which of the following structures is most likely to have caused the defect of the diaphragm?

A 44-year-old man with a 1-year history of angina pectoris comes to the emergency department because of increasingly severe chest pain during the past 2 days. He has had five previous similar episodes, which required treatment with increasing doses of nitroglycerin to resolve. His temperature is 37°C (98.6°F), pulse is 105/min, respirations are 16/min, and blood pressure is 150/90 mm Hg. Cardiac examination shows an S4. An ECG shows ST-segment depression in the precordial leads. In addition to aspirin, heparin, and nitroglycerin, he is given a dose of a monoclonal antibody against the platelet llb/llla receptor. This antibody will most likely prevent binding of which of the following substances to platelets?

An 18-month-old girl is brought to the physician for a follow-up examination because of macrosomia. She was 53 cm (21 in) in length and weighed 4200 g (9 lb 4 oz) at birth. She is now at the 95th percentile for length and weight. Physical examination shows a nevus flammeus on the forehead, a large tongue, and an abdominal mass. Abdominal ultrasonography shows a tumor in the left kidney. A biopsy specimen of the resected mass shows nephroblastoma (Wilms tumor). Genetic testing of the patient shows abnormal methylation at KCNQ10T1 (DMR2) of maternal 11 p15. Which of the following genetic mechanisms is the most likely cause of these findings?

A 43-year-old woman comes to the physician for a routine health maintenance examination. The physician is 30 minutes late for the appointment because of an emergency, and when he enters the examining room, the patient checks her watch. Which of the following initial statements by the physician is most appropriate?

A previously healthy 73-year-old man with benign prostatic hyperplasia comes to the physician because of a 2-day history of pain with urination and a 12-hour history of fever and chills. His temperature is 38.3°C (101°F). Physical examination shows moderate tenderness of the left flank. Urinalysis shows 50 to 100 WBC/hpf. Culture of urine grows 100,000 colonies/mL of a gram-positive organism. Which of the following is the most likely causal organism?

Fatty acids are infused into the proximal small intestine of an experimental animal. Which of the following is the most likely change in peptide secretion in this animal?

In order to investigate possible treatment options for acute respiratory distress syndrome (ARDS), experimental animals are anesthetized and subjected to smoke inhalation (cotton smoke) according to a well-established experimental protocol. The experimental animals are then given compounds designed to upregulate specific mediators involved in the inflammatory cascade. Upregulation of which of the following mediators would most likely prevent or ameliorate the lung injury induced in this experimental model of ARDS?

A 72-year-old woman comes to the physician because of diffuse muscle pain and weakness for 6 months. The muscle pain is exacerbated by activity. Physical examination shows proximal muscle weakness and tenderness over the surface of both shins. The dot on the nomogram shown indicates the relationship between her serum calcium and parathyroid hormone concentrations. Which of the following conditions is the most likely cause of this patient’s symptoms?

A healthy 8-year-old boy is brought to the physician by his parents because of a long history of disruptive behavior at school and poor academic performance. During class, he talks out of turn, wanders around the room, and pesters classmates. He is easily distracted and cannot keep his attention on a topic very long. His homework is sloppy and usually incomplete; he often explains that he leaves segments of assignments undone because he “just didn’t notice them.” He has had similar problems since kindergarten. He has normal developmental milestones. He is bright and cheerful and has a caring family. A drug with which of the following actions is most likely to be useful for this patient?

An otherwise healthy 15-year-old boy is brought to the physician 2 days after the onset of a headache. His vital signs are within normal limits. Physical examination shows mild tenderness over the right occipital area. An x-ray of the skull shows a 2-cm lytic lesion in the right occipital bone. A photomicrograph of a biopsy specimen of the lesion stained with hematoxylin and eosin is shown. Which of the following is the most likely diagnosis?

The diagram shows the major factors that determine blood pressure. Which of the following labeled factors is most responsible for the antihypertensive effect of a dihydropyridine calcium-channel blocking agent?

A 32-year-old woman comes to the physician because of a 1-week history of a progressive, itchy rash. The rash initially appeared as an oval patch on her abdomen and has since spread over her abdomen and back. She has not had fever, chills, or sweating. She has no history of major medical illness. She has been sexually active with two male partners during the past year, and she uses an oral contraceptive. Her vital signs are within normal limits. Physical examination shows the findings in the photograph. Which of the following is the most likely diagnosis?