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

USMLE USMLE-STEP-1 Online Questions & Answers

• Question 231:

  A 43-year-old woman with a long history of chronic allergies visits her primary care physician with a 2-week history of progressive left perinasal pain and nasal pressure, increasing episodes of yellowish- green nasal discharge, and a fever 1 day prior of 100.8<pdf2txt-u>癋</pdf2txt-u>. Sign ificant findings on physical examination include a temperature of 101.0<pdf2txt-u>癋</pdf2txt-u>, tenderness to palpation ove r the left maxillary sinus, and nasal speculum observation of obstruction of the left middle meatus by a large, pale, polypoid mass with a small focus of ulceration and a similar but smaller mass seen in the right middle meatus. A clinical diagnosis of left maxillary sinusitis is made and the patient is started on antibiotics. She is subsequently referred to an otolaryngologist who excises the bilateral masses to relieve the sinus obstruction. Which of the following findings would you expect the pathologist to see on microscopic examination of these masses?

  A. hyperkeratotic squamous epithelium with a submucosal core of myxoid connective tissue, frequent blood vessels, mild fibrosis, and a mononuclear infiltrate
  B. myofibroblastic proliferation in a dense fibrovascular stroma with numerous endothelial-lined channels
  C. papillomatous proliferation of squamous epithelium extending downward through the submucosal connective tissue
  D. respiratory epithelium containing an edematous, loose stroma and a mixed inflammatory infiltrate, with a prominence of neutrophils and eosinophils
  E. undifferentiated large epithelial cells with round vesicular nuclei and prominent nucleoli in a syncytial arrangement with a marked lymphocytic infiltration
  D. respiratory epithelium containing an edematous, loose stroma and a mixed inflammatory infiltrate, with a prominence of neutrophils and eosinophils

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  Explanation

  Section: Pathology and Path physiology Given the history of allergies and the finding of bilateral polypoid masses, it is most likely that this patient has nasal polyps, the typical histology of which is as described. Hyperkeratotic squamous epithelium with a submucosal core of myxoid connective tissue, frequent blood vessels, mild fibrosis, and a mononuclear infiltrate (choice A) is the histological description of a vocal cord polyp. Myofibroblastic proliferation in a dense fibrovascular stroma with numerous endothelial-lined channels (choice B) describes the histology of a nasopharyngeal angiofibroma. Papillomatous proliferation of quamous epithelium extending downward through the submucosal connective tissue (choice C) refers to an inverted papilloma. An undifferentiated large epithelial cells with round vesicular nuclei and prominent nucleoli in a syncytial arrangement with a marked lymphocytic infiltration (choice E) is the histological description of an undifferentiated nasopharyngeal carcinoma.

• Question 232:

  A 50-year-old woman complains of a lump in her thyroid gland. Fine-needle aspiration of this lump is reported as medullary carcinoma. A test of her serum would most likely reveal an increased level of which of the following?

  A. alpha-Fetoprotein
  B. cancer antigen (CA) 125
  C. CA 153
  D. calcitonin
  E. human chorionic gonadotropin
  D. calcitonin

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  Explanation

  Section: Pathology and Path physiology Calcitonin is a hormone secreted by the parafollicular C cells of the thyroid gland. Medullary carcinoma arises from malignant transformation of these cells. Alpha-fetoprotein (choice A) may be elevated in the serum in association with hepatocellular carcinomas and gonadal tumors. CA 125 (choice B) is a tumorassociated glycoprotein frequently expressed by ovarian carcinomas. CA 153 (choice C) is a tumor- associated glycoprotein frequently expressed by breast carcinomas. Elevations of human chorionic gonadotropin (choice E) in the serum may be seen in normal pregnancies, gonadal tumors, and choriocarcinomas.

• Question 233:

  Which of the following implies the multiaxial diagnostic system in psychiatric disorders?

  A. All psychiatric disorders are personality disorders.
  B. Psychiatric disorders and other diseases can coexist.
  C. Psychiatric disorders are a subset of medical diseases.
  D. Psychiatric disorders are complex.
  B. Psychiatric disorders and other diseases can coexist.

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  Explanation

  Section: Behavioral Science and Biostatics Axis I of the multiaxial system is for clinical psychiatric disorders such as schizophrenia and mood disorders. Axis II is for personality disorders and mental retardation. Axis III is for general medical conditions (such as myocardial infarction). Axis IV is for psychosocial and environmental problems and Axis V is for global assessment of functioning. This classificatory system clearly indicates that psychiatric disorders (Axis I) and general medical disorders (Axis III) often do coexist and may influence each other.

  Choices A, C, and D are not part of the multiaxial system.

• Question 234:

  The great cerebral vein of Galen indicated by arrow 4 in following figure is formed by the union of two internal cerebral veins and drains into which of the following?

  

  A. confluence of sinuses
  B. frontal sinus
  C. sphenoid sinus
  D. straight sinus
  E. superior sagittal sinus
  D. straight sinus

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  Explanation

  Section: Anatomy The great cerebral vein of Galen (arrow 4) drains posteriorly into the straight sinus (arrow 5). The union of the superior sagittal sinus (choice E; arrow 3) and the straight sinus forms the confluence of sinuses (choice A). The straight sinus and superior sagittal sinus are dural venous sinuses: they contain venous blood draining form the brain, skull, and scalp. The frontal sinus (choice B) and the sphenoid sinus (choice C) are bony sinuses: they are hollow, airfilled structures and do not drain venous blood.

• Question 235:

  Exhibit #1:

  

  Exhibit #2:

  

  Below figure shows the change in the membrane potential of a postsynaptic neuron caused by addition, at the arrow, of a neurotransmitter. The resting membrane potential of this cell is -80 mV. Relevant equilibrium potentials for +, , +, , and are, respectively, +120 mV, +60 mV,

  

  0 mV, -80 mV, and -90 mV. This neurotransmitter likely increases the conductance of which of the following ions?

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

• Question 236:

  The graph in below figure shows the jugular vein pressure curve of this patient. If the first heart sound occurs between letters C and D, which part of the curve represents the atrial contraction?

  

  A. peak A
  B. peak C
  C. peak D
  D. trough B
  E. trough E
  B. peak C

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  Explanation

  Section: Physiology below figure shows the jugular vein pressure curve. Pressure in the jugular vein reflects atrial pressure and is highest during the atrial contraction (named the "a wave"). The "v wave" (choice A) represents the rise in atrial pressure before the tricuspid valve opens during diastole. The "y notch" (choice D) is due to the fall in atrial pressure during the ventricular filling phase. The "c wave" (choice C) is due to the rise in atrial pressure produced by the bulging of the tricuspid valve during isovolumetric contraction of the right ventricle. The "x notch" (choice E) coincides with the ventricular ejection phase.

• Question 237:

  An 8-year-old boy is referred to a neurologist by his family physician because he has developed progressive slow and clumsy walking. On examination, the patient has difficulty with standing and running. While standing, he adopts a wide-based gait with constant shifting of position to maintain his balance. Sitting or standing, he also displays a constant tremor of the head and trunk. When asked to walk, his feet strike the ground in an uneven and irregular rhythm; if he attempts to correct his imbalance, he displays wild and abrupt movements. A magnetic resonance image (MRI) reveals demyelination in the dorsal columns, corticospinal and spinocerebellar tracts. The child is diagnosed with Friedreich's ataxia, an autosomal recessive neurological disorder resulting from mutation of a gene locus on chromosome 9. Second-order neurons of the dorsal (posterior) spinocerebellar tracts are located in which of the following?

  A. deep cerebellar nuclei
  B. dorsal root ganglion
  C. nucleus cuneatus
  D. nucleus dorsalis (Clarke's column)
  E. Rexed's lamina IX of the spinal cord
  D. nucleus dorsalis (Clarke's column)

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  Explanation

  Section: Anatomy The nucleus dorsalis (Clarke's column, Rexed's lamina VII of the spinal cord) contains the cell bodies of the second order neurons of the dorsal (posterior) spinocerebellar tract. Axons from these neurons ascend ipsilaterally in the lateral funiculus of the spinal cord, join the restiform body of the inferior cerebellar peduncle, and terminate in the vermis of the cerebellum as mossy fibers. The dorsal (posterior) spinocerebellar tract conveys proprioception from muscle spindles and Golgi tendon organs. Collateral branches of this tract also terminate in the deep cerebellar nuclei (choice A). The dorsal root ganglion (choice B) contains the cell bodies of sensory neurons, including the first-order neurons of the dorsal (posterior) spinocerebellar tract. The nucleus cuneatus (choice C) contains the second order neurons of the dorsal column pathways, responsible for conveying sensations of fine touch, pressure, and vibration sense. Rexed's lamina IX of the spinal cord (choice E) contains the spinal cord motorneurons responsible for the innervations of voluntary muscles.

• Question 238:

  Potassium supplementation is often necessary for patients taking large doses of which of the following drugs?

  A. amiloride
  B. captopril
  C. hydrochlorothiazide
  D. losartan
  E. spironolactone
  C. hydrochlorothiazide

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  Explanation

  Section: Pharmacology Hydrochlorothiazide causes potassium wasting and may lead to hypokalemia requiring dietary potassium supplementation. Potassium wasting is characteristic of diuretics that present more sodium to the collecting tubule, where sodium is conserved in exchange for potassium under the control of aldosterone. Therefore, diuretics that act in the proximal convoluted tubule (carbonic anhydrase inhibitors), ascending limb of the loop of Henle (loop diuretics), and distal convoluted tubule (thiazides) cause potassium wasting and may lead to dangerous hypokalemia. Angiotensin antagonists (because they interfere with aldosterone secretion) and aldosterone inhibitors have the opposite effect. Amiloride (choice A) and spironolactone (choice E) are aldosterone antagonists; captopril (choice B) and losartan (choice D) are angiotensin antagonists. The latter agents cause potassium retention and may cause hyperkalemia, not hypokalemia.

• Question 239:

  Muscle membrane will depolarize in response to acetylcholine binding its receptors at the neuromuscular junction. Associated with this depolarization are changes in glycogen metabolism in skeletal muscle cells. Which of the following represents the correct changes in enzyme activity seen in response to acetylcholine binding?

  A. decreased glycogen phosphorylase kinase activity due to an increase in calcium binding to its calmodulin subunit
  B. decreased phosphorylation of, and inhibited activity of glycogen phosphorylase kinase
  C. increased glycogen phosphorylase kinase activity due to an activation of phosphoprotein phosphatase
  D. increased glycogen phosphorylase kinase activity due to an increase in calcium binding to its calmodulin subunit
  E. increased phosphorylation of, and inhibited activity of glycogen phosphorylase kinase
  D. increased glycogen phosphorylase kinase activity due to an increase in calcium binding to its calmodulin subunit

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  Explanation

  Section: Biochemistry The binding of acetylcholine to its receptor at the neuromuscular junction results in depolarization of the muscle membrane. This event triggers the release of calcium ions from the sarcoplasmic reticulum. The increase in intracellular calcium concentration leads to many changes in enzyme activity. One effect of calcium is that it is bound by various calciumregulated binding proteins. One of the subunits of glycogen phosphorylase kinase is calmodulin, a calcium-binding protein. The interaction of calcium with calmodulin alters the conformation of calmodulin, which leads to an activation of glycogen phosphorylase kinase activity in the absence of phosphorylation. The activity of glycogen phosphorylase kinase is increased not decreased (choice A) by calcium interaction with calmodulin present in the enzyme complex. Increases in intracellular calcium (as in response to acetylcholine binding at the neuromuscular junction) do not affect the level of phosphorylation of glycogen phosphorylase kinase (choices B and E) nor does it affect the activity of phosphoprotein phosphatase (choice C).

• Question 240:

  A newborn infant suffers from cyanotic heart disease caused by transposition of the great arteries (TGA). In this situation, the aorta arises from which of the following structures?

  A. ductus arteriosus
  B. left atrium
  C. left ventricle
  D. right atrium
  E. right ventricle
  E. right ventricle

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  Explanation

  Section: Anatomy In TGA, the aorta arises from the right ventricle and the pulmonary trunk arises from the left ventricle (choice C). This is the reverse of the normal situation and gives rise to the cyanotic condition in the newborn. The large arteries arise from the truncus arteriosus in the developing heart and thus could not develop from the atria (choices B and D), which are formed from the sinus venosus. The truncus arteriosus and the sinus venosus are at opposite ends of the heart. The ductus arteriosus (choice A) is the vessel that shunts oxygenated blood from the pulmonary trunk to the arch of the aorta in the fetus. It does not give rise to the aorta.