USMLE-STEP-1 Online Practice Questions and Answers

Correct Answer: B

Section: Anatomy Arrow 2 points to the base of the gastric glands where chief or peptic (zymogenic) cells tend to be clustered. Arrow 1 points to the luminal surface of the stomach where mucus-secreting cells are found. Arrow 3 points to the muscularis mucosae. Arrow 4 points to the middle of the gastric glands where parietal or oxyntic cells tend to be most numerous. Arrow 5 point to the side of a gastric pit where mucus-secreting cells are also found.

Correct Answer: C

Section: Anatomy The lactiferous duct is lined by a two-cell layered cuboidal epithelium. All other epithelial choices are not found in the breast tissue and are thus incorrect.

Correct Answer: A

Section: Biochemistry Enzymes that are destined for the lysosomes (lysosomal enzymes) are directed there by a specific carbohydrate modification. During transit through the Golgi apparatus a residue of Nacetylglucosamine- 1phosphate is added to carbon 6 of one or more specific mannose residues that have been incorporated into these enzymes. The N-acetylglucosamine is activated by coupling to UDP and is transferred by an Nacetylglucosamine phosphotransferase yielding N-acetylglucosamine-1- phosphate-6-mannoseprotein. A second reaction removes the Nacetylglucosamine leaving mannose residues phosphorylated in the sixth position. Aspecific mannose-6-phosphate receptor is present in the membranes of the Golgi apparatus. Binding of mannose-6-phosphate to this receptor targets proteins to the lysosomes. Defects in the proper targeting of glycoproteins to the lysosomes can also lead to clinical complications. Deficiencies in Nacetylglucosamine phosphotransferase lead to the formation of dense inclusion bodies in fibroblasts. Two disorders related to deficiencies in the targeting of lysosomal enzymes are termed I-cell disease (mucolipidosis II) and pseudo-Hurler polydystrophy (mucolipidosis III). I-cell disease is characterized by severe psychomotor retardation, skeletal abnormalities, coarse facial features, painful restricted joint movement, and early mortality. Pseudo- Hurler polydystrophy is less severe; it progresses more slowly, and afflicted individuals live to adulthood. Each of the other choices (B, C, D, and E) represent other potential pathways that are not affected in the processing, delivery, or presentation of lysosomal enzymes or the receptors that recognize the properly processed enzymes.

Correct Answer: B

Section: Microbiology/Immunology

H. pylori is a spiral-shaped gram-negative motile rod that is associated with antral gastritis and duodenal (peptic) ulcer disease. It is oxidase-positive, catalase-positive, and a strong producer of urease. Antimicrobial therapy that clears H. pylori results in improvement of gastritis and duodenal ulcer disease. Hence, choice B is the correct answer. C. jejuni (choice A) infections are widespread and usually cause abdominal pain and profuse bloody diarrhea, not gastritis and ulcer manifestations. Ureasepositive P. mirabilis (choice C) and other Proteus species produce infections in humans when the bacteria leave the intestinal tract, being very significant in urinary tract and bacteremia infections. P. retteri (choice D) is a member of the normal intestinal flora, often resistant to antimicrobial therapy, and is seen in urinary tract infections. V. cholerae is a comma-shaped curved rod and is widely distributed in marine and surface waters in nature. It is oxidase positive and many species are salt tolerant. V. cholerae (choice E) produces a heat-labile enterotoxin whose action increases cAMP in intestinal cells, resulting in prolonged hypersecretion of water and electrolytes.

Correct Answer: A

Section: Pathology and Path physiology Hirschsprung disease is caused by the congenital absence of parasympathetic ganglion cells in the submucosal and myenteric plexus. This presents clinically soon after birth as an inability to pass stool and abdominal distention. The diagnosis is usually confirmed by a full-thickness colon biopsy showing disorganized, nonmyelinated nerve fibers replacing the missing ganglion cells. In Hirschsprung disease, the ganglion cells, not the nerve fibers (choice B), are missing. Muscular hypertrophy (choice D) and atrophy (choice C) are not specific diagnostic findings with Hirschsprung disease. Mucosal polyp development (choice E) is not associated with Hirschsprung disease.

Correct Answer: D

Section: Pathology and Path physiology

Carcinomas in the head of the pancreas often obstruct the ampulla of Vater and the common bile duct,

producing jaundice; carcinoma in the body and tail do not obstruct and remain clinically silent much longer.

A dull, continuous abdominal pain is also a typical symptom and many patients report that the pain

decreases when they lean forward. About 10% of patients with pancreatic carcinoma develop a migratory

thrombophlebitis known as Trousseau syndrome. Alcoholic cirrhosis (choice A), cholecystitis (choice B),

cholelithiasis (choice C), and viral hepatitis (choice E) may all be associated with abdominal pain and

jaundice, but not the other findings in this case.

Correct Answer: A

Section: Pathology and Path physiology Syphilitic saccular aneurysms of the thoracic aorta result from endarteritis obliterans of the vasa vasorum with subsequent mural ischemic necrosis. Hypersensitivity reactions, multinucleate giant cells, and fibrinoid necrosis (choice B) play no significant role in the development of syphilitic aortic aneurysms. Immune complex formation and complement activation (choice C) may be seen with tertiary syphilis, but involve only the small vessels, without aneurysm formation. Intimal fibroplasias and lipid deposition (choice D) are the early lesions of atherosclerosis. Cystic medial necrosis (choice E) is a noninfectious disorder characterized by abnormally weak connective tissue in the aortic media and deposits of myxoid substances.

Correct Answer: B

Section: Pharmacology

Cyclosporine and tacrolimus (not listed) are associated with nephrotoxicity as a major adverse effect.

Antilymphocyte globulin (choice A) is associated with foreign protein reactions, including anaphylaxis.

Mycophenolate mofetil (choice C) causes GI disturbances and myelosuppression. Prednisone (choice D)

causes a variety of chronic toxicities conveniently summarized as "Cushingoid effects" but has little acute

toxicity. Sirolimus (choice E) is associated with bone marrow suppression.

Correct Answer: E

Section: Pharmacology The agents listed are the primary drugs used in the treatment of tuberculosis. Streptomycin (choice E) and other aminoglycosides cause eighth nerve damage, which is often irreversible and may take the form of auditory or vestibular dysfunction. Isoniazid and rifampin are the most efficacious and least toxic, but even when used together are insufficient in many cases to prevent the development of resistance. Therefore, most cases of tuberculosis are treated with three or even four agents in an effort to eradicate the infection before resistance develops. Because each drug has different toxicities, it is sometimes possible to achieve a cure without severe toxicity. Ethambutol (choice A) causes visual dysfunction and possible retinal damage, not hearing loss. Isoniazid (choice B) causes peripheral neuropathies and hepatic damage. Fortunately, hepatitis is uncommon in children treated with this drug. Pyrazinamide (choice C) causes joint pains and swelling, GI upset, and rash. Rifampin (choice D) causes proteinuria, rash, and thrombocytopenia.

Correct Answer: A

Section: Pharmacology The current drug of choice for acute AV nodal reentrant tachycardia (a supraventricular tachycardia [SVT]) is the nucleoside adenosine. This agent, when given as a bolus, causes marked hyperpolarization of AV node tissue and transiently blocks conduction of AV node action potentials. This abolishes the reentrant impulse and allows normal sinus rhythm to be reestablished. The half-life of adenosine is about 3 seconds and the duration of action of the dose used is about 15 seconds, so toxicities from this therapy are minimal. Calcium channel blockers such as verapamil and diltiazem are also effective in SVT. Bethanechol (choice B) is a muscarinic agonist and produces hypotension and other muscarinic effects. It is ineffective in SVT. Isoproterenol (choice C) is a beta-selective adrenoreceptor agonist that causes hypotension and reflex sympathetic discharge to the heart, along with direct stimulation. It is more likely to cause than to abolish arrhythmias. Metoprolol (choice D) slows AV conduction and might abolish the AV reentrant rhythm. However, beta blockers are not very effective in converting preexisting SVT. Procainamide (choice E) and related group 1A antiarrhythmic drugs are not as effective as adenosine in converting SVT to normal sinus rhythm and much more toxic.