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

USMLE USMLE-STEP-1 Online Questions & Answers

• Question 141:

  Additive and potentially dangerous sedative interactions may occur between sedativehypnotic drugs and which of the following herbal preparations?

  A. Echinacea
  B. gingko biloba
  C. ginseng
  D. kava
  E. St John's wort
  D. kava

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  Explanation

  Section: Pharmacology Unregulated herbal preparations are in heavy use by the public and several have been documented to interact with regularly prescribed drugs. Kava (choice D) has sedative actions and interacts additively with sedativehypnotics and sedative-antihistaminics. Echinacea (choice A) has no reported drug interactions to date but many preparations contain alcohol, which may increase sedation with alcohol- containing beverages. Gingko biloba (choice B) has antiplatelet activity and should not be used with aspirin or other antiplatelet drugs. Ginseng (choice C) may cause CNS stimulation and should not be used by patients with epilepsy and those taking psychoactive drugs. St John's wort (choice E) may inhibit metabolism of certain drugs.

• Question 142:

  The incretins are hormones that are released in response to the consumption of food. Which of the following represents one of the major effects of incretin release from intestinal epithelial cells?

  A. activation of gastric emptying ensuring release of ingested food
  B. enhancement in adipocyte triacylglycerol synthesis
  C. enhancement of insulin secretion from the pancreas
  D. repression of pancreatic cell proliferation
  E. stimulation of gastric acid secretion to aid in digestion
  C. enhancement of insulin secretion from the pancreas

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  Explanation

  Section: Biochemistry The incretins are molecules associated with food intake-stimulation of insulin secretion from the pancreas. Two of the many GI hormones have significant effects on insulin secretion and glucose regulation. These hormones are GLP-1 and glucose-dependent insulinotropic peptide (GIP). Both of these gut hormones represent the incretins. In contrast to activation of gastric emptying (choice A) and repression of pancreatic cell proliferation (choice D), GLP-1 inhibits gastric emptying and promotes a sense of satiety, induces proliferation, and represses apoptosis of pancreatic beta-cells. The incretins do not enhance adipose triacylglycerol synthesis (choice B). Repression of gastric acid secretion, not sitmulation (choice E) is one of the additional functions of GIP.

• Question 143:

  Corneal abrasions produce eye pain and excessive lacrimation. Which cranial nerve innervates the cornea?

  A. fifth (trigeminal)
  B. fourth (trochlea)
  C. second (optic)
  D. sixth (abducens)
  E. third (oculomotor)
  A. fifth (trigeminal)

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  Explanation

  Section: Anatomy The ophthalmic division of cranial nerve V (trigeminal) provides general sensory innervations to the eyeball, including the cornea. Cranial nerve II (optic, choice C) carries the visual function of the retina of the eye. Cranial nerves IV (trochlea, choice B) and VI (abducens, choice D) innervate the superior oblique and lateral rectus muscles, respectively. The innervation of all other extraocular muscles is performed by cranial nerve III (oculomotor, choice E).

• Question 144:

  A 78-year-old woman is found to have a first morning urine specific gravity of 1.010. Assuming that she has not had anything to drink since yesterday evening, this is most indicative of which of the following?

  A. acute pyelonephritis
  B. advanced renal failure
  C. diabetic glomerulosclerosis
  D. hyperlipidemia
  E. normal kidney function
  B. advanced renal failure

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  Explanation

  Section: Pathology and Path physiology Aurine specific gravity of 1.010 is the same as the specific gravity of glomerular filtrate (i.e., isosthenuric). Thus, this woman was not concentrating her urine overnight (usual SG > 1.020) which is an indication of severe renal damage as seen in advanced renal failure. Patients with acute pyelonephritis (choice A), diabetic glomerulosclerosis (choice C), and hyperlipidemia (choice D) who are not in advanced renal failure would still be expected to show some overnight concentrating ability as, of course, would normal kidney function (choice E).

• Question 145:

  Which of the following chemotherapeutic agents' mechanisms of action involves inhibition of topoisomerase II and results in DNA strand breakage?

  A. dacarbazine
  B. etoposide
  C. lomustine
  D. prednisone
  E. vincristine
  B. etoposide

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  Explanation

  Section: Pharmacology Etoposide is a semisynthetic derivative of podophyllotoxin, a constituent of the mandrake plant. Etoposide is an inhibitor of topoisomerase II, an enzyme that relaxes supercoiled DNA by breaking one strand and passing the second strand through the break before closing the break. Etoposide inhibits the closure step and results in an accumulation of DNA strand breaks, leading to cell death. Etoposide is used to treat testicular tumors and small cell carcinoma of the lung in combination with cisplatin.

  Leukopenia is the dose- limiting toxicity seen with this drug. Dacarbazine (choice A) is a synthetic prodrug activated in the liver to a metabolite that alkylates DNA leading to cytotoxicity. The drug is useful against melanoma and Hodgkin lymphoma. Lomustine (CCNU, choice C) is a lipid-soluble nitrosourea agent that acts as an alkylating agent. The nitrosoureas are unusual in having relatively good access to the CNS and are therefore useful in treating brain tumors. Prednisone (choice D) is a potent, orally active corticosteroid with good lymphotoxic potency. Its mechanism is not fully understood but may involve activation of apoptotic pathways in lymphocytes. Vincristine (choice E) is a natural product isolated from the vinca plant. It is classified as a spindle poison and inhibits mitosis by inhibiting microtubule assembly. This drug is particularly useful in treating acute leukemias in children and Hodgkin lymphoma.

• Question 146:

  Synthesis of glycogen is inhibited in hepatocytes in response to glucagon stimulation primarily as a result of which of the following?

  A. a decrease in the level of phosphoprotein phosphatase
  B. a decrease in the level of phosphorylated phosphorylase kinase
  C. a decrease in the levels of phosphorylated phosphoprotein phosphatase inhibitor-1
  D. an increase in the level of the dephosphorylated form of glycogen synthase
  E. an increase in the level of the phosphorylated form of glycogen synthase
  E. an increase in the level of the phosphorylated form of glycogen synthase

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  Explanation

  Section: Biochemistry Glucagon is released from the pancreas in response to low blood glucose and stimulates hepatocytes to synthesize glucose for delivery to the blood. Therefore, it would be counterproductive for hepatocytes to divert any of the gluconeogenically derived glucose into glycogen. This is accomplished by inhibition of glycogen synthase. Glucagon exerts its effects on the liver through the glucagon receptor. When glucagon binds, the receptor activates adenylate cyclase leading to increased production of cAMP. In turn, cAMP activates cAMP-dependent protein kinase, which then phosphorylates a number of substrates. Glucagon has no effect on the level of phosphoprotein phosphatase (choice A). One of the substrates of PKA is glycogen synthase/phosphorylase kinase. Therefore, there would not be a decrease in the level of phosphorylated phosphorylase kinase (choice B). In turn, synthase/phosphorylase kinase phosphorylates glycogen phosphorylase and glycogen synthase. Therefore, there is no increase in the level of dephosphorylated glycogen synthase (choice D). Phosphorylation inhibits glycogen synthase activity and activates phosphorylase. In addition, PKA itself can phosphorylate glycogen synthase. The net effect is an increase in the rate of glucose phosphorolysis from glycogen and a reduced incorporation of glucose into glycogen. An additional PKA substrate is phosphoprotein phosphatase inhibitor-1, and therefore therewould not be a decrease in the level of the phosphorylated form of this enzyme (choice C).

• Question 147:

  A 22-year-old Hispanic man worked for a company that processed animal products and provided no medical coverage benefits. One week after working with wool imported from a Caribbean island, he developed a small lesion on his arm resembling an insect bite. One week later, the lesion was 2.5 cm in diameter with a central, black sloughed-skin area. Two weeks later, he presented at an emergency room with early stages of sepsis. Which of the following microbes is responsible for the infection?

  A. Bacillus anthracis
  B. Bacteroides melanogenicus
  C. Hemophilus ducreyi
  D. M. scrofulaceum
  E. Treponema pallidum
  A. Bacillus anthracis

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  Explanation

  Section: Microbiology/Immunology A patient with cutaneous anthrax usually presents with a pruritic macule or papule that enlarges into a round ulcer in several days. Then 12 mm vesicles that discharge clear or sanguinous fluid might appear. Purulent drainage ordinarily does not occur. This is followed by the development of a painless, depressed, blackcolored eschar. If it is not treated early, dissemination of the disease in about 10% of cases results in septicemia and meningitis. H. ducreyi (choice C) produces a disease called chancroid or soft chancre, which is not associated with the formation of black eschars. T. pallidum (choice E) produces hard chancres without black eschars. B. melanogenicus (choice B) causes abscesses. M. scrofulaceum (choice D) is associated with scrofula which is cervical adenitis.

• Question 148:

  A 48-year-old male patients is brought to the emergency room because of intense pain of the right face and neck with transient visual loss of the right eye. On examination, the patient has palsy of the oculomotor nerve on the right side with resulting diplopia, along with a right lateralized painful Horner syndrome. This constellation of signs is suggestive of a cervical carotid dissection, which is a separation of the arterial tunical intima from the subjacent tunica media. Which numbered structure in following figure, is the tunica intima?

  A. 1
  B. 2
  C. 3
  D. 4
  E. 5
  D. 4

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  Explanation

  Section: Anatomy Arrow 3 points to the tunica intima. The carotid artery is an elastic artery, which contains the following layers aside from the tunica intima: Tunica externa (arrow 1), and tunica media (arrow 5). In a carotid dissection, the tunica intima can elevate or separate from the tunica media with accompanying hemorrhage of the arterial wall. The most common clinical signs are ophthalmological manifestations including painful Horner syndrome, palsy of the oculomotor nerve, diplopia, and transient monocular visual loss. Arrow 2 points to a vasa vasorum, vessels which nourish the thick wall of the aorta. Arrow 4 points to the adipose tissue in the tunica externa.

• Question 149:

  A number of children are hospitalized with bloody diarrhea and severe hematological abnormalities. A4- year-old girl dies of kidney failure shortly after admittance. Epidemiological investigation establishes that all of the patients developed symptoms soon after consuming hamburgers from the same fast-food restaurant chain. Which of the following organisms is most likely to be responsible for the outbreak?

  B. non-01 serogroup ofV. cholera
  C. O157:H7 serotype of
  D. S. typhimurium
  E. Shigella dysenteriae
  C. O157:H7 serotype of

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  Explanation

  Section: Microbiology/Immunology The enterobacteriaceae are a large, heterogeneous group of gram-negative rods that normally inhabit the intestinal tract of humans and animals. The Escherichia genus (usual flora) can incidentally cause disease while Salmonella and Shigella genera are regularly pathogenic for humans. E. coli is the most common cause of urinary tract infection, but there are also several E. coli-associated diarrheal diseases that occur worldwide. Enterohemorrhagic E. coli (EHEC) produces verotoxin and is associated with hemorrhagic colitis and hemolytic uremic syndrome. E. coli serotype O157:H7 (choice C) is the most common strain for these disease presentations. Many outbreaks could be prevented by thoroughly cooking ground beef. EPEC is a strain that causes diarrhea in infants while ETEC is a common cause of traveler's diarrhea. C. jejuni (choice A) can be responsible for a shigella-like illness that is self- limited. Milk or undercooked fowl are frequent vectors of this organism. Non- 01 serogroup of V. cholerae (choice B) only causes a cholera- like illness occasionally. Salmonella (choice D) enterocolitis can be caused by 1400 serotypes. Nausea, headache, vomiting, and profuse diarrhea with low-grade fever are common and resolve in 23 days. The natural habitat of shigellae (choice E) is limited to the intestinal tract of humans and other primates, where they produce bacillary dysentery.

• Question 150:

  A 45-year-old female patient presents to the emergency room with a headache and complains of abnormal sensations on the left side of her body. She claims that the sensory changes came on rapidly in the last few hours. Her laboratory reports come back normal, a spinal tap reveals normal cerebrospinal fluid (CSF), and her mental ability seems good. You perform a neurological examination and find she has greatly reduced sensation on the entire left side of her body, including her face. The sensory loss includes all modalities. The motor examination is normal, as is her visual examination and hearing examination. Based on the neurological findings, which of the following thalamic nuclei would be involved?

  A. lateral and medial geniculate nuclei
  B. lateral dorsal and lateral posterior nuclei
  C. pulvinar
  D. ventral anterior and ventral lateral nuclei
  E. ventral posterior lateral and ventral posterior medial nuclei
  E. ventral posterior lateral and ventral posterior medial nuclei

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  Explanation

  Section: Anatomy The ventral posterior lateral (VPL) and ventral posterior medial (VPM) nuclei are sensory relay thalamic nuclei. The lateral and medial geniculate nuclei (choice A) are respectively concerned with visual and auditory sensory information. The lateral dorsal (LD) and lateral posterior (LP) nuclei (choice B), and the pulvinar (choice C) are association or multimodal relay nuclei. The ventral anterior (VA) and ventral lateral (VL) are motor relay nuclei.