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

USMLE USMLE-STEP-1 Online Questions & Answers

• Question 581:

  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
  B. B

• Question 582:

  A 15-month-old baby girl is brought to the emergency room by her parents for a 1-week history of malaise, poor feeding, mild fever, and diarrhea. Physical examination is unremarkable. This is the sixth such occasion for which the parents have brought their daughter to a physician. Past visits have revealed repeated infections, including Candida, cytomegalovirus, and M. avium-intracellulare. A complete blood count (CBC) is remarkable only for a low total lymphocyte count. Immunoglobulin levels are normal.

  Alymph node biopsy is remarkable for paracortical cell depletion, but is otherwise normal. Which of the following is the most likely diagnosis?

  A. Bruton congenital agammaglobulinemia
  B. chronic granulomatous disease of childhood
  C. severe combined immunodeficiency disease
  D. thymic hypoplasia
  E. Wiskott-Aldrich syndrome
  D. thymic hypoplasia

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  Explanation

  Section: Pathology and Path physiology In thymic hypoplasia, the congenital developmental failure of the thymus leads to a lack of T- lymphocytes in the blood as well as in appropriate areas of lymph nodes (paracortical area). Deficient T-cell immunity will thus lead to severe, recurrent viral, mycobacterial, fungal, or protozoal infections during infancy. Thymic hypoplasia is best described in association with DiGeorge syndrome, in which defective embryological development of the third and fourth pharyngeal pouches results in developmental failure of thymus and parathyroid formation, congenital heart defects, and severe hypocalcemia, secondary to hyperparathyroidism. An associated, but less well-defined, entity is Nezelof syndrome, in which there is hypoplasia of the thymus, retention of normal parathyroid function, and possible varying degrees of humoral immunodeficiency. Bruton congenital agammaglobulinemia (choice A) is an Xlinked recessive disorder characterized by the failure of B-cell precursors to differentiate into mature B-lymphocytes, which are absent in the peripheral blood, lymph nodes, tonsils, and spleen. Serum immunoglobulin levels are decreased; however, the thymus and Tlymphocyte development are normal and cell-mediated immunity is intact. Chronic granulomatous disease of childhood (choice B) refers to a group of X-linked or autosomal recessive disorders characterized by different enzyme deficiencies of neutrophils and macrophages that lead to inhibition of hydrogen peroxide formation. Although still capable of bacterial phagocytosis, neutrophils and macrophages cannot kill bacteria, particularly the catalase-positive species such as Staphylococcus, Serratia, and Salmonella, which destroy their own endogenous hydrogen peroxide by virtue of catalase production. The disease occurs chiefly in males who present with recurrent bacterial infections of the skin, lymph nodes, lungs, and bones; widespread abscesses and granulomas are present. Severe combined immunodeficiency disease (choice C) is one of the most dramatic forms of congenital immunodeficiency in which a defect of lymphoid stem cells leads to failure of development of both Band T- lymphocytes. Although probably an embodiment of several different inherited diseases, most patients with severe combined immunodeficiency have the autosomal recessive form, and greater than half of these lack the enzyme adenosine deaminase, resulting in the accumulation of lymphotoxic metabolites. Failure of both cellular and humoral immunity causes a variety of severe viral, bacterial, fungal, and protozoal infections early in life, with death usually occurring within the first year. Wiskott-Aldrich syndrome (choice E) is an X-linked recessive disease characterized by thrombocytopenia, eczema, and immunodeficiency; both cellular and humoral immunity is impaired. Progressive T-cell deficiency occurs despite a morphologically normal thymus, and serum IgM levels are low, although IgG levels are usually normal. Recurrent bacterial, viral, and fungal infections occur, particularly with S. pneumonia and Haemophilus influenzae as these organisms have polysaccharide antigens that mainly elicit IgM antibody response. Thrombocytopenia may be severe and approximately one-third of patients die from hemorrhage. Patients are prone to developing lymphoma.

• Question 583:

  The anterior two-thirds of the tongue differ from the posterior one-third of the tongue by its special visceral afferent (SVA; taste) innervation. The perikarya of neurons providing the sensation of taste in the anterior two-thirds of the tongue are found in which of the following?

  A. geniculate ganglion
  B. otic ganglion
  C. pterygopalatine (sphenopalatine) ganglion
  D. submandibular ganglion
  E. trigeminal (gasserian) ganglion
  A. geniculate ganglion

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  Explanation

  Section: Anatomy SVA (taste) fibers have their perikarya in the geniculate ganglion located in the petrous portion of the temporal bone. These neurons project their axons to the gustatory nucleus in the brainstem. The otic ganglion (choice B) receives preganglionic parasympathetic fibers originating from the inferior salivatory nucleus by way of the ninth cranial (glossopharyngeal) nerve. In turn, it projects postganglionic parasympathetic fibers to the parotid salivary gland. The pterygopalatine (sphenopalatine) ganglion (choice C) is also a parasympathetic ganglion, which receives preganglionic fibers from the superior salivatory nucleus by way of the ninth cranial (glossopharyngeal) nerve. In turn, it sends postganglionic parasympathetic fibers to the lacrimal gland and mucous glands in the nose. The submandibular ganglion (choice D) receives preganglionic parasympathetic fibers from the chorda tympani, a branch of the nervus intermedius which runs with the seventh cranial nerve. It innervates the submandibular and sublingual salivary glands. The trigeminal (gasserian) ganglion (choice E) receives sensations from the face, mucosa, cornea, teeth, gum, palate, and the anterior two- thirds of the tongue. It sends projections to the principal sensory and spinal trigeminal nuclei in the brainstem.

• Question 584:

  A stroke resulting from obstruction of the structure indicated by arrow 1 in following figure, may result in ischemia in which of the following brain regions?

  A. Broca's area in the left frontal lobe
  B. cerebellum
  C. medial aspect of the right frontal lobe
  D. pons
  E. Wernicke's area in the left frontal lobe
  C. medial aspect of the right frontal lobe

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  Explanation

  Section: Anatomy Arrow 1 points to the right internal carotid artery which supplies the anterior and middle cerebral arteries in the brain. The territory of the right anterior cerebral artery includes the rightmedial aspect of the frontal lobe, which will be affected by obstruction of the internal carotid artery. Broca's (choice A) and Wernicke's (choice E) areas are located in the majority of the population in the left cerebral hemisphere and are supplied by the left middle cerebral artery from the left internal carotid artery. They will not be affected in this case. The cerebellum (choice B) and pons (choice D) receive their blood supply from the basilar artery (arrow 2) which is formed from the vertebral arteries.

• Question 585:

  An opera singer, who has maintained a demanding work schedule, worries about the effect on her vocal cords. The epithelium covering the vocal cords is which of the following?

  A. pseudostratified ciliated
  B. simple columnar
  C. simple cuboidal
  D. simple squamous
  E. stratified squamous
  E. stratified squamous

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  Explanation

  Section: Anatomy A stratified squamous epithelium covers the vocal cords or folds. This epithelium protects the underlying tissue from the mechanical stress acting on the surface of the vocal cords. A simple squamous epithelium (choice D) is not suitable for protection. The rest of the larynx is covered with a pseudostratified ciliated epithelium (ie, a respiratory epithelium [choice A]). Simple columnar (choice B) and simple cuboidal (choice C) epithelia are found more commonly in organs with secretory or absorptive functions.

• Question 586:

  A3-month-old infant who otherwise appeared normal during the first 2 months of life except for a bout of hyperbilirubinemia is now clearly exhibiting developmental delay. In addition, the infant's hair has become grayish and dull and there is a stubble of broken hair over the occiput and temporal regions. The facial appearance has also changed such that the infant has very pudgy cheeks, abnormal eyebrows, and sagging jowls. The occurrence of frequent convulsions was the stimulus for the parents to bring their child to the emergency room. These rapidly deteriorating symptoms are indicative of which of the following disorders?

  A. Crigler-Najjar syndrome type I
  B. Gilbert syndrome
  C. hemochromatosis
  D. Menkes disease
  E. Refsum disease
  D. Menkes disease

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  Explanation

  Section: Biochemistry Menkes disease is an X-linked recessive disorder that is manifest by a defect in copper absorption. This defect leads to dysfunction of numerous enzymes that need copper as a cofactor, leading to the typical symptoms observed in this patient. In fact, Menkes disease is also referred to as steely hair disease, because of the characteristic brittleness of the hair, which is easily broken. Crigler-Najjar syndrome type I (choice A) is also due to defective bilirubin metabolism as a result of a loss of UDP- glucuronosyltransferase (UGT) activity. UGT is required to transfer 2 moles of glucuronic acid to bilirubin, generating bilirubindiglucuronide, which makes bilirubin much more water soluble and therefore facilitates its excretion. Crigler-Najjar syndrome results in nonhemolytic icterus (jaundice) within the first few days of life and is generally fatal during neonatal life due to severe kernicterus. Gilbert syndrome (choice B) results from a defect in bilirubin metabolism. It is typically diagnosed in young adults and is characterized by mild, chronic, and unconjugated hyperbilirubinemia without associated hemolysis. Hemochromatosis (choice C) is the term applied when organ structure and function are impaired by the presence of excess amounts of iron. The liver, heart, pancreas, skin, joints, and endocrine organs are the principal tissues affected by iron accumulation. Symptoms include cirrhosis, cardiomyopathy, arthritis, abnormal skin pigmentation, and hypogonadism, as well as diabetes mellitus. Refsum disease (choice E) results from a defect in the metabolism of phytanic acid, a plant lipid which must be oxidized by a separate pathway from that of animal fats. Cardinal symptoms include retinitis pigmentosa, peripheral neuropathy, and cerebellar ataxia.

• Question 587:

  Which of the following is an id function?

  A. aggression
  B. cognition
  C. conscience
  D. perception
  E. psychological defense mechanisms
  A. aggression

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  Explanation

  Section: Behavioral Science and Biostatics The id is the collection of psychological functions having to do with basic instincts, such as sex and survival. Aggression is a basic instinct, therefore, an id function. The ego functions to mediate between the personality system on one hand and the demands of external reality and the superego on the other hand. Thus, psychological defense mechanisms (choice E), perception (choice D), and cognition (choice B) are all ego functions. Superego is the part of the personality system that encompasses conscience (choice C).

• Question 588:

  A 71-year-old woman suffers severe head injuries in a mugging and is hospitalized in a comatose state. While in the hospital, she develops severe pneumonia and on day 11 goes into cardiac arrest and cannot be resuscitated. At autopsy she is found to have advanced coronary atherosclerosis and a pulmonary embolism judged to have occurred within the past 23 days. The coroner should list which of the following on the death certificate as the underlying (or proximate) cause of death?

  A. atherosclerosis
  B. blunt trauma to the head GI
  C. cardiopulmonary arrest
  D. pneumonia
  E. pulmonary embolism
  B. blunt trauma to the head GI

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  Explanation

  Section: Pathology and Path physiology The proximate or underlying cause of death is the initiating event that led to the person's death and is what should be listed on the death certificate as the cause of death. In this case, if the woman had not been struck on the head she would not have been hospitalized, not contracted a nosocomial pneumonia (choice D), not had a pulmonary embolism due to the prolonged immobilization (choice E), and not had a cardiopulmonary arrest (choice C). Atherosclerosis (choice A) must have been present for many years prior to the mugging and had no role in her death.

• Question 589:

  A 34-year-old woman has a history of menorrhagia. Within the wall of her uterus are several solid nodules of various sizes. The histological appearance of one of the nodules is depicted in below figure.

  These nodules represent which of the following?

  

  A. adenomyosis
  B. Krukenberg tumors
  C. leiomyomas
  D. metastatic malignancy
  E. Ovarian ectopias
  C. leiomyomas

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  Explanation

  Section: Pathology and Path physiology Figure displays interweaving bundles of smooth muscle cells, which, as a discrete myometrial nodule, define a leiomyoma. These are common tumors that may be asymptomatic or produce menorrhagia. Gross appearance is that of a solid white nodule. Adenomyosis (choice A) may clinically and grossly mimic leiomyomas. Adenomyosis, however, has a triphasic microscopic appearance consisting of benign endometrial glands, benign endometrial stroma, and smooth muscle hypertrophy. AKrukenberg tumor (choice B) is replacement of the ovary by metastatic GI adenocarcinoma. The diagnosis of metastatic malignancy (choice D) is not supported by the photomicrograph of a benign process. Ovarian ectopia (choice E) is exceedingly rare and is incompatible with the histology of the photomicrograph.

• Question 590:

  Two days following surgery to repair a defective valve, a patient developed an acute infection caused by a penicillin-resistant strain of S. aureus. below figure shows the penicillin molecule. Which numbered bond in the structure is the site of action of penicillinase?

  

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

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  Explanation

  Section: Microbiology/Immunology An important part of the penicillin molecule is the beta-lactam group. This group is composed of two carbon and two hydrogen atoms at the top of the group. The bottom part of the group contains one carbon, which is linked to one nitrogen atom and one oxygen atom. Penicillinase breaks the bond between the bottom carbon and nitrogen atom, and destroys the antibacterial activity of penicillin, along with that of cephalosporin, which also possesses a beta-lactam group.