USMLE USMLE Certifications USMLE-STEP-1 Questions & Answers

• Question 21:

  A 23-year-old woman complains of depression and anxiety. While describing her symptoms, she looks dazed. A minute later, she looks around the room slowly, and says, in a heavily accented voice with a different tone, "Where am I?" Which of the following does this presentation suggest?

  A. adjustment disorder

  B. catatonia

  C. dissociative identity disorder

  D. major depression

  E. schizophrenia

  Correct Answer: C

  Section: Behavioral Science and Biostatics Dissociative identity disorder (multiple personality disorder) is often associated with memory disturbance and an alternate personality, who may have a different speech tone, accent, or voice. Schizophrenia (choice E) is unlikely; there is no sign of psychosis. Major depression (choice D) is unlikely; there is no sign of depression. Catatonia (choice B) refers to muscle rigidity and mutism, and adjustment disorder (choice A) is a broad diagnostic category that does not include this presentation.

• Question 22:

  Which of the following represents the average age for puberty?

  A. 11 for boys and 13 for girls

  B. 11 for girls and 13 for boys

  C. 14 for boys and 16 for girls

  D. 14 for girls and 16 for boys

  E. 15 for both girls and boys

  Correct Answer: B

  Section: Behavioral Science and Biostatics The onset of puberty varies, but girls usually enter puberty 1218 months earlier than boys. The average age is 11 (range, 813) for girls and 13 (range, 1014) for boys. Choices A, C, and E are incorrect because they do not distinguish between girls and boys. Choice D is above the upper limit for both girls and boys.

• Question 23:

  Which of the following is a normal sexual function?

  A. anorgasmia

  B. dyspareunia

  C. masturbation

  D. pedophilia

  Correct Answer: C

  Section: Behavioral Science and Biostatics Masturbation is virtually universal among men and women of all cultures. It is common among married as well as single people. Many sex therapists recommend self-stimulation as an auxiliary treatment technique for a variety of sexual dysfunctions. Choices A, B, and D are sexual dysfunctions.

• Question 24:

  Potassium supplementation is often necessary for patients taking large doses of which of the following drugs?

  A. amiloride

  B. captopril

  C. hydrochlorothiazide

  D. losartan

  E. spironolactone

  Correct Answer: C

  Section: Pharmacology Hydrochlorothiazide causes potassium wasting and may lead to hypokalemia requiring dietary potassium supplementation. Potassium wasting is characteristic of diuretics that present more sodium to the collecting tubule, where sodium is conserved in exchange for potassium under the control of aldosterone. Therefore, diuretics that act in the proximal convoluted tubule (carbonic anhydrase inhibitors), ascending limb of the loop of Henle (loop diuretics), and distal convoluted tubule (thiazides) cause potassium wasting and may lead to dangerous hypokalemia. Angiotensin antagonists (because they interfere with aldosterone secretion) and aldosterone inhibitors have the opposite effect. Amiloride (choice A) and spironolactone (choice E) are aldosterone antagonists; captopril (choice B) and losartan (choice D) are angiotensin antagonists. The latter agents cause potassium retention and may cause hyperkalemia, not hypokalemia.

• Question 25:

  Which of the following statements about the leukotrienes LT LT and LT is most correct?

  

  A. Their biosynthesis is inhibited by aspirin.

  B. They are chemotactic agents for polymorphonuclear leukocytes.

  C. They are potent bronchoconstrictor substances.

  D. They are synthesized and stored in platelet granules.

  E. They have few cardiovascular effects.

  Correct Answer: C

• Question 26:

  The mechanism of action for the therapeutic effect of saquinavir involves which of the following?

  A. incorporation into RNA

  B. inhibition of thymidylate synthase

  C. inhibition of viral DNA polymerase

  D. inhibition of viral protease

  E. inhibition of viral reverse transcriptase

  Correct Answer: D

  Section: Pharmacology Saquinavir is an HIV protease inhibitor. Viral protease cleavage of a polyprotein is necessary for production of the viral coat protein. The HIV protease inhibitors include ritonavir, indinavir, nelfinavir, and amprenavir in addition to saquinavir. Currently available HIV protease inhibitors are not sufficient for monotherapy because of the rapid emergence of resistance due to mutations in the viral protease. Combination therapy using saquinavir with two reverse transcriptase inhibitors such as zidovudine, lamivudine, abacavir, or didanosine is currently effective in reducing viral load. Incorporation into RNA (choice A) is part of the mechanism of action for the antitumor agent 5-fluorouracil (5-FU). Inhibition of thymidylate synthase (choice B) is another part of the mechanism of action for the antitumor agent 5-FU. 5-FU is converted to 5- FdUMP, a potent inhibitor of thymidylate synthase. Inhibition of viral DNA polymerase (choice C) is a mechanism of action for the antiherpesvirus nucleosides acyclovir, valacyclovir, famciclovir, and ganciclovir. These agents are metabolized to their nucleotide triphosphate forms, which competitively inhibit the herpesvirus polymerase. Acyclovir and valacyclovir also cause DNA chain termination. Inhibition of viral reverse transcriptase (choice E) is a property of the nucleosides zidovudine (AZT), didanosine (ddI), lamivudine (3TC), stavudine (d4T), and zalcitabine (ddC). These nucleosides are metabolized to the triphosphate forms that competitively inhibit reverse transcriptase. Nonnucleoside reverse transcriptase inhibitors include nevirapine, delavirdine, and efavirenz. Combinations of agents are used because resistance, through mutations in the reverse transcriptase sequence, frequently arises during monotherapy.

• Question 27:

  Which structure most effectively prevents toxic molecules from penetrating an epithelium by passing between adjacent epithelial cells?

  A. desmosome

  B. gap junction

  C. hemidesmosome

  D. terminal bar

  E. tight junction

  Correct Answer: E

  Section: Anatomy The space between plasmalemmas of adjacent epithelial cells is obliterated at the tight junction (zonula occludens), which forms by fusion of the membranes along narrow anastomosing bands. The tight junction is the apical--most part of the junctional complex, which is typical of epithelia lining tubular and hollow organs. The zonula adherens and desmosome (choice A) also contribute to the junctional complex, but they hold adjacent cells together. The gap junction (choice B) functions to electrically and chemically couple adjacent cells. It consists of direct channels (connexons) between cells, but there is a significant space (about 2 nm) separating the membranes between the channels. The hemidesmosome (choice C) is a specialization for adhesion of a cell to its basement membrane. The terminal bar (choice D) is not a type of junction, but rather a manifestation of the junctional complex seen with the light microscope.

• Question 28:

  A 57-year-old female patient has suffered a major stroke and as a result is in a coma. The attending neurologist is very concerned because the patient is developing ataxic breathing. The pneumotaxic center and apneustic centers of the brain are located in which of the following?

  A. diencephalon

  B. midbrain

  C. pons

  D. spinal cord

  E. telencephalon

  Correct Answer: C

  Section: Anatomy

  The pneumotaxic center is located in the upper one-third of the pons, whereas the apneustic center is in

  the lower two-thirds. The apneustic center promotes inspiration and the pneumotaxic center, expiration.

  The telencephalon (choice E), diencephalon (choice A), midbrain (choice B), and spinal cord (choice D)

  are not known to contain pneumotaxic or apneustic centers.

• Question 29:

  During the first 57 days of life, the umbilical vein can be catherized and used for central venous pressure monitoring. The umbilical vein leads to which of the following vessels?

  A. descending aorta

  B. ductus arteriosus

  C. ductus venosus

  D. inferior vena cava

  E. portal vein

  Correct Answer: C

  Section: Anatomy In the fetus, the umbilical vein connects directly to the ductus venosus, a fetal vessel which bypasses the liver to bring oxygenated blood to the inferior vena cava (choice D). The descending aorta (choice A) distributes blood to the body and, in the fetal circulation, brings blood to the umbilical arteries by way of the iliac arteries for return to the placenta for oxygenation. The ductus arteriosus (choice B) is a fetal vessel which allows bypass of the oxygenated blood from the pulmonary trunk to the arch of the aorta. The portal vein (choice E) is formed by the union of the splenic vein and the superior mesenteric vein; it returns blood from the digestive system to the liver.

• Question 30:

  A 30-year-old patient displays ataxia of extremities and asynergy with decomposition of movement. He also has dysmetria (past-pointing phenomenon), dysdiadochokinesia (the inability to perform rapidly alternating movements), and intention tremor. These neurological signs are characteristic of a lesion in the structure indicated by which arrow in following figure ?

  

  A. 1

  B. 2

  C. 3

  D. 4

  E. 5

  Correct Answer: D

  Section: Anatomy The collective neurological signs are characteristic of a lesion of the neocerebellum (cerebellar hemispheres). Alesion in the archicerebellum (cerebellar vermis; arrow 5, choice E) results in loss of equilibrium. None of the other choices apply to the collection of neurological signs displayed by this patient: arrow 1 (choice A) points to the temporal lobe, arrow 2 (choice B) to the eyeball, and arrow 3 (choice C) to the pons.