A 1 -year-old girl is brought to the physician because of multiple bacterial infections since birth. She is at the 40th percentile for length and 40th percentile for weight. She has white hair, pale skin, blue irises, and prominent red pupils. A complete blood count shows neutropenia. A peripheral smear shows giant granules in the neutrophils. This patient’s disorder is most likely due to which of the following pathogenetic mechanisms?

A 33-year-old nulligravid woman comes to the physician with her 35-year-old husband because she has not been able to conceive for 18 months. Previous evaluation of the husband showed no abnormalities. Physical and pelvic examinations show no abnormalities. Examination of an endometrial biopsy specimen shows secretory glands and a decidualized stroma. Which of the following hormonal changes underlies the maturation of this patient’s endometrium?

A 7-year-old boy is brought to the physician because of a 3-day history of cramping abdominal pain, blood in his urine, and a rash on his arms, legs, and buttocks. He had pharyngitis 2 weeks ago. Physical examination shows a hemorrhagic rash involving the extensor surfaces of the upper and lower extremities and feet. There is generalized abdominal tenderness. Test of the stool for occult blood is positive. A renal biopsy specimen shows an increased mesangial matrix that stains positive for IgA on immunofluorescence. Which of the following is the most likely diagnosis?

A 4-year-old boy undergoes radiographic imaging studies of the urinary tract after having two bacterial urinary infections during the past year. His left kidney is found to be abnormally small and nonfunctional. The right kidney appears normal. He undergoes a left nephrectomy and ureterectomy. A photograph of the resected specimen is shown. Which of the following disorders most likely accounts for the pathologic changes in this kidney?

An 80-year-old woman is brought to the emergency department by police 30 minutes after she was found wandering in the street, confused and disoriented. She says that she has no medical conditions and takes no medications. During history taking, she becomes annoyed and agitated, saying, “Stop being so nosey! There’s nothing wrong with me! I feel fine and I just want to go home.” She appears frail but alert. Her vital signs are within normal limits. Physical examination shows mildly dry mucous membranes. There is no evidence of trauma. She is oriented to person but not to place or time. She is able to provide her home address. Which of the following is the most appropriate action by the physician?

A 24-year-old woman comes to the clinic because of facial flushing and diffuse pruritus. The symptoms began shortly after she ingested a new nutritional supplement from a health food store. Examination shows erythema of the face and upper portion of the neck. The remainder of the skin shows no gross abnormalities. There is no perioral or neck edema. Findings on lung examination are normal. Which of the following nutritional supplements is the most likely cause of her symptoms?

Tissue obtained on renal biopsy from a 45-year-old woman with proteinuria is shown. These findings are most consistent with which of the following?

A 58-year-old woman comes to the physician because of a 3-week history of shortness of breath after walking 2 blocks. She has been receiving doxorubicin as part of chemotherapy for breast cancer for 6 months. Her pulse is 110/min, and respirations are 32/min. Inspiratory crackles are heard over both lung fields. Physical examination shows 2+ pitting edema of the ankles. A chest x-ray shows cardiomegaly and interstitial edema. Cardiac studies show a decreased ejection fraction of the left ventricle. Which of the following is the most likely cause of the cardiac findings in this patient?

A 14-year-old boy is brought to the emergency department by his friend because of palpitations. His friend to have tachycardia and increased mean arterial pressure. Which of the following mechanisms is the most says the symptoms began shortly after he “snorted” cocaine. He is found likely cause of these adverse effects?

An investigator is studying the regulation of pulmonary lymphatic flow using an animal model. Catheters are implanted in the femoral vein, pulmonary artery, and main lymphatic vessel draining the lungs in anesthetized, intubated, mechanically ventilated animals. Drugs may be injected directly into the pulmonary artery catheter and inspired gas mixtures altered at the ventilator; timed collection of lymph from the catheters is used to calculate lymphatic flow. Which of the following interventions will most likely increase the flow of pulmonary lymph in these animals?

A pale 62-year-old man has had increasing fatigue and indigestion over the past few months and decreasing appetite over the past few weeks. He has moderate splenomegaly but no lymphadenopathy. Laboratory studies show:

The lymphocytes have cytoplasmic projections and positivity for acid phosphatase even in the presence of tartrate. Which of the following is the most likely diagnosis?

A 35-year-old man comes to the physician because of progressively painful erections during the past year. Examination of the penis shows abnormal curvature, shortening on erection, and a subcutaneous plaque on the dorsal surface. Which of the following is the most likely diagnosis?

A 73-year-old man comes to the physician because of a 4-month history of localized mid-back pain. He has hypertension and type 2 diabetes mellitus. He is in mild discomfort but is able to walk without problems. There is pain with percussion over the lower thoracic spine. Neurologic examination shows no focal findings. Serum studies show:

X-rays of the spine show vertebral cortical thickening of the end-plates, creating “picture frame” vertebrae. Technetium 99m scan shows increased areas of uptake in the skull, thoracic spine, lumbar spine, and right proximal femur. Which of the following best describes the primary underlying pathophysiologic mechanism of this condition?

A 72-year-old man with multiple myeloma agrees to participate in an investigational chemotherapy clinical trial. Prior to enrollment in the study, peripheral blood B and T lymphocytes are isolated and undergo Southern blot analysis of lymphoid cell-specific genes. Using a single B-lymphocyte J-region probe, analysis of the B-lymphocyte DNA shows a 1.5-kb band. Analysis of the T-lymphocyte DNA using the same J-region probe shows a 6-kb band. The 6-kb band most likely signifies which of the following?

A 6-month-old girl is brought to the emergency department by her parents because of vomiting for 6 hours. She has been feeding poorly for 1 day because of an upper respiratory tract infection. Her temperature is 37°C (98.6°F), pulse is 100/min, respirations are 18/min, and blood pressure is 88/58 mm Hg. Physical examination shows lethargy and a clear nasal discharge. Laboratory studies show:

This patient most likely has a deficiency of which of the following enzyme activities?

A 46-year-old man receives the diagnosis of squamous cell carcinoma of the esophagus. A barium swallow is shown. Esophagectomy at the region indicated by the arrows is most likely to involve ligation of arterial branches of which of the following vessels?

A 34-year-old woman comes to the burn unit where her 14-year-old son was admitted 2 weeks ago after he injured his hand while lighting firecrackers with his friends. In preparation for his discharge, the woman is taught to change the dressing and apply cream to the burn. She says that she feels revulsion when viewing the affected area and changing the dressing, but she tries to look cheerful for the sake of her son. Which of the following best describes this mother’s defense mechanism?

A 62-year-old woman has an abdominal aortic aneurysm repaired. Forty-eight hours after surgery, her right distal leg is dusky and cool, and there are dark purple-to-black necrotic lesions on several toes as shown. A biopsy of one of the lesions would most likely show occluded small arteries with needle-shaped clefts. Which of the following is the most likely cause of the lesions?

A 50-year-old man with chronic back pain has taken a variety of analgesics (including aspirin, acetaminophen, and ibuprofen) daily and in large doses for the past 25 years. He is found dead. A photograph of his kidneys at autopsy is shown. Prior to his death, which of the following changes in urine volume and urine osmolality would be expected after administration of ADH (vasopressin)?

The initial event in muscle contraction is the release of calcium ion from the sarcoplasmic reticulum. Which of the following is most likely responsible for buffering the concentration of calcium ion in the sarcoplasmic reticulum?

A 25-year-old woman comes to the physician because of a 3-month history of difficulty falling and remaining asleep. She says that she has been under stress and anxious during this period. Physical examination shows no abnormalities. Nocturnal polysomnography shows normal sleep architecture, including normal volumes and latencies of all non-REM and REM sleep stages. There is no evidence of sleep-disordered breathing or other sleep-fragmenting disorder. Compared with this patient’s non-REM stage 3 to 4 (deep) sleep, which of the following is most likely to be increased in her REM sleep?

A 57-year-old man with alcoholism has a distended abdomen with shifting dullness and a fluid wave. He has caput medusae, palmar erythema, and spider angiomata. Which of the following is the most likely additional finding?

A 14-year-old girl is brought to the physician because of a recent growth spurt of 15 cm (6 in) during the past year. She also has had increasing fatigue and palpitations during this period. Her father is 193 cm (6 ft 4 in). Her paternal aunt has a history of palpitations and severe myopia. The patient is at the 95th percentile for height and 50th percentile for weight. Physical examination shows a long, thin face. Ophthalmologic examination shows dislocated lenses. Cardiac examination shows a hyperdynamic precordium with early click and systolic murmur. Echocardiography shows an enlarged aortic root and mitral valve prolapse. Which of the following genetic mechanisms best explains the findings in this family?

A 50-year-old man has had progressive dyspnea on exertion over the past 6 months. He now has dyspnea at rest. He has had a persistent dry cough since having an upper respiratory tract bacterial infection 1 year ago. Examination of lung tissue obtained on biopsy shows chronic inflammation and fibrous thickening of the alveolar septa. Which of the following is the most likely diagnosis?

An investigator is studying the mechanisms of nerve regeneration after injury. A repetition injury is induced in a peripheral nerve in an experimental animal. It is found that sensory and motor axons are lost by Wallerian degeneration beyond the site of the injury. Further study is most likely to show which of the following cell structures acting as a path-finding guide for the regeneration of the damaged axons?

An investigator is studying the thyroid hormone receptor. It is found that the receptor binds chromatin in both the presence and absence of triiodothyronine (T3). Results show that this binding inhibits transcription in the absence of the hormone and activates transcription in the presence of the hormone. It is theorized that binding of the hormone causes an allosteric conformational change that decreases affinity for complex 1 and increases affinity for complex 2. Complex 1 and complex 2 most likely contain which of the following enzyme activities?

During an experiment, Drug X is administered to treat trematode and cestode infestations. Results show that Drug X increases the permeability of the cell membranes to calcium, causing paralysis, dislodgement, and death of the parasite. Drug X most closely resembles which of the following?

A 32-year-old woman undergoes a laparoscopic cholecystectomy after ultrasonography showed a thickened gallbladder wall and gallstones. The surgeon will be unable to inspect directly which of the following organs during this procedure?

A 78-year-old man who is a Vietnam War veteran comes to the physician because of a 3-month history of low back pain that has become increasingly severe during the past 2 weeks, and has caused difficulty walking because of pain radiating down his left leg. He has a 3-week history of night sweats and an intermittent low-grade fever. He also has had a 9-kg (20-lb) weight loss during the past 3 months. He appears ill. He is 173 cm (5 ft 8 in) tall and weighs 55 kg (121 lb); BMI is 18 kg/m2. His temperature is 38.1°C (100.6°F), and pulse is 85/min. Physical examination shows pallor, right convex lumbar scoliosis, and tenderness over the L2-3 area. He has difficulty climbing onto the examination table. Coronal and axial views of a CT scan of the abdomen and pelvis with contrast are shown. Which of the following active motions of the left hip is likely to be the most painful for this patient?

Investigators are evaluating oxygen consumption by different segments of the renal tubules in experimental animals. Arterial oxygen saturation is decreased in blood delivered to isolated perfused pig kidneys. Results show that as oxygen delivery declines, urine output decreases. A biopsy specimen of the ischemic model is obtained. Tubular cell death is most likely to be observed in which of the following areas?

A 50-year-old man is admitted to the hospital after being diagnosed with a pulmonary embolus. Treatment is started with intravenous heparin. Twenty-four hours later, warfarin is added. On day 2, his partial thromboplastin time is 52 seconds (control 26 sec), and prothrombin time is 12 seconds (control 12.1 sec; INR=1). Which of the following is the best explanation for the normal prothrombin time and INR measurements in this patient?

A 5-year-old boy is brought to the physician by his mother because of progressive clumsiness and fatigue during the past 6 months. He says that his legs are tired. He was delivered at term after an uncomplicated pregnancy. He has met all developmental milestones, although there was some delay compared with other children his age. He is alert.
He has difficulty rising from the chair; he uses his arms to push himself into a standing position. He is unable to jump with both feet together. Physical examination shows hypertrophy of the calf muscles. This patient most likely has weak hip adduction as a result of dysfunction of the muscle inserting onto the femur from which of the following locations?

A 1-year-old girl has recurrent and chronic suppurative infections caused by staphylococci and some gram-negative rods. She recovers normally from viral infections. Examination of serum shows normal concentrations of complement components and immunoglobulins. Studies of leukocyte function are most likely to show defects in which of the following mechanisms?

A25-year-old woman who is at 12 weeks’ gestation asks for prenatal counseling. Her husband has a clinically variable autosomal dominant disorder with 100% penetrance that is evident within the first year of life and for which linkage analysis is available. They have two unaffected daughters 3 and 5 years old. A pedigree is shown. A single polymorphic marker has a recombination fraction of 0.1 (10%) and is informative. Alleles 1 and 2 for this marker are indicated in the pedigree. Which of the following is the risk that this fetus will have this disorder?

A 70-year-old man dies of coronary artery disease. He had a cerebral infarction 8 years ago. A photograph of a specimen of the brain stem is shown. Which of the following neurologic deficits was most likely present in this patient after his cerebral infarction?

A 2-week-old boy is brought to the physician because of persistent cyanosis. Hemoglobin concentration and erythrocyte morphology are normal. An x-ray of the chest and an echocardiogram disclose no abnormalities. Which of the following is the most likely cause of the cyanosis?

A 4-year-old girl is brought to the physician by her parents 2 days after the mother noticed streaks of blood on the child’s well-formed stools. Her father has pigmented macules on his lips. A paternal aunt had breast cancer. Physical examination shows several 2- to 3-mm pigmented macules on the lips and buccal mucosa. Rectal examination shows no abnormalities. Test of the stool for occult blood is positive. Colonoscopy is done and three polyps are removed, the largest measuring 1x1x1 cm. This patient’s polyps are most likely which of the following types?

A study is conducted to assess the effectiveness of injections of lidocaine into “trigger points” of pain symptoms in patients with fibromyalgia. Fifty patients are randomly assigned to biweekly trigger-point injections with 0.9% saline only or 0.9% saline plus lidocaine. The graph shows daily self-reported pain scores in relation to the injections. Which of the following is the most likely explanation for these findings?

A 30-year-old woman is being evaluated for infertility. Menarche occurred at age 12 years, and she had regular menses until approximately 3 years ago. At that time, she noticed increased spacing between her menstrual periods and decreasing flow. Physical examination shows no abnormalities. Laboratory findings show normal serum testosterone and prolactin concentrations and an increased serum follicle-stimulating hormone concentration. Which of the following is the most likely cause of the amenorrhea?

A 27-year-old man is admitted to the hospital because of fever, fatigue, malaise, anemia, and lymphadenopathy. He is a marine and had been stationed in Saudi Arabia. He has a history of a lesion that developed at the site of a sand fly bite 2 weeks before his current symptoms began. Blood cultures are negative. A biopsy specimen of a skin lesion shows enlarged macrophages containing numerous intracellular organisms. Which of the following is the most likely causal organism?

A 33-year-old man comes to the physician for a physical examination prior to starting a new job. He feels well and recently became engaged to be married. Physical examination shows a 1.5-cm fixed, nontender mass on the right side of the neck. During the examination, he appears anxious and says, “You seem to be spending a lot of time examining my neck. Is there something wrong? Do I have cancer?” After informing the patient about the discovery of the suspected mass, which of the following is the most appropriate initial statement by the physician?

A 72-year-old man comes to the physician because of a 1-month history of discoloration of his legs. He lives alone and his diet consists mostly of oatmeal and prepared meats. Physical examination shows ecchymoses of the lower extremities, splinter hemorrhages of the nailbeds, perifollicular purpura, and corkscrew hairs. A deficiency of which of the following vitamins is most likely responsible for these findings?

A study is conducted to examine the effects of polychemotherapy on patients with lung carcinoma. Bronchoalveolar lavage samples taken before and after treatment with methotrexate, doxorubicin, cyclophosphamide, and lomustine are examined for changes in pulmonary surfactant. In order to access a lingular bronchus for lavage, the bronchoscope must pass through which of the following bronchi?

A 65-year-old man is brought to the emergency department 12 hours after the onset of chest pain. He dies 5 days later of cardiogenic shock. At autopsy, examination of the heart shows blockage of the coronary arteries and massive amounts of ventricular necrosis. A lack of which of the following best explains the inability of this patient’s heart muscle to repair itself?

A 29-year-old woman has had three spontaneous abortions between the third and fourth weeks of gestation. The most likely cause is failure of her ovaries to produce sufficient quantities of which of the following hormones?

During ligand-binding experiments, a new adrenergic drug displays potent binding to a-adrenergic receptors. In healthy volunteers, the drug causes a significant increase in blood pressure. However, when used in the emergency department to increase blood pressure in trauma victims, the drug decreases blood pressure. This drug is most likely from which of the following classes?

A study is conducted to assess the relationship between a history of cigarette smoking and the development of transitional cell carcinoma. In 10,000 patients with transitional cell carcinoma of the bladder, 6750 had a history of cigarette smoking; in 10,000 patients without transitional cell carcinoma, 1250 had a history of cigarette smoking. Which of the following best describes this study design?

A 75-year-old woman with chronic obstructive pulmonary disease comes to the physician because of a 3-month history of shortness of breath while performing household chores and swelling of her feet at night. She smoked 214 packs of cigarettes daily for 50 years until she decreased to one-half pack daily 2 years ago. She takes no medications and does not use supplemental oxygen. Her respirations are 18/min and labored. Physical examination shows cyanosis of the lips and fingertips. Crackles, rhonchi, and wheezing are heard over all lung fields bilaterally. There is a markedly prolonged expiration phase. Arterial blood gas analysis on room air is most likely to show which of the following sets of findings in this patient?

A 17-year-old boy comes to the physician for a follow-up examination. One year ago, he sustained a deep laceration to his right lower extremity in a motorcycle collision. He underwent operative repair of a severed neurovascular bundle below the popliteal fossa. During the next 10 months, he received regular physical therapy. Physical examination now shows no apparent atrophy of the right lower extremity. Motor and sensory functions are intact. Which of the following changes is most likely in the muscle fibers of the patient’s right foot?

A 63-year-old woman comes to the physician because of fatigue and weakness for the past 3 months. She has not had abdominal pain or a change in bowel habits. Findings on physical examination are unremarkable. Laboratory studies show:

Adenocarcinoma of the colon is suspected. Which of the following best describes the most likely location of the primary tumor in the large intestine?