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

USMLE USMLE-STEP-1 Online Questions & Answers

• Question 541:

  A 75-year-old male presented with a 6-month history of early satiety and with upper abdominal discomfort for many years. Physical examination revealed mild epigastric tenderness. Esophago-gastro- duodenoscopy showed a large, ulcerated mass in the upper stomach, which was found to be cancerous. Surgery resulting in the removal of the gastric fundus was performed. After successful surgery, the patient was advised to eat small portions and to drink small volumes because of which of the following?

  A. almost complete absence of gastric motility
  B. distorted emptying of liquids
  C. inadequate mixing of large food boluses
  D. lack of receptive relaxation in the stomach
  E. weaker and slower propulsion of food toward the pylorus
  D. lack of receptive relaxation in the stomach

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  Explanation

  Section: Physiology The receptive relaxation reflex is a feature of the orad stomach, composed of the fundus and upper stomach body. Without food, the orad stomach shows low frequency, sustained contractions that are responsible for generating a basal pressure within the stomach. When food enters the stomach, a reflex is initiated, which allows gastric accommodation of large increases in volume with only small increases in intragastric pressure. The tonic contractions of the orad stomach also contribute to some extent to gastric emptying (choice B), since they generate a pressure gradient from the stomach to the intestine. However, neural and hormonal components play a more important role in regulating gastric emptying, which makes this not the best choice. Since the lower stomach is not affected by the surgery, characteristic motility patterns of the distal stomach remain (choice A). Features of the distal stomach include strong peristaltic waves of contractions, which cause the mixing of the chyme with digestive secretions (choice C), the grinding of the particles to a small size, and the propulsion through the gastroduodenal junction (choice E). All these motility patterns would still be a feature of the remaining stomach.

• Question 542:

  Which label in following figure indicates the typical plane of separation at which retinal detachment occurs?

  

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

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  Explanation

  Section: Anatomy Retinal separation typically occurs at the interface between the retinal pigment epithelium and the outer limit of the sensory (neural) retina. The weakness of this plane is attributed to the manner in which the retina develops, a process that involves obliteration of the space between two of the layers of the optic cup--an inner layer from which the sensory retina arises and an outer layer from which the retinal pigment epithelium arises. Other retinal layers are bridged by neuronal processes, and Müller cells (the retina's glial cells) span the entire thickness of the neural retina. Plane A(choice A) marks the boundary between the nerve fiber layer above and the ganglion cell layer below. The nerve fiber layer is composed of axons of the retinal ganglion cells. Plane B (choice B) is within the inner plexiform layer, the site of synaptic contacts between bipolar neurons, retinal ganglion cells, and amacrine cells. Plane C (choice C) is within the outer plexiform layer, the site of synapses among bipolar cells, rods and cones, and horizontal cells. The boundary between the choroid (of the middle vascular tunic or uvea) and the sclera (of the external, fibrous tunic) is marked by plane E (choice E).

• Question 543:

  Which of the following is true concerning factitious disorder?

  A. It is a form of psychosis.
  B. It is an integral part of borderline personality.
  C. It is an intentional antisocial act.
  D. It is a sick-role addiction.
  D. It is a sick-role addiction.

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  Explanation

  Section: Behavioral Science and Biostatics The caring environment of hospitalization and exemption from normal responsibilities accompanying the sick-role may be the unconscious motivation for many patients with factitious disorders to undergo very uncomfortable and often painful procedures or self-inflicted injuries to become a patient. There is no clear- cut learning, psychosis, or personality disorder that accompanies this condition; choices A, B, and C are incorrect.

• Question 544:

  An overworked surgical resident is resecting an acinic cell carcinoma from the inferior aspect of the parotid gland when he makes a careless incision and nicks a branch of the facial (seventh cranial) nerve. Which of the following muscles may be affected by this injury?

  A. omohyoid
  B. sternohyoid
  C. sternothyroid
  D. stylohyoid
  E. thyrohyoid
  D. stylohyoid

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  Explanation

  Section: Anatomy The stylohyoid is innervated by the facial (seventh cranial) nerve. During the embryonic period, the muscles developing from the second pharyngeal arch include the stylohyoid, stapedius, posterior belly of the digastric, auricular muscles, and muscles of facial expression. The nerve supplying the second pharyngeal arch, and thus all these muscles, is the facial (seventh cranial) nerve. All the other muscles, omohyoid (choice A), sternohyoid (choice B), sternothyroid (choice C), and thyrohyoid (choice E) form the infrahyoid muscle. They are supplied as a group by branches of the ansa cervicalis derived from C1, C2, and C3.

• Question 545:

  A 59-year-old man complains of periorbital edema and ankle swelling which has been gradually increasing over the past few months. Blood pressure is 120/80 mm Hg. Urinalysis shows a 4+ proteinuria but no cells or casts. Serum albumin is moderately decreased but blood urea nitrogen (BUN) and creatinine are normal. Which of the following is the most likely diagnosis?

  A. acute proliferative glomerulonephritis
  B. diabetic nephropathy
  C. IgA nephropathy
  D. lupus nephritis
  E. membranous glomerulopathy
  E. membranous glomerulopathy

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  Explanation

  Section: Pathology and Path physiology This patient has nephrotic syndrome as indicated by the edema, 4+ proteinuria, and hypoproteinemia and the most common cause of this syndrome in adults is membranous nephropathy. Acute proliferative glomerulonephritis (choice A) produces a nephritic syndrome marked by a mild proteinuria, hematuria, azotemia, and hypertension. Diabetic nephropathy (choice B) does produce proteinuria that is sometimes sufficient to cause nephrotic syndrome, but hypertension is often present along with some indication of chronic renal failure neither of which are seen in this case. IgA nephropathy or Berger disease (choice C) is a cause of nephrotic syndrome but with hematuria often associated with an upper respiratory infection unlike the presentation in this case. Patients with lupus nephritis (choice D) may present with either nephritic or nephritic syndrome, but certainly this is a much less common cause of nephrotic syndrome than membranous glomerulonephritis.

• Question 546:

  The histological structure marked by the asterisk in Fig. 1-4 is which of the following structures from the integumentary system?

  

  A. aprocrine sweat gland
  B. dermal papilla
  C. eccrine sweat gland
  D. hair follicle
  E. sebaceous gland
  C. eccrine sweat gland

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  Explanation

  Section: Anatomy This is the secretory portion of the eccrine sweat gland, recognizable by its three cell types. The apical dark cells (arrow 1) are closest to the lumen. The clear or basal cells (arrow 2) and the myoepithelial cells (arrow 3) are located against the basal lamina. Characteristically, these cells are large and the lumen is small. The apocrine sweat gland (choice A) is lined with simple cuboidal epithelium and thus has a large lumen. The dermal papilla (choice B) is formed by fibroblasts, not epithelia. The hair follicle (choice D) is formed by three concentric zones of keratinized cells and does not have a lumen. The sebaceous glands (choice E) are appendages of the hair follicle and their lumen is lined by stratified squamous epithelium.

• Question 547:

  A 35-year-old lifeguard requests a consultation for a lesion on his upper back that his girlfriend first noticed about a year ago. He states that he is more concerned since it has increased in size. Your examination reveals a 15 ?16 mm raised nodule with irregular borders and variable areas of dark and light pigmentation. This most likely represents which of the following?

  A. actinic keratosis
  B. compound nevus
  C. Lentigo simplex
  D. malignant melanoma
  E. seborrheic keratosis
  D. malignant melanoma

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  Explanation

  Section: Pathology and Path physiology Askin lesion that is >10 mm, increasing in size, has variable pigmentation, and irregular borders elicits extreme concern and is most probably a malignant melanoma. Actinic keratoses (choice A) are potentially premalignant skin lesions that, as the name suggests, are the result of chronic sun exposure; they are typically <1 cm in diameter. The accumulation of keratin on the surface imparts a rough or scaly texture to the skin. Compound nevi (choice B) (moles) develop when nests of nevi cells (modified melanocytes) extend from the dermoepidermal junction (junction nevus) into the underlying dermis; they are typically brown or flesh-colored, raised, dome-shaped lesions that are symmetrical and uniform. Lentigo simplex (choice C) refers to a benign focal hyperplasia of melanocytes; lesions typically appear as small (<1 cm) brown, sharply defined, oval macules. They have no predisposition to neoplastic change. Seborrheic keratoses (choice E) are benign pigmented skin tumors that are usually found on older individuals; lesions are flat, round waxy plaques that may seem to be glued on to the skin. Close inspection reveals pore-like structures with keratin plugs which helps to differentiate them from melanomas. These lesions have no malignant potential, but the sudden appearance of multiple lesions could be a paraneoplastic syndrome indicating a visceral malignancy (sign of Leser-Tr<pdf2txt-u>閘</pdf2txt-u>at).

• Question 548:

  Molecular studies on a certain carcinoma demonstrate DNA containing multiple sites of adjacent pyrimidine cross-linking to form pyrimidine dimers. This malignancy most likely arose in which of the following sites?

  A. bladder
  B. colon
  C. lung
  D. pancreas
  E. skin
  E. skin

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  Explanation

  Section: Pathology and Path physiology DNApyrimidine dimer formation is a possible carcinogenic consequence induced by the ultraviolet (UV) component of solar radiation. UV radiation comprises three wavelength ranges that are designated UVA, UVB, and UVC. UVB is the principal fraction responsible for the induction of squamous cell carcinoma, basal cell carcinoma, and possibly malignant melanoma of the skin (UVC is also carcinogenic, but is more effectively absorbed by the ozone layer). Aberrant pyrimidine linkages are normally corrected by DNA repair genes (nucleotide excision pathway); however, some errors remain uncorrected if these mechanisms are overwhelmed by excessive sun exposure, potentially leading to transcription errors and oncogenesis. Bladder, colon, lung, and pancreatic cancers (choices AD) frequently arise from mutations in various RAS oncogene proteins, resulting in defective guanine triphosphate (GTP) enzyme activity and increased growth factor signal transduction.

• Question 549:

  Climbing fibers provide excitation to the deep cerebellar nuclei and the Purkinje neurons. The climbing fibers originate from which of the following structures?

  A. inferior olivary nucleus
  B. pontine nuclei
  C. spinal cord
  D. superior olivary nucleus
  E. vestibular nuclei
  A. inferior olivary nucleus

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  Explanation

  Section: Anatomy The inferior olivary nucleus in the medulla oblongata is the sole source of climbing fibers to the cerebellum. All other sources of fibers to the cerebellum such as the pontine nuclei (choice B), spinal cord (choice C), or vestibular nuclei (choice E) provide mossy fibers to the cerebellum. The superior olivary nucleus (choice D) receives auditory fibers from the cochlear nuclei and projects back to the cochlea by way of the olivocochlear bundle. It modifies the sensory input from the organ of Corti in the cochlea and is not involved with cerebellar circuitry.

• Question 550:

  Which of the following agents produces vasodilation by increasing nitric oxide synthesis in endothelial cells?

  A. diazoxide
  B. histamine
  C. minoxidil
  D. nitroprusside
  E. verapamil
  B. histamine