USMLE 1 MCQ7

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    (10)<1>A 68-year-old female who recently had a cholecystectomy develops a
    fever of 103°F and has persistent drainage from her biliary catheter.
    She is given cephalothin and gentamicin for 10 days. Her serum creatinine
    level increases to 7.6 mg/dL. Her urine output is 1.3 L/day and has not
    diminished over the past few days. There is no history of hypotension
    and her vital signs are normal. Renal ultrasonography shows no evidence
    of obstruction. The most likely etiology of the patient's condition is
    A. acute glomerulonephritis
    B. acute renal failure secondary to cephalothin
    C. gentamicin nephrotoxicity
    D. renal artery occlusion
    E. sepsis
    Answer
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    <2>A 45-year-old man presents to a physician with back pain and facial pain.
    Physical examination demonstrates coarse facial features and kyphosis.
    Laboratory examination is remarkable for elevated alkaline phosphatase
    . X-ray studies demonstrate skull thickening with narrowing of foramina,
    and bowing of the femur and tibia. Bone biopsy reveals a mosaic
    pattern of bone spicules with prominent osteoid seams. Which of
    the following neoplasms occurs at an increased frequency in patients
    with this disorder?
    A. Astrocytoma
    B. Hodgkin's lymphoma
    C. Meningioma
    D. Non-Hodgkin's lymphoma
    E. Osteosarcoma
    Answer
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    <3> Which of the labeled structures is responsible for the secretion
    of renin?
    A. A
    B. B
    C. C
    D. D
    E. E
    Answer

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    <4>A 42-year-old African-American man sustains severe injuries in an
    automobile accident and is admitted to the intensive care unit.
    Examination of a peripheral blood smear on the 3rd day of admission
    reveals helmet cells, schistocytes, and decreased platelets. Which of
    the following is most strongly suggested by these findings?
    A. Autoimmune hemolysis
    B. Disseminated intravascular coagulation (DIC)
    C. Hereditary spherocytosis
    D. Megaloblastic anemia
    E. Sickle cell anemia
    Answer
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    <5>A 12-month-old child is diagnosed with an atrial septal defect.
    What is the most common cause of such a congenital heart malformation?
    A. Failure of formation of the septum primum
    B. Failure of formation of the septum secundum
    C. Incomplete adhesion between the septum primum and septum secundum
    D. Malformation of the membranous interventricular septum
    E. Malformation of the muscular interventricular septum
    Answer
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    <6>A 72-year-old man with prostate cancer is treated with leuprolide.
    What is the mechanism of action of this drug?
    A. It inhibits 5a-reductase
    B. It is a competitive antagonist at androgen receptors
    C. It is a competitive inhibitor of LH
    D. It is a synthetic analog of GnRH
    E. It is a testosterone agonist
    Answer
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    <7>An XX genotypic infant is born with ambiguous genitalia. Laboratory
    examination reveals hypoglycemia, hyperkalemia, and salt wasting. S
    erum 17-OH progesterone is markedly increased. Which of the following is
    the most likely diagnosis?
    A. 5-alpha-reductase deficiency
    B. 11-beta-hydroxylase deficiency
    C. 17-alpha-hydroxylase deficiency
    D. 21-hydroxylase deficiency
    E. Complete androgen resistance
    Answer
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    <8>A 57-year-old fisherman with a history of alcoholism is hospitalized in
    Gulfport, Mississippi with a 1-day history of severe, watery diarrhea after
    eating several raw oysters. He is badly dehydrated on admission, and within
    12 hours, he becomes severely hypotensive and dies. Which of the following
    pathogens is the most likely cause of this man's death?
    A. Citrobacter diversus
    B. Enterotoxigenic E. coli
    C. Providencia stuartii
    D. Vibrio cholerae
    E. Vibrio vulnificus
    Answer
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    <9>An Hispanic male is referred to the dermatology clinic of a major medical
    center. On physical examination, the man has several disfiguring lesions on
    his face and there is loss of cutaneous sensation to fine touch, pain, and
    temperature. An acid-fast organism is observed in scrapings from a skin
    lesion. Which of the following organisms is the most likely cause of this
    patient's disease?
    A. Bartonella henselae
    B. Listeria monocytogenes
    C. Mycobacterium avium-intracellulare
    D. Mycobacterium leprae
    E. Nocardia asteroides
    Answer
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    <10>Microscopic examination of a section of a normal young adult ovary
    reveals large numbers of unusually large cells surrounded by a single
    layer of flat epithelial cells. In which phase of the cell cycle are
    these cells arrested?
    A. Diplotene stage of the 1st meiotic division
    B. Diplotene stage of the 2nd meiotic division
    C. Metaphase stage of mitosis
    D. Prophase stage of mitosis
    E. Prophase stage of the 2nd meiotic division
    Answer
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    <11>A 3-year-old child is seen by a pediatrician because he has developed
    multiple isolated lesions on his face and neck. Physical examination
    reveals many lesions up to 4 cm in diameter with golden crusts, while
    in other sites small blisters and weeping areas are seen. Which of the
    following is the most likely diagnosis?
    A. Aphthous ulcers
    B. Erysipelas
    C. Herpes simplex I
    D. Impetigo
    E. Measles
    Answer
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    <12>A 2-year-old-boy is brought to the pediatrician by his mother because
    he has had several episodes of rectal bleeding. Evaluation with a
    technetium-99m perfusion scan reveals a 3-cm ileal outpouching located
    60 cm from the ileocecal valve. This structure likely contains which of
    the following types of ectopic tissue?
    A. Duodenal
    B. Esophageal
    C. Gastric
    D. Hepatic
    E. Jejunal
    Answer
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    <13>A 19-year-old college student presents to the student health clinic
    complaining of weakness, malaise, and a chronic cough. He has a fever of
    100 degrees F and a dry cough; no sputum can be obtained for laboratory
    analysis, so a bronchial lavage is performed and the washings are
    submitted to the laboratory. The laboratory reports that the organism
    is "slow-growing." Serodiagnosis reveals Strep MG agglutinins in the
    patient's serum. Which of the following organisms is the most likely
    cause of this student's illness?
    A. Klebsiella pneumoniae
    B. Mycoplasma pneumoniae
    C. Parainfluenza virus
    D. Respiratory syncytial virus
    E. Streptococcus pneumoniae
    Answer
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    <14>A 52-year-old male is brought into the emergency room by his wife
    because he has been complaining of a severe headache. Physical exam
    reveals ptosis of the right eyelid with the right eye facing down and out.
    There is a fixed and dilated right pupil with an inability to accommodate.
    Subarachnoid blood appears on noncontrast CT scan. Magnetic resonance
    angiography (MRA) would be expected to reveal an aneurysm of which of
    the following vessels?
    A. Anterior cerebral artery
    B. Anterior choroidal artery
    C. Anterior communicating artery
    D. Middle cerebral artery
    E. Ophthalmic artery
    F. Posterior communicating artery
    G. Posterior inferior cerebellar artery
    Answer
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    <15>A 24-year-old graduate student presents to a physician with complaints
    of severe muscle cramps and weakness with even mild exercise. Muscle
    biopsy demonstrates glycogen accumulation, but hepatic biopsy is
    unremarkable. Which of the following is the most likely diagnosis?
    A. Hartnup's disease
    B. Krabbe's disease
    C. McArdle's disease
    D. Niemann-Pick disease
    E. Von Gierke's disease
    Answer

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    <16>A baby is born with a flat facial profile, prominent epicanthal folds,
    and simian crease. She vomits when fed, and upper GI studies demonstrate
    a "double bubble" in the upper abdomen. Which of the following
    cardiovascular abnormalities might this child also have?
    A. Atrial septal defect
    B. Berry aneurysm
    C. Coarctation of the aorta
    D. Endocardial cushion defect
    E. Tetralogy of Fallot
    Answer
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    <17>An asymptomatic, 24-year-old African-American woman in her second
    trimester of pregnancy has the following laboratory findings: Based
    on the laboratory data, which of the following tests is necessary for fur
    ther evaluation of this patient?
    A. Creatinine clearance
    B. Oral glucose tolerance test
    C. Serum ferritin
    D. Sickle cell preparation
    E. No further study is necessary
    Answer
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    <18>Endometrial biopsy demonstrates a thick endometrium with long,
    coiled glands lined by a columnar epithelium with prominent cytoplasmic
    vacuoles adjacent to the gland lumen. Earlier in the menstrual cycle,
    the glands were much smaller and were lined with cells that did not
    have vacuoles. Which of the following hormones is primarily responsible
    for inducing this change in appearance?
    A. Aldosterone
    B. Cortisol
    C. Estrogen
    D. Progesterone
    E. Thyroxine

    Answer
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    <19>A 28-year-old man discovers a mass in his neck while buttoning
    his shirt collar. Physical examination reveals a 2 cm mass in one
    thyroid lobe, which is "cold" on scintiscan. Aspiration of the
    nodule demonstrates small "solid balls" of neoplastic follicular
    cells. Careful examination of these tissue balls reveals that
    they contain microscopic blood vessels and fibrous stroma in
    their centers. Which of the following is the most likely diagnosis?
    A. Follicular carcinoma
    B. Hashimoto's disease
    C. Medullary carcinoma
    D. Papillary carcinoma
    E. Thyroid adenoma
    Answer
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    <20>Nissl bodies correspond to which of the following cytoplasmic organelles?
    A. Golgi apparatus
    B. Mitochondria
    C. Nucleoli
    D. Rough endoplasmic reticulum
    E. Smooth endoplasmic reticulum
    Answer
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    <21>A 40-year-old man with sleep apnea participates in a sleep study.
    During his evaluation, normal sawtooth waves are observed on his EEG
    tracing. This pattern is associated with which period of sleep?
    A. REM
    B. Stage 1
    C. Stage 2
    D. Stage 3
    E. Stage 4
    Answer
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    <22>A United Nations representative from a poor African country has an
    influenza-like illness that resolves in a few days. Less than a week later,
    however, he develops muscle pain, spasms, and sensory disturbances.
    Two days after this, flaccid paralysis occurs. Which of the following
    is most likely to be immediately life-threatening in this patient?
    A. Acute renal failure
    B. Bowel paralysis
    C. Fulminant liver failure
    D. Gastrointestinal bleeding
    E. Respiratory paralysis
    Answer
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    <23>What is the normal myeloid to erythroid ratio in bone marrow?
    A. 1:1
    B. 1:3
    C. 1:10
    D. 3:1
    E. 10:1
    Answer
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    <24>A 45-year-old male complains of fatigue and increased frequency of
    urination. Questioning reveals that he is somewhat confused. Physical
    examination reveals a 5'10", 240 lb. individual whose fat is centrally
    distributed. Urine is positive for glucose, but negative for ketones.
    A blood sample drawn from this patient is likely to exhibit which of
    the following compared to that of a normal individual?
    A. Decreased concentration of C-peptide
    B. Decreased pH
    C. Increased antibodies against islet cell proteins
    D. Increased concentration of b-hydroxybutyrate
    E. Increased osmolarity
    Answer
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    <25>At which of the following ages does fetal movement first occur?
    A. 1 month
    B. 2 months
    C. 4 months
    D. 6 months
    E. 7 months
    Answer
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    <26>A child with retinoblastoma is found to have a 13q14 deletion.
    The Rb gene, which resides at this locus, produces which kind of
    tumor-associated protein?
    A. Cell cycle regulator
    B. Growth factor
    C. Growth factor-binding protein
    D. Growth factor receptor
    E. Transcription activator
    Answer
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    <27>A 29-year-old woman is involved in an automobile accident, and
    is taken to the emergency room by paramedics. X-rays reveal a
    fracture of her pelvis. During the healing of the pelvic fracture,
    the obturator nerve becomes entrapped in the bone callus. Compression
    of this nerve by the growing bone may result in weakness of which of
    the following muscles?
    A. Adductor magnus
    B. Biceps femoris
    C. Rectus femoris
    D. Sartorius
    E. Vastus medialis
    Answer
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    <28>An African child develops massive unilateral enlargement of his lower
    face in the vicinity of the mandible. Biopsy demonstrates sheets of
    medium-sized blast cells with admixed larger macrophages. This
    type of tumor has been associated with which of the following?
    A. Epstein-Barr virus and t(8;14)
    B. Hepatitis B and t(9;22)
    C. Herpesvirus and CD5
    D. Human immunodeficiency virus and CD4
    E. Human papillomavirus and t(2;5)
    Answer
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    <29>A 57-year-old man presents for a routine physical. His blood pressure
    is 161/98 mm Hg. The patient's only complaint is that over the past
    several months he has had difficulty urinating. His urine stream is
    intermittent, and he has recently begun experiencing nocturia and
    profound urinary urgency. Digital rectal exam reveals diffuse
    enlargement of the prostate. Which of the following agents
    would be most likely to effectively treat the man's urinary
    tract symptoms as well as his hypertension?
    A. Finasteride
    B. Guanfacine
    C. Hydralazine
    D. Labetalol
    E. Terazosin
    Answer
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    <30>A 54-year-old male with extensive, severe atherosclerosis sustains
    a thrombotic occlusion of the celiac trunk. The organs that receive
    their blood supply from this artery continue to function normally.
    Anastomoses between which of the following pairs of arteries would
    explain this phenomenon?
    A. Left gastric artery and right gastric artery
    B. Left gastroepiploic artery and right gastroepiploic artery
    C. Proper hepatic artery and gastroduodenal artery
    D. Right colic artery and middle colic artery
    E. Superior pancreaticoduodenal artery and inferior pancreaticoduodenal artery
    Answer
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    <31>A cardiovascular pharmacologist is researching the effects of new
    compounds on arteriolar resistance. Drug X maximally increases vascular
    resistance by 50% at a dose of 20 mg/mL. Drug Y maximally increases
    vascular resistance by 75% at a dose of 40 mg/mL. Which of the
    following conclusions can the researcher draw from this experiment?
    A. Drug X has a smaller volume of distribution than Drug Y
    B. Drug X has a shorter half-life than Drug Y
    C. Drug X is less efficacious than Drug Y
    D. Drug X is less potent than Drug Y
    E. Drug X has a lower LD50 than Drug Y
    Answer
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    <32>A 74-year-old woman, in otherwise good health, tripped and injured
    her right leg 2 days previously and has been bedridden since the accident
    . Two hours ago, she became delirious. On physical examination, her
    temperature is 99 F, blood pressure is 120/70 mm Hg, heart rate is
    110, and respiratory rate is 32. Pulse oximetry shows an oxygen
    saturation of 80%, and a chest x-ray film is normal. Which of the
    following is the most likely diagnosis?
    A. Acute cerebral hemorrhage
    B. Acute cerebral infarction
    C. Myocardial infarction
    D. Pulmonary infarction
    E. Pulmonary thromboembolism
    Answer
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    <33>A 25-year-old pregnant woman complains to her obstetrician of dysuria.
    Microscopic examination of the urine demonstrates many gram-negative rods,
    many neutrophils, and a few WBC casts. Which of the following is the
    specific significance of the presence of WBC casts?
    A. One or both kidneys are involved in the infection
    B. One or both ureters are involved in the infection
    C. The bladder is involved in the infection
    D. The urethra is involved in the infection
    E. The uterus is involved in the infection
    Answer
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    <34>A 45-year-old female with a long history of progressive myopia develops
    sudden patchy loss of vision in her right eye. She is very alarmed
    and rushes to her family doctor. Funduscopic examination
    reveals a large retinal detachment in the right eye.
    The retina in the left eye is normal. When
    the pupillary light reflex is tested by shining a light
    in the right eye, the physician would likely note
    A. constriction of the right pupil and constriction of the left
    B. constriction of the right pupil and dilatation of the left
    C. dilatation of the right pupil and constriction of the left
    D. dilatation of the right pupil and dilatation of the left
    E. no reaction of the right pupil and constriction of the left
    Answer
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    <35>Physical examination of a young boy reveals discharge of urine
    from the umbilicus. The physician concludes that the urachus has failed
    to fuse. Which of the following structures is the normal adult remnant
    of the fused urachus?
    A. Lateral umbilical fold
    B. Medial umbilical fold
    C. Medial umbilical ligament
    D. Median umbilical fold
    E. Median umbilical ligament
    Answer
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    <36> In this section of a healing bone fracture, which of the following
    best describes the cell at the arrow?
    A. Apoptotic cell
    B. Bone-lining macrophage
    C. Dividing osteoblast
    D. Necrotic cell
    E. Typical osteoblast
    Answer

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    <37>A retarded 45-year-old man living in Mexico becomes ill with pneumonia
    and his family brings him across the border to the United States. He
    succumbs to his illness and an autopsy is performed. Neuropathological
    examination of his brain reveals neuritic plaques and neurofibrillary
    tangles. Which of the following was the most likely cause of this man's
    retardation?
    A. Down's syndrome
    B. Edwards' syndrome
    C. Fragile X syndrome
    D. Patau syndrome
    E. Supernumerary Y syndrome


    Answer
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    <38>A 59-year-old woman presents with complaints of "feeling tired." She
    also admits to frequent headaches, which occur on one side and are
    throbbing. Physical examination is remarkable for a temperature of
    100°F (37.8°C) and tenderness over both temples. Laboratory tests
    reveal a slightly decreased hematocrit and an elevated erythrocyte
    sedimentation rate. This patient should be treated aggressively to
    prevent the development of
    A. blindness
    B. deafness
    C. loss of tactile sensation
    D. loss of the ability to speak
    E. paralysis
    Answer
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    <39>A newborn baby has projectile vomiting shortly after each feeding. It is determined that there is obstruction of the digestive tract as a result of an annular pancreas. Annular pancreas is a result of an abnormality in which of the following processes?
    A. Rotation of the dorsal pancreatic bud around the first part of the duodenum
    B. Rotation of the dorsal pancreatic bud around the second part of the duodenum
    C. Rotation of the dorsal pancreatic bud around the third part of the duodenum
    D. Rotation of the ventral pancreatic bud around the first part of the duodenum
    E. Rotation of the ventral pancreatic bud around the second part of the duodenum
    Answer
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    <40>A debilitated 72-year-old woman develops dry cough, fever, headache,
    and muscular pains. She treats herself with aspirin and ampicillin without
    any improvement. Her children take her to a local hospital, where chest
    x-ray films reveal scattered opacities, suggestive of interstitial
    infiltration. Laboratory investigations demonstrate the presence of
    cold agglutinins. She is treated with erythromycin, and her symptoms
    rapidly improve. Which of the following is the most likely etiologic
    agent of this patient's condition?
    A. Influenza virus
    B. Mycoplasma pneumoniae
    C. Pneumocystis carinii
    D. Respiratory syncytial virus
    E. Streptococcus pneumoniae
    Answer
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    <41>Which of the following hormones is most important in initiating gall
    bladder contraction?
    A. Cholecystokinin (CCK)
    B. Gastric inhibitory peptide (GIP)
    C. Gastrin
    D. Secretin
    E. Vasoactive intestinal polypeptide (VIP)
    Answer
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    >42>A patient complains to her family physician that "When it's time to go
    to work, I just can't seem to get out of the house. I have a lot of
    windows, and I need to check them all three times. Then, I can never
    be sure the door is locked, so I check it 3 times. I've been late for
    work a few times, but this is the only way I can be sure the house is
    safe. Sometimes I think I'm going to go crazy." Which of the following
    is the most likely diagnosis?
    A. Adjustment disorder with anxiety
    B. Agoraphobia without history of panic disorder
    C. Generalized anxiety disorder
    D. Obsessive compulsive disorder
    E. Panic disorder with agoraphobia
    Answer
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    <43>A 32-year-old male, infected with HIV, is diagnosed with Hodgkin's
    lymphoma. If the patient's CD4 count is 505/mm3, which of the following
    agents would be suitable for the treatment of this patient's
    lymphoma
    without further compromising his immune system?
    A. Busulfan
    B. Cisplatin
    C. Cyclophosphamide
    D. Paclitaxel
    E. Vincristine
    Answer
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    <44>A 62-year-old Type 2 diabetic patient presents with complaints of
    malaise, myalgias, respiratory distress, and increased somnolence. If
    laboratory examination reveals an anion gap of 26 mmol/L, HCO3- of 17
    mmol/L and an arterial blood pH of 7.27, the patient is most likely
    receiving
    A. glyburide
    B. metformin
    C. repaglinide
    D. miglitol
    E. troglitazone
    Answer
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    <45>A 24-year-old delivery driver is involved in an accident and sustains
    a wide abrasion over his left elbow. The abrasion results in the total
    loss of epidermis over a large area of his left arm, but one month
    later, the abrasion has healed, with regrowth of the epidermis.
    Which of the following mechanisms accounts for the restoration
    of the epidermis over the abraded area?
    A. Growth of epidermis from hair follicles and sweat glands in the dermis
    B. Migration of endothelial cells from newly grown capillaries
    C. Transformation of dermal fibroblasts into epidermal cells
    D. Transformation of macrophages into epidermal cells
    E. Transformation of melanocytes into epidermal cells
    Answer
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    <46> The diagram above shows spirographic tracings of forced expirations
    from two different individuals. Trace X was obtained from a person with
    healthy lungs. Which of the following is most likely represented by
    trace Y?
    A. Asthma
    B. Bronchospasm
    C. Emphysema
    D. Interstitial fibrosis
    E. Old age
    Answer

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    <47>A patient has multiple, pearly papules on the face. Biopsy shows a
    malignant tumor. Which of the following features would most likely be
    seen on microscopic examination?
    A. Cytoplasmic viral inclusions
    B. Keratin "pearls"
    C. Melanin
    D. Palisading nuclei
    E. S-100 positivity
    Answer
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    <48>A neonate develops marked unconjugated hyperbilirubinemia. No hemolysis
    can be demonstrated and other liver function tests are normal. There is no
    bilirubin found in the urine. This infant's condition continues to
    deteriorate and he dies at 2 weeks of age. To which of the following
    conditions did the infant most likely succumb?
    A. Crigler-Najjar syndrome, Type I
    B. Crigler-Najjar syndrome, Type II
    C. Dubin-Johnson syndrome
    D. Gilbert's syndrome
    E. Rotor syndrome
    Answer
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    <49>A 41-year-old woman presents with chronic widespread musculoskeletal
    pain, fatigue, and frequent headaches. She states that her musculoskeletal
    pain improves slightly with exercise. On examination, painful trigger
    points are produced by palpitation of the trapezius and lateral
    epicondyle of the elbow. If objective signs of inflammation are
    absent and laboratory studies are normal, this patient would most
    likely be responsive to which of the following drugs?
    A. Amitriptyline
    B. Cefaclor
    C. Naproxen
    D. Oxycodone
    E. Prednisone
    Answer
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    <50>A 29-year-old medical student developed a positive PPD (purified protein
    derivative) test. She was started on isoniazid (INH) and rifampin
    prophylaxis. Three months into her therapy, she began to experience
    muscle fasciculations and convulsions. Administration of which of
    the following vitamins might have prevented these symptoms?
    A. Niacin
    B. Pyridoxine
    C. Riboflavin
    D. Thiamine
    E. Vitamin C
    Answer
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    Answers
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    1The correct answer is C. A small percentage of patients (5% to 10%) develop a nonoliguric form of acute renal failure when treated with aminoglycosides such as gentamicin. Gentamicin can accumulate in the kidney to produce a delayed form of acute renal failure resulting in an elevation of the serum creatinine level. The nonoliguric form of renal failure, seen in this patient, is the typical presentation for gentamicin nephrotoxicity.
    Acute glomerulonephritis (choice A) is typically associated with hypertension and the appearance of an active urinary sediment containing casts and red blood cells.
    Cephalothin (choice B) is a first-generation cephalosporin commonly used in the treatment of severe infection of the genitourinary tract, gastrointestinal tract, and respiratory tract, as well as skin infections. This antibiotic can produce an acute interstitial nephritis; however, the patient's presentation is consistent with gentamicin nephrotoxicity. Interstitial nephritis is commonly associated with the development of acute renal failure, fever, rash, and eosinophilia.
    Renal artery occlusion (choice D) is commonly caused by thrombosis or embolism. The clinical features of acute renal artery occlusion are hematuria, flank pain, fever, nausea, elevated LDH, elevated SGOT and acute renal failure.
    Since the patient has normal vital signs and no history of hypotension, a diagnosis of sepsis (choice E) is unlikely.
    --------------------------------------------------------------------------------2The correct answer is E. The phrase "mosaic pattern" of newly formed woven bone is a specific tip-off for Paget's disease of bone, and is not seen in other bone conditions. The clinical and radiologic presentation are typical; an increased hat size may also be a clue. In its early stages, Paget's disease is characterized by osteolysis, producing patchwork areas of bone resorption with bizarre, large osteoclasts. In the middle stage of the disease, secondary osteoblastic activity compensates with new bone formation, producing the mosaic pattern. In late Paget's, the bones are dense and osteosclerotic. Paget's disease is suspected to be related to prior viral infection, but the cause remains mysterious. Complications include myelophthisic anemia, high output cardiac failure, pain secondary to nerve compression, deformities secondary to skeletal changes, and in about 1% of patients, osteosarcoma or other sarcoma, typically involving the jaw, pelvis, or femur.
    An increased incidence of astrocytomas (choice A) is associated with tuberous sclerosis.
    Hodgkin's lymphoma (choice B) is usually a disease of young adults, although older patients may have the lymphocyte-depleted form.
    Meningiomas (choice C) are mostly benign tumors that affect adults, especially females. There may be an association with breast cancer, possibly related to high estrogen states.
    Non-Hodgkin's lymphoma (choice D) is more common in AIDS and other immunodeficiency states, although the incidence in the immunocompetent is increasing.
    --------------------------------------------------------------------------------3The correct answer is C. This question required that you know two pieces of information: (1) renin is secreted from the juxtaglomerular (JG) cells; and (2) the location of the JG cells in a picture that includes both the glomerulus and the juxtaglomerular apparatus. Remember that renin is responsible for converting angiotensinogen to angiotensin I, which is subsequently converted to angiotensin II in the lungs by an important enzyme appropriately called angiotensin-converting enzyme. Angiotensin II helps preserve blood pressure both by its potent vasoconstrictor properties and by its ability to stimulate aldosterone secretion from the adrenal cortex.
    The label for choice A points to the glomerular basement membrane.
    The label for choice B points to the epithelium of Bowman's capsule.
    The label for choice D points to the macula densa cells, which are thought to sense sodium concentration in the distal convoluted tubule.
    The label for choice E points to the Polkissen cells. Their function is unknown.
    --------------------------------------------------------------------------------4The correct answer is B. The findings suggest disseminated intravascular coagulation (DIC), which is a feared complication of many other disorders, such as obstetrical catastrophes, metastatic cancer, massive trauma, and bacterial sepsis. The basic defect in DIC is a coagulopathy characterized by bleeding from mucosal surfaces, thrombocytopenia, prolonged PT and PTT, decreased fibrinogen level, and elevated fibrin split products. Helmet cells and schistocytes (fragmented red blood cells) are seen on peripheral blood smear.
    Autoimmune hemolysis (choice A) and hereditary spherocytosis (choice C) would be characterized by spherocytes in the peripheral smear.
    Macro-ovalocytes and hypersegmented neutrophils can be seen in megaloblastic anemia (choice D).
    Sickle cells are seen in sickle cell anemia (choice E).
    --------------------------------------------------------------------------------5The correct answer is C. The most common form of atrial septal defect is located near the foramen ovale (not to be confused with a patent foramen ovale, which is of little or no hemodynamic significance). They result from incomplete adhesion between the septum primum and the septum secundum during development.
    Atrial septal defects less commonly result from failures of formation of the septum primum (choice A) and septum secundum (choice B).
    Malformations of the interventricular septum (choices D and E) cause ventricular septal defects rather than atrial septal defects.
    --------------------------------------------------------------------------------6The correct answer is D. Leuprolide is a GnRH analog. Given long-term in a continuous fashion, it will inhibit FSH and LH release, thereby decreasing testosterone production and exacting a chemical castration in men. It can be used in the treatment of prostate cancer, polycystic ovary syndrome, uterine fibroids, and endometriosis.
    Inhibition of 5a-reductase (choice A) is the mechanism of action of finasteride. It thereby inhibits the production of dihydrotestosterone. It is used in the treatment of benign prostatic hyperplasia (BPH).
    Flutamide is another drug used in the treatment of prostate cancer. It is a competitive antagonist at androgen receptors (choice B).
    Since LH activates interstitial cells to secrete testosterone, a synthetic analog of LH (choice C) would not be appropriate treatment for prostatic cancer. The same goes for a testosterone analog (choice E).
    Here is a brief chart that will aid you in remembering the actions of these similar sounding drugs:
    Drug Action Indication
    Leuprolide GnRh analog Prostate CA
    Flutamide Competitive androgen antagonist Prostate CA
    Finasteride 5a-reductase inhibitor BPH
    Remember, "loo"prolide and "floo"tamide are both used for prostate cancer. Finasteride is used for BPH.
    --------------------------------------------------------------------------------
    7The correct answer is D. 21-hydroxylase deficiency is the most common form of congenital adrenal hyperplasia. The simple virilizing variant (without salt wasting) is most common, but with severe 21-hydroxylase deficiency, virilization and salt wasting occur. The infant described above exhibits salt wasting and hyperkalemia because aldosterone secretion is diminished by the enzyme deficiency. The hypoglycemia is due to cortisol deficiency. Because cortisol secretion is diminished in congenital adrenal hyperplasia, ACTH secretion from the anterior pituitary is increased due to loss of negative feedback inhibition. The high levels of ACTH are responsible for the adrenal hyperplasia and the increased secretion of the adrenal androgens, dehydroepiandrosterone and androstenedione, which are responsible for the virilization of the external genitalia. 17-OH progesterone is the steroid precursor just proximal to 21-hydroxylase and is also increased because of the excessive drive to the adrenal cortex by ACTH.
    5-alpha-reductase deficiency (choice A) in male fetuses will produce normal differentiation of the internal reproductive tracts, but the external genitalia will be feminized. This is because testosterone needs to be converted to dihydrotestosterone (by 5-alpha-reductase) in the external genitalia and the prostate for normal differentiation into the male phenotype.
    11-beta-hydroxylase deficiency (choice B) is another form of congenital adrenal hyperplasia. It is characterized by salt retention due to excessive secretion by the inner zones of the adrenal cortex of the weak mineralocorticoid, deoxycorticosterone. Again, the excessive drive to the adrenal cortex is due to increased ACTH resulting from diminished negative feedback suppression by cortisol. The adrenal also secretes excessive androgens and virilization occurs in female fetuses.
    17-alpha-hydroxylase deficiency (choice C) is another from of congenital adrenal hyperplasia that is accompanied by salt retention. The high levels of ACTH drive the adrenal cortex to secrete increased amounts of deoxycorticosterone and corticosterone, both of which have weak mineralocorticoid activity. Without the ability to 17-alpha-hydroxylate progesterone or pregnenolone, steroid-secreting cells cannot produce sex steroids. When 17-alpha-hydroxylase deficiency is present in the adrenal cortex, it is also present in the gonads. Hence, whether it occurs in a male or female fetus, sex steroid production will be diminished. Female fetuses will develop normal reproductive tracts and genitalia since these structures are programmed in utero to "automatically" become female. Male fetuses, however, will have their reproductive tracts and genitalia feminized.
    Complete androgen resistance (choice E) results in feminization of affected male fetuses. It is characterized by an XY genotypic male with phenotypically female external genitalia and a vagina that ends as a blind sac.
    --------------------------------------------------------------------------------8The correct answer is E. Vibrio vulnificus is an extremely invasive organism, producing a septicemia in patients after eating raw shellfish, or causing wound infections, cellulitis, fasciitis, and myositis after exposure to seawater or after cleaning shellfish. Patients at high risk for septicemia include those with liver disease, congestive heart failure, diabetes mellitus, renal failure, hemochromatosis, and immunosuppression.
    Citrobacter diversus (choice A) produces neonatal meningitis and can be frequently cultured from the umbilicus.
    Enterotoxigenic E. coli (choice B) produces the classic traveler's diarrhea. The toxin is ingested in water and salads. The incubation period is approximately 12 hours. The diarrhea is non-inflammatory and treatment is supportive.
    Providencia stuartii (choice C) is a gram-negative rod related to Proteus. It is a common cause of nosocomial bacteremia in nursing home patients with chronic catheterization.
    Vibrio cholerae (choice D) produces a non-invasive, non-inflammatory, high-volume secretory diarrhea that is toxin-mediated.
    --------------------------------------------------------------------------------9The correct answer is D. The disease in question is leprosy, or Hansen's disease. A key feature in the description is the fact that the organism is acid-fast. Both of the mycobacteria, M. avium-intracellulare and M. leprae are strongly acid-fast, that is they retain the carbol fuchsin dye in the face of acid-alcohol decolorization. M. leprae has a predilection for the skin and cutaneous nerves, thereby producing the symptoms of depigmentation and anesthetic cutaneous lesions. This loss of peripheral nerve function leads to many of the disfiguring features of the disease; because the patients do not have normal pain sensation, they sustain repeated injuries. In addition, the organism attacks cartilage and causes granuloma formation in the skin, leading to some of the facial disfigurement.
    Bartonella henselae (choice A) is a very small, gram-negative bacterium that is closely related to the rickettsia, although it is able to be cultured on lifeless media. It is the cause of cat-scratch disease, a local, chronic lymphadenitis most commonly seen in children, and bacillary angiomatosis, a disease seen particularly in AIDS patients.
    Listeria monocytogenes (choice B) is a ubiquitous microbe that causes disease in over 100 animal species. Although it is best known as an agent of meningitis in the newborn, it is a cause of multiple other diseases. A characteristic feature of these infections is the development of granulomas at the site of the infection. The organism is not acid-fast and has no particular predilection for skin or nervous tissues.
    M. avium-intracellulare (choice C) causes tuberculosis-like pulmonary disease in the immunosuppressed.
    Nocardia asteroides (choice E) primarily produces pulmonary infections in humans. The organism is consider to be "weakly" acid-fast, meaning that if the amount of HCl used in the decolorization step is reduced, the organisms will retain the carbolfuchsin primary stain.
    --------------------------------------------------------------------------------10The correct answer is A. The cells described are the primordial eggs, which remain stopped in the diplotene stage of the first meiotic division from before birth until fertilization, a period which may be 40 or more years.
    Choices B and E are incorrect because the oocytes are stopped in the first, not second meiotic division.
    Choices C and D are incorrect because the cells described are oocytes and are not in mitosis.
    --------------------------------------------------------------------------------11The correct answer is D. This is impetigo, which is typically seen in preschool children with poor hygiene, particularly in the summer in warm climates. The characteristic lesion has a large golden crust. Most cases are caused by Staphylococcus aureus; Streptococcus pyogenes is occasionally implicated. Impetigo is highly infectious, and mini-epidemics can occur in daycare settings. The initial treatment is typically with penicillins and topical preparations. Methicillin-resistant strains are presently rare in this setting, but can occur.
    Aphthous ulcers (choice A), commonly known as "canker sores," are painful, shallow ulcers of the oral cavity.
    Erysipelas (choice B) is a different type of skin infection, often caused by Streptococcus pyogenes (also sometimes others including Staphylococcus), and is characterized by large erythematous patches.
    Herpes simplex I (choice C) causes tiny oral and perioral vesicles, but not large golden crusts.
    Measles (choice E) causes a blotchy erythematous rash.
    --------------------------------------------------------------------------------12The correct answer is C. This little boy has a Meckel's diverticulum, an ileal outpocketing typically located within 50-75 cm of the ileocecal valve. It is a congenital anomaly resulting from the persistence of the vitelline (omphalomesenteric) duct. Approximately half cause ulceration, inflammation, and gastrointestinal bleeding due to the presence of ectopic acid-secreting gastric epithelium. Pancreatic tissue may sometimes occur in these diverticula as well. Note that this is the most common type of congenital gastrointestinal anomaly.
    Something else to keep in mind: A favorite question attendings ask on the wards is the rule of 2's associated with Meckel's diverticulum: it occurs in about 2% of children, occurs within approximately 2 feet of the ileocecal valve, contains 2 types of ectopic mucosa (gastric and pancreatic), and its symptoms usually occur by age 2.
    All of the other answer choices have no relationship to Meckel's diverticulum.
    --------------------------------------------------------------------------------13The correct answer is B. The patient has primary atypical pneumonia caused by Mycoplasma pneumoniae. This organism is fastidious and difficult to culture in the laboratory, however serodiagnosis can be most helpful. Patients typically produce one or two heterophile antibodies during the course of the infection; one agglutinates human O+ RBCs in the cold (the cold hemagglutinin) while the other causes the agglutination of a strain of Streptococcus salivarius termed strain MG (the Strep MG agglutinins).
    Klebsiella pneumoniae (choice A) is readily cultured on routine laboratory media and characteristically produces pneumonia with blood clots in the sputum (red currant jelly sputum), which may be indicative of pulmonary abscess development.
    Parainfluenza viruses (choice C) cause croup, which is characterized by a dry, "barking" cough. It is more of a tracheitis, bronchitis, and bronchiolitis than a pneumonitis. No heterophile antibodies are produced in these patients.
    Respiratory syncytial virus (choice D) causes an atypical pneumonitis in infants. It is usually diagnosed by the observation of syncytial masses in respiratory secretions. Cold hemagglutinins and Strep MG agglutinins are absent.
    Streptococcus pneumoniae (choice E) is the number one cause of pneumonia in adults. It also causes septicemia and meningitis in the elderly. The patient has a classical acute pneumonia with a productive cough, high fever with chills, leukocytosis, tachycardia, rapid respirations and other signs of serious respiratory disease. A vaccine, composed of the capsular carbohydrate of 23 serotypes of this organism, is routinely given to individuals over the age of 60, as well as to individuals with splenic abnormalities (e.g., sickle cell disease) who are at increased risk for pneumococcal sepsis.
    --------------------------------------------------------------------------------14The correct answer is F. Aneurysm of the posterior communicating artery is the second most common aneurysm of the circle of Willis (anterior communicating artery is most common) and can result in third cranial nerve palsy (paralysis). The oculomotor nerve (CN III) innervates the levator palpebrae muscle. CN III paralysis would therefore result in ptosis (drooping of the upper eyelid). CN III also innervates all of the extraocular muscles, except for the superior oblique (CN IV) and the lateral rectus muscles (CNVI). Thus, CN III palsy would result in unopposed action of the superior oblique and lateral rectus muscles, causing the affected eye to look down and out. CN III also supplies parasympathetic innervation to the sphincter muscle of the iris (which constricts the pupil) and to the ciliary muscle. Interruption of this pathway leads to a dilated and fixed pupil and to paralysis of accommodation.
    Note that this question teaches you about another Boards-favorite pathology: subarachnoid hemorrhage (SAH). (In this case, it was due to rupture of a posterior communicating artery aneurysm). A classic clue to the diagnosis is a patient presenting with "the worst headache of their life." When you are presented a case of sudden severe headache, SAH should rank highly on your differential diagnosis list.
    The anterior cerebral artery (choice A) supplies the medial surface of the cerebral hemisphere, from the frontal pole to the parieto-occipital sulcus. Occlusion may produce hypesthesia and paresis of the contralateral lower extremity.
    The anterior choroidal artery (choice B) arises from the internal carotid artery and is not part of the circle of Willis. It perfuses the lateral ventricular choroid plexus, the hippocampus, parts of the globus pallidus and posterior limb of the internal capsule.
    The anterior communicating artery (choice C) connects the two anterior cerebral arteries. It is the most common site of aneurysm in the circle of Willis and may cause aphasia, abulia (impaired initiative), and hemiparesis.
    The middle cerebral artery (choice D) supplies the lateral convexity of the cerebral hemisphere, including Broca's and Wernicke's speech areas and the face and arm areas of the motor and sensory cortices. It also gives rise to the lateral striate arteries, which supply the internal capsule, caudate, putamen, and globus pallidus. The middle cerebral artery is the most common site of stroke.
    The ophthalmic artery (choice E) enters the orbit with the optic nerve (CN II) and gives rise to the central artery of the retina. Occlusion results in blindness.
    The posterior inferior cerebellar artery (choice G) supplies the dorsolateral medulla and the inferior surface of the cerebellar vermis. Occlusion may result in Wallenberg's syndrome: cerebellar ataxia, hypotonia, loss of pain and temperature sensation of the ipsilateral face, absence of corneal reflex ipsilaterally, contralateral loss of pain and temperature sensation in the limbs and trunk, nystagmus, ipsilateral Horner's syndrome, dysphagia, and dysphonia.
    --------------------------------------------------------------------------------15The correct answer is C. A variety of glycogen storage diseases exist, corresponding to defects in different enzymes in glycogen metabolism; most of these involve the liver. McArdle's disease (Type V glycogen storage disease), due to a defect in muscle phosphorylase, is restricted to skeletal muscle. The presentation described in the question stem is typical. Many affected individuals also experience myoglobinuria. Definitive diagnosis is based on demonstration of myophosphorylase deficiency.
    Hartnup's disease (choice A) is a disorder of amino acid transport.
    Krabbe's disease (choice B) is a lysosomal storage disease.
    Niemann-Pick disease (choice D) is a lysosomal storage disease.
    Von Gierke's disease (choice E) is a glycogen storage disease with prominent involvement of liver, intestine, and kidney.
    --------------------------------------------------------------------------------16The correct answer is D. The disease is Down syndrome (trisomy 21). In addition to mental retardation and the characteristic physical findings described in the question stem, duodenal atresia is fairly common, as evidenced by the "double bubble" sign on x-ray. These children are also likely to have various cardiac anomalies; endocardial cushion defect is the most common.
    Atrial septal defect (choice A) is one of the most common genetic defects in the general population, but is less common than endocardial cushion defect in patients with Down syndrome.
    Berry aneurysms (choice B), also known as saccular aneurysms, are typically located in the circle of Willis on the ventral surface of the brain. They occur more frequently in patients with adult polycystic disease. Rupture can produce subarachnoid hemorrhage.
    Coarctation of the aorta (choice C) occurs more commonly in females with a 45, XO genotype (Turner syndrome).
    Tetralogy of Fallot (choice E) is the most common cause of early cyanosis, consisting of a ventricular septal defect, right ventricular outflow tract obstruction, an overriding aorta, and right ventricular hypertrophy.
    --------------------------------------------------------------------------------17The correct answer is E. All of the laboratory data in this pregnant woman are normal, hence no further study is necessary. In a normal pregnancy, both the plasma volume and RBC mass are increased with a greater increase in the plasma volume than RBC mass (2:1 ratio). This has a dilutional effect on many laboratory tests.
    Increasing plasma volume in pregnancy increases the creatinine clearance (choice A) due to the expected elevation in the glomerular filtration rate (GFR). The reference intervals for serum blood urea nitrogen and creatinine are lower than normal, due to the dilutional effect of increased plasma volume and increased clearance of both analytes in the urine caused by the rise in the GFR.
    The threshold for glucose is reduced in pregnancy, so patients can have a positive dipstick test for glucose in the presence of a normal serum glucose. Therefore, an oral glucose tolerance test (choice B) is not indicated.
    The hemoglobin (Hb) concentration in pregnancy is normally decreased because of the dilutional effect of increased plasma volume. Since the Hb is normal (for a pregnant woman) in this patient, a serum ferritin (choice C) to rule out iron deficiency is unnecessary. Furthermore, iron deficiency is usually associated with a low MCV (microcytic anemia), and her MCV is normal.
    Although sickle disease is the most common genetic hemoglobinopathy among African Americans, the patient is not anemic, so there is no reason to order a sickle cell preparation (choice D).
    --------------------------------------------------------------------------------18The correct answer is D. The endometrial phase with small glands is the proliferative phase; the one with large glands with secretory cells is the secretory phase. Estrogen (choice C) is necessary for both phases, but it is the addition of progesterone (choice D), secreted by the corpus luteum after the Graafian follicle ruptures, that triggers the switch from proliferative to secretory endometrium.
    Glucocorticoids (choice B) and the mineralocorticoid aldosterone (choice A) are secreted by the adrenal glands. They do not produce the endometrial changes described.
    Thyroxine (choice E) is secreted by the thyroid gland, and is unrelated to the observed morphologic changes in the endometrium.
    --------------------------------------------------------------------------------19The correct answer is D. The distinctive cell balls described are broken-off papillary clusters, and are considered pathognomic for papillary carcinoma of the thyroid. This is the most common form of thyroid carcinoma. It tends to present in the 3rd to 5th decade and shows a modest female predominance. Despite its propensity for local lymphatic intrusion (which may cause multifocality of tumor in the thyroid or cervical lymph node metastases), the tumor generally has an excellent prognosis with 90% 20-year survival.
    Follicular carcinoma (choice A) is characterized by follicular cells and colloid on aspiration, and cannot be reliably distinguished from thyroid adenoma.
    Distinctive features of Hashimoto's disease (choice B) on aspiration are lymphocytes, plasma cells, and macrophages.
    The most distinctive feature of medullary carcinoma (choice C) on aspiration is the presence of amyloid.
    Thyroid adenoma (choice E) shows follicular cells and colloid on aspiration, and cannot be reliably distinguished from follicular carcinoma.
    --------------------------------------------------------------------------------20The correct answer is D. This is a straightforward question relating to the definition of Nissl bodies. Rough endoplasmic reticulum present in neurons are called Nissl bodies. They stain intensely with basic dyes and are found in the cell body and proximal dendrites, but not in the axon hillock or axon.
    --------------------------------------------------------------------------------21The correct answer is A. Sawtooth waves appearing in bursts are associated with REM sleep.
    Stage 1 (choice B) is associated with 4-7 Hz theta waves.
    Stage 2 (choice C) is associated with 12-14 Hz sleep spindles and K-complexes.
    Stage 3 (choice D) is associated with < 4 Hz, high-amplitude delta waves.
    Stage 4 (choice E) is characterized by an EEG composed of about 50% delta waves.
    Note that beta waves (15-18 Hz) occur during periods of more intense mental activity while awake. Alpha waves (8-12 Hz) occur during awake, relaxed states. REM is the stage of sleep that most resembles the awake state on the EEG.
    --------------------------------------------------------------------------------22The correct answer is E. The disease is poliomyelitis. Most infections with poliovirus cause only the influenza-like symptoms, but a small percentage progress to paralytic poliomyelitis. The most common causes of death are aspiration and airway obstruction as a result of bulbar paralysis and paralysis of respiratory muscles. Arrhythmias can also be life-threatening.
    Acute renal failure (choice A) is usually not seen in poliomyelitis, although the bladder may become paralyzed.
    Bowel paralysis (choice B) can be seen, but is not usually life-threatening.
    Fulminant liver failure (choice C) is not a feature of poliomyelitis.
    Gastrointestinal bleeding (choice D) can be seen in poliomyelitis, but is not usually life-threatening.
    --------------------------------------------------------------------------------23The correct answer is D. The ratio of cells in bone marrow developing along myeloid lines to cells developing along erythroid lines is 3:1. An alternative way to remember the normal marrow composition is that it typically contains about 60% granulocytes and their precursors; 20% erythroid precursors; 10% lymphocytes, monocytes, and their precursors; and 10% unidentified or disintegrating cells. These numbers are worth remembering, because shifts away from normal values may be a subtle clue to marrow abnormalities.
    --------------------------------------------------------------------------------24The correct answer is E. An obese adult with glucosuria, but not ketonuria, likely has type 2 diabetes mellitus. Type 2 diabetes is characterized by insulin resistance resulting in hyperglycemia and increased serum osmolarity. The dehydration associated with osmotic diuresis makes the hyperosmolarity worse. As the osmolarity increases above 330 mOsm/L, the osmotic loss of water from neurons is sufficient to produce coma. In nonketotic, hyperosmolar coma, blood glucose values can range from 800 to 2,400 mg/dL and produce serum osmolarities of 330-440 mOsm/L.
    Since type 2 diabetes is due to insulin resistance, plasma levels of insulin are usually normal to increased. Because b cells secrete insulin and C-peptide in a 1:1 ratio, plasma concentration of C-peptide would also be normal to increased (not decreased, choice A) in type 2 diabetes.
    Even small amounts of insulin are sufficient to prevent ketosis. In type 2 diabetes there is enough insulin effect to prevent significant lipolysis and subsequent formation of excess ketone bodies. Hence, acidosis (choice B) is not typically associated with this disorder. Since b-hydroxybutyrate is a ketone body, its concentration in plasma is not likely to be increased (choice D).
    While there is a significant autoimmune component to type 1 diabetes, type 2 diabetes is not associated with increased circulating antibodies (choice C) against b cell proteins such as glutamic acid decarboxylase.
    --------------------------------------------------------------------------------25The correct answer is B. Neuromuscular development is sufficient to allow fetal movement in the eighth week of life. Other features of week 8 include the first appearance of a thin skin, a head as large as the rest of the body, forward-looking eyes, appearance of digits on the hands and feet, appearance of testes and ovaries (but not distinguishable external genitalia), and a crown-rump length of approximately 30 mm. By the end of the eighth week, nearly all adult structures have at least begun to develop, and the fetus "looks like a baby".
    --------------------------------------------------------------------------------26The correct answer is A. The Rb gene is an example of a tumor suppressor gene. Tumor suppressor genes encode proteins that downregulate cell growth; consequently, their deletion leads to the development of cells with a growth advantage over normal cells. Even if you know nothing about the Rb protein, choice A is still the only logical answer because it is the only example of a protein that, if absent, would favor cell growth. The Rb protein binds to transcription factors in the nucleus, preventing cells from progressing from the S1 to M stages of the cell cycle. Children born with a 13q14 deletion have only one chromosome encoding Rb; therefore only a single "hit " is required to completely knock out Rb production and lead to the development of retinoblastoma. All of the incorrect choices are proteins encoded by oncogenes, rather than tumor suppressor genes. Oncogenes favor tumorigenesis through overexpression, not deletion.
    Growth factors (choice B) are oncoproteins that are produced by tumors and have a positive feedback effect. Examples of growth factors are PDGF and fibroblast growth factor; the oncogenes encoding them are sis and hst-1, respectively.
    The prototypical growth factor-binding protein (choice C) is ras, which is mutated in a large variety of cancers. Ras normally functions as an activator of protein kinases that regulate cell growth. Overactivity of the ras protein is highly mitogenic.
    Growth factor receptors (choice D) are either expressed as mutant forms or overexpressed in tumors, leading to upregulation of growth. An example of a growth factor receptor oncogene is erb-B2, present in some breast cancers.
    Transcription activators (choice E) are DNA-binding proteins that promote DNA transcription. Amplification of these oncogenes causes cancer by promoting the transcription of growth-related genes.
    --------------------------------------------------------------------------------27The correct answer is A. The obturator nerve innervates the muscles of the medial compartment of the thigh. These include the adductor longus, adductor brevis, adductor magnus, and gracilis muscles. The adductor magnus is also innervated by the tibial nerve.
    The biceps femoris (choice B) is in the posterior compartment of the thigh. The long head of the biceps femoris is innervated by the tibial portion of the sciatic nerve, and the short head of the biceps femoris is innervated by the common peroneal portion of the sciatic nerve.
    The rectus femoris (choice C) and vastus medialis (choice E) are two of the four heads of the quadriceps femoris muscle. All four heads of the quadriceps femoris muscle are in the anterior compartment of the thigh, and are innervated by the femoral nerve.
    The sartorius muscle (choice D) is in the anterior compartment of the thigh, and is innervated by the femoral nerve.
    --------------------------------------------------------------------------------
    28The correct answer is A. The patient has Burkitt's lymphoma. This type of lymphoma is a high-grade B-cell lymphoma that occurs in endemic form in Africa (it is the most common neoplasm in children in an equatorial belt that includes Africa and New Guinea) and sporadically in the United States and Europe. The sporadic form is often in an abdominal site and occurs in young adults. The African form of Burkitt's lymphoma has been strongly associated with antibodies directed against Epstein-Barr virus; the association is weaker in sporadic cases. A characteristic translocation, t(8;14) (q24.l3;q32.33) has been described.
    Hepatitis B (choice B) is associated with hepatocellular carcinoma. t(9;22) is the Philadelphia chromosome, which is seen in some cases of CML and AML.
    Herpesvirus (choice C) does not have a strong tumor association, although a link to cervical cancer has intermittently been proposed. CD5 is a marker seen in small lymphocytic and mantle cell lymphomas.
    HIV (choice D) is linked to Kaposi's sarcoma (and AIDS). Some patients also develop primary lymphomas (not usually Burkitt's). CD4 is a marker for helper T cells and some T cell lymphomas.
    Human papillomavirus (choice E) is linked with common warts, genital condylomata, and genital cancers. t(2;5) is linked to anaplastic large cell lymphoma.
    --------------------------------------------------------------------------------29The correct answer is E. The patient is presenting with hypertension and signs and symptoms of benign prostatic hyperplasia (BPH). The essential diagnostic characteristics of BPH include a decrease in the force and caliber of the urinary stream, nocturia, high post-void residual volume, urinary retention, and azotemia. Terazosi
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