USMLE USMLE-STEP-1 Online Practice Questions and Exam Preparation

USMLE USMLE-STEP-1 Online Questions & Answers

• Question 471:

  An advertisement promotes energy bars containing fructose as an ideal food to take on extreme mountain- climbing expeditions. Which of the following statements concerning fructose absorption is true?

  A. absorption of fructose into an intestinal epithelial cell is by facilitated transport and thus does not require energy
  B. metabolism of fructose generates more energy than glucose
  C. some fructose is already absorbed in the mouth and hence is the fastest way to get energy
  D. the presence of fructose aids in absorption of vitamin A, C, and D
  E. the presence of fructose inhibits reabsorption of glucose, which is then more readily available for muscle activity
  A. absorption of fructose into an intestinal epithelial cell is by facilitated transport and thus does not require energy

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  Explanation

  Section: Physiology Carbohydrate absorption occurs at enterocytes of the upper region of small intestinal villi. Fructose absorption is via the facilitated transporters GLUT5 across the apical enterocyte membrane and GLUT2 across the basolateral enterocyte. Glucose and galactose on the other hand are transported into enterocytes on carriers in combination with a sodium ion. The energy for this secondary active transport is provided by the electrochemical sodium gradient that is created by Na/K-ATPases. Experimental conditions that collapse the sodium electrochemical gradient, hypoxia, or poisoning of the Na-KATPase by ouabain inhibit glucose, but not fructose absorption. Nevertheless, the physiological importance of "saving energy" under extreme conditions such as mountain climbing through the use of fructose as energy source is questionable. For instance, fructose absorption is much slower than absorption of glucose and galactose.

  The statements in choices B, C, D, and E are incorrect.

• Question 472:

  Which of the following is the most treatable dementing disease?

  A. Alzheimer's disease
  B. Creutzfeldt-Jakob disease
  C. multi-infarct dementia
  D. Pick disease
  E. Wernicke syndrome
  E. Wernicke syndrome

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  Explanation

  Section: Behavioral Science and Biostatics Wernicke syndrome is caused by thiamine deficiency associated with alcohol withdrawal, and can be treated effectively. Alzheimer's disease (choice A) is the most common primary dementia in the elderly. About 50% of brains of demented patients show evidence of Alzheimer's disease. Creutzfeldt- Jakob (choice B) disease and kuru are slow virus infections that show clinical and histologic features similar to Alzheimer's disease. Multiinfarct dementia (choice C) is secondary to repeated cerebrovascular accidents (CVAs) in patients with underlying atherosclerosis or hypertension. It is more common among men than women. Pick disease (choice D) is a rare cause of cortical dementia. The presence of unilateral cortical atrophy in Pick disease contrasts with the bilateral atrophy evident in Alzheimer's disease. Microscopically, Pick bodies composed of densely packed neurofilaments are seen within diseased neurons.

• Question 473:

  A 22-year-old man is evaluated for repeated episodes of pulmonary infections, including a recent one that is productive of foul, purulent sputum, accompanied by shortness of breath. Past medical history is also significant for chronic sinus infections with mucopurulent discharge. Physical examination is remarkable for scattered rhonchi and rales throughout all lung fields. Imaging studies show abnormally dilated and thickened airways extending close to the pleural surface and a cardiac silhouette in the right thorax. Bronchoscopy demonstrates numerous mucopurulent plugs. Which of the following is most likely responsible for these changes?

  A. abnormal neutrophilic function resulting in impaired degranulation
  B. alpha-1 antiprotease deficiency (PiZZ phenotype)
  C. cell membrane defect resulting in abnormally viscous glandular secretions
  D. defect in ciliary motility due to the absence of dynein arms
  E. hypersensitivity reaction associated with c-ANCA and granuloma formation
  D. defect in ciliary motility due to the absence of dynein arms

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  Explanation

  Section: Pathology and Path physiology Kartagener syndrome is defined by the triad of bronchiectasis, sinusitis, and situs inversus that, in this patient, were apparent from the foul sputum, history of sinusitis, and location of the heart in the right chest. The cause of this syndrome is the lack of ciliary motility leading to poor clearing of the respiratory tract and susceptibility to infections. During embryogenesis, cilia assist with cell migration and the situs inversus is most probably the result of their lack of function. Abnormal neutrophilic function resulting in impaired degranulation (choice A) has been observed in different conditions including in HIV-infected patients but this cannot explain the situs inversus. Alpha-1 antiprotease deficiency (PiZZ phenotype) (choice B) is a cause of emphysema and liver cirrhosis, but is not associated with the findings in this patient. Cell membrane defect resulting in abnormally viscous glandular secretions (choice C) is a description of cystic fibrosis that is associated, among other things, with recurrent lung infections but not situs inversus. Hypersensitivity disease associated with c-ANCA and granuloma formation (choice E) is a description of Wegener granulomatosis which is associated with lung infections and sinusitis, but once again has no association with situs inversus.

• Question 474:

  A 10-year-old boy living in a wooded area of northern California is taken to the emergency room after developing a typical erythema migrans (EM) rash around what appears to bea tick bite, and complaining of severe headache. Which of the following is the most likely diagnosis?

  A. Lyme disease caused by
  B. recurrentis and transmitted by a body louse (Pediculus humanus)
  C. Lyme disease caused by
  D. relapsing fever caused by
  E. relapsing fever caused by
  I. pacifica
  B. recurrentis and transmitted by a body louse (Pediculus humanus)

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  Explanation

  Section: Microbiology/Immunology Lyme disease is named after the town of Lyme, Connecticut, where clusters of cases were identified in children. Lyme disease is caused by the spirochete B. burgdorferi, which grows most readily in a complex liquid medium. It has been isolated most easily from the characteristic skin lesion called erythema migrans. B. burgdorferi is transmitted by a small, hard-bodied tick of the genus Ixodes. The vector in the Northeast and Midwest is I. scapulous and I. pacificus on the West coast of the United States.

  There is often flu-like illness when the erythema migrans lesion (flat, reddened area with central clearing) is present. Late manifestations of arthralgia and arthritis are seen if early diagnosis and treatment (doxycycline or amoxicillin) is missed. Only B. burgdorferiappears to be etiologic and only hard-bodies Ixoid ticks appear to be vectors.

• Question 475:

  Which of the following drugs is used to accelerate pulmonary maturation in the fetus in women with premature labor?

  A. aminoglutethimide
  B. betamethasone
  C. mifepristone
  D. misoprostol
  E. prostacyclin
  B. betamethasone

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  Explanation

  Section: Pharmacology Glucocorticoids help accelerate maturation of the lungs in the fetus at the end of term. In preterm labor, these drugs help prevent respiratory failure in the newborn. Betamethasone is the preferred corticosteroid for this purpose because it is poorly bound in the maternal serum and transfers into the fetal circulation more readily. The other drugs listed (choices A, CE) are of no value in this setting.

• Question 476:

  A 50-year-old man is brought to the emergency room by the police because he was on the street screaming that the air was being poisoned. The man is very agitated, and requires restraint by the attendants. As you, the on-call physician, try to interview him, he tries to hit you and screams at you. Which of the following is the most appropriate first step in management?

  A. administer amobarbital by mouth
  B. give him an injection of haloperidol
  C. give him an injection of naloxone
  D. perform a physical examination
  E. reason with him that the air is not poisoned
  B. give him an injection of haloperidol

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  Explanation

  Section: Behavioral Science and Biostatics The management of acute psychosis involves use of parenteral antipsychotic drugs, such as haloperidol. Reasoning with a delusional patient (choice E) is usually futile, and an agitated and uncooperative patient is unlikely to permit a physical examination (choice D) or take an oral medication (choice A). Unless you know that the patient is intoxicated with opiates, naloxone (choice C) is unlikely to be of benefit.

• Question 477:

  Serotonin (5-HT) is one of several mediators of the signs and symptoms of carcinoid tumor. When released from this neoplasm, most of the manifestations of 5-HT are the result of activation of the 5-H receptor. These manifestations are therefore likely to include which of the following effects?

  

  A. bronchospasm
  B. constipation
  C. skeletal muscle weakness
  D. tachycardia
  E. ulceration of the stomach or duodenum
  A. bronchospasm

• Question 478:

  Cell adhesion molecules enable intercellular contacts in epithelial as well as nonepithelial cells. Which of the following cell adhesion molecules are calcium-dependent molecules?

  A. disintegrins
  B. integrins
  C. intercellular adhesion molecules (I-CAM)
  D. neural cell adhesion molecules (N-CAM)
  E. selectins
  E. selectins

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  Explanation

  Section: Anatomy

  Cell adhesion molecules are divided into two major classes on the basis of their dependence on calcium. Calcium-dependent cell adhesion molecules are the cadherins and the selectins. Calcium- independent cell adhesion molecules include members of the immunoglobulin superfamily, the I-CAM (choice C), and the N- CAM, as well as the integrins (choice B). Disintegrins (choice A) are found in snake venom and disrupt the integrin-mediated cell binding to extracellular matrix proteins such as laminin or fibronectin.

• Question 479:

  The phosphorylase kinase-associated regulatory protein identified by the letter A in below figure is a calcium-binding protein. Which of the following proteins represents this regulatory subunit?

  

  A. calmodulin
  B. fructose-2,6-bisphosphate
  C. glycogen synthase kinase-3
  D. phosphoprotein phosphatase
  E. phosphoprotein phosphatase inhibitor-1
  A. calmodulin

• Question 480:

  After total thyroidectomy as a result of a car accident, a 47-year-old woman is positive for Trousseau sign. It is manifested as carpopedal spasm occurring after an inflated blood pressure cuff is held above systolic blood pressure for a few minutes. Which of the following would best describe her postoperative condition when compared to preoperative?

  A. decreased deep tendon reflexes
  B. higher serum calcitonin levels
  C. lower serum calcium levels
  D. lower serum phosphate levels
  E. shorter Q-T interval of her ECG
  C. lower serum calcium levels

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  Explanation

  Section: Physiology A positive Trousseau sign indicates increased neuromuscular irritability, which is caused by low serum calcium levels. Apositive Trousseau sign or a positive Chvostek sign (spasms of facial muscles) can often diagnose hypocalcemia before other gross manifestations develop. Serum calcium is regulated by parathyroid hormone produced by the parathyroid glands. During the woman's accident, the glands, or their vasculature, were most likely damaged enough so that they could not be saved during the total thyroidectomy. If total thyroidectomy occurs as a consequence of thyroid cancer, damage to all four parathyroid glands would be considered an operative mishap. A consequence of hypocalcemia is hyperreflexia and not hyporeflexia (choice A). Calcitonin is secreted by parafollicular or "C" cells in the thyroid gland. Since no other cells of the body make this hormone, serum calcitonin levels do not rise (choice B), but instead go to zero postoperative. Low serum phosphate levels (choice D) typically signify secondary hyperparathyroidism or low dietary phosphate intake. In the current case, high or unchanged serum phosphate would be expected. The Q-T interval of the ECG represents the time for both ventricular depolarization and repolarization to occur. It therefore roughly estimates the duration of an average ventricular action potential. Hypocalcemia leads to a long Q-T interval, not a short Q-T as in choice E. In severe cases, this can lead to arrhythmias, hypotension, and heart failure.