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

USMLE USMLE-STEP-1 Online Questions & Answers

• Question 741:

  below figure depicts an electrophoretic pattern of serum proteins. This electrophoretic pattern is likely to be obtained from a 6-month-old infant suffering from recurrent pyogenic infections. He has which of the following diseases?

  

  A. Addison disease
  B. Bruton disease
  C. Graves disease
  D. Goodpasture syndrome
  E. Myasthenia gravis
  B. Bruton disease

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  Explanation

  Section: Microbiology/Immunology Bruton disease is an X-linked congenital agammaglobulinemia. Thus, electrophoresis of the serum of infants, after the passively transferred maternal antibodies have been eliminated, reveals the absence or very low levels of gamma globulin. In contrast to Bruton disease all the other diseases listed will reveal a gamma globulin peak. Goodpasture syndrome (choice C) and Addison disease (choice A) are caused by autoantibody production to basement membrane of kidney and adrenal cortex, respectively.

  Myasthenia gravis (choice E) involves autoantibody production to acetylcholine receptor of the neuromuscular junctions. Graves disease (choice D) is caused by autoantibody production to thyroid- stimulating hormone receptors.

• Question 742:

  A 28-year-old man has a long history of intermittent bloody diarrhea. The colon is surgically removed and displayed in below figure. The most likely diagnosis is which of the following?

  

  A. amebic colitis
  B. collagenous colitis
  C. gangrenous colitis
  D. pseudomembranous colitis
  E. ulcerative colitis
  E. ulcerative colitis

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  Explanation

  Section: Pathology and Path physiology The colon segment in figure demonstrates ulcerative colitis. The disease is limited to the colon and preferentially involves in continuity the rectum, sigmoid, and descending colon. The affected colon demonstrates a red, granular mucosa with occasional pseudopolyp formation. Deep fissures, skip lesions with alternating areas of diseased and normal colon, and strictures do not typically occur. Amebic colitis (choice A) is usually limited to the right colon and displays multiple, scattered, separate ulcerations. In collagenous colitis (choice B), the colon appears grossly normal. Gangrenous colitis (choice C) has an acute clinical course. Grossly, the colon demonstrates a transmural area of blackened, thinned tissue. Pseudomembranous colitis (choice D) is usually an acute colitis occurring after antibiotic therapy. White, custard-like debris that partially coats the mucosal surface is the characteristic gross observation of pseudomembranous colitis.

• Question 743:

  A newborn infant suffers from epidermolysis bullosa simplex, characterized by skin blistering soon after birth. The blisters appear at sites of pressure or rubbing such as the fingers. You explain to the distressed parents that this condition is a disease of intermediate filaments and results from mutant genes for keratins K5 and K14. Which cells of the skin normally produce keratins K5 and K14?

  A. adipose cells in the hypodermis
  B. basal cells of the epidermis
  C. fibrocytes of the dermis
  D. melanocytes of the epidermis
  E. upper differentiating cells of the epidermis
  B. basal cells of the epidermis

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  Explanation

  Section: Anatomy Basal cells of the epidermis produces keratins K5 and K14. Adipose cells in the hypodermis (choice A), fibrocytes of the dermis (choice C), and melanocytes of the epidermis (choice D) do not synthesize keratins. Upper differentiating cells of the epidermis (choice E) produce keratins K1 and K10. A keratin K9 is also found in the palmar or plantar regions of the epidermis.

• Question 744:

  Ayoung woman presents to the physician with the chief complaint of palpitations. She also complains of feelings that she is going to die, with feelings of dizziness. Which of the following is the most useful question to ask?

  A. Are you anxious?
  B. Do you have a heart disease?
  C. Has anything like this happened before?
  D. What drugs do you use?
  E. Why do you think you will die?
  C. Has anything like this happened before?

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  Explanation

  Section: Behavioral Science and Biostatics The patient presents with acute anxiety symptoms that might be due to panic or other acute situations. Panic disorder usually is recurrent and history of previous episodes would be extremely helpful. Choice A is inappropriate; the patient is obviously anxious. Choices B, D, and E may be useful but not yield as much information.

• Question 745:

  Aliver biopsy of a 61-year-old man reveals the presence of clusters of cells with large, intracellular vacuoles and nuclei eccentrically displaced to the cell periphery. From which of the following conditions does this patient most likely suffer?

  A. alcoholism
  B. chronic liver congestion
  C. hepatitis A
  D. metastatic colon carcinoma
  E. portal vein thrombosis
  A. alcoholism

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  Explanation

  Section: Pathology and Path physiology The biopsy findings are descriptive of macrovesicular fatty change, a characteristic morphological change in the liver of patients with alcohol abuse. Morphological changes in chronic liver congestion (choice B) would demonstrate areas of centrilobular necrosis and hemorrhage, with hemosiderin-laden macrophages and varying degrees of acute inflammation. Fatty change is unusual in hepatitis A (choice C), and in most forms of hepatitis overall with the possible exception of hepatitis C, where typical morphological changes would include cellular edema, a cytoplasmic ground glass appearance, lymphocytic infiltrate, and focal or centrizonal necrosis. Histological findings for metastatic colon carcinoma (choice D) would demonstrate pleomorphic cells with hyperchromatic nuclei, and possible mitotic figures. Liver biopsy of an area with portal vein thrombosis (choice E) would reveal sinusoidal distention with areas of hemorrhage and hepatocellular atrophy.

• Question 746:

  Which of the following statements correctly associates a CNS drug with its mechanism of action?

  A. bupropion--activation of endocannabinoid receptors
  B. diazepam--facilitation of GABAstimulated chloride channel opening
  C. fluoxetine--selective inhibition of presynaptic norepinephrine reuptake
  D. pentobarbital--inhibition of NMDA receptors
  E. tranylcypromine--inhibition of O-methylation of catecholamines
  B. diazepam--facilitation of GABAstimulated chloride channel opening

• Question 747:

  A 57-year-old woman presents with an arterial pressure of 180/115 mm Hg, and blood creatinine levels are elevated. Renal angiography reveals a severe bilateral stenosis of the renal arteries. Which of the following are elevated also?

  A. ADH secretion
  B. GFR
  C. para-aminohippurate (PAH) clearance
  D. renin secretion
  E. urine output
  D. renin secretion

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  Explanation

  Section: Physiology The bilateral renal artery stenosis will reduce renal perfusion pressure. Hence the juxtaglomerular apparatus will greatly increase renin secretion which causes the large rise in arterial pressure because of the vasoconstrictor action of angiotensin II. A reduced renal perfusion pressure will decrease PAH clearance (choice C), which estimates renal blood flow and will reduce GFR (choice B). The decreased formation of tubular fluid will result in reduced urine output (choice E) and the large rise in arterial pressure will activate arterial baroreceptors and suppress ADH secretion from the posterior pituitary (choice A).

• Question 748:

  The occurrence of Type II diabetes (NIDDM) in adolescent females can lead to the development of polycystic ovarian syndrome (PCOS). PCOS is the result of follicular atresis and ovulatory dysfunction brought about by a hyperandrogenic microenvironment in the ovary. Which of the following statements reflects the underlying cause of the hyperandrogenic state in females with NIDDM?

  A. Hyperinsulinemia, associated with NIDDM, reduces the level of sex hormone-binding globulin leading to increased free testosterone.
  B. NIDDM in adolescents is primarily the result of obesity and the associated disruption in fatty acid metabolism negatively affects adrenal estrogen production.
  C. The increased level of circulating lipid in NIDDM patients competes for steroid binding to sex hormone- binding globulin, resulting in a reduced transport of estrogen within the ovary.
  D. The persistent hyperglycemia associated with NIDDM causes increased levels of glycosylated hemoglobin, which interferes with the need for increased ovarian vascularization at puberty.
  A. Hyperinsulinemia, associated with NIDDM, reduces the level of sex hormone-binding globulin leading to increased free testosterone.

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  Explanation

  Section: Biochemistry Adolescent females with Type II diabetes have a high occurrence of PCOS, which is brought on by the hyperinsulinemia associated with Type II diabetes. Insulin effects on the ovary drive conversion of progesterone to testosterone and a reduction in serum hormonebinding globulin (SHBG). Taken together, the effects of hyperinsulinemia lead to a hyperandrogenic state in the ovary resulting in follicular atresis and ovulatory dysfunction. None of the other options (choices BD) are associated effects caused by Type II diabetes leading to PCOS.

• Question 749:

  A 72-year-old man is discovered wandering in the hot sun by hospital staff several hours after being reported missing. Recommended testing involves analysis of serum electrolytes. The assay revealed the following serum values: Na+ 150 mEq/L, K+ 5.2 mEq/L. Which of the following is the most likely diagnosis?

  A. Alzheimer's disease
  B. delirium
  C. lewy body dementia
  D. secondary dementia
  E. seizure disorder
  B. delirium

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  Explanation

  Section: Behavioral Science and Biostatics The hypernatremia and hyperkalemia are indicative of dehydration, which is a common cause of delirium.

  Choices A, C, D, and E do not explain this phenomenon.

• Question 750:

  Which of the following statements concerning total body energy storage is correct?

  A. Most of the body's energy store is held as carbohydrate.
  B. Most of the body's energy store is held as lipid.
  C. Most of the body's energy store is held as plasma glucose.
  D. Most of the body's energy store is held as protein.
  E. Total body's energy storage approximately equals resting metabolic rate.
  B. Most of the body's energy store is held as lipid.

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  Explanation

  Section: Physiology Lipid is the most concentrated form of energy storage, holding 9.4 kcal/g. For a typical 70 kg human over 130,000 kcal is typically stored as fat. Storage of energy as available protein (choice D) is about 20,000 kcal, while storage as carbohydrate (choice A) is about 3,000 kcal. Though blood glucose (choice C) is critically important, in particular as a source of energy for the brain, blood glucose does not provide a significant fraction of total body energy storage. While total body energy stores typically exceed 150,000 kcal, resting metabolic rate (depending on age and body mass) is about 2100 kcal/day (choice E).