USMLE USMLE Certifications USMLE-STEP-1 Questions & Answers

• Question 11:

  A 60-year-old woman is admitted to the hospital with a fever and severe diarrhea for the last 24 hours. Cultures of blood, cerebrospinal fluid, urine, and stool are all negative for pathogens. The profile of gut hormones reveals elevated levels of VIP. An analogue of which of the following would most likely lower her VIP levels?

  A. erythromycin

  B. histamine

  C. motilin

  D. somatostatin

  E. trypsin

  Correct Answer: D

  Section: Physiology VIP is a neurotransmitter in the brain and in the parasympathetic nerves of the digestive tract. It also acts as a hormone. VIP has a secretin-like effect on the pancreas. It increases the volume of water and bicarbonate output and affects GI blood flow and motility. All this contributes to severe secretory diarrhea in the case of VIP overproduction. Somatostatin is the best choice because it has a broad range of inhibitory effects, inhibiting GI secretions, slowing GI motility, and reducing splanchnic blood flow. An analogue of somatostatin, called octreotide, was found useful for treatment of syndromes related with VIP overproduction. Octreotide has a longer half-life than physiologic somatostatin. Erythromycin (choice A) is known to have antibiotic features. This is not the best choice, since no pathogens were found. Histamine (choice B) is a physiologic stimulant of gastric hydrochloric acid secretion, potentiating the effects of acetylcholine and gastrin. Motilin (choice C) stimulates gastric motility, which is contraindicated for diarrhea. Trypsin (choice E) is a protease released by pancreatic cells, breaking peptide bonds as well as converting many other proteolytic enzymes to their active form. All of the negative choices will not affect, and in fact may even worsen the VIPrelated symptoms.

• Question 12:

  After total thyroidectomy as a result of a car accident, a 47-year-old woman is positive for Trousseau sign. It is manifested as carpopedal spasm occurring after an inflated blood pressure cuff is held above systolic blood pressure for a few minutes. Which of the following would best describe her postoperative condition when compared to preoperative?

  A. decreased deep tendon reflexes

  B. higher serum calcitonin levels

  C. lower serum calcium levels

  D. lower serum phosphate levels

  E. shorter Q-T interval of her ECG

  Correct Answer: C

  Section: Physiology A positive Trousseau sign indicates increased neuromuscular irritability, which is caused by low serum calcium levels. Apositive Trousseau sign or a positive Chvostek sign (spasms of facial muscles) can often diagnose hypocalcemia before other gross manifestations develop. Serum calcium is regulated by parathyroid hormone produced by the parathyroid glands. During the woman's accident, the glands, or their vasculature, were most likely damaged enough so that they could not be saved during the total thyroidectomy. If total thyroidectomy occurs as a consequence of thyroid cancer, damage to all four parathyroid glands would be considered an operative mishap. A consequence of hypocalcemia is hyperreflexia and not hyporeflexia (choice A). Calcitonin is secreted by parafollicular or "C" cells in the thyroid gland. Since no other cells of the body make this hormone, serum calcitonin levels do not rise (choice B), but instead go to zero postoperative. Low serum phosphate levels (choice D) typically signify secondary hyperparathyroidism or low dietary phosphate intake. In the current case, high or unchanged serum phosphate would be expected. The Q-T interval of the ECG represents the time for both ventricular depolarization and repolarization to occur. It therefore roughly estimates the duration of an average ventricular action potential. Hypocalcemia leads to a long Q-T interval, not a short Q-T as in choice E. In severe cases, this can lead to arrhythmias, hypotension, and heart failure.

• Question 13:

  Exhibit:

  

  Please refer to the exhibit.

  Cardioactive steroids, like digoxin, exert a positive ionotropic effect on heart muscle cells. Because of this

  activity, they can be used clinically to increase contraction of a failing heart. Which of the following proteins

  is important in the mechanism of action of digoxin on the cardiac muscle cell?

  A. A

  B. B

  C. C

  D. D

  E. E

  Correct Answer: B

• Question 14:

  A 68-year-old postmenopausal female with a history of osteoprosis and essential hypertension is placed on the thiazide diuretic chlorothiazide, which has a beneficial action toward both conditions. Which letter in below figure depicts the tubular location of epithelial cells containing a / cotransport

  

  protein inhibited by thiazide diuretics?

  

  A. A

  B. B

  C. C

  D. D

  E. E

  Correct Answer: D

• Question 15:

  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

  Correct Answer: A

  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 16:

  Nancy was tending the goose eggs when they hatched. The young goslings started following Nancy, even when the mother was calling them. Which of the following phenomenon is this an example of?

  A. cognitive map

  B. imprinting

  C. instinctual behavior

  D. maternal bonding E. operant conditioning

  Correct Answer: B

  Section: Behavioral Science and Biostatics Imprinting is an ethologic term that indicates a critical period in a newborn animal's life. For example, if goslings are exposed to humans rather than geese shortly after hatching, they will follow humans rather than their own mother.

• Question 17:

  A 58-year-old male visits your office and complains about impotence. Upon questioning you learn that he is capable of erections, but that they do not last as long and that they are of lesser strength than the previous ones. Which of the following neurotransmitters is primarily responsible for dilation of the penile artery during erections?

  A. acetylcholine

  B. epinephrine

  C. GABA

  D. nitric oxide

  E. norepinephrine

  Correct Answer: D

  Section: Physiology Nitric oxide has important neurotransmitterlike functions. Its short half-life, due to spontaneous decay, limits its range and action. Nitric oxide acts on smooth muscle cells in a generally inhibitory manner; it relaxes the GI muscles and sphincters and dilates blood vessels. In blood vessels, nitric oxide is derived from endothelial cells and has been identified as the long-hypothesized endothelium-derived relaxing factor (EDRF). Acetylcholine (choice A) is the classic neurotransmitter of the parasympathetic nervous system. Although activation of the pelvic parasympathetic nerves leads to erection, it is nitric oxide and not acetylcholine that relaxes penile artery smooth muscle cells. GABA (choice C) is an inhibitory neurotransmitter found in the central nervous system. Epinephrine (choice B) and norepinephrine (choice E) play a role during the ejaculation phase of the male sexual act, but do not contribute to penile artery dilation during the erectile phase.

• Question 18:

  Which of the following drugs is useful for the treatment of panic disorder?

  A. bupropion

  B. olanzapine

  C. phenobarbital

  D. sertraline

  E. valproic acid

  Correct Answer: D

  Section: Behavioral Science and Biostatics In addition to SSRIs such as sertraline, paroxetine and fluoxetine, tricyclic antidepressants, MAOIs, and high-potency benzodiazepines such as alprazolam and clonazepam may be effective in panic disorder. Olanzapine (choice B) is an atypical antipsychotic and has not been shown to be effective in panic disorder. Bupropion, an antidepressant (choice A), phenobarbital, a CNS depressant (choice C), and valproic acid, an anticonvulsant and antimanic drug (choice E) are also ineffective in panic disorder.

• Question 19:

  Your patient confides in you that she has been losing weight with loss of appetite, has been unable to concentrate, and has had difficulty sleeping through the night. She has also been thinking of the means of killing herself. Which of the following is the most likely diagnosis?

  A. borderline personality disorder

  B. factitious disorder

  C. generalized anxiety disorder

  D. hypochondriasis

  E. major depression

  Correct Answer: E

  Section: Behavioral Science and Biostatics Depression is often accompanied by vague physical symptoms. When a depressed patient presents to a primary physician, it is important that the presence of depression be ascertained by careful history; depressed patients are often suicidal, and about 70% of successful suicides have seen their physician in the previous month. Choices A, B, C, and D are not supported by the signs presented.

• Question 20:

  Robert is 9 years old and has been suspended from school for failing to control his disruptive behavior in the classroom. His parents take him to a psychologist and report that he has been hyperactive and impulsive since the age of 5. Which of the following is the drug of choice for the treatment of this child?

  A. buspirone

  B. clomipramine

  C. dextroamphetamine

  D. nefazodone

  E. paroxetine

  Correct Answer: C

  Section: Behavioral Science and Biostatics Dextroamphetamine and methylphenidate are effective in treating ADHD. Paroxetine (choice E) and nefazodone (choice D) are antidepressants, clomipramine (choice B) is a tricyclic that has special use in obsessive-compulsive disorders, and buspirone (choice A) is an antianxiety agent.