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

USMLE USMLE-STEP-1 Online Questions & Answers

• Question 211:

  Worldwide, one of the most common parasitic infections is schistosomiasis. Assume a complete blood cell count is performed in a patient with this condition. Which of the following blood cells would most likely be present in elevated amounts?

  A. eosinophils
  B. erythrocytes
  C. monocytes
  D. neutrophils
  E. platelets
  A. eosinophils

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  Explanation

  Section: Physiology Eosinophils normally constitute about 2% of all blood leukocytes. These cells are phagocytic and exhibit chemotaxis. Their primary role is in fighting parasitic infection. In schistosomiasis the eosinophil attaches to the immature parasite and, by releasing various cytotoxic compounds, is able to kill the parasite. Erythrocytes (choice B) are the most numerous blood cells. They are not leukocytes, but function in blood gas transport. Erythrocyte number would not be increased in schistosomiasis. Monocytes (choice C) are leukocytes found in the blood. They are immature cells which migrate to the tissues, where they mature into macrophages. These cells are very active in phagocytosis and play a prominent role in the inflammatory response. They are not, however, particularly important in parasitic infections. Neutrophils (choice D) are another type of leukocyte that, though essential to combat bacterial infections, are not particularly sensitive to parasitic challenge. Platelets (choice E) are not leukocytes. The platelet is a cell fragment that functions in hemostasis.

• Question 212:

  Protein zero (P0) is the predominant protein in myelin in the peripheral nervous system and its function is to stabilize adjacent plasma membranes by interaction with similar P0 molecules. Which of the following cells manufacture P0?

  A. fibrous astrocytes
  B. microglia
  C. oligodendrocytes
  D. protoplasmic astrocytes
  E. Schwann cells
  E. Schwann cells

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  Explanation

  Section: Anatomy Schwann cells produce myelin in the peripheral nervous system whereas oligodendrocytes produce myelin in the central nervous system. Oligodendrocytes manufacture the proteolipid protein, the functional equivalent to P0 in the central nervous system. Fibrous (choice A) and protoplasmic (choice D) astrocytes are supportive cells which play a role in the regulation of brain metabolism. Microglia (choice B) are mesodermal in origin and have phagocytotic activity in the central nervous system.

• Question 213:

  Which of the following is the drug of choice to reverse bronchoconstriction in an acute asthma attack?

  A. albuterol
  B. aminophylline
  C. cromolyn
  D. ipratropium
  E. salmeterol
  A. albuterol

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  Explanation

  Section: Pharmacology Inhaled albuterol (or other beta-2-selective receptor agonists including bitolterol, metaproterenol, pirbuterol, and terbutaline) are the usual agents of choice for treating bronchoconstriction in an acute asthma attack. These beta-2-selective agonists produce bronchial relaxation by stimulating cyclic AMP (cAMP) formation in bronchiolar smooth muscle and cause less tachycardia than nonselective beta agonists. Unfortunately, they do cause some tachycardia and skeletal muscle tremor. Aminophylline (choice B) and other methylxanthines are rarely used to terminate acute episodes of asthma because they must be administered parenterally for rapid onset of effect. Cromolyn sodium (choice C) must be used prophylactically to prevent acute episodes and probably acts by stabilizing mast cells. It is not a smooth muscle relaxing agent and is not effective in reversing bronchospasm. Inhaled ipratropium (choice D) has less general efficacy in acute attacks than beta agonists. Salmeterol (choice E) is an effective beta- 2- selective agonist but has a slow onset and long duration of action. Therefore, it is used for prophylaxis, not treatment of acute attacks.

• Question 214:

  A neurologist is performing the neurological examination on a patient who recently suffered a head trauma. You note that, as part of the examination, she uses a cotton swab to touch the upper part of the auricle, the external auditory meatus, and the lobule. The external auditory meatus of the ear is innervated by which of the following?

  A. vagus (tenth cranial) nerve
  B. great auricular nerve
  C. auriculotemporal nerve
  D. greater occipital nerve
  E. facial (seventh cranial) nerve
  A. vagus (tenth cranial) nerve

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  Explanation

  Section: Anatomy The vagus (tenth cranial) nerve innervates the external auditory meatus of the ear. The great auricular nerve (choice B) innervates the lobule of the auricle and the auriculotemporal nerve (choice C), the superior aspect of the auricle. In fact, a sensory test which includes these three parts of the ear tests the integrity of the trigeminal (fifth cranial) nerve by the auriculotemporal nerve, the vagus (tenth cranial) nerve by its branch innervating the auditory meatus, and spinal nerves C2-3 by their great auricular branch. The test thus covers the upper and lower medulla and the upper spinal cord. The greater occipital nerve (choice D) is a branch of the cervical plexus originating from C2 and innervates the scalp of the back of the head. The facial (seventh cranial) nerve provides only motor innervation to the face and scalp areas.

• Question 215:

  A 72-year-old woman is brought to the clinic by her family because she is exhibiting confusion. Upon mental status examination, the patient demonstrates fluctuating levels of awareness. For example, she seems lucid 1 minute, then becomes somnolent or stuporous the next. Which of the following is most likely?

  A. delirium
  B. dementia
  C. factitious illness
  D. malingering
  E. stupor
  A. delirium

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  Explanation

  Section: Behavioral Science and Biostatics Fluctuating levels of awareness are characteristic of delirium, which is indicative of an encephalopathy due to metabolic derangement of the brain, such as anoxia, electrolyte imbalance, or hypoglycemia. Although delirium may be superimposed on dementia, at this point there is no evidence that the patient has the more stable cognitive deficits characteristic of dementia (choice B). Coma (choice D) and stupor (choice E) refer to more severe disturbance of sensorium. Factitious illness (choice C) is unlikely unless there is evidence of selfinduced metabolic derangement.

• Question 216:

  Which of the following agents is most effective as a cardiac stimulant in the treatment of severe beta- blocker overdose?

  A. atrial natriuretic peptide
  B. epinephrine
  C. glucagon
  D. human growth hormone
  E. insulin
  C. glucagon

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  Explanation

  Section: Pharmacology The cardiac manifestations of beta-blocker intoxication can be very severe, resulting in bradycardia, AV blockade, and markedly reduced force of contraction and cardiac output. Hypotension is common. However, the heart has glucagon receptors that are linked to stimulation of adenylyl cyclase independent of beta adrenoreceptors, which mediate marked increases in rate and force and substitute for the blocked beta response. (Glucagon also plays a primary role in raising blood glucose levels through activation of glycogenolysis and gluconeogenesis.) Atrial natriuretic peptide (choice A) is released from the cardiac atria and causes vasodilation through activation of membranebound guanylyl cyclase in arteriolar smooth muscle, and sodium excretion in the urine through an increase in glomerular filtration rate and consequent increase in filtration fraction. It is of no value in beta-blocker overdose. If the beta-blocker overdose is sufficient, administration of beta agonists such as epinephrine (choice B) is inadequate to overcome the blockade. Human growth hormone (choice D) is a peptide hormone produced by the anterior pituitary. It stimulates growth at open epiphyses through production of the insulin-like growth factors. It has no direct effect on cardiac function. Insulin (choice E) activates entry of glucose into most tissues and promotes glycogen and triglyceride storage. It has no direct effects on cardiac function.

• Question 217:

  Apatient has been severely injured in the back of the head during a mugging attempt and imaging studies reveal possible fracture of the skull along with the C1 (atlas) vertebra. The patient is also hemorrhaging from the vertebral artery in this location, and the attending surgeon will attempt to stop the bleeding by access through the suboccipital triangle. Which of the following muscles attaches from the transverse process of C1 to the occipital bone and forms the lateral border of the suboccipital triangle?

  A. obliquus capitis inferior
  B. obliquus capitis superior
  C. rectus capitis posterior major
  D. rectus capitis posterior minor
  E. semispinalis cervicis
  B. obliquus capitis superior

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  Explanation

  Section: Anatomy The obliquus capitis superior, attached between the transverse process of C1 and the suboccipital bone between the nuchal lines. It forms the lateral border of the suboccipital triangle. The obliquus capitis inferior (choice A) is the inferior border of the triangle, attaching from the spinous process of C2 to the transverse process of C1. The rectus capitis posterior major (choice C) inserts from the spinous process of C2 into the inferior nuchal line on the occipital bone; it forms the medial border of the suboccipital triangle. The rectus capitis posterior minor (choice D) lies medial to the rectus capitis posterior major. The semispinalis cervicis (choice E) does not participate in the formation of the suboccipital triangle.

• Question 218:

  In the brain, the amygdala plays an important role in emotional processing. Patients with lesion of the amygdala display impairment in enhanced perception of emotionally salient events. Which of the following is a major output pathway from the amygdala?

  A. fasciculus arcuatus
  B. fasciculus cuneatus
  C. fasciculus of Vicq d'Azyr
  D. fornix
  E. stria terminalis
  E. stria terminalis

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  Explanation

  Section: Anatomy The stria terminalis or fasciculus of Foville is one of the major output pathways from the amygdala to the septal, hypothalamic, and thalamic nuclei. Another main amygdaloid output pathway is the ventral amygdalofugal pathway. The fasciculus arcuatus (choice A) or superior longitudinal fasciculus is a bundle of fibers in the cerebrum connecting ipsilateral regions of the frontal, temporal, parietal, and occipital lobes. The fasciculus cuneatus (choice B) carries ascending sensory fibers in the dorsal funiculus of the spinal cord and terminates in the nucleus cuneatus of the medulla oblongata. The fasciculus of Vicq d'Azyr (choice C) or mammillothalamic tract connects the mammillary bodies to the anterior nuclei of the thalamus. This bundle of fibers forms part of Papez circuit, which is also involved in emotional processing. Another part of Papez circuit is the fornix (choice D), a large efferent pathway from the hippocampus.

• Question 219:

  Which of the following is the earliest developmental phase according to Piaget?

  A. concrete operations
  B. formal operations
  C. Oedipus complex
  D. preoperational phase
  E. sensorimotor period
  E. sensorimotor period

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  Explanation

  Section: Behavioral Science and Biostatics Piaget described the development of intelligent thinking in stages. The first is the sensorimotor period, 18 months2 years. This is followed by preoperational phase, 27 years (choice D); and the phase of concrete operations, 711 years (choice A), and the period of formal operations from adolescence through adulthood (choice B). Oedipus complex (choice C) is not a Piagetian stage, but is characteristic of ages 35.

• Question 220:

  Small, "fried-egg" colonies are produced in agar medium by which of the following pairs of agents?

  A. Acinetobacter and Legionella species
  B. Legionella and Mycoplasma species
  C. Mycoplasma and Acinetobacter species
  D. Mycoplasma and Gardnerella species
  E. Mycoplasma and L-form bacteria
  E. Mycoplasma and L-form bacteria

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  Explanation

  Section: Microbiology/Immunology Mycoplasma are cell-wall-free bacteria, as are L-form (L=Lister Institute) bacteria who temporarily lose their cell wall due to antibiotic treatment. Mycoplasma never possesses a cell wall but L-form bacteria will regain their cell walls when the antimicrobial affecting cell wall synthesis is removed. L- form bacteria have been a suggested mechanism for maintenance of some chronic infections, a controversial concept. All other genera (Acinetobacter, Legionella-- choice A, Gardnerella--choice D) form regular colonies on agar medium. Mycoplasma and Lform bacteria have very small colonies on the agar surface and substantial growth down into the agar medium in the colony center, giving the perception of "fried-egg" morphology to the colony.