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

USMLE USMLE-STEP-1 Online Questions & Answers

• Question 221:

  A 32-year-old man presents with diarrhea and symptoms of peptic ulcer disease. Endoscopy reveals two ulcers, one in the first portion of the duodenum and one in the midduodenum. However, they do not respond to the usual peptic ulcer treatment programs. The most likely explanation for the findings in this patient is which of the following?

  A. antibodies to intrinsic factor
  B. ectopic hypersecretion of gastrin
  C. gastric mucosal atrophy
  D. pressure ulceration from bezoars
  E. vascular abnormality
  B. ectopic hypersecretion of gastrin

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  Explanation

  Section: Pathology and Path physiology Peptic ulcerations seen in ZollingerEllison syndrome are due to ectopic hypersecretion of gastrin. An islet cell tumor of the pancreas is the most frequent ectopic site. Antibodies to intrinsic factor (choice A) are seen with pernicious anemia and usually cause gastric mucosal atrophy and metaplasia. Gastric mucosal hypertrophy, not atrophy (choice C), is the expected result with an increased secretion of gastrin as is seen with ZollingerEllison syndrome. Pressure ulceration from bezoars (choice D) and vascular abnormalities (choice E) are not the etiology of the peptic ulcerations seen with Zollinger Ellison syndrome.

• Question 222:

  Which of the following drugs is useful for the treatment of panic disorder?

  A. bupropion
  B. olanzapine
  C. phenobarbital
  D. sertraline
  E. valproic acid
  D. sertraline

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  Explanation

  Section: Behavioral Science and Biostatics In addition to SSRIs such as sertraline, paroxetine and fluoxetine, tricyclic antidepressants, MAOIs, and high-potency benzodiazepines such as alprazolam and clonazepam may be effective in panic disorder. Olanzapine (choice B) is an atypical antipsychotic and has not been shown to be effective in panic disorder. Bupropion, an antidepressant (choice A), phenobarbital, a CNS depressant (choice C), and valproic acid, an anticonvulsant and antimanic drug (choice E) are also ineffective in panic disorder.

• Question 223:

  A 17-year-old male college student is brought to the emergency room, displaying vomiting, fever, and diarrhea. The patient reports that for a period of 24 hours prior to admission, he suffered from abdominal pain first centered around the navel and then moving inferiorly to the right. As the patient talks, you realize that he is gesturing toward McBurney's point. You tentatively diagnose acute appendicits and request emergency surgery. Accurate visual identification of the appendix during surgery can be verified by using which of the following landmarks?

  A. bifurcation of the abdominal aorta
  B. epiploic appendages
  C. haustra
  D. inferior border of the right kidney
  E. taeniae coli
  E. taeniae coli

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  Explanation

  Section: Anatomy The position of the appendix varies depending on the patient. The taeniae coli are three longitudinal bands of smooth muscle running the length of the colon. Since the appendix is part of the colon, the taeniae coli can be accurately followed to this structure. The bifurcation of the abdominal aorta (choiceA) and inferior border of the right kidney (choice D) are retroperitoneal and would not be of value in identification of the appendix. The epiploic appendages (choice B) are small pockets of fatty tissue along the length of the colon, but they are not found on the appendix. The haustra (choice C) are sacculations of the large intestine resulting from contractions of the taeniae coli.

• Question 224:

  A 35-year-old woman with hypertension is planning to become pregnant. Which of the following is contraindicated in pregnancy?

  A. clonidine
  B. hydralazine
  C. hydrochlorothiazide
  D. losartan
  E. methyldopa
  D. losartan

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  Explanation

  Section: Pharmacology Losartan causes renal damage in the fetus, and renal impairment in renovascular disease. It is contraindicated in pregnancy. Clonidine (choice A) causes some sedation and rebound hypertension when stopped suddenly, but is not contraindicated in pregnancy. Hydralazine (choice B) causes a reversible type of lupus erythematosus. Hydrochlorothiazide (choice C) may cause hypokalemia, dilutional hyponatremia, elevated lipids, hyperuricemia, and glucose intolerance. Methyldopa (choice E) causes sedation and formation of red blood cell antibodies, but has been shown to be safe in pregnancy.

• Question 225:

  A rabbit is repeatedly injected with a peptide hapten. Two weeks later, its serum is subjected to a gel diffusion assay with the hapten and a carrier protein. Which of the following would be the expected result of the gel diffusion assay?

  A. A line of identity between serum and both the carrier and the hapten will be present.
  B. A line of identity between the serum and carrier protein will be detected.
  C. A line of nonidentity between serum, carrier, and hapten will be detected.
  D. A line of partial identity between serum, carrier, and hapten will be detected.
  E. No precipitin line will be present.
  E. No precipitin line will be present.

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  Explanation

  Section: Microbiology/Immunology By definition, a hapten is a substance of low molecular weight that by itself does not elicit the formation of antibodies. However, when attached to a carrier protein, antibody production becomes possible. The haptencarrier approach has been employed to produce antibodies against penicillin, steroids, nucleotides, lipids, and even 2,4-dinitrophenol. Since the rabbit has been repeatedly injected with the hapten only, the serum cannot be expected to have antibodies against the hapten. It is clear that when the serum is subjected to a gel diffusion assay with the hapten and a carrier protein not used to complex the hapten during immunization, no antigen-antibody precipitin lines of either identity, partial identity, or nonidentity can be expected to form (choices A, B, C, and D).

• Question 226:

  Exhibit #1:

  Missing Exhibit #2:

  

  The data in below figure indicate that the lung compliance in this patient (solid line) is altered relative to the norm. This patient is most likely suffering from which of the following conditions?

  A. A
  B. B
  C. C
  D. D
  E. E
  B. B

• Question 227:

  A 28-year-old male patient suffering from head trauma resulting from a car accident is brought unconscious to the emergency room. In performing the pupillary light reflex, you notice that even though the left pupil constricts when you shine a light directly into the left eye, it does not do so when you shine a light into the right eye. This is best explained by a disconnection between which of the following bilateral structures?

  A. Edinger-Westphal nucleus
  B. habenula
  C. inferior colliculus
  D. lateral geniculate nucleus
  E. medial geniculate nucleus
  A. Edinger-Westphal nucleus

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  Explanation

  Section: Anatomy The central visual pathway for the papillary light reflex is organized as follows: fibers from the ganglionic layer of the retina project posteriorly to the pretectum, which in turn innervates the Edinger- Westphal nucleus. Preganglionic parasympathetic neurons in the Edinger- Westphal nucleus project to the ciliary ganglion, which sends postganglionic parasympathetic innervation back to the constrictor pupillae of the eye. The Edinger-Westphal nuclei from each side of the midbrain are also connected to each other by projections running through the posterior commissure. Disconnection of these fibers will result in loss of the consensual papillary light reflex on the contralateral side, as happens in this case. The habenula (choice B) is a nucleus of the thalamus, which does not participate in the central visual pathways. The lateral geniculate nucleus (choice D) receives fibers from the ganglionic layer of the retina. However, fibers participating in the papillary light reflex run through this structure without synapsing and terminate in the pretectum. Thus, the lateral geniculate nucleus does not participate in the pupillary light reflex. The inferior colliculus (choice C) and the medial geniculate nucleus (choice E) are components of the auditory system.

• Question 228:

  A middle-aged, markedly obese male patient presents to the emergency room with pain in the inguinal region. Examination reveals an abnormal bulge which increases in size when the patient performs the Valsava maneuver. The bulge can be reduced manually when the patient is lying supine. However, as soon as the patient stands up and coughs, the bulge reappears. The patient is diagnosed with an inguinal hernia. The chief resident in surgery asks for a determination of whether the hernia is direct or indirect. Which of the following is a useful landmark to distinguish an indirect from a direct inguinal hernia?

  A. anterior superior iliac spine
  B. inferior epigastric vessels
  C. inguinal ligament
  D. pubic tubercle
  E. umbilicus
  B. inferior epigastric vessels

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  Explanation

  Section: Anatomy The inferior epigastric vessels lie medial to the deep inguinal ring. An indirect inguinal hernia leaves the abdominal cavity through the deep inguinal ring and is thus always localized lateral to the inferior epigastric vessels. Adirect inguinal hernia results from weakness in the posterior wall of the inguinal canal and pushes through the conjoint tendon to reach the superficial inguinal ring. The direct inguinal hernia is thus always located medial to the inferior epigastric vessels. The anterior superior iliac spine (choice A) and pubic tubercle (choice D) are respectively located too far laterally or medially to be of use in distinguishing indirect from direct hernias. The inguinal ligament (choice C) is used to istinguish a femoral hernia which is always located inferior to this structure. The umbilicus (choice E) is the site for an umbilical hernia and not inguinal hernias.

• Question 229:

  Five weeks after returning from visiting relatives in New England, a 22-year-old man develops severe headaches, fever, chills, fatigue, and multiples skin lesions. During the physical examination, the skin lesions are noted to be slightly raised and erythematous but are nontender. He states that a similar single lesion appeared on his thigh just before his return, but he was otherwise asymptomatic. Based upon this information, the most likely causative agent is which of the following?

  A. Borrelia burgdorferi
  B. Francisella tularensis
  C. Rickettsia rickettsii
  D. Toxoplasma gondii
  E. Yersinia pestis
  A. Borrelia burgdorferi

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  Explanation

  Section: Pathology and Path physiology Lyme disease (caused by the spirochete B. burgdorferi) occurs worldwide but in the United States is found principally in northeastern and some mid-western states. It is transmitted by the Ixodes tick and the site of its bite is usually indicated by an expanding erythematous lesion with central clearing (erythema chronicum migrans (stage 1), which corresponds to the lesion the patient found just prior to his return home. Days or weeks following this stage, the organisms spread hematogenously and may cause secondary skin lesions, fever, chills, fatigue, severe headaches, arthralgias, and cardiac arrhythmias as well as many other findings (stage 2). It was at this point that the patient presented to is physician. Without treatment, many months later patients may enter stage 3 and develop more severe complications, including frank arthritis and encephalopathy. Tularemia is a zoonosis caused by F. tularensis (choice B); transmission occurs from contact with wild animals or biting insects. It is common in the southern Midwestern region. Infection typically results in an ulcerative lesion at the inoculation site and regional lymphadenopathy. R. rickettsii (choice C) causes Rocky Mountain spotted fever, the most severe of the rickettsial diseases. Intracellular infection of systemic and pulmonary endothelial cells via tick or insect vector causes a macular rash, appearing first on the wrists and ankles with subsequent spread to the full extremity and the trunk. Typically by 1 week lesions become hemorrhagic and form petechiae.

  Extensive microcirculatory infection may cause significant multisystemic effects, causing mortality in 35% of cases. Infection with the parasite T. gondii (choice D) is most often associated with immunocompromised patients; transmission typically occurs from ingestion of soil contaminated with cysts shed in cat feces or from undercooked meat. Common manifestations include cervical lymphadenopathy in immunocompetent individuals and CNS involvement in the immunocompromised. Y. pestis (choice E) is the bacterium responsible for causing plague, a zoonotic disease carried by rats and wild rodents; it is transmitted to humans by bites from infected fleas. There are three forms of plague--bubonic, septicemic, and pneumonic. Bubonic is the most common, and is associated with a characteristic lymphadenopathy of rapid onset in which enlarging lymph nodes (buboes) become progressively painful and tender, often surrounded by considerable edema.

• Question 230:

  Naloxone would be contraindicated in an apparently psychotic patient if one were to also discover which of the following?

  A. The patient had a psilocybin-induced psychosis.
  B. The patient has hypertension.
  C. The patient has just suffered a fracture.
  D. The patient is a placebo responder.
  E. The patient is an alcohol abuser.
  C. The patient has just suffered a fracture.

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  Explanation

  Section: Behavioral Science and Biostatics Naloxone is an opiate antagonist, and would be contraindicated in a patient with fracture who would require rapid pain relief. The placebo analgesic effect seems to be endorphin mediated, and naloxone would block it. The other choices do not deal with naloxone's specific anti-opioid activity.