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

USMLE USMLE-STEP-1 Online Questions & Answers

• Question 631:

  A 10-year-old boy is brought to a pediatric clinic by his mother, who states that he has been voiding brown- colored urine for the past 2 days. The child's history is negative except for a sore throat about 2 weeks ago. Physical examination reveals moderate periorbital edema and mild hypertension. Urinalysis demonstrates red cells, both red and white cell casts, and 2+ protein. If a renal biopsy were obtained, what would be the characteristic light and/or electron microscopic finding in the glomeruli?

  A. hypercellularity with duplication of the basement membrane
  B. hypercellularity with subepithelial "humps"
  C. hypercellularity with "wire loop"lesions
  D. normocellularity with effacement of epithelial cell foot processes
  E. normocellularity with segmental sclerosis
  F. normocellularity with thickened basement membranes
  B. hypercellularity with subepithelial "humps"

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  Explanation

  Section: Pathology and Path physiology Acute postinfectious (poststreptococcal) glomerulonephritis occurs more commonly in young children following a sore throat or, less frequently, a skin infection. They usually present with mild periorbital edema, mild to moderate hypertension, and urinary changes. Urinalysis will show hematuria, mild proteinuria, and red and white cells casts. Light microscopy of a renal biopsy will reveal hypercellularity due to proliferation of endothelial and mesangial cells and the infiltration of neutrophils and monocytes.

  Immune complexes are deposited in the subepithelium of the glomerular basement membrane and may be seen as subepithelial "humps" by electron microscopy. Choices A, C, D, E, and F refer to the microscopic findings in membranoproliferative glomerulonephritis type 1, lupus nephritis, nil disease, focal segmental glomerulosclerosis, and membranous glomerulopathy, respectively.

• Question 632:

  An 18-year-old male patient was thrown from a horse and suffered extensive damage to the back and pelvic region. After 2 weeks of recovery, it is noted that the patient has a spastic neurogenic urinary bladder. Although the patient is unable to initiate micturition, the bladder periodically empties itself. Where is the lesion affecting control of the bladder in this patient located?

  A. cauda equine
  B. spinal cord, above the level of S2
  C. spinal cord, at the level of S2
  D. spinal cord, at the level of S3
  E. spinal cord, at the level of S4
  B. spinal cord, above the level of S2

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  Explanation

  Section: Anatomy Since the patient presents with a spastic neurogenic bladder, the lesion is in the spinal cord above the level of S2. The micturition reflex works as follows: when the bladder becomes distended, sensory impulses travel back from the bladder to synapse onto preganglionic parasympathetic neurons located at the levels of S2-S4. These neurons, in turn, excite postganglionic parasympathetic neurons which innervate and cause contraction of the detrusor muscle of the urinary bladder, thus emptying the bladder.

  This primitive reflex loop comes under supraspinal influence in early childhood when the child learns control of the micturition reflex. When the supraspinal influence is removed, as happens with spinal lesions above the level of S2, the primitive reflex loop remains and the neurogenic spastic bladder empties itself reflexively whenever it becomes full. Lesions in the cauda equina (choice A), or in the spinal cord at the level of S2 (choice B), S3 (choice D), or S4 (choice E) will result in a flaccid bladder because of loss of innervation to the detrusor muscle. In this case, the bladder does not contract by itself and the patient will have to be catherized to prevent cystitis.

• Question 633:

  An investigational diabetes treatment involving a hypoglycemia-inducing drug has been developed. This drug is designed to inhibit dipeptidylpeptidase IV (DPP IV) activity and has been shown to decrease plasma glucose concentration and pancreatic glucagon secretion. DPP IV hydrolyzes which of the following hormones such that its inhibition results in the observed effects?

  A. glucagon
  B. glucagon-like peptide-1 (GLP-1)
  C. insulin
  D. insulin-like growth factor-I (IGF-I)
  E. pancreatic polypeptide
  B. glucagon-like peptide-1 (GLP-1)

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  Explanation

  Section: Biochemistry GLP-1 is derived from the product of the proglucagon gene. This gene encodes a preproprotein that is differentially cleaved depending on the tissue in which it is synthesized. In the gut, prohormone convertase 1/3 action leads to release of several peptides including GLP-1. On nutrient ingestion GLP- 1 is secreted from intestinal enteroendocrine Lcells. Bioactive GLP-1 consists of two forms: GLP-1(7- 37) and GLP-1(7-36) amide, where the latter form constitutes the majority (80%) of the circulating hormone. The primary physiologic responses to GLP-1 are glucose-dependent insulin secretion, inhibition of glucagon secretion, and inhibition of gastric acid secretion and gastric emptying. The latter effect will lead to increased satiety with reduced food intake along with a reduced desire to ingest food. The action of GLP-1 at the level of insulin and glucagon secretion results in significant reduction in circulating levels of glucose following nutrient intake. The glucose-lowering activity of GLP-1 is highly transient as the halflife of this hormone in the circulation is less than 2 minutes. Removal of bioactive GLP-1 is a consequence of N- terminal proteolysis catalyzed by DPP IV. DPP IV is also known as the lymphocyte surface antigen CD26 and has numerous activities unrelated to hormone inactivation. Although targeting compounds that can inhibit the enzymatic action of DPP IV would seem like ideal candidates for treating the hyperglycemia of uncontrolled diabetes, there are several unknowns associated with DPP IV inhibition. One of these issues is the fact that GLP-1 is only one of the many known substrates for DPP IV cleavage. Thus, prolonged inhibition of DPP IV enzymatic activity may have unexpected consequences unrelated to control of hyperglycemia. DPP IV is not known to hydrolyze glucagons (choice A), insulin (choice C), IGF-I (choice D), nor pancreatic polypeptide (choice E).

• Question 634:

  A 66-year-old woman initially develops some subtle changes in memory, judgment, and behavior. However, this is followed by a very severe and rapidly progressive dementia that is accompanied by startle myoclonus. She dies 8 months after the original onset of her symptoms. Her disease is most likely the result of which of the following?

  A. acquired or inherited prion
  B. hereditary lysosomal storage disease
  C. increased neurofibrillary tangles (NFTs)
  D. protozoan infection
  E. repeated exposure to a chemical toxin
  A. acquired or inherited prion

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  Explanation

  Section: Pathology and Path physiology Creutzfeldt-Jakob disease is caused by a prion that may either be inherited or acquired during life. Prions are composed of protein only and behave like a slow viral infection. Human prion disease has recently become more prominent with the outbreak of mad cow disease in England due to human consumption of beef tainted with prions. Creutzfeldt- Jakob disease is not known to be inherited as a lysosomal storage disease (choice B) or to be caused by protozoan infections (choice D). Increased NFTs (choice C) are seen with Alzheimer's disease (AD), not Creutzfeldt- Jakob disease. Repeated exposure to chemical toxins (choice E) can cause dementia. Alcohol is a common example. However, the histology of chemical dementia usually differs in character and distribution from the cortical spongiform changes seen in Creutzfeldt-Jakob disease.

• Question 635:

  Diltiazem as used in angina pectoris has several beneficial actions that contribute to the prevention of the anginal symptoms. Which of the following actions is detrimental in angina?

  A. reduced arterial blood pressure
  B. increased diastolic heart size
  C. reduced systolic myocardial fiber tension
  D. bradycardia
  E. slowed AV conduction
  B. increased diastolic heart size

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  Explanation

  Section: Pharmacology Calcium channel blockers cause a decrease in arterial pressure, heart rate, and cardiac contractility, all of which help to reduce myocardial oxygen requirement and thereby reduce angina pain. However, the reduction in contractility increases diastolic cardiac size, which increases oxygen requirement and is therefore detrimental. The other effects listed (choices A, C, and E) are all valid beneficial actions of calcium blockers in angina. Slowed AV conduction E. occurs, but is of no significance in angina.

• Question 636:

  A 64-year-old man with long-standing hypertension experiences severe abdominal pain and loses consciousness. He dies en route to the hospital. Significant autopsy findings include dilation of the aorta just above the iliac bifurcation and massive abdominal hemorrhage. Which of the following was most likely the initiating event that resulted in his fatal lesion?

  A. antibody-mediated endothelial damage
  B. autosomal dominant inheritance of an abnormal gene on chromosome 15
  C. intimal proliferation with fibrous cap formation
  D. luminal narrowing of the vasa vasorum leading to medial degeneration and fibrosis
  E. ossification of calcific deposits in the tunica media
  C. intimal proliferation with fibrous cap formation

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  Explanation

  Section: Pathology and Path physiology This man had a ruptured abdominal aortic aneurysm. Most commonly, this is the result of severe atherosclerotic changes that lead to weakening, dilation, and possible rupture of the affected aorta. (In this case, the hypertension would have accelerated the atherosclerotic changes and increased the likelihood of rupture of the aneurysm.) Initial vascular changes found in atherosclerosis include intimal thickening and fibrous cap formation. Antibodymediated endothelial damage (choice A) is a common cause of vasculitis but is not involved in atherosclerosis. Of the diseases that result from autosomal dominant inheritance of an abnormal gene on chromosome 15 (choice B), the most common is probably adult polycystic disease but this has no bearing on the development of atherosclerosis. Luminal narrowing of the vasa vasorum leading to medial degeneration and fibrosis (choice D) is seen in the development of a syphilitic aortic aneurysm but has no role in this patient's disease process. Ossification of calcific deposits in the tunica media (choice E) and other areas of dystrophic calcification may occur as a complication of atherosclerotic plaques, but even if present in this patient, this process would not represent the initiating event.

• Question 637:

  A 22-year-old man complains to his family physician of fatigue, night sweats, and a dry unproductive cough. Until the past few months, he had apparently been in good health. Acomplete blood count (CBC) and differential blood count reveal that he is lymphopenic. X-ray examination reveals an interstitial pneumonia. Skin test reactions to a battery of materials are normal. Which of the following should be the next step in evaluating this patient's illness?

  A. CH50 complement assay
  B. chemotaxis assay
  C. identification of the organism that is causing the pneumonia
  D. intracellular killing assay
  E. nitroblue tetrazolium reduction assay
  C. identification of the organism that is causing the pneumonia

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  Explanation

  Section: Microbiology/Immunology The patient described in the question probably has AIDS. Such individuals will be lymphopenic and have greatly reduced immunity. AIDS victims commonly develop P. carinii pneumonia. The most important evaluative procedure for the patient described is determining the cause of the pneumonia so the problem can be corrected. Identifying the infecting organism may assist in the overall diagnosis. Choices A, B, D, and E involve innate immunity; either complement activity or phagocytic cell functions, and thus, would not be of much diagnostic assistance.

• Question 638:

  "Executive monkeys" as described by Brady tended to develop bleeding ulcers. Which of the following statements best characterizes them?

  A. Alpha monkeys that have the highest level of testosterone in the colony.
  B. Beta-male monkeys having too many decisions to make.
  C. Male monkeys that had too many available females.
  D. Monkeys that had to keep pressing bars to avoid shock.
  E. Monkeys that had to press a bar to get a pellet of food.
  D. Monkeys that had to keep pressing bars to avoid shock.

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  Explanation

  Section: Behavioral Science and Biostatics Monkeys that were placed in a highly complex operant conditioning program to avoid electric shock developed bleeding gastric ulcers, while yoked controls who received the same amount of shock, but did not have to perform the complex task, did not. The lack of a confirmatory feedback (such as a safe light or food to indicate a shock-free interval) seems to be especially ulcerogenic in Brady's "executive monkeys." Choices A, B, C, and E are incorrect.

• Question 639:

  Your young female patient has a large bulge on the anterior thigh below the inguinal ligament. You suspect an abdominal hernia that has passed through the femoral ring into the femoral sheath and then through the saphenous hiatus into the subcutaneous layer of the upper thigh. In addition to the hernia sac, you would expect the femoral canal to contain which of the following?

  A. connective tissue and lymph nodes
  B. femoral artery
  C. femoral nerve
  D. femoral vein
  E. great saphenous vein
  A. connective tissue and lymph nodes

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  Explanation

  Section: Anatomy The femoral canal, the medial compartment of the femoral sheath, contains only a slight amount of loose connective tissue and one or two lymphatic vessels and nodes. The femoral artery (choice B) is found in the lateral compartment of the femoral sheath with the genital branch of the genitofemoral nerve. The femoral nerve (choice C) is the most lateral structure in the femoral triangle, but it does not lie within the femoral sheath. The femoral vein (choice D) occupies the intermediate compartment of the femoral sheath. The saphenous vein (choice E) is a superficial vein that passes through the saphenous hiatus to end in the femoral vein. It does not lie within the femoral canal.

• Question 640:

  Ahemagglutination (HA) assay was performed with influenza virus. Afixed number of chicken red blood cells were mixed with increasing dilutions of the influenza virus. The results of the assay are shown in below figure. Which of the following represents the HA titer of the virus?

  

  A. 20
  B. 40
  C. 80
  D. 160
  E. 320
  C. 80

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  Explanation

  Section: Microbiology/Immunology The ability of certain viruses, such as influenza, mumps, and parainfluenza viruses, to agglutinate red blood cells is used to diagnose these viruses. In general, chicken or human type O red blood cells are employed for the identification of influenza and other viruses. Red blood cells have receptors for the surface component of the influenza virus called hemagglutinin. This hemagglutinin is a glycoprotein. In an HA assay, a fixed number of red blood cells is mixed with increasing dilutions of the influenza virus.

  Following incubation at 4°C for 2 hours, the tubes containing the red blood cells and the virus are examined for HA. Cells agglutinated by the virus form a lattice that covers the entire bottom of the test tube (virus dilutions 1:20; 1:40; 1:80). The HA titer of the virus is the highest dilution of virus that forms a lattice. In this case, the HA titer is 1:80. Unagglutinated cells form a dark bottom (virus dilutions 1:160; 1:320) (choices D and E).