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

USMLE USMLE-STEP-1 Online Questions & Answers

• Question 181:

  A 25-year-old man has experienced chronic blistering and scarring of his skin when exposed to sunlight. This man is a smoker and drinks heavily, both of which exacerbate his responses to sunlight. Analysis of his urine and plasma indicates a high accumulation of complex porphyrins, predominantly uroporphyrin. The symptoms and clinical signs displayed by this patient indicate he is suffering from which of the following disorders?

  A. acute intermittent porphyria (AIP)
  B. hereditary coproporphyria (HCP)
  C. porphyria cutanea tarda (PCT)
  D. variegate porphyria
  E. X-linked sideroblastic anemia
  C. porphyria cutanea tarda (PCT)

• Question 182:

  Approximately 6 months ago, a 59-year-old man developed a dull, continuous abdominal pain that radiated to the right upper quadrant and was relieved by bending forward. He has also had recurrent thrombophlebitis. He now develops jaundice. Of the following, which is the condition that would most likely explain all of these findings?

  A. alcoholic cirrhosis
  B. cholecystitis
  C. cholelithiasis
  D. pancreatic adenocarcinoma
  E. viral hepatitis
  D. pancreatic adenocarcinoma

  ---

  Explanation

  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.

• Question 183:

  Which of the following drugs corrects the anemia of pernicious anemia and prevents the neurological consequences of the disease?

  A. beta-carotene
  B. ferrous sulfate
  C. folic acid
  D. hydroxocobalamin
  E. vitamin E
  D. hydroxocobalamin

• Question 184:

  Which of the following is a true statement regarding renal clearance of a substance?

  A. is measured in milligram per minute
  B. glucose is greater than that of insulin in the normal kidney
  C. insulin is zero
  D. PAH remains constant regardless of the plasma level
  E. potassium clearance will increase after an injection of aldosterone
  E. potassium clearance will increase after an injection of aldosterone

  ---

  Explanation

  Section: Physiology Choice E is correct since the clearance of potassium is normally regulated by the action of aldosterone on the distal tubule exchange of sodium reabsorption with potassium secretion. Choice Ais incorrect because renal clearance represents the volume of plasma completely cleared of a substance per unit time, hence the units for renal clearance are milliliter per minute, and not milligram per minute. Choice B is incorrect because a normal kidney reabsorbs 100% of the filtered glucose, so glucose clearance is zero. By contrast, a significant amount of inulin is usually cleared by the kidney. Choice C is incorrect because although inulin is not secreted by the tubule as is PAH, inulin is filtered but not reabsorbed and thus a normal kidney will clear approximately 20% of the inulin from the plasma. Choice D is incorrect because PAH is actively secreted by the proximal tubule. Above a certain plasma level, PAH secretion no longer can increase and thus clearance (calculated as the ratio of urine to plasma concentration multiplied by urine flow) will decline as plasma PAH concentration increases faster than urine PAH concentration.

• Question 185:

  A patient presented with an acute abdomen including fever, marked abdominal distension, acidosis, and leukocytosis. Laparoscopy revealed that large parts of the small intestine were necrotic and as a consequence, the entire ileum of the patient was resected. It is expected that very soon after the surgery the patient will have considerable problems resulting from the malabsorption of which of the following?

  A. iron
  B. bile acids
  C. sodium
  D. vitamin
  E. protein
  B. bile acids

• Question 186:

  Exhibit:

  

  Please refer to the exhibit.

  Which of the following mechanisms most accurately describes the blocking action of methimazole?

  A. A
  B. B
  C. C
  D. D
  E. E
  B. B

• Question 187:

  Antibodies against acetylcholine neural receptors were measured in a 35-year-old woman and are thought to be involved in the pathogenesis of which of the following?

  A. acute idiopathic polyneuritis
  B. Guillain-Barr syndrome
  C. multiple sclerosis
  D. myasthenia gravis
  E. postpericardiotomy syndrome
  D. myasthenia gravis

  ---

  Explanation

  Section: Microbiology/Immunology Anti-acetylcholine receptor antibodies are found in more than 90% of myasthenia gravis patients. If the clinical symptoms are suggestive of myasthenia gravis, this finding alone is often considered diagnostic. Multiple sclerosis patients tend to have high levels of measles virus antibodies in their spinal fluid. However, the role of this agent in the disease is undetermined (choice C). Guillain-Barr syndrome (also called acute idiopathic polyneuritis) is a demyelinating disease of peripheral nerves. It commonly occurs after a viral infection or an injection, such as influenza immunization. The disease seems to be caused by a T-cell response to nervous tissue (choices A and B). Postpericardiotomy syndrome is a term used to describe a disorder following surgery of the pericardium to remove cysts or tumors or to correct a malformation (choice E).

• Question 188:

  The terminal ileum was removed from a 50-year-old woman during excision of a tumor. About 3 years later, the patient was admitted to the hospital. She is very pale. Hemoglobin is 9 g/dL, MCV (mean corpuscular volume) has increased to 110 (110 fL). The provisional diagnosis is a vitamin

  

  deficiency. Which of the following vitamins is the most likely one causing the symptoms?

  A. A
  B. B1
  C. B6
  D. B12
  E. K
  D. B12

• Question 189:

  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
  C. ductus venosus

  ---

  Explanation

  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 190:

  A 35-year-old male patient suffering from pulmonary hypertension has been diagnosed with ostium secundum atrial septal defect. Abnormal development of which of the following structures is responsible for this developmental defect?

  A. aorticopulmonary septum
  B. endocardial cushion
  C. interventricular septum
  D. septum primum
  E. sinus venosus
  D. septum primum

  ---

  Explanation

  Section: Anatomy Abnormal development of either the septum primum or septum secundum results in ostium secundum atrial septal defects in the area of the fossa ovalis. This common type of congenital heart defect is manifested by a patent foramen ovale between right and left atria. This is well-tolerated during childhood, but symptoms usually appear after 30 years of age. The aorticopulmonary septum (choice A) divides the truncus arteriosus of the developing heart and gives rise to the ascending aorta and pulmonary trunk. The endocardial cushions (choice B) give rise to the right and left atrioventricular canals. The interventricular septum (choice C) forms between the right and left ventricles. The sinus venosus (choice E) becomes incorporated into the atria, as well as giving rise to the openings of the pulmonary veins and the venae cavae.