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

USMLE USMLE-STEP-1 Online Questions & Answers

• Question 1:

  A 35-year-old male with end-stage renal disease must undergo a kidney transplant. Which of the following is true of immunologic suppression for transplantation?

  A. It can occur by antilymphocyte globulin.
  B. It cannot be achieved by cyclosporine administration.
  C. It cannot occur by lymphoid irradiation.
  D. It is facilitated by gamma interferon administration.
  E. It is not likely to respond to steroid administration.
  A. It can occur by antilymphocyte globulin.

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  Explanation

  Section: Microbiology/Immunology There are various ways by which immunologic suppression for transplanted tissue can occur. One of these ways is administration of antilymphocyte globulin. Other means used to obtain immunologic suppression for transplantation include destruction of B and T lymphocytes by irradiation (choice C). Cyclosporin is also used to achieve immunologic suppression for transplantation. It is thought to inhibit interleukin-2, which drives antigen-activated cells to proliferate (choice B). Steroid administration is an effective means to suppress the immune system (choice E). Suppression of transplanted tissue cannot be obtained by interferon administration, because interferon inhibits translation of viral mRNA (choice D).

• Question 2:

  During development, the notochord grows in a cranial direction until it reaches the prechordal plate. This plate is the primordium of the oropharyngeal (or buccopharyngeal) membrane, which, in the embryo, will separate the stomodeum from the foregut. At 26 days of gestation, the oropharyngeal membrane will break down, allowing communication of the foregut with the oral cavity. Of the following structures in the adult, which one lies at the same location as the embryonic oropharyngeal membrane?

  A. buccinators
  B. palatoglossus
  C. palatopharyngeus
  D. stylopharyngeus
  E. superior constrictor
  B. palatoglossus

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  Explanation

  Section: Anatomy The palatoglossus muscle, which can be observed in the oral cavity to form the palatoglossal arch anterior to the palatine tonsil, lies in the same location as the embryonic oropharyngeal membrane. It lies at the junction line between the stomodeum and the foregut. The buccinator (choice A) is a muscle of the cheek and thus is located in the original stomodeum. The palatopharyngeus (choice C) is located posterior to the palatoglossus and palatine tonsil, forming the palatopharyngeal arch. The palatopharyngeus, stylopharyngeus (choice D), and superior constrictor (choice E) muscles are all pharyngeal muscles and thus are located in the original foregut.

• Question 3:

  A foul-smelling specimen was obtained from a 26-year-old female with a pelvic abscess. Culture grew both aerobic and anaerobic gramnegative bacteria. Which of the following represent the cultured organisms?

  A. israelii and
  B. fragilis
  C. difficile and
  E. coli and Peptostreptococcus spp.
  C. difficile and

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  Explanation

  Section: Microbiology/Immunology Medically important infections due to anerobic bacteria are common. The infections are often polymicrobic, being mixed with other anerobes, facultative anerobes, and aerobes. Anerobes are found in all parts of the body including skin, intestinal tract, oral cavity, and urogenital mucosa. Infection usually occurs when anerobes contaminate usually sterile body sites or are heavily inoculated with anerobes. Most of the B. fragilis bacteria contain small amounts of catalase and SOD, allowing them to survive oxygen toxicity. Their usual clinical manifestation is an abscess. Anerobes produce an extremely foul odor from abscess pus or growth on media. In this scenario, choice C could be the proper answer. A. israelii (choice A) is anerobic but not usually involved in intra-abdominal/pelvic abscess formations. L. monocytogenes (choice B) enters the GI tract by ingestion of contaminated food (cheese or vegetables). L. monocytogenes is usually found in intrauterine infections, bacteremias, and CNS infections. C.

  difficile (choice D) is usually present in small numbers and increases when broad- spectrum antibiotics have been used with the patient. C. difficile produces toxins that act on the intestinal lining, producing severe diarrhea. Peptostreptococci (choice E) are anerobic streptococci, usually found in the intestine. These and E. coli would not likely to be routinely found as etiologic causes of pelvic abscesses.

• Question 4:

  Below figure is a high magnification photomicrograph of the gall bladder. The arrow points to the internal lining that is formed by which of the following?

  A. pseudostratified columnar epithelium
  B. simple columnar epithelium
  C. stratified cuboidal epithelium
  D. stratified squamous epithelium
  E. transitional epithelium
  B. simple columnar epithelium

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  Explanation

  Section: Anatomy The lining of the gallbladder is a simple columnar epithelium identifiable by tall cells with elongated nuclei arranged at the same level. Pseudostratified epithelium (choice A) is distinguishable from the simple columnar epithelium by the cell nuclei being arranged at different levels. Stratified cuboidal epithelium (choice C) is characterized by short cells with nuclei arranged at different levels. Stratified epithelium (choice D) has a characteristic cellular basal layer with flat degenerate cells in its upper layer.

  Transitional epithelium (choice E) is a type of stratified epithelium exclusively confined to the urinary tract.

• Question 5:

  S-pyogenes, Group A, is subdivided into specific antigenic types principally on the immunologic differences in which of the following?

  A. hyaluronic acid capsule
  B. M protein
  C. streptolysin O
  D. streptolysin S
  E. TSST
  B. M protein

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  Explanation

  Section: Microbiology/Immunology M protein (choice B) is a major virulence factor of Group AS. pyogenes. M proteins appear as hair-like projections of the cell wall which resist phagocytosis by PMNs. Group A Streptococci are nonvirulent, and antibodies to specific M proteins will protect against reinfection. There are, however, more than 80 types of M protein, with little cross-protection observed. M protein may well have an important role in the pathogenesis of rheumatic fever. Purified streptococcal cell wall membranes induce antibodies that cross- react with human cardiac sarcolemma. Acomponent of the cell wall of selected M types induces antibodies that react with cardiac muscle tissue. The M protein serotypes are used to subdivide Group A streptococci into 80 different serotypes. The other choices (A, C, D, and E) are all virulence factors of Group Astreptococci, but do not form the basis of identifying antigenic different subgroups or serotypes.

• Question 6:

  A 14-year-old boy presents with weight loss and diarrhea. His tongue becomes sore and blistery after eating oatmeal or rye bread, which leads to the diagnosis of celiac disease. The boy and his parents are advised to be sensitive to symptoms of tetany and paresthesias, since they can occur as a consequence of malabsorption of which of the following?

  A. calcium
  B. carbohydrates
  C. fat
  D. iron
  E. water
  A. calcium

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  Explanation

  Section: Physiology In patients with celiac disease the protein gluten, which is found in bread, oats, and many other foods containing wheat, barley, or rye, triggers an autoimmune response that causes damage to the small intestine leading to widespread manifestations of malabsorption. Calcium is difficult to absorb, so patients frequently experience symptoms of hypocalcemia such as muscle cramping, titanic contractions, numbness, and tingling sensations. For sensory and motor nerves, calcium is a critical second messenger involved in normal cell function, neural transmission, and cell membrane stability. The nerves respond to a lack of calcium with hyperexcitability. The inability to absorb nutrients such as carbohydrates (choice B) leads to weight loss as experienced by the boy. Fat malabsorption (choice C) is not uncommon in patients with celiac disease as a consequence of greatly diminished absorptive surface. It would manifest in steatorrhea. Iron (choice D), like calcium, is difficult to absorb and may lead to anemia. The general decrease in electrolyte absorption leads to decreased water absorption (choice E). The increased osmotic load in the GI lumen accounts for the boy's diarrhea.

• Question 7:

  Evaluating the cause for a coma can be challenging. As a first step, the causes can be divided into two broad categories, structural/ surgical and metabolic/medical reasons. Which of the following findings suggests a metabolic cause in a comatose patient?

  A. failure to withdraw from painful stimuli
  B. gross blood in the cerebrospinal fluid
  C. impaired pupillary light responses
  D. posturing of limbs
  E. serum sodium of 115 meq/L
  E. serum sodium of 115 meq/L

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  Explanation

  Section: Physiology Hyponatremia of this magnitude for any reason is likely to cause seizures and coma, especially if the deviation from normal occurred rapidly (e.g., over 1 or 2 days). Withdrawal from painful stimuli (choice A) is a normal reaction. If intact, it would have provided information on the intactness of sensation and motor reflexes on the tested side. However, lack of withdrawal would be consistent with either a structural or a metabolic cause of coma, and therefore does not help. Blood in the cerebral spinal fluid (choice B) in a nontraumatic lumbar puncture suggests a structural rather than a metabolic cause of coma. Pupillary light responses (choice C) are typically preserved in metabolic encephalopathies. Posturing of limbs (choice D) is suggestive of a focal process involving the brainstem or midbrain rather than a metabolic encephalopathy.

• Question 8:

  Normal metabolism by the body generates large quantities of acid. In spite of this, normal blood pH is a slightly alkaline 7.4. This extracellular fluid alkalinity is maintained primarily by the body's removal of which of these?

  A. ammonia
  B. carbon dioxide
  C. keto acids such a acetoacetic acid
  D. lactic acid
  E. titratable acids such as phosphoric acid
  B. carbon dioxide

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  Explanation

  Section: Physiology The vast majority of metabolic acid excretion is in the form of the volatile acid carbon dioxide which is removed via the lungs. Much smaller quantities of nonvolatile acids must be excreted in the urine. Titratable acids, such as phosphoric acid (choice E), make up a large fraction of the acids normally excreted in the urine. When stored fats are metabolized in large quantities, such as in diabetes mellitus, keto acids such as acetoacetic acid (choice C) make up a larger portion of the renal excreted titratable acids. Likewise, when the ischemic tissues pursue anaerobic metabolism, lactic acid (choice D) makes up a larger portion of the renal excreted titratable acids. Ammonia (choice A) is not a titratable cid, but it provides a mechanism for the kidney to excrete large amounts of acid during chronic metabolic acidosis.

• Question 9:

  Mifepristone has antagonist action at which of the following receptors?

  A. beta adrenoceptors
  B. dopamine receptors
  C. insulin receptors
  D. low-density lipoprotein receptors
  E. progesterone receptors
  E. progesterone receptors

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  Explanation

  Section: Pharmacology Mifepristone, also known as RU 486, is an effective antagonist at progesterone and glucocorticoid receptors. It has no effect on the other receptors listed (choices AD).

• Question 10:

  A 45-year-old man is bitten by a poisonous snake the venom of which triggers the release of thromboplastin in his circulation. Which of the following would you most expect to see as a consequence of this event?

  A. abnormal neutrophilic degranulation resulting in small vessel vasculitis and subsequent hemorrhage or thrombosis
  B. deposition of antigen-antibody complexes in various tissue beds, causing vasculitis with thrombosis, glomerulonephritis, and arthritis
  C. formation of multiple, migratory peripheral venous thromboses without evidence of tissue ischemia or hemorrhage
  D. immediate mast cell degranulation of vasoactive amines followed by progressive vascular leakage and subsequent tissue ischemia
  E. widespread development of thrombi in the microvasculature followed by hemorrhage
  E. widespread development of thrombi in the microvasculature followed by hemorrhage

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  Explanation

  Section: Pathology and Path physiology Thromboplastin-like substances (or tissue factor) released into the circulation can initiate disseminated intravascular coagulation (DIC). In this situation, thromboplastin activates the coagulation cascade, leading to the formation of multiple thrombi distributed throughout the microvasculature. As this process progresses, platelets and coagulation factors are consumed and hemorrhage can occur; bleeding is exacerbated by activation of the fibrinolytic system. Abnormal neutrophilic degranulation resulting in small vessel vasculitis and subsequent hemorrhage or thrombosis (choice A) is an example of a type II hypersensitivity reaction associated with circulating antineutrophil cytoplasmic antibodies (ANCA); examples of ANCA-associated vasculitides include Wegener granulomatosis and Churg-Strauss syndrome. Deposition of antigen-antibody complexes in various tissue beds, causing vasculitis with thrombosis, glomerulonephritis, and arthritis (choice B) describes a nonspecific systemic type III hypersensitivity response (which takes several days to develop). Formation of multiple, migratory peripheral venous thromboses without evidence of tissue ischemia or hemorrhage (choice C) refers to igratory thrombophlebitis, a condition associated with certain types of cancers, particularly adenocarcinomas in which hypercoagulability occurs as a paraneoplastic syndrome; this is referred to as Trousseau syndrome. These and other tumors are also independently capable of initiating DIC. Immediate mast cell degranulation of vasoactive amines followed by progressive vascular leakage and subsequent tissue ischemia (choice D) describes anaphylaxis, a type I hypersensitivity reaction.