NBME 13 Section 4 (Qst 1-50)

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| By Chachelly

Chachelly

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Questions: 50 | Attempts: 2,740 | Updated: Mar 21, 2023

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1.

An 18-year-old man has had temperatures to 38.3°C (101°F), a sore throat, and cervical lymph node enlargement for 8 days. A latex agglutination test result for Epstein-Barr virus antibody is positive. Atypical cells with abundant lacey cytoplasm in the peripheral blood smear are most likely derived from which of the following types of cells?
- A.
  
  B lymphocytes
- B.
  
  Basophils
- C.
  
  Neutrophils
- D.
  
  Plasma cells
- E.
  
  T lymphocytes
Correct Answer
E. T lymphocytes

Explanation
¢Lymphocytosis
¢Blood smear: Atypical lymphocytes (T cells) = mononuclear cells
More than 10% atypical lymphocytes
¢ Detection of EBV DNA or RNA by hybridization
¢ In situ methods for visualization of infected cells.
Some prep on the cell and
¢Serology: Heterophile antibody test
***ATYPICAL LYMPHOCYTES are enlarged lymphocytes that have abundant cytoplasm, vacuoles, and indentations of the cell membrane , CD8+ cells predominate among the atypical lymphocytes.
T cells are activated by infected B cells: TheT cells appear as atypical lymphocytes called Downey cells

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2.

A 6-year-old boy is brought to the physician by his mother because of a 2-day history of fever, sore throat and occasional vomiting. His temperature is 39'C (102.2°F). Physical examination shows erythema and purulent exudate over the posterior pharyngeal wall and tonsils. The anterior cervical glands are enlarged and tender. A throat culture grows group A Streptococcus. Because he is allergic to penicillin, treatment with erythromycin is begun. His condition improves during the next 2 days. The effectiveness of this antibiotic is most likely due to which of the following actions in protein synthesis?
- A.
  
  Causes misreading of mRNA information
- B.
  
  Functions as an analog of aminoacyl-tRNA
- C.
  
  Inactivates elongation factor-2
- D.
  
  Interferes in aminoacyl-tRNA binding
- E.
  
  Interferes with translocation
Correct Answer
E. Interferes with translocation

Explanation
Erythromycin interferes with translocation in protein synthesis. Translocation is the process in which the ribosome moves along the mRNA strand, allowing for the addition of the next amino acid to the growing peptide chain. By interfering with this process, erythromycin disrupts protein synthesis and inhibits the growth of bacteria, including group A Streptococcus. This is why the boy's condition improves after starting treatment with erythromycin.

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3.

A male newborn at 34 weeks’ gestation is delivered vaginally. Physical examination shows no abnormalities except for a 1-cm, raised, red area on the anterior section of the neck. His mother is concerned, and the physician explains that the lesion is a hemangioma, a benign growth. This neoplasm most likely originated in which of the following tissues?
- A.
  
  Ectoderm
- B.
  
  Endothelium
- C.
  
  Neural crest cells
- D.
  
  Notochord
- E.
  
  Yolk sac
Correct Answer
B. Endothelium

Explanation
The correct answer is endothelium because a hemangioma is a benign growth that originates from the endothelial cells, which line the blood vessels. The raised, red area on the newborn's neck is likely a result of abnormal proliferation of these endothelial cells.

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4.

A 21-year-old woman who is a medical student comes to the physician for evaluation of recurrent throbbing headache associated with sensitivity to light and sound. Neurologic examination shows no abnormalities. Sumatriptan is initiated for suspected migraine. This drug is most appropriate for this patient because of its ability to activate which of the following types of receptors?
- A.
  
  Acetylcholine
- B.
  
  ү-Aminobutyric acid
- C.
  
  Dopamine
- D.
  
  Neurotensin
- E.
  
  Serotonin
Correct Answer
E. Serotonin

Explanation
Lippincott’s Pharmacology E
Triptans: This class of drugs includes sumatriptan [SOO-ma-triptan], naratriptan [NAR-a-trip-tan], rizatriptan [rye-za-TRIP-tan], eletriptan [EH-leh-trip-tan], almotriptan [AL-moh-trip-tan], frovatriptan (frova-TRIP-tan), and zolmitriptan [zole-ma-TRIP-tan]. These agents rapidly and e!ectively abort or markedly reduce the severity of migraine headaches in about 70 percent of patients. The triptans are serotonin agonists, acting at a subgroup of serotonin receptors found on small peripheral nerves that innervate the intracranial vasculature. The nausea that occurs with dihydroergotamine and the vasoconstriction caused by ergotamine (see below) are much less pronounced with the triptans, particularly rizatriptan and zolmitriptan. Sumatriptan is given subcutaneously, intranasally, or orally. Zolmitriptan is available orally and by nasal spray. [Note: All other agents are taken orally.] The onset of the parenteral drug (which is indicated for treatment of cluster headaches) is about 20 minutes, compared with 1 to 2 hours when the drug is administered orally. The drug has a short duration of action, with an elimination half-life
of 2 hours. Headache commonly recurs within 24 to 48 hours after a single dose of drug, but in most patients, a second dose is e!ective in aborting the headache. Rizatriptan and eletriptan are modestly more efective than sumatriptan, the prototype drug, whereas, naratriptan and almotriptan are better tolerated. Frovatriptan is the longest-acting triptan, with a half-life of more than 24 hours. Individual responses to triptans vary, and more than one drug trial may be necessary before treatment is successful. Significant elevation of blood pressure and cardiac events have been reported with triptan use. Therefore, triptans should not be administered to patients with risk factors for coronary artery disease without performing a cardiac evaluation prior to administration. Other adverse events with the use of triptans include pain and pressure sensations in the chest, neck, throat, and jaw.

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5.

A screening test is used to detect prostate cancer in a population of 100,000 men. The test has a sensitivity of 70% and a specificity of 90%. The test is then used to screen a second population in which the prevalence of prostate cancer is different. Which of the following is the most likely effect on the positive predictive value of this test?
- A.
  
  Decreases as prevalence increases
- B.
  
  Increases as prevalence decreases
- C.
  
  Increases as prevalence increases
- D.
  
  No change as prevalence changes
Correct Answer
C. Increases as prevalence increases

Explanation
The positive predictive value (PPV) of a test is the probability that a positive result is truly positive. In this case, as the prevalence of prostate cancer increases in the second population, the likelihood of a positive result being a true positive also increases. This is because a higher prevalence means there are more true positives in the population, increasing the chances of a positive result being a true positive. Therefore, the PPV of the test is expected to increase as the prevalence increases.

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6.

A 60-year-old man comes to the physician because of progressive weakness of his hands during the past 6 months. He works as a carpenter and has had difficulty handling his tools. He has smoked 1 pack of cigarettes daily for 45 years. He drinks two beers daily during the workweek and approximately six beers daily on weekends. Physical examination shows no lymphadenopathy. There is decreased strength (4/5) in the upper and lower extremities and atrophy of the muscles of the hands. He has diffuse hyperreflexia. Fasciculations are noticed on the muscles of the hands and upper extremities. Sensory examination is normal. Over the course of this disease, which of the following findings is most likely?
- A.
  
  Dementia
- B.
  
  Difficulty swallowing
- C.
  
  Loss of facial sensation
- D.
  
  Loss of peripheral vibratory sensation
- E.
  
  Nystagmus
Correct Answer
B. Difficulty swallowing

Explanation
The patient's symptoms, such as weakness, atrophy of hand muscles, hyperreflexia, and fasciculations, suggest a motor neuron disease. Difficulty swallowing, also known as dysphagia, is a common symptom in motor neuron diseases such as amyotrophic lateral sclerosis (ALS). In ALS, the degeneration of upper and lower motor neurons leads to muscle weakness and atrophy, including the muscles involved in swallowing. Therefore, difficulty swallowing is the most likely finding in this patient.

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7.

A 55-year-old man comes to the physician because of a 3-day history of fever and shaking chills. He has end-stage renal disease treated with hemodialysis. His temperature is 39.2°C (102.6˚F), pulse is 110/min, and blood pressure is 156/92 mm Hg. Physical examination shows a tunneled central venous catheter entering the right side of the chest below the clavicle; the area surrounding the catheter is not tender. Echocardiography shows a 3-cm vegetation on the tricuspid valve. Which of the following is the most likely causal organism?
- A.
  
  Escherichia coli
- B.
  
  KIebsiella pneumoniae
- C.
  
  Staphylococcus aureus
- D.
  
  Streptococcus pyogenes (group A)
- E.
  
  Viridans streptococcus
Correct Answer
C. Staphylococcus aureus

Explanation
Staphylococcus aureus is the most likely causal organism in this patient. The presence of a tunneled central venous catheter and a vegetation on the tricuspid valve suggests infective endocarditis, which is commonly caused by Staphylococcus aureus in patients with end-stage renal disease and hemodialysis. The history of fever and shaking chills further supports the diagnosis.

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8.

A 3-year-old girl is found to have a grade 4/6, loud, harsh, high-pitched holosystolic murmur that radiates over the precordium and a palpable thrill at the left sternal border. Which of the following defects is most likely in this patient?
- A.
  
  Aortic regurgitation
- B.
  
  Aortic stenosis
- C.
  
  Atrial septal defect
- D.
  
  Coarctation of the aorta
- E.
  
  Mitral regurgitation
- F.
  
  Mitral stenosis
- G.
  
  Patent ductus arteriosus
- H.
  
  Pulmonic stenosis
- I.
  
  Tricuspid regurgitation
- J.
  
  Ventricular septal defect
Correct Answer
J. Ventricular septal defect

Explanation
The most likely defect in this patient is a ventricular septal defect (VSD). The loud, harsh, high-pitched holosystolic murmur that radiates over the precordium and the palpable thrill at the left sternal border are characteristic findings of a VSD. A VSD is a congenital heart defect where there is an abnormal opening between the ventricles, allowing blood to flow from the left ventricle to the right ventricle. This results in a left-to-right shunt and the murmur and thrill are caused by the increased flow of blood across the defect.

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9.

A 48-year-old woman comes to the emergency department because of a 3-hour history of nausea and acute, sharp, right-sided lower abdominal pain that radiates to her back. She says the pain started 30 minutes into her aerobics class and has increased in severity since then. Physical examination shows an enlarged right ovary. The result of a urine pregnancy test is negative. Ultrasonography of the pelvis confirms the presence of an enlarged ovary, and Doppler ultrasonography shows decreased adnexal flow. Which of the following structures is most likely affected in this patient?
- A.
  
  Mesometrium
- B.
  
  Oviduct
- C.
  
  Round ligament of the uterus
- D.
  
  Suspensory ligament
- E.
  
  Transverse cervical ligament
Correct Answer
D. Suspensory ligament

Explanation
The suspensory ligament is most likely affected in this patient. The patient's symptoms of acute, sharp, right-sided lower abdominal pain that radiates to her back, along with an enlarged right ovary and decreased adnexal flow on Doppler ultrasonography, suggest ovarian torsion. Ovarian torsion occurs when the ovary twists on its suspensory ligament, leading to compromised blood flow and subsequent ischemia. This condition typically presents with sudden onset of severe pain and can result in ovarian infarction if not promptly treated.

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10.

A 20-year-old man comes to the physician because of cramping abdominal pain and diarrhea during the past 3 weeks; he has had a 4.5-kg (10-lb) weight loss during this period. The pain is exacerbated following meals. He went on a camping trip in upstate New York 3 weeks ago, swimming in the nearby lakes and hiking in the mountains. His vital signs are normal. Physical examination shows no abnormalities. Which of the following diagnostic tests is most likely to identify the causal organism of this patient's condition?
- A.
  
  Culture of the stool for enteric bacterial pathogens
- B.
  
  Electron microscopy of the stool for small round viruses
- C.
  
  Microscopic examination of the stool for ova and parasites
- D.
  
  Polymerase chain reaction test of the stool for Shiga toxin
- E.
  
  Proctoscopy and rectal biopsy
Correct Answer
C. Microscopic examination of the stool for ova and parasites

Explanation
The patient's symptoms of cramping abdominal pain, diarrhea, and weight loss, along with a history of swimming in lakes and hiking in the mountains, suggest a possible parasitic infection. Microscopic examination of the stool for ova (eggs) and parasites is the most appropriate diagnostic test to identify the causal organism in this patient's condition. This test can help identify the presence of parasites such as Giardia lamblia, which is commonly associated with recreational water activities and can cause symptoms similar to those described by the patient.

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11.

11. A 43-year-old woman with metastatic colon cancer has maintained remission by taking bevacizumab as a single agent. The ability to administer this agent despite it being a foreign protein is most likely a result of which of the following?
- A.
  
  The agent being a humanized antibody
- B.
  
  The agent containing the variable region of a murine antibody molecule directed against vascular endothelial growth factor
- C.
  
  B-cell dysfunction
- D.
  
  The immunosuppressive effect of previously administered chemotherapy
- E.
  
  T-cell dysfunction
Correct Answer
A. The agent being a humanized antibody

Explanation
The ability to administer bevacizumab, despite it being a foreign protein, is most likely a result of the agent being a humanized antibody. Humanized antibodies are designed to minimize the immunogenic response by incorporating human sequences into the antibody structure, reducing the likelihood of an immune response against the drug. This allows for better tolerance and prolonged use of the medication in patients.

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12.

A previously healthy 35-year-old man comes to the physician because of a 2-year history of gradually decreasing libido and intermittent inability to achieve erection or orgasm; he also has had decreased growth of facial hair during this period. Puberty began at the age of 12 years. He takes no medications. He does not smoke or drink alcohol. He is 180 cm (5 ft 11 in) tall and weighs 75 kg (165 lb); BMI is 23 kg/m². His vital signs are within normal limits. Physical examination shows a typical male-pattern distribution of hair. Genital examination shows no abnormalities. Serum studies shows thyroid-stimulating hormone concentration of 2 µU/mL, prolactin concentration of 120 ng/mL, and total testosterone concentration of 25 mmol/L (N=10— 35). Semen analysis shows a markedly decreased sperm count with impaired motility. An MRI of the brain shows a 1-cm lesion in the pituitary gland. Administration of which of the following is the most appropriate treatment for this patient?
- A.
  
  Bromocriptine
- B.
  
  Gonadotropin-releasing hormone
- C.
  
  Human chorionic gonadotropin
- D.
  
  Sildenafil
- E.
  
  Testosterone
- F.
  
  Thyroxine
Correct Answer
A. Bromocriptine

Explanation
The patient's symptoms and laboratory findings suggest a diagnosis of hypogonadotropic hypogonadism, which is characterized by decreased libido, erectile dysfunction, decreased facial hair growth, and low testosterone levels. The presence of a pituitary lesion on MRI further supports this diagnosis. Bromocriptine is a dopamine agonist that inhibits prolactin secretion, which can be elevated in patients with pituitary tumors. By reducing prolactin levels, bromocriptine can restore normal gonadotropin secretion and stimulate testosterone production, thereby improving the patient's symptoms of hypogonadism.

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13.

A 42-year-old man has an autoimmune disorder resulting in proximal muscle weakness of the lower extremities. Arrows in the photomicrograph shown indicate membranes that contain high concentrations of channels that are targeted by this condition. Which of the following is the most likely diagnosis?
- A.
  
  Multiple sclerosis
- B.
  
  MyasItenia gravis
- C.
  
  Myasthenic (Lambert-Eaton) syndrome
- D.
  
  Periodic paralysis
- E.
  
  Tetany
Correct Answer
C. Myasthenic (Lambert-Eaton) syndrome

Explanation
The correct answer is Myasthenic (Lambert-Eaton) syndrome. This is supported by the description of a 42-year-old man with an autoimmune disorder and proximal muscle weakness of the lower extremities. Myasthenic (Lambert-Eaton) syndrome is a neuromuscular disorder characterized by muscle weakness and fatigue, particularly in the proximal muscles. It is caused by an autoimmune attack on the presynaptic voltage-gated calcium channels at the neuromuscular junction, leading to impaired release of acetylcholine and subsequent muscle weakness.

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14.

An investigator is studying the human immune response to tumor cell antigens in malignancies. Which of the following sets of cancer types and tumor antigens is most likely to produce the highest antibody titer? Cancer Type Tumor Antigen A) B-cell lymphoma CD19 B) Breast cancer HER2/neu C) Cervical cancer human papillomavirus type 16 E6 protein D) Melanoma tyrosinase E) Prostate cancer prostatic acid phosphatase
- A.
  
  A
- B.
  
  B
- C.
  
  C
- D.
  
  D
- E.
  
  E
Correct Answer
C. C

Explanation
Cervical cancer and the human papillomavirus type 16 E6 protein are most likely to produce the highest antibody titer. This is because cervical cancer is caused by the human papillomavirus (HPV) type 16, and the E6 protein is a viral protein produced by HPV 16. The immune response against the E6 protein in cervical cancer is expected to be strong, leading to a high antibody titer.

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15.

A 45-year-old woman has a 2-week history of a heart murmur and hepatomegaly. She has a 3-month history of flushing with hypotension and crampy diarrhea. Which of the following is the most likely site of a primary neoplasm in this patient?
- A.
  
  Adrenal gland
- B.
  
  Bone marrow
- C.
  
  Kidney
- D.
  
  Ovary
- E.
  
  Small intestine
Correct Answer
E. Small intestine

Explanation
Based on the patient's symptoms of flushing, hypotension, and crampy diarrhea, along with the presence of a heart murmur and hepatomegaly, the most likely site of a primary neoplasm in this patient is the small intestine. These symptoms are consistent with a condition called carcinoid syndrome, which is commonly caused by a neuroendocrine tumor (carcinoid tumor) in the small intestine. The tumor secretes serotonin and other vasoactive substances, leading to the symptoms described.

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16.

A 22-year-old woman comes to the physician 3 months after she noticed a painless, slowly enlarging mass on the left side of her neck. Physical examination shows a freely mobile, soft, cystic mass with a cutaneous surface opening. The physician explains that it is from incomplete fusion during embryonic development. Which of the following is the most likely location of the opening of the duct leading to the mass in this patient?
- A.
  
  Anterior to the sternocleidomastoid muscle
- B.
  
  Midline on the neck
- C.
  
  Postauricular
- D.
  
  Posterior to the parotid gland
- E.
  
  Submental
Correct Answer
A. Anterior to the sternocleidomastoid muscle

Explanation
The correct answer is "Anterior to the sternocleidomastoid muscle." Incomplete fusion during embryonic development suggests the presence of a branchial cleft cyst. Branchial cleft cysts are derived from the branchial apparatus, which is a series of arches and clefts that form during embryogenesis. The most common type of branchial cleft cyst is a second branchial cleft cyst, which presents as a painless, slowly enlarging mass on the lateral side of the neck, anterior to the sternocleidomastoid muscle. These cysts often have a cutaneous surface opening, and their location and characteristics are consistent with the findings described in the question.

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17.

A 42-year-old man comes to the physician because of a 4-week history of muscle cramping and pain. Two months ago, he began treatment with simvastatin (80 mg daily) for hypercholesterolemia. After 1 month, marked improvement was noted in his serum LDL-cholesterol concentration, but serum triglyceride concentration remained increased. At that time, gemfibrozil was added to his regimen to decrease his triglyceride concentration. Physical examination today shows no abnormalities. This patient’s myalgia is most likely related to which of the following effects of gemfibrozil on simvastatin?
- A.
  
  Decreased bioavailability
- B.
  
  Increased absorption
- C.
  
  Inhibition of cytochrome P450 metabolism
- D.
  
  Inhibition of hepatic glycosylation
- E.
  
  Inhibition of hepatic sulfation
Correct Answer
C. Inhibition of cytochrome P450 metabolism

Explanation
Gemfibrozil is known to inhibit the cytochrome P450 enzyme system, which is responsible for the metabolism of many drugs, including simvastatin. By inhibiting the metabolism of simvastatin, gemfibrozil can increase its concentration in the body, leading to a higher risk of adverse effects. In this case, the patient's myalgia is likely a result of the increased concentration of simvastatin due to the inhibition of its metabolism by gemfibrozil.

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18.

A 30-year-old woman and her 25-year-old husband come to the physician for advice about their risk for having another child with Tay-Sachs disease. Their 6-month-old son was recently diagnosed with this disease. There is a history of this disease in both the woman's and the man's families. Which of the following best represents the risk for this couple’s next child to have Tay-Sachs disease?
- A.
- B.
  
  10%
- C.
  
  25%
- D.
  
  50%
- E.
  
  100%
Correct Answer
C. 25%

Explanation
The risk for this couple's next child to have Tay-Sachs disease is 25%. Tay-Sachs disease is an autosomal recessive disorder, meaning that both parents must be carriers of the gene mutation in order for the child to inherit the disease. Since both the woman and the man have a family history of Tay-Sachs disease, it is likely that they are carriers. When two carriers have a child, there is a 25% chance that the child will inherit the disease.

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19.

An 18-month-old boy is brought to the physician because of progressive facial abnormalities and slow growth during the past 6 months. He has an older brother with similar abnormalities who also has mental retardation. The patient is below the 3rd percentile for length and at the 10Ih percentile for weight. Physical examination shows coarse facial features, hepatosplenomegaly, and joint stiffness. His urine concentrations of dermatan sulfate and heparan sulfate are increased. A deficiency of which of the following enzyme activities is the most likely cause of the findings in this patient?
- A.
  
  Galactosidase
- B.
  
  Glycosylase
- C.
  
  Hexosaminidase A
- D.
  
  Lduronate sulfatase
- E.
  
  Lipoxygenase
Correct Answer
D. Lduronate sulfatase

Explanation
The patient's presentation of progressive facial abnormalities, slow growth, coarse facial features, hepatosplenomegaly, and joint stiffness are consistent with a lysosomal storage disorder known as mucopolysaccharidosis (MPS). The increased urine concentrations of dermatan sulfate and heparan sulfate further support this diagnosis. The most likely enzyme deficiency causing these findings is iduronate sulfatase, which is responsible for the degradation of dermatan sulfate and heparan sulfate. This enzyme deficiency leads to the accumulation of these substances in various tissues, resulting in the clinical manifestations observed in the patient.

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20.

A 3-year-old girl is brought to the emergency department by her mother 1 hour alter she was found with a half-empty bottle other grandmother's diabetes medication. The mother tells the physician that the child consumed approximately 25 metformin tablets. Physical examination shows no abnormalities. This patient is at greatest risk for which of the following serum abnormalities?
- A.
  
  Decreased calcium concentration
- B.
  
  Decreased glucose concentration
- C.
  
  Decreased sodium concentration
- D.
  
  Increased AST and ALT activities
- E.
  
  Increased creatinine concentration
- F.
  
  Increased lactic acid concentration
Correct Answer
F. Increased lactic acid concentration

Explanation
Metformin is a medication commonly used to treat type 2 diabetes. In overdose, it can cause a condition called lactic acidosis, which is characterized by an increased level of lactic acid in the blood. Lactic acidosis is a potentially life-threatening condition that can lead to metabolic acidosis and organ dysfunction. In this scenario, the 3-year-old girl consumed a large number of metformin tablets, putting her at risk for developing lactic acidosis. The other serum abnormalities listed in the answer choices are not typically associated with metformin overdose.

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21.

A 5-year-old boy is brought to the physician by his mother because of a 3-month history of headache, clumsiness, and fatigue. He had a generalized tonic-clonic seizure 1 month ago. His mother says that he often falls while running. Ophthalmologic examination shows ptosis of the left eye and bilateral external ophthalmoplegia. Physical examination shows weakness of the left lower extremity. Serum studies show an increased lactate concentration. Analysis of a calf muscle biopsy specimen obtained from the left lower extremity shows ragged red fibers. Which of the following metabolic processes is most likely impaired in this patient?
- A.
  
  Fatty acid oxidation
- B.
  
  Gluconeogenesis
- C.
  
  Glycolysis
- D.
  
  Oxidative phosphorylation
- E.
  
  Pentose phosphate pathway
Correct Answer
D. Oxidative phosphorylation

Explanation
This patient's symptoms and findings are consistent with a mitochondrial disorder, specifically a mitochondrial encephalomyopathy. The presence of ragged red fibers on muscle biopsy is a characteristic finding in mitochondrial disorders. Oxidative phosphorylation is the process by which ATP is generated in the mitochondria, and impairment of this process can lead to a decrease in ATP production, resulting in the symptoms seen in this patient. Fatty acid oxidation, gluconeogenesis, glycolysis, and the pentose phosphate pathway are not directly involved in ATP production in the mitochondria.

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22.

A 25-year-old woman comes to the physician because of a 2-day history of decreasing urine output despite ample fluid intake. She underwent operative removal of a perforated appendix 3 weeks ago. She received intravenous gentamicin for 2 weeks. Physical examination shows no abnormalities. Laboratory studies show: Histologic examination of this patient's kidneys would most likely show necrotic cells in which of the following components of the nephron?
- A.
  
  Bowman capsule
- B.
  
  Collecting tubule
- C.
  
  Glomerular basement membrane
- D.
  
  Mesangium
- E.
  
  Proximal tubule
Correct Answer
E. Proximal tubule

Explanation
The patient's history of decreasing urine output and recent use of gentamicin suggests the possibility of acute tubular necrosis (ATN), a common cause of acute kidney injury. ATN primarily affects the proximal tubules of the nephron. Therefore, histologic examination of the patient's kidneys would most likely show necrotic cells in the proximal tubule.

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23.

A 43-year-old man comes to the physician for a routine health maintenance examination. He is 170 cm (5 ft 7 in) tall and weighs 86 kg (188 lb); BMI is 30 kg/m². Physical examination and laboratory studies show no other abnormalities. He tells the physician, "My older brother just got diagnosed with diabetes. I don't want that to happen to me. What should I do?” Which of the following diets is most likely to be effective in decreasing this patients risk for type 2 diabetes mellitus?
- A.
  
  Low-calorie
- B.
  
  Low-carbohydrate
- C.
  
  Low-cholesterol
- D.
  
  Low-protein
- E.
  
  Low-sodium
Correct Answer
A. Low-calorie

Explanation
A low-calorie diet is most likely to be effective in decreasing this patient's risk for type 2 diabetes mellitus. This is because obesity is a major risk factor for developing type 2 diabetes, and this patient has a BMI that indicates obesity. By reducing calorie intake, the patient can achieve weight loss, which can improve insulin sensitivity and reduce the risk of developing diabetes. Additionally, a low-calorie diet can help control blood sugar levels and prevent excessive weight gain, further reducing the risk of diabetes.

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24.

A 4-year-old boy is brought to the emergency department because of a 1-hour history of headache, nausea and vomiting, and dizziness. Physical examination shows severe lethargy. His venous blood is bright red; carboxyhemoglobin saturation is 30% (reference range < 5%). Which of the following steps in the electron transport pathway is primarily affected in this patient?
- A.
  
  A
- B.
  
  B
- C.
  
  C
- D.
  
  D
- E.
  
  E
Correct Answer
E. E

Explanation
The patient's symptoms, along with the presence of bright red venous blood and elevated carboxyhemoglobin saturation, indicate carbon monoxide (CO) poisoning. CO binds to hemoglobin with a higher affinity than oxygen, leading to impaired oxygen delivery to tissues. In the electron transport pathway, complex IV (cytochrome c oxidase) is primarily affected by CO poisoning, as it is responsible for transferring electrons to oxygen to form water. Therefore, the correct answer is E.

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25.

A 20-year-old man has cramping periumbilical pain. After several hours, the pain shifts to the right lower quadrant and becomes constant. His temperature is 40°C (104°F), and his leukocyte count is 20.000/mm³ with 90% neutrophils. Which of the following mediators is most likely causing this patients fever and leukocytosis?
- A.
  
  Interleukin-1 (IL-1)
- B.
  
  Interleukin-2 (IL-2)
- C.
  
  Leukotriene B₄
- D.
  
  Leukotriene C₄
- E.
  
  Prostaglandin D₂
Correct Answer
A. Interleukin-1 (IL-1)

Explanation
Interleukin-1 (IL-1) is most likely causing this patient's fever and leukocytosis. IL-1 is a pro-inflammatory cytokine that is released by activated macrophages and other cells in response to infection or tissue injury. It acts on the hypothalamus to increase body temperature, resulting in fever. IL-1 also stimulates the production of acute phase reactants, including leukocytes, leading to leukocytosis. The patient's symptoms of fever and elevated leukocyte count, along with the presence of cramping periumbilical pain that shifts to the right lower quadrant, suggest acute appendicitis, which is commonly associated with an inflammatory response mediated by IL-1.

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26.

A researcher in a pharmaceutical company designs a new protease inhibitor that inhibits replication of HIV in T lymphocytes in culture. In subsequent assays, which of the following findings is most likely to indicate that the compound is working specifically as a protease inhibitor?
- A.
  
  The drug prevents integration of proviral DNA into the host genome
- B.
  
  The RNA is partially reverse transcribed into proviral DNA
- C.
  
  There is a lack of a mature core
- D.
  
  Transcription from the HIV promoter is blocked
- E.
  
  The virus does not bind to CD4 in the presence of the drug
Correct Answer
C. There is a lack of a mature core

Explanation
The presence of a mature core in the virus is an important step in the replication of HIV. A mature core is formed when the viral protease cleaves the viral polyprotein into its individual components. Therefore, if there is a lack of a mature core, it suggests that the compound is specifically inhibiting the protease activity, preventing the cleavage of the polyprotein and the formation of a mature core. This finding indicates that the compound is working specifically as a protease inhibitor.

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27.

47-year-old man is brought to the emergency department 3 hours after the sudden onset of sharp left flank pain and fever He has had similar episodes during the past 5 years. His temperature is 38.3°C (100.9°F). Abdominal examination shows exquisite tenderness in the left costovertebral region. Laboratory studies show: Imaging studies show hydronephrosis of the left kidney and a staghorn calculus. A nephrectomy is done; the calculus is composed of magnesium ammonium phosphate (struvite). Culture of a urine sample is roost likely to grow which of the following organisms?
- A.
  
  Escherichia coli
- B.
  
  Proteus
- C.
  
  Pseudomonas aeruginosa
- D.
  
  Serratia marcescens
- E.
  
  Staphylococcus aureus
Correct Answer
B. Proteus

Explanation
Struvite stones
About 10–15% of urinary calculi are composed of struvite (ammonium magnesium phosphate, NH4MgPO4·6H2O).[38] Struvite stones (also known as "infection stones", urease or triple-phosphate stones), form most often in the presence of infection by urea-splitting bacteria. Using the enzyme urease, these organismsmetabolize urea into ammonia and carbon dioxide. This alkalinizes the urine, resulting in favorable conditions for the formation of struvite stones. Proteus mirabilis, Proteus vulgaris, and Morganella morganii are the most common organisms isolated; less common organisms include Ureaplasma urealyticum, and some species ofProvidencia, Klebsiella, Serratia, and Enterobacter. These infection stones are commonly observed in people who have factors that predispose them to urinary tract infections, such as those with spinal cord injury and other forms of neurogenic bladder, ileal conduit urinary diversion, vesicoureteral reflux, and obstructive uropathies. They are also commonly seen in people with underlying metabolic disorders, such as idiopathic hypercalciuria, hyperparathyroidism, and gout. Infection stones can grow rapidly, forming large calyceal staghorn (antler-shaped) calculi requiring invasive surgery such as percutaneous nephrolithotomy for definitive treatment.[38]

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28.

A 43-year-old man comes to the emergency department because of a 1-year history chow back pain. Before the examination, the patient says, "My physician is arrogant and insensitive. He never returns my phone calls, I always have to wait forever to be seen, the tests he orders are painful and unnecessary, and he can never tell me what is causing my back pain or how to treat it Which of the following is the most appropriate response by the emergency department physician about this patient's complaints?
- A.
  
  Reassure the patent that his physician's behavior is not unusual and that low back pain can be difficult to assess
- B.
  
  Encourage the patient to make an appointment with his physician to communicate his concerns
- C.
  
  Explain to the patient how he may register a complaint against his physician with the state medical licensing board
- D.
  
  Provide the patient with a copy of the Patients' Bill of Rights
- E.
  
  Telephone the patient's physician to make him aware that the patient is very dissatisfied with treatment
Correct Answer
B. Encourage the patient to make an appointment with his physician to communicate his concerns

Explanation
The most appropriate response by the emergency department physician is to encourage the patient to make an appointment with his physician to communicate his concerns. This response acknowledges the patient's complaints and suggests a direct approach to address them. It allows the patient to express his concerns and potentially resolve any issues with his physician.

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29.

Choices A- J A 42-year-old woman comes to the physician because of a 3-week history of numbness of the fingers on the left hand. Neurologic examination shows loss of touch graphesthesia and loss of two-point discrimination in be left hand, This patient most likely has a lesion in which of the following locations of the hemispheres shown?
- A.
  
  A
- B.
  
  B
- C.
  
  C
- D.
  
  D
- E.
  
  E
- F.
  
  F
- G.
  
  G
- H.
  
  H
- I.
  
  I
- J.
  
  J
Correct Answer
B. B

Explanation
The patient's symptoms of numbness, loss of touch graphesthesia, and loss of two-point discrimination in the left hand suggest a sensory deficit. The sensory cortex is responsible for processing sensory information, including touch and discrimination. Therefore, a lesion in the sensory cortex, which is located in the parietal lobe, would most likely cause these symptoms. Answer B shows the parietal lobe, which is the correct location for the lesion.

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2
1
30.

A 15-year-old boy is brought to the physician because of painless swelling in his left breast for 1 month. There is no family history of breast cancer. He is at the 55th percentile for height and 70th percentile for weight. His pulse is 65(min, and blood pressure is 116/76 mm Hg. Physical examination shows mild facial acne, thickening of mustache hair on the face, and the presence of axillary hair. There is no adenopathy. The left breast appears mildly enlarged with a palpable breast bud: the right breast is normal with no gynecomastia. His genitalia are Tanner stage 3. Which piths following is the most appropriate initial statement by the physician regarding this patient's breast finding?
- A.
  
  “Have you tried Smoking marijuana recently? That has been known to cause breast enlargement "
- B.
  
  "Some teenagers experiment with their parents' prescription drugs, even birth control pills. Are you?”
- C.
  
  “This is a common condition for teenage boys and should resolve in time."
- D.
  
  “This may be a sign of a chromosomal problem. We need to do some genetic testing”
- E.
  
  “This may be a sign of a more serious condition. We'll have to do more tests to be sure."
Correct Answer
C. “This is a common condition for teenage boys and should resolve in time."

Explanation
The most appropriate initial statement by the physician regarding this patient's breast finding is "This is a common condition for teenage boys and should resolve in time." This is because the patient's presentation is consistent with physiologic gynecomastia, which is a common occurrence during puberty. It is characterized by the development of a palpable breast bud in one or both breasts, usually resolving within 6 months to 2 years. The absence of any concerning findings, such as family history of breast cancer or other symptoms, suggests that this is a benign condition that does not require further testing or intervention.

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31.

A 60-year-old man has had episodes °fluctuating weakness for the past 2 years. The weakness was first noticed when he had difficulty lifting books. At times, he has had drooping of the eyelids and double vision, Recently, he has had difficulty climbing stairs and regurgitation of liquids into his nose. On physical examination, the weakness increases with repeated exercise. An X-ray of the chest shows a mass in the mediastinum Which of the following laboratory assays is most likely to be positive?
- A.
  
  Acetylcholine receptor antibody
- B.
  
  Botulinum toxin
- C.
  
  C-reactive protein
- D.
  
  Rapid plasma reagin
- E.
  
  Rheumatoid factor
Correct Answer
A. Acetylcholine receptor antibody

Explanation
Wikipedia http://en.wikipedia.org/wiki/Myasthenia_gravis
Myasthenia gravis (from Greek μύς "muscle", ἀσθένεια "weakness", and Latin: gravis "serious"; abbreviatedMG) is an autoimmune neuromuscular disease leading to fluctuating muscle weakness and fatigability. It is anautoimmune disorder, in which weakness is caused by circulating antibodies that block acetylcholine receptorsat the postsynaptic neuromuscular junction,[1] inhibiting the excitatory effects of the neurotransmitteracetylcholine on nicotinic receptors throughout neuromuscular junctions. Myasthenia is treated medically withacetylcholinesterase inhibitors or immunosuppressants, and, in selected cases, thymectomy. The diseaseincidence is 3–30 cases per million per year and rising as a result of increased awareness.[2] MG must be distinguished from congenital myasthenic syndromes that can present similar symptoms but offer no response to immunosuppressive treatments.

B. Botulism would be more acute and lead to flaccid paralysis
C. CRP is a good measure of inflammation, however it is unspecific.
D. Rapid Plasma Reagin test is used to detect antibodies against Treponema Pallidum which is the causative agent in syphilis.
E. Rheumatoid Factor is an antibody active against the Fc portion of immunoglobulins(Ig’s). This level will be elevated in diseases such as Rheumatoid arthritis and Sjogren’s Syndrome.

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32.

A 77-year-old woman dies in the hospital after a long illness. Her vertebral column, obtained at autopsy, is shown in the photograph. The process shown is most likely associated with an increase in which of the following?
- A.
  
  Calcium
- B.
  
  Estrogen
- C.
  
  Interleukin-1 (IL-1)
- D.
  
  Monoclonal immunoglobulin
- E.
  
  Vitamin D
Correct Answer
C. Interleukin-1 (IL-1)

Explanation
The process shown in the photograph is most likely associated with an increase in Interleukin-1 (IL-1). IL-1 is a pro-inflammatory cytokine that plays a role in bone resorption. It stimulates the activation of osteoclasts, which are responsible for breaking down bone tissue. In conditions such as osteoporosis or chronic inflammation, there can be an increase in IL-1 levels, leading to increased bone resorption and potentially resulting in structural changes in the vertebral column, as seen in the photograph.

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33.

A 32-year-old woman comes to the physician because of a 1-month history of progressive shortness of breath and anxiety. She says that her symptoms become much more pronounced as the day progresses. She is 170 cm (5 ft 7 in) tall and weighs 70 kg (155 lb). BMI is 24 kg/m2. Breath sounds are normal on auscultation of the chest, but the patient has difficulty taking a long, deep breath. Arterial blood gas analysis on room air shows: pH 7.33 Pco2 70 mm Hg Po2 65 mm Hg Pulmonary function testing shows a decreased vital capacity, tidal volume, and expiratory reserve volume. Her residual volume is within the reference range. Which of the following is the most likely underlying cause of this patient’s condition?
- A.
  
  A1 Antitrypsin deficiency
- B.
  
  Central nervous system neoplasm
- C.
  
  Chronic bronchitis
- D.
  
  Chronic opiate use
- E.
  
  Myasthenia gravis
- F.
  
  Obesity
Correct Answer
E. Myasthenia gravis

Explanation
Myasthenia gravis is the most likely underlying cause of this patient's condition. Myasthenia gravis is an autoimmune disorder characterized by muscle weakness and fatigue, which can affect the muscles involved in breathing. The patient's symptoms of progressive shortness of breath and difficulty taking a long, deep breath are consistent with respiratory muscle weakness. The arterial blood gas analysis shows an elevated Pco2 and a decreased Po2, indicating respiratory acidosis and impaired gas exchange, which can occur in myasthenia gravis due to respiratory muscle weakness. The pulmonary function testing findings of decreased vital capacity, tidal volume, and expiratory reserve volume further support the diagnosis of myasthenia gravis.

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34.

A 42-year-old man seeks medical attention because of the gradual onset of shortness of breath, night sweats. weight loss, and fatigue. An X-ray of the chest snows enlargement of the hilar lymph nodes and nodular infiltrates in both lungs. A PPD skin test is negative. Examination of lung tissue obtained on biopsy shows multiple noncaseating granulomas with many giant cells. No organisms are seen on sections stained with hematoxylin and eosin, acid-fast stain, or silver stain. Which of the following is the most likely diagnosis?
- A.
  
  Asbestosis
- B.
  
  Idiopathic pulmonary fibrosis
- C.
  
  Puemocystis jiroveci (formerly P. carinii) pneumonia
- D.
  
  Sarcoidosis
- E.
  
  Tuberculosis
Correct Answer
D. Sarcoidosis

Explanation
The patient's symptoms of shortness of breath, night sweats, weight loss, and fatigue, along with the findings of enlarged hilar lymph nodes and nodular infiltrates in both lungs on chest X-ray, are consistent with sarcoidosis. The negative PPD skin test and absence of organisms on staining suggest that tuberculosis is unlikely. Sarcoidosis is characterized by the formation of noncaseating granulomas with giant cells, which were seen on examination of lung tissue obtained on biopsy. Therefore, sarcoidosis is the most likely diagnosis in this case.

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35.

A 48-year-old man comes to the physician because he is concerned about his weight. He is 178 cm (5 ft 10 in) tall and weighs 91 kg (200 lb); BMI is 29 kg/m2. His waist circumference is 103 cm (41 in). His blood pressure is 140/90 mm Hg. Physical examination shows a protuberant abdomen. Laboratory studies show fasting serum glucose and insulin concentrations that are increased and remain increased 2 hours after the patient receives 75 g of oral glucose. Which of the following sets of additional laboratory findings in serum is most likely in this patient?
- A.
  
  A
- B.
  
  B
- C.
  
  C
- D.
  
  D
- E.
  
  E
- F.
  
  F
Correct Answer
C. C

Explanation
The patient in this case has a BMI of 29 kg/m2, which falls into the category of overweight. He also has a protuberant abdomen and increased waist circumference, indicating central obesity. Additionally, his blood pressure is elevated at 140/90 mm Hg. These findings suggest that the patient may have metabolic syndrome, a cluster of conditions that increase the risk of heart disease, stroke, and diabetes. The most likely set of additional laboratory findings in this patient would be elevated triglyceride levels, decreased HDL cholesterol levels, and increased fasting plasma glucose levels, as seen in option C. These findings would further support the diagnosis of metabolic syndrome.

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36.

In a healthy person, the thyroid gland produces and secretes thyroxine (T4), maintaining metabolism. Which of the following best describes the T4-binding substance in the blood and the type of cellular receptor for T4 in the peripheral tissues?
- A.
  
  A
- B.
  
  B
- C.
  
  C
- D.
  
  D
- E.
  
  E
- F.
  
  F
Correct Answer
C. C
37.

A 23-year-old man comes to the physician because of a low-grade fever, nasal congestion, and muscle aches for 1 week. He states that his girlfriend recently told him that his eyes appeared yellow. He has not had clay-colored stools or dark urine. His only medication is ibuprofen. He has no recent history of foreign travel tattoos, use of intravenous drugs, or exposure to blood products. He is 183 cm (68) tall and weighs 77 kg (170 lb); BMI is 23 kg/m2. Physical examination shows mild scleral icterus but no subungual icteris. The remainder of the examination shows no abnormalities. Serum studies show: Which of the following is the most likely diagnosis?
- A.
  
  Gilbert syndrome
- B.
  
  Hepatitis D
- C.
  
  Hereditary spherocytosis
- D.
  
  Idiopathic cirrhosis
- E.
  
  Steatohepatitis
Correct Answer
A. Gilbert syndrome

Explanation
The most likely diagnosis in this case is Gilbert syndrome. This is supported by the patient's mild scleral icterus, which is a common finding in this condition. Gilbert syndrome is a benign, inherited disorder characterized by a deficiency of the enzyme glucuronyl transferase, leading to impaired bilirubin conjugation and mild unconjugated hyperbilirubinemia. It is often asymptomatic but can be triggered by factors such as fasting, stress, and certain medications, which may explain the patient's symptoms. The absence of other symptoms such as clay-colored stools or dark urine, as well as the lack of risk factors for other liver diseases, further support this diagnosis.

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38.

A 65-year-old woman with diabetic ketoacidosis has had a fever and proptosis of the left eye over the past 3 days. She is unable to move the left eye. A black eschar is present on the nasal mucosa. Which of the following is the most likely diagnosis?
- A.
  
  Aspergillosis
- B.
  
  Candidiasis
- C.
  
  Coccidioidomycosis
- D.
  
  Cryptococcasis
- E.
  
  Histoplasmosis
- F.
  
  Mucormycosis
Correct Answer
F. Mucormycosis

Explanation
The most likely diagnosis for this patient is mucormycosis. Mucormycosis is a fungal infection caused by the Mucorales order of fungi. It typically affects immunocompromised individuals, such as those with uncontrolled diabetes. The presence of a black eschar on the nasal mucosa is a characteristic finding in mucormycosis. Proptosis of the left eye and inability to move the eye can be attributed to the invasive nature of the infection, which can spread to the orbit and surrounding structures. Fever is a common systemic symptom seen in mucormycosis.

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39.

A 44-year-old woman has had pain, swelling. and stiffness in both hands over the past 6 months. The pain and stiffness are worst in the mornings, but symptoms improve with activity. Examination shows painless nodules on the extensor surfaces of the arms and tenderness and swelling of the metacarpophalangeal and proximal interphalangeal joints. Which of the following is involved in the pathologic process affecting her joints?
- A.
  
  Bacterial invasion
- B.
  
  Caseating necrosis
- C.
  
  Crystal deposition
- D.
  
  Necrotizing vasculitis
- E.
  
  Pannus formation
Correct Answer
E. Pannus formation

Explanation
The patient's symptoms of pain, swelling, and stiffness in both hands, along with the presence of nodules on the extensor surfaces of the arms and tenderness and swelling of the metacarpophalangeal and proximal interphalangeal joints, suggest the presence of rheumatoid arthritis (RA). Pannus formation is a characteristic feature of RA and refers to the abnormal growth of synovial tissue in the joints. This pannus tissue can invade and destroy cartilage and bone, leading to joint deformity and functional impairment. Therefore, pannus formation is the most likely pathologic process affecting the patient's joints in this case.

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40.

Two clinical trials, Trial X and Trial Y. are conducted to assess the potential therapeutic efficacy of a new experimental antibiotic compared to the currently used antibiotic for treatment of urinary tract infections. The two studies are identical, except the statistical power is 0.6 in Study X, and 0.9 in Study Y. Which of the following is the most accurate conclusion regarding the likelihood of a type II error?
- A.
  
  Greater in Trial X than in Trial Y
- B.
  
  Greater in Trial Y than in Trial X
- C.
  
  The same in Trial X and in Trial Y
- D.
  
  Cannot be calculated from the data given
Correct Answer
A. Greater in Trial X than in Trial Y

Explanation
The statistical power of a study is the probability of correctly rejecting the null hypothesis when it is false. In this case, Trial X has a statistical power of 0.6, while Trial Y has a statistical power of 0.9. Since the statistical power is directly related to the likelihood of a type II error (failing to reject the null hypothesis when it is false), it can be concluded that the likelihood of a type II error is greater in Trial X than in Trial Y.

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41.

A 60-year-old woman with a 1-year history of diabetes mellitus has had decreasing vision over the past year. Examination of the eyes shows milky opacity of both lenses. Which of the following aberrant metabolites of glucose is most likely responsible for the formation of this abnormality?
- A.
  
  Fructose
- B.
  
  Glycogen
- C.
  
  Lactose
- D.
  
  Sorbitol
- E.
  
  Sucrose
Correct Answer
D. Sorbitol

Explanation
Sorbitol is the most likely aberrant metabolite of glucose responsible for the formation of milky opacity in the lenses of the eyes. In diabetes mellitus, excess glucose in the blood is converted to sorbitol by the enzyme aldose reductase. Sorbitol accumulates in the lens and draws water into it, causing swelling and opacity. This condition is known as diabetic cataracts and can lead to vision loss.

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42.

A 12-year-old African American girl is brought to the emergency department by her mother because of a 6-hour history of fever and severe rib pain. She has had numerous episodes in the past. Her paternal aunt and uncle have had similar symptoms since youth. Her temperature is 39°C (102.2°F). The lungs are clear to auscultation. Abdominal examination shows tenderness to palpation. A peripheral blood smear is shown in the photomicrograph. Which of the following is the most likely underlying cause of this patient’s symptoms?
- A.
  
  Abnormal folding of the hemoglobin molecule caused by increased PCo2
- B.
  
  Abnormal hydrogen bonding in the hemoglobin caused by amino acid substitution on the a chain
- C.
  
  Decreased oxygen affinity caused by an amino acid substitution in the hemoglobin a chain
- D.
  
  Erythrocyte fragility caused by an amino acid substitution in glycoproteins on the cell surface
- E.
  
  Polymerization of hemoglobin with hypoxic conditions due to amino acid substitution in the B chain
Correct Answer
E. Polymerization of hemoglobin with hypoxic conditions due to amino acid substitution in the B chain

Explanation
This patient's symptoms, including fever, severe rib pain, and a history of similar symptoms in her paternal aunt and uncle, are consistent with sickle cell disease. Sickle cell disease is caused by a mutation in the hemoglobin beta (B) chain, resulting in the substitution of valine for glutamic acid at position 6. This amino acid substitution leads to the polymerization of hemoglobin under hypoxic conditions, causing the characteristic sickle shape of red blood cells. This can lead to vaso-occlusive crises and tissue ischemia, explaining the patient's symptoms.

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43.

A previously healthy 54-year-old man comes to the clinic because of light-headedness for 6 hours. His symptom began after skiing at a resort at an altitude of 2743 m (9000 ft). He has been taking a carbonic anhydrase inhibitor since 2 days before arrival at the resort. His blood pressure is 110/60 mmHg while sitting and 95/50 mmHg while standing. Physical examination shows no other abnormalities. Which of the following is the most likely cause of his orthostatic hypotension?
- A.
  
  High-altitude sickness
- B.
  
  Hypovolemia
- C.
  
  Hypoxia
- D.
  
  Impaired sympathetic nerve activity
- E.
  
  Respiratory alkalosis
Correct Answer
B. Hypovolemia

Explanation
The most likely cause of this patient's orthostatic hypotension is hypovolemia. The patient's symptoms began after skiing at a high altitude, which can cause fluid loss and dehydration. Additionally, the patient has been taking a carbonic anhydrase inhibitor, which can lead to increased urinary bicarbonate excretion and subsequent volume depletion. The low blood pressure while standing further supports the diagnosis of hypovolemia. High-altitude sickness, hypoxia, impaired sympathetic nerve activity, and respiratory alkalosis are less likely causes in this scenario.

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44.

A 5-y/o 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 B-globin chain is 15% to 20% of normal. Sequencing of the B-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 B-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?
- A.
  
  Capping with GTP
- B.
  
  Cleavage and polyadenylation
- C.
  
  Silencing of the promoter
- D.
  
  Splicing of the initial mRNA transcript in the nucleus
- E.
  
  Transport of the mRNA out of the nucleus
Correct Answer
B. Cleavage and polyadenylation

Explanation
The sequence AATAAA is known as the polyadenylation signal sequence, which is involved in the cleavage and polyadenylation of mRNA. Cleavage and polyadenylation is an important step in mRNA processing, where the pre-mRNA is cleaved and a poly(A) tail is added to the 3' end. This poly(A) tail protects the mRNA from degradation and is important for mRNA stability and translation. In this case, the point mutation in the sequence AATAAA leads to a decrease in the amount of mRNA for B-globin, indicating a defect in the cleavage and polyadenylation process.

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45.

An 18-year-old primigravid woman at approximately 16 weeks gestation comes to the physician because of a 3-month history of nausea and vomiting. She has not had any prenatal care. Physical examination shows a uterus consistent in size with a 20-week gestation. Her serum B-human chorionic gonadotropin concentration is markedly increased. Urinalysis shows 4+ protein. Ultrasonography of the abdomen shows echogenic material within the endometrial cavity but no fetus. The most likely cause of her condition is proliferation of which of the following?
- A.
  
  Allantois
- B.
  
  Blastocysts
- C.
  
  Decidua basalis
- D.
  
  Decidua capsularis
- E.
  
  Trophoblastic tissue
Correct Answer
E. Trophoblastic tissue

Explanation
The patient's presentation of a markedly increased serum beta-human chorionic gonadotropin (beta-hCG) concentration, a uterus consistent in size with a 20-week gestation, and the presence of echogenic material within the endometrial cavity but no fetus suggests a molar pregnancy, specifically a complete hydatidiform mole. In a complete mole, there is proliferation of trophoblastic tissue, which leads to the characteristic findings seen in this patient. The other answer choices, such as allantois, blastocysts, decidua basalis, and decidua capsularis, are not associated with the specific findings seen in a molar pregnancy.

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46.

A 60-year-old man conies to the physician because of skin blistering for 1 week. Six months ago, he had blisters in his mouth that easily ruptured. Physical examination shows scattered blisters over the upper and lower extremities and trunk intermingled with crusted denuded areas. A biopsy specimen of an early lesion shows intraepidermal vesicle formation. Direct immunofluorescence microscopy of intact skin shows deposits of IgG on keratinocytes. Which of the following structures is most likely involved in the skin disorder in this patient?
- A.
  
  Adherens junctions (zonulae adherentes)
- B.
  
  Desmosomes (maculae adherentes)
- C.
  
  Gap junctions
- D.
  
  Hemidesmosomes
- E.
  
  Tight junctions (zonulae occludentes)
Correct Answer
B. Desmosomes (maculae adherentes)

Explanation
The patient's presentation of skin blistering and crusted denuded areas, along with the biopsy findings of intraepidermal vesicle formation and deposits of IgG on keratinocytes, suggests a diagnosis of pemphigus vulgaris. Pemphigus vulgaris is an autoimmune disorder that affects desmosomes, which are specialized cell junctions that provide strong adhesion between epithelial cells. Disruption of desmosomes leads to separation of the epidermis, resulting in the formation of blisters. Therefore, desmosomes (maculae adherentes) are most likely involved in the skin disorder in this patient.

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47.

A 55-year-old man recovered from a stroke 2 months ago He lives alone. He is at increased risk for which of the following psychiatric disorders?
- A.
  
  Agoraphobia
- B.
  
  Major depressive disorder
- C.
  
  Obsessive-compulsive disorder
- D.
  
  Post-traumatic stress disorder
- E.
  
  Social phobia
Correct Answer
B. Major depressive disorder

Explanation
After recovering from a stroke, individuals may experience a range of emotional and psychological changes. The man in this scenario lives alone, which can contribute to feelings of isolation and loneliness. Major depressive disorder is a psychiatric disorder characterized by persistent feelings of sadness, hopelessness, and a loss of interest in activities. Given the man's age, recent stroke, and living situation, he is at an increased risk for developing major depressive disorder.

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48.

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 (98.67), pulse is 105/min, respirations are 161rnin, and blood pressure is 150/90 mmHg. 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 IIb/IIIa receptor. This antibody will most likely prevent binding of which of the following substances to platelets?
- A.
  
  Adenosine
- B.
  
  ADP
- C.
  
  Fibrinogen
- D.
  
  Serotonin
- E.
  
  Thrombin
- F.
  
  Thromboxane A2
Correct Answer
C. Fibrinogen

Explanation
The monoclonal antibody against the platelet IIb/IIIa receptor is given to prevent binding of fibrinogen to platelets. Fibrinogen is an essential protein for platelet aggregation and clot formation. By blocking the binding of fibrinogen to platelets, the antibody helps to prevent further clot formation and reduce the risk of thrombus formation. This is important in the management of the patient's angina pectoris, as it helps to prevent the progression of his symptoms and reduce the risk of myocardial infarction.

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49.

An investigator breeds a transgenic strain of mice that develops severe fasting hypoglycemia. Administration of glucagon does not correct the hypoglycemia, but administration of epinephrine results in an increase in the serum glucose concentration. Which of the following proteins is most likely defective in this mouse strain?
- A.
  
  Adenylyl cyclase
- B.
  
  Glucagon receptor
- C.
  
  Glycogen phosphorylase
- D.
  
  Heterotrimeric G protein
- E.
  
  Phosphorylase kinase
- F.
  
  Protein kinase A
Correct Answer
B. Glucagon receptor

Explanation
The correct answer is the glucagon receptor. The fact that administration of glucagon does not correct the hypoglycemia suggests that there is a problem with the receptor that normally binds to glucagon. This receptor is responsible for activating adenylyl cyclase, which in turn stimulates the production of glucose. Since administration of epinephrine, which acts through a different pathway, results in an increase in serum glucose concentration, it indicates that the problem lies specifically with the glucagon receptor.

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50.

A 3-year-old boy with a history of unexplained fever, lack of perspiration, absence of response to noxious stimuli, and self-mutilating behavior is diagnosed with congenital insensitivity to pain with anhidrosis. Genetic analysis shows a missense mutation of the tyrosine kinase domain of the TrkA gene. Assuming this is the only signaling defect in this patient, which of the following processes has most likely been disrupted?
- A.
  
  Binding of nerve growth factor to its receptor
- B.
  
  Formation of TrkA homodimer in response to nerve growth factor
- C.
  
  Phosphorylation of downstream molecules in response to nerve growth factor
- D.
  
  Retrograde transport of nerve growth factor from nerve terminals
- E.
  
  Synthesis of nerve growth factor
Correct Answer
C. Phosphorylation of downstream molecules in response to nerve growth factor

Explanation
http://hmg.oxfordjournals.org/content/10/3/179.fullNerve growth factor (NGF) supports the survival of sympathetic ganglion neurons and nociceptive sensory neurons in dorsal root ganglia derived from the neural crest and ascending cholinergic neurons of the basal forebrain. Human TRKA (also named NTRK1) was isolated from a colon carcinoma as a potential new member of the tyrosine kinase gene family and expression of TRKA(trk) was later found in the nervous system. TRKA is a receptor tyrosine kinase which is phosphorylated in response to NGF . The binding of NGF to TRKA stimulates homodimer formation and activation of tyrosine kinase activity. Phosphorylated tyrosine residues in the TRKA cytoplasmic domain serve as anchors for BINDING DOWNSTREAM SIGNALING MOLECULES.

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NBME 13 Section 4 (Qst 1-50)

A 3-year-old girl is found to have a grade 4/6, loud, harsh, high-pitched holosystolic murmur that radiates over the precordium and a palpable thrill at the left sternal border. Which of the following defects is most likely in this patient?

11. A 43-year-old woman with metastatic colon cancer has maintained remission by taking bevacizumab as a single agent. The ability to administer this agent despite it being a foreign protein is most likely a result of which of the following?

A 42-year-old man has an autoimmune disorder resulting in proximal muscle weakness of the lower extremities. Arrows in the photomicrograph shown indicate membranes that contain high concentrations of channels that are targeted by this condition. Which of the following is the most likely diagnosis?

A 45-year-old woman has a 2-week history of a heart murmur and hepatomegaly. She has a 3-month history of flushing with hypotension and crampy diarrhea. Which of the following is the most likely site of a primary neoplasm in this patient?

A researcher in a pharmaceutical company designs a new protease inhibitor that inhibits replication of HIV in T lymphocytes in culture. In subsequent assays, which of the following findings is most likely to indicate that the compound is working specifically as a protease inhibitor?

A 77-year-old woman dies in the hospital after a long illness. Her vertebral column, obtained at autopsy, is shown in the photograph. The process shown is most likely associated with an increase in which of the following?

In a healthy person, the thyroid gland produces and secretes thyroxine (T4), maintaining metabolism. Which of the following best describes the T4-binding substance in the blood and the type of cellular receptor for T4 in the peripheral tissues?

A 65-year-old woman with diabetic ketoacidosis has had a fever and proptosis of the left eye over the past 3 days. She is unable to move the left eye. A black eschar is present on the nasal mucosa. Which of the following is the most likely diagnosis?

A 60-year-old woman with a 1-year history of diabetes mellitus has had decreasing vision over the past year. Examination of the eyes shows milky opacity of both lenses. Which of the following aberrant metabolites of glucose is most likely responsible for the formation of this abnormality?

A 55-year-old man recovered from a stroke 2 months ago He lives alone. He is at increased risk for which of the following psychiatric disorders?