Discussion in 'USMLE STEP 1' started by Guest, Jun 8, 2005.

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    1> A normal, healthy, 25-year-old man lives at the beach. His twin brother has
    been living in a mountain cabin for the past 2 years. Which of the
    following indices would be expected to be higher in the man living at
    sea level?
    A. Diameter of pulmonary vessels
    B. Erythropoietin production
    C. Mitochondrial density in a muscle biopsy
    D. Renal bicarbonate (HCO3-) excretion
    E. Respiratory rate
    2>A woman presents to a dermatologist because she has lost almost all the
    hair on her body, including scalp hair, eye brows, eye lashes, arm pit and
    groin hair, and the fine hairs on her body and extremities. She most likely
    has a variant of which of the following?
    A. Alopecia areata
    B. Androgenic alopecia
    C. Chronic cutaneous lupus erythematosus
    D. Lichen planopilaris
    E. Trichotillomania

    3>The greater omentum is derived from which of the following embryonic
    A. Dorsal mesoduodenum
    B. Dorsal mesogastrium
    C. Pericardioperitoneal canal
    D. Pleuropericardial membranes
    E. Ventral mesentery

    4>A 34-year-old woman is prescribed an antidepressant, which she has taken
    for the past 3 months. She is on no other medications and is in generally
    good health. After attending a party, at which she consumed wine and
    cheese, she is rushed to the emergency room with tachycardia, headache,
    and a blood pressure of 200/100. Which antidepressant is she most likely
    A. Amitriptyline
    B. Fluoxetine
    C. Phenelzine
    D. Sertraline
    E. Trazodone

    5>Which of the following hormones is secreted by anterior pituitary cells
    that stain with acidic dyes?
    A. ACTH
    B. FSH
    C. LH
    D. Prolactin
    E. TSH

    6>A 23-year-old male graduate student gets into a serious argument with
    one of his college professors, making a physical threat to the professor,
    and necessitating a call to campus security. The argument was precipitated
    by an incident between the professor and the student's girlfriend; when
    the professor corrected the student's girlfriend in class, the student
    felt the professor was verbally abusive. Which of the following is
    the most likely diagnosis ?
    A. Dependent personality disorder
    B. Histrionic personality disorder
    C. Narcissistic personality disorder
    D. Paranoid personality disorder
    E. Passive aggressive personality disorder

    7>Which of the following would shift the oxygen-hemoglobin dissociation curve
    to the right?
    A. Carbon monoxide poisoning
    B. Decreased PCO2
    C. Decreased pH
    D. Decreased temperature
    E. Decreased 2,3-DPG

    8>The wife of a 48-year-old male patient brings him to the emergency room and
    says that his memory has progressively gotten worse over the last several
    years. She also says his personality has been changing. The physician notes
    abnormal writhing movements of the man's limbs and hyperreactive reflexes
    . MRI reveals a loss of volume in the neostriatum and cortex. This disease
    is inherited via an
    A. autosomal dominant trait
    B. autosomal recessive trait
    C. x-linked dominant trait
    D. x-linked recessive trait

    9>A man presents to a dermatologist because of a severe mucocutaneous rash
    that involves most of his body, including his palms and soles. Questioning
    reveals that he is a merchant marine who several months previously had an
    encounter with a prostitute in Southeast Asia. Which of the following is
    the most likely causative agent of this rash?
    A. Herpes simplex I
    B. Herpes simplex II
    C. HIV
    D. Neisseria gonorrhoeae
    E. Treponema pallidum

    10>A patient with familial hypercholesterolemia undergoes a detailed serum
    lipid and lipoprotein analysis. Studies demonstrate elevated cholesterol
    in the form of increased LDL without elevation of other lipids.
    This patient's hyperlipidemia is best classified as which of the
    following types?
    A. Type 1
    B. Type 2a
    C. Type 2b
    D. Type 3
    E. Type 5

    11>A mutation affecting the development of the diencephalon could interfere
    with the secretion of which of the following hormones?
    A. Adrenocorticotrophic hormone (ACTH)
    B. Epinephrine
    C. Oxytocin
    D. Prolactin
    E. Thyroid stimulating hormone (TSH)

    12>Which of the following organisms is the most common cause of
    community-acquired pneumonia?
    A. Chlamydia pneumoniae
    B. Haemophilus influenzae
    C. Mycoplasma pneumoniae
    D. Staphylococcus aureus
    E. Streptococcus pneumoniae

    13>A 54-year-old male with acute lymphocytic leukemia develops a blast crisis.
    He is treated with intensive systemic chemotherapy. Following treatment,
    the patient will be at increased risk for the development of
    A. bile pigment gallstones
    B. cholesterol gallstones
    C. cystine kidney stones
    D. struvite kidney stones
    E. uric acid kidney stones

    14>A 65-year-old man with mild heart failure is treated with a loop diuretic
    . A few days later the man complains of muscle weakness. Laboratory results
    are shown below. Arterial PCO2: 48 mm Hg Arterial pH: 7.49
    Plasma HCO3-: 35 mEq/L Which of the following is most likely
    decreased in this man?
    A. Plasma aldosterone
    B. Plasma potassium
    C. Potassium excretion
    D. Renin secretion
    E. Sodium excretion

    15>A 27-year-old white male presents with a 3-week history of several swollen
    and painful toes and knees. He has a past history of conjunctivitis. He
    also describes some low back stiffness that is more severe in the morning.
    Which of the following is the most likely diagnosis?
    A. Gout
    B. Lyme disease
    C. Reiter's syndrome
    D. Rheumatoid arthritis
    E. Septic arthritis

    16>A 37-year-old woman who was diagnosed with AIDS 3 years earlier is unable
    to work, is physically debilitated, and requests her physician to provide
    her with medications with which to take her own life. The most common
    emotional disorder that results in such requests by patients is
    A. bipolar I disorder, manic type
    B. borderline personality disorder
    C. factitious disorder
    D. major depressive disorder
    E. schizophrenic disorder
    A 25-year-old man presents with a chief complaint of persistent,
    high-pitched ringing noises in his ears. Questioning reveals that
    he has also been losing his balance lately. CT of the head demonstrates
    bilateral tumors involving the vestibulocochlear nerve. Which of the
    following chromosomes contains the tumor suppressor gene most likely to
    be involved in this case?
    A. 5q
    B. 13q
    C. 17q
    D. 18q
    E. 22q

    18> An autopsy is performed on a man who suddenly began vomiting voluminous
    quantities of blood and exsanguinated. Which of the following organisms is most
    likely implicated in the pathogenesis of this disease?
    A. Cryptosporidium parvum
    B. Entamoeba histolytica
    C. Escherichia coli
    D. Helicobacter pylori
    E. Mycobacterium tuberculosis

    19>During embryological development, hematopoiesis occurs in different organs
    at different times. Which of the following are the correct organs, in the
    correct sequence, at which hematopoiesis occurs embryologically?
    A. Amnion, yolk sac, placenta, bone marrow
    B. Placenta, liver and spleen, yolk sac, bone marrow
    C. Placenta, spleen and lymphatic organs, bone marrow
    D. Yolk sac, bone marrow, liver and spleen
    E. Yolk sac, liver, spleen and lymphatic organs, bone marrow

    20>A 27-year-old male is brought into the emergency room by the police,
    who found him walking aimlessly, shouting the names of former Presidents.
    Urine toxicology is negative, and the man appears to be oriented with
    respect to person, place, and time. He has had five similar admissions
    over the past year. Attempts to interview the patient are fruitless,
    as he seems easily derailed from his train of thought. A phone call
    to a friend listed in the chart provides the additional information
    that the man is homeless, and unable to care for himself. This patient
    is exhibiting the signs and symptoms of
    A. schizoaffective disorder
    B. schizoid personality disorder
    C. schizophrenia
    D. schizophreniform disorder
    E. schizotypal personality disorder

    21>Molecular genetic studies are performed on a family with known familial
    hypercholesterolemia. In this particular family, the defect in the LDL
    receptor gene involves a messenger mutation near the 11th exon, in the
    region of homology with epidermal growth factor receptor precursor. A
    defect at this site would be most likely to produce which of the following
    A. Decreased transcription of LDL receptor gene
    B. Poor internalization of LDL bound to LDL receptor
    C. Poor retention of the LDL receptor in the membrane
    D. Reduced binding of LDL
    E. Trapping of the LDL receptor in the endoplasmic reticulum

    22>A 27-year-old woman is giving birth. During the birth, the placental
    membranes tear and amniotic fluid is expressed into a lacerated cervical
    vein. Which of the following is the woman most likely to experience
    immediately following this event?
    A. Hemiplegia
    B. Placental abruption
    C. Renal failure
    D. Respiratory distress
    E. Splinter hemorrhages

    23>A 30-year-old pregnant woman complains to her physician of feeling very
    tired during her pregnancy. A complete blood count with differential
    reveals a hematocrit of 30%, with hypersegmented neutrophils and large,
    hypochromic red cells. Deficiency of which of the following would be
    most likely to produce these findings?
    A. Ascorbic acid
    B. Calcium
    C. Copper
    D. Folate
    E. Iron

    24>An otherwise healthy 3-year-old child is brought to the pediatrician with
    umbilicated, flesh-colored papules on his trunk. This condition is related
    to infection with which of the following viruses?
    A. Cytomegalovirus
    B. Herpesvirus 6
    C. Parvovirus
    D. Poxvirus
    E. Variola

    25>Which of the following renal structures is most medially located?
    A. Major calyx
    B. Minor calyx
    C. Renal cortex
    D. Renal pelvis
    E. Renal pyramid

    26>A 48-year-old female is being treated for breast carcinoma. Over the past
    few days, she has been complaining of dysuria and frequency. Laboratory
    examination revealed the presence of microscopic hematuria. The next day
    the patient developed gross hematuria. Which of the following agents most
    likely caused the development of these signs and symptoms?
    A. Cyclophosphamide
    B. Mitomycin
    C. Paclitaxel
    D. Tamoxifen
    E. Vincristine

    27>A child who has had abnormal development of the membranous bones has a
    broad skull with associated facial and dental anomalies. Which other bones
    are most likely to also be affected?
    A. Clavicles
    B. Femurs
    C. Metatarsals
    D. Phalanges
    E. Tibias

    28>A 3-year-old child is referred to a major medical center because of an
    abdominal mass arising from his right adrenal gland. Biopsy of the lesion
    demonstrates sheets of small cells with hyperchromatic nuclei containing
    occasional pseudorosettes composed of circles of tumor cells with central
    young nerve fibers arising from the tumor cells. Which of the following
    oncogenes is associated with this patient's tumor?
    A. erb-B2
    B. c-myc
    C. L-myc
    D. N-myc
    E. ret

    29>A 3-year-old child develops headaches and is brought to the family doctor.
    Funduscopic examination reveals papilledema; one retina also shows a very
    vascular tumor. CT of the head demonstrates a cystic tumor of the
    cerebellum. This child has a high likelihood of later developing
    which of the following?
    A. Berry aneurysm of the basilar system
    B. Bilateral renal cell carcinoma
    C. Cancer of a peripheral nerve
    D. Choreiform movements related to decreased GABA and acetylcholine
    E. Serum cholesterol of greater than 700 mg/dL

    30>Administration of an experimental drug that acts on PNS myelin is shown
    to increase the space constant of an axon in a peripheral nerve. Action
    potentials traveling down the axon would be predicted to be
    A. faster
    B. larger
    C. slower
    D. smaller
    E. unchanged

    31>A 26-year-old man presents to his physician with a chronic cough. The man
    is a smoker, and states that he also gets frequent headaches and aches in
    his legs when he exercises. Chest x-ray demonstrates notching of his
    ribs. Which of the following undiagnosed congenital defects may be
    responsible for these findings?
    A. Coarctation of the aorta
    B. Eisenmenger's syndrome
    C. Tetralogy of Fallot
    D. Transposition of great vessels
    E. Ventricular septal defect

    32>A 36-year-old Asian male complains of difficulty swallowing.
    Esophagoscopy reveals a polypoid mass that is subsequently biopsied.
    In addition to tumor cells, the esophageal biopsy show normal smooth
    muscle and striated muscle in the same section. Which portion of the
    esophagus was the source of this biopsy?
    A. Lower esophageal sphincter
    B. Lower third of the esophagus
    C. Middle third of the esophagus
    D. Upper esophageal sphincter
    E. Upper third of the esophagus

    33> A 25-year-old woman with sickle cell anemia complains of steady pain in
    her right upper quadrant with radiation to the right shoulder, especially
    after large or fatty meals. Her physician diagnoses gallstones. Of which
    of the following compounds are these stones most likely composed?
    A. Calcium bilirubinate
    B. Calcium oxalate
    C. Cholesterol
    D. Cholesterol and calcium bilirubinate
    E. Cystine

    34>A 54-year-old alcoholic presents with complaints of tremors and muscle
    twitching. Physical examination reveals the presence of Trousseau's sign.
    Laboratory data show that serum magnesium is < 1 mEq/L
    (normal, 1.4 - 2.2 mEq/L). Which of the following findings
    would be most consistent with this information?
    A. Decreased serum calcium
    B. Decreased serum phosphate
    C. Increased bone density
    D. Increased plasma parathyroid hormone concentration
    E. Increased urinary cAMP concentration

    35>A young boy presents with failure to thrive. Biochemical analysis of a
    duodenal aspirate after a meal reveals a deficiency of enteropeptidase
    (enterokinase). The levels of which of the following digestive enzymes
    would be affected?
    A. Amylase
    B. Colipase
    C. Lactase
    D. Pepsin
    E. Trypsin

    36>A Guatemalan child with a history of meconium ileus is brought to a
    clinic because of a chronic cough. The mother notes a history of respiratory
    tract infections and bulky, foul-smelling stools. After assessment of the
    respiratory tract illness, the physician should also look for signs of
    A. cystinuria
    B. hypoglycemia
    C. iron deficiency anemia
    D. sphingomyelin accumulation
    E. vitamin A deficiency

    37>An infant is born with an abnormally developed falciform ligament.
    The hepatogastric and hepatoduodenal ligaments are also malformed
    . These developmental anomalies are most likely due to abnormal
    development of the
    A. dorsal mesoduodenum
    B. dorsal mesogastrium
    C. pericardioperitoneal canal
    D. pleuropericardial membranes
    E. ventral mesentery

    38>A 26-year-old man is admitted through the emergency department to the
    hospital for a heroin overdose. His heart rate is 45 beats/min, and his
    blood pressure is 75/40 mm Hg. Which of the following best depicts the
    results from an arterial blood sample ?
    pH PaCO2 (mm Hg) HCO3- (mEq/L)
    A. 7.22 66 26
    B. 7.34 29 15
    C. 7.40 40 24
    D. 7.47 20 14
    E. 7.49 48 35

    39>A 15-year-old boy presents to his physician with several weeks of slowly
    worsening pruritus of both of his feet. He is otherwise well and taking
    no medications. On examination, he has bilateral, erythematous, dry
    scaling lesions that are most obvious in the interdigital web spaces
    and on the soles. There is no bleeding or exudate. What would most
    likely be found in a potassium hydroxide (KOH) mount of a scrapin
    g of the affected skin?
    A. Branching hyphae with rosettes of conidia
    B. Branching, septate hyphae
    C. Budding yeasts
    D. Hyphae, arthroconidia, and blastoconidia
    E. Pigmented, septate hyphal fragments
    F. Short, curved hyphae and round yeasts

    40>A 48-year-old white female secretary presents with progressive difficulty
    typing over the past month. She also notes that her hands begin to feel
    numb and weak after typing for long periods of time. Upon testing,
    which of the following deficits would be predicted?
    A. Difficulty in abducting the fifth finger
    B. Difficulty in adducting the thumb
    C. Difficulty in flexing digits two and three at the metacarpophalangeal joints
    D. Loss of sensation over the lateral half of the dorsum of the hand
    E. Loss of sensation over the lateral half of the palm
    F. Loss of sensation over the medial half of the dorsum of the hand
    G. Loss of sensation over the medial half of the palm

    41>A 15-year-old girl is brought into the emergency room with severe abdominal
    pain and a fever. Laboratory examination is remarkable for an elevated
    white blood cell count and a pregnancy test is positive. Upon questioning,
    it is determined that she attempted to terminate her pregnancy by
    inserting a sharp object into her vagina. The physician determines
    that the wall of the posterior fornix of the vagina has been penetrated. Into what region did the sharp object penetrate?
    A. Deep perineal pouch
    B. Ischioanal space
    C. Rectouterine space
    D. Rectovesical space
    E. Vesicouterine space

    42>Which of the following is found in the respiratory zone of the lung?
    A. Goblet cells
    B. Main bronchi
    C. Mucous cells
    D. Terminal bronchioles
    E. Type I epithelial cells

    43>A patient presents with a bulge in the groin, which his physician
    diagnoses as an inguinal hernia. To determine whether it is an indirect
    or direct inguinal hernia, the physician applies pressure over the deep
    inguinal ring while palpating over the superficial inguinal ring. The
    patient is then asked to cough. The physician notes that the hernia
    does not push out of the abdomen and concludes that it is an indirect
    inguinal hernia. Where did the physician apply pressure?
    A. Immediately lateral to the lacunar ligament
    B. Immediately lateral to the pubic tubercle
    C. Immediately medial to the femoral vein
    D. One half inch above the midpoint of the inguinal ligament
    E. One half inch below the midpoint of the inguinal ligament

    44>A 68-year-old woman presents for a routine check-up. Her only complaint
    is that she occasionally experiences a little swelling in her ankles.
    Her serum potassium is 3.5 mEq/L, so the physician wants to avoid
    unnecessary potassium losses. Which of the following diuretics would
    be most appropriate for this patient?
    A. Furosemide
    B. Hydrochlorothiazide
    C. Indapamide
    D. Metolazone
    E. Spironolactone

    45>A 15-year-old boy is evaluated by a clinician for failure to develop normal
    male secondary sexual characteristics. Physical examination reveals small
    testes, a small penis, and gynecomastia. The boy has had some difficulties
    in school, and the parents say that the school psychometrist said he had
    an IQ of 90. This patient's condition is most likely to be related to
    which of the following?
    A. Deletion
    B. Nondisjunction of an autosomal chromosome
    C. Nondisjunction of a sex chromosome
    D. Non-Robertsonian translocation
    E. Robertsonian translocation

    46>A 5-year-old boy falls off his bike and fractures his humerus. He is taken
    to the emergency room, and the bone is set by one of the emergency room
    physicians. Which of the following is responsible for producing the
    majority of the new bone that will reunite the two fragments?
    A. Cancellous bone
    B. Cartilage
    C. Compact bone
    D. Marrow
    E. Periosteum

    47>A 25-year-old man presents with a 4-cm mass above the clavicle. Chest X-ray
    demonstrates marked mediastinal widening. Excisional biopsy of the
    supraclavicular mass demonstrates areas with the appearance shown in
    the photomicrograph above. The large cell (indicated with the arrow)
    is most likely which of the following?
    A. Langhans cell
    B. LE cell
    C. Mott cell
    D. Reed-Sternberg cell
    E. Touton cell


    48>A 50 -year-old electrician reports pain in his left upper extremity and
    tingling and numbness in his 4th and 5th digits of his left hand. Ther
    e is mild swelling of the left hand. The man reports most of his pain
    and numbness occurs when he is doing electrical work with his arms
    overhead. X-ray reveals the presence of a cervical rib. Which of the
    following structures is most likely being compressed?
    A. Axillary artery
    B. Brachial artery
    C. Brachiocephalic artery
    D. Subclavian artery
    E. Subscapular artery

    49>The left adrenal vein drains directly into which of the following veins?
    A. Hemiazygos vein
    B. Inferior vena cava
    C. Left renal vein
    D. Splenic vein
    E. Superior mesenteric vein


    50>To which of the following diseases is pyruvate kinase deficiency most
    similar clinically?
    A. a-thalassemia
    B. b-thalassemia
    C. Glucose-6-phosphate dehydrogenase deficiency
    D. Hereditary spherocytosis
    E. Iron deficiency anemia


    1>The correct answer is A. A number of physiologic changes occur in a person living at high altitude. The diminished barometric pressure at high altitude causes alveolar hypoxia and arterial hypoxia. Pulmonary vasoconstriction occurs in response to alveolar hypoxia; therefore, the diameter of the pulmonary vessels would be greater in the brother living at sea level. All the other choices describe physiologic processes that would be enhanced by living at high altitude.
    Increased erythropoietin production (choice B), caused by arterial hypoxia, leads to increases in hematocrit in people living at high altitude.
    Mitochondrial density increases (choice C) in people chronically exposed to the hypoxemia caused by living at high altitude.
    At high altitudes, the ventilation rate increases, causing a respiratory alkalosis. The kidney then compensates by increasing the excretion of HCO3- (choice D).
    Increasing the rate of respiration (choice E) is a very useful adaptation to the hypoxic conditions of high altitude. The primary stimulus is the hypoxic stimulation of peripheral chemoreceptors.
    2>The correct answer is A. Alopecia areata is caused by an autoimmune attack on hair follicles. It has a wide range of clinical severity, with most cases involving a localized patch of hair (which regrows within 1 year in half of the patients). The hair that does regrow may be gray or depigmented. More severe cases can involve the entire scalp (alopecia totalis) or, as in this patient, the entire body surface (alopecia universalis). These more severe cases are less likely to resolve adequately. Treatment of alopecia areata is often unsuccessful, but topical steroids are typically tried.
    Androgenic alopecia (choice B) is common male pattern baldness.
    Chronic cutaneous lupus erythematosus (choice C) can produce localized baldness.
    Lichen planopilaris (choice D) can produce localized baldness.
    Trichotillomania (choice E), also called traumatic alopecia, is alopecia due to trauma, such as hair pulling or tight braids.
    --------------------------------------------------------------------------------3>The correct answer is B. Both the omental bursa and the greater omentum are derived from the dorsal mesogastrium, which is the mesentery of the stomach region.
    The dorsal mesoduodenum (choice A) is the mesentery of the developing duodenum, which later disappears so that the duodenum and pancreas come to lie retroperitoneally.
    The pericardioperitoneal canal (choice C) embryologically connects the thoracic and peritoneal canals.
    The pleuropericardial membranes (choice D) become the pericardium and contribute to the diaphragm.
    The ventral mesentery (choice E) forms the falciform ligament, ligamentum teres, and lesser omentum.
    --------------------------------------------------------------------------------4>The correct answer is C. Wine and cheese (and many other fermented foods) contain tyramine, an indirect sympathomimetic that can trigger excess catecholamine release and lead to a hypertensive crisis when ingested by patients taking MAO inhibitors. The only such drug listed among the answer choices is phenelzine. Other MAO inhibitors with similar effects include tranylcypromine, isocarboxazid, and iproniazid. Whenever this particular drug class is mentioned in a question stem, consider the possibility of interactions with foods or other medications the patient may have taken.
    Amitriptyline (choice A) is a tricyclic antidepressant. Tricyclic antidepressant drugs (particularly amitriptyline) are known for their anticholinergic side effects. They also produce postural hypotension (because they block alpha-adrenergic receptors) and are sedative.
    Fluoxetine and sertraline (choices B and D) are antidepressants that are selective serotonin reuptake inhibitors (SSRIs). Fluoxetine is also useful in treatment of obsessive-compulsive disorders.
    Trazodone (choice E) is an atypical antidepressant with substantial sedative side effects. Its most serious side effect is priapism, a medical emergency.
    --------------------------------------------------------------------------------5>The correct answer is D. The cells of the anterior pituitary can be classified as chromophils (love dyes) or chromophobes (do not stain with dyes). The chromophils can be further divided into acidophils (stain with acidic dyes) and basophils (stain with basic dyes). The acidophils include the somatotropes, which secrete growth hormone, and the mammotropes, which secrete prolactin. The basophils include the corticotropes, which secrete ACTH (choice A), the gonadotropes, which secrete FSH and LH (choices B and C), and the thyrotropes, which secrete TSH (choice E).
    --------------------------------------------------------------------------------6>The correct answer is D. Persons with this condition often perceive attacks and danger in relatively innocuous situations. They are quick to respond with anger, and, because personality disorders are ego-syntonic, individuals with personality disorders do not believe themselves to be in error.
    The individual with dependent personality disorder (choice A) does not confront others but wants others to take care of him.
    The individual with histrionic personality disorder (choice B) is flamboyant and seductive, not confrontational and angry.
    The individual with narcissistic personality disorder (choice C) is characterized by feelings of entitlement because they are so "special."
    And the individual with passive aggressive personality disorder (choice E) expresses anger indirectly (e.g., always being late) rather than confronting
    --------------------------------------------------------------------------------7>The correct answer is C. The loading of O2 is facilitated when the oxygen dissociation curve shifts to the left, and the unloading of O2 is facilitated when the oxygen dissociation curve shifts to the right. A good way to remember the conditions that promote dissociation of O2 is to think of exercising muscle, which has decreased pH (choice C) because of the accumulation of lactic acid, increased PCO2 (compare with choice B) because of the increased rate of aerobic metabolism, increased temperature (compare with choice D), and increased 2,3-DPG (2,3-diphosphoglycerate; compare with choice E) because of increased glycolysis.
    Carbon monoxide poisoning (choice A) left-shifts the oxygen dissociation curve, which interferes with the unloading of O2. Carbon monoxide also strongly binds to available sites on hemoglobin.
    --------------------------------------------------------------------------------8>The correct answer is A. This patient has Huntington's disease, which has autosomal dominant inheritance. It is characterized by severe degeneration of the caudate nucleus along with degenerative changes in the putamen and cortex. In addition to chorea, these patients frequently suffer from athetoid (writhing) movements, progressive dementia, and behavioral disorders.
    --------------------------------------------------------------------------------9>The correct answer is E. The rash described is that of secondary syphilis, caused by Treponema pallidum. Involvement of palms and soles by a rash is unusual, and secondary syphilis should come to mind. Not all patients with secondary syphilis have a severe form of the rash, and consequentially some cases are missed. Primary syphilis takes the form of a painless, button-like mass called chancres. Tertiary syphilis, which is now rare, has a propensity for involving the aorta and central nervous system and can also cause "gummas" (granulomatous-like lesions) in many sites, notably including liver and bone.
    Herpes simplex I (choice A) usually causes perioral vesicular lesions.
    Herpes simplex II (choice B) usually causes genital vesicular lesions.
    HIV (choice C) does not itself cause a rash, although co-infection with other organisms can result in a rash.
    Neisseria gonorrhoeae (choice D) does not typically cause a rash.
    --------------------------------------------------------------------------------10>The correct answer is B. Hyperlipidemia has been subclassified based on the lipid and lipoprotein profiles. Type 2a, which this patient has, can be seen in a hereditary form, known as familial hypercholesterolemia, and also in secondary, acquired forms related to nephritic syndrome and hyperthyroidism. The root problem appears to be a deficiency of LDL receptors, which leads to a specific elevation of cholesterol in the form of increased LDL. Heterozygotes for the hereditary form generally develop cardiovascular disease from 30 to 50 years of age. Homozygotes may have cardiovascular disease in childhood.
    Type 1 (choice A) is characterized by isolated elevation of chylomicrons.
    Type 2b (choice C) is characterized by elevations of both cholesterol and triglycerides in the form of LDL and VLDL.
    Type 3 (choice D) is characterized by elevations of triglycerides and cholesterol in the form of chylomicron remnants and IDL.
    Type 5 (choice E) is characterized by elevations of triglycerides and cholesterol in the form of VLDL and chylomicrons.
    --------------------------------------------------------------------------------11The correct answer is C. The neurohypophysis (posterior pituitary) is derived from an evagination of diencephalic neurectoderm. This structure is responsible for releasing oxytocin and vasopressin to the general circulation. Both hormones are synthesized in cell bodies contained within the hypothalamus.
    ACTH (choice A), prolactin (choice D), and TSH (choice E) are all synthesized and released by the anterior pituitary, or adenohypophysis, which is derived from an evagination of the ectoderm of Rathke's pouch, a diverticulum of the primitive mouth. Remnants of this pouch may give rise to a craniopharyngioma in later life.
    Epinephrine (choice B) is synthesized and released into the circulation by the adrenal medulla, a neural crest derivative.
    --------------------------------------------------------------------------------12>The correct answer is E. The most common bacteria implicated in community-acquired pneumonia is the pneumococcus, Streptococcus pneumoniae. Other organisms frequently implicated in patients less than age 60 without comorbidity include Mycoplasma pneumoniae, respiratory viruses, Chlamydia pneumoniae, and Haemophilus influenzae. When community-acquired pneumonia occurs in elderly patients or patients with comorbidity, aerobic gram-negative bacilli and Staphylococcus aureus are added to the list.
    The organisms listed in choices A, B, and C are important causes of community-acquired pneumonia, but are not the most frequent causes.
    Staphylococcus aureus (choice D) is an important cause of community-acquired pneumonia (particularly in the elderly and in patients with comorbidity), but is not the most frequent cause.
    --------------------------------------------------------------------------------13>The correct answer is E. Uric acid kidney stones in patients with leukemia are secondary to increased production of uric acid from purine breakdown during periods of active cell proliferation, especially following treatment. Vigorous hydration and diuresis are generally instituted after the diagnosis of acute leukemia is made. Uric acid kidney stones are also associated with inborn errors of purine metabolism, such as gout.
    Pigment gallstones (choice A) are associated with hemolytic disease. The incidence of this type of gallstone is not increased in treated leukemias.
    Cholesterol gallstones (choice B) are associated with diabetes mellitus, obesity, pregnancy, birth control pills, and celiac disease.
    Cystine kidney stones (choice C) are rare; they are found in cystinuria.
    Struvite kidney stones (choice D) are associated with infection by urea-splitting organisms, such as Proteus.
    --------------------------------------------------------------------------------14>The correct answer is B. The data shown in the table indicate that the man has developed metabolic alkalosis (increased PCO2, pH, and HCO3-), which occurs commonly with overuse of diuretics (thiazides and loop diuretics). The overuse of a loop diuretic increases the excretion of sodium (choice E) and potassium (choice C) by the kidneys. The increase in potassium excretion leads to a decrease in plasma potassium levels (choice B). The decrease in plasma potassium stimulates aldosterone secretion, which raises plasma aldosterone levels (choice A). The sodium depletion stimulates renin secretion (choice D), which in turn raises angiotensin II levels in the plasma (which also stimulates aldosterone secretion
    --------------------------------------------------------------------------------15>The correct answer is C. This is a case of Reiter's syndrome. Patients typically present with the acute onset of arthritis (usually asymmetric and additive), with involvement of new joints occurring over a period of a few days to 2 weeks. Joints of the lower extremities are the most commonly involved, but wrists and fingers can also be affected. Dactylitis (sausage digit), a diffuse swelling of a solitary finger or toe, is a distinctive feature of Reiter's arthritis and psoriatic arthritis. Tendonitis and fasciitis are common. Spinal pain and low back pain are common. Conjunctivitis, urethritis, diarrhea, and skin lesions are also associated with Reiter's syndrome. Up to 75% of patients are HLA-B27 positive. Microorganisms which can trigger Reiter's syndrome include Shigella spp., Salmonella spp., Yersinia spp., Campylobacter jejuni, and Chlamydia trachomatis. Most patients are younger males.
    Gout (choice A) usually presents as an explosive attack of acute, very painful, monarticular inflammatory arthritis. Hyperuricemia is the cardinal feature and prerequisite for gout. The first metatarsophalangeal joint is involved in over 50% of first attacks.
    Lyme disease (choice B), caused by Borrelia burgdorferi, presents with a red macule or papule at the site of the tick bite. This lesion, called erythema chronicum migrans, slowly expands to form a large annular lesion with a red border and central clearing. The lesion is warm, but usually not painful. The patient also has severe headache, stiff neck, chills, arthralgias, and profound malaise and fatigue. Untreated infection is associated with development of arthritis. The large joints (e.g., knees) are usually involved with the arthritis lasting for weeks to months.
    Rheumatoid arthritis (choice D) begins insidiously with fatigue, anorexia, generalized weakness, and vague musculoskeletal symptoms leading up to the appearance of synovitis. Pain in the affected joints, aggravated by movement, is the most common manifestation of established rheumatoid arthritis. Generalized stiffness is frequent and is usually greatest after periods of inactivity. Morning stiffness of greater than 1 hour in duration is very characteristic. Rheumatoid arthritis is more common in females. The metacarpophalangeal and proximal interphalangeal joints of the hands are characteristically involved.
    Septic arthritis (choice E) is caused by a variety of microorganisms, including Neisseria gonorrhoeae and Staphylococcus aureus. Hematogenous spread is the most common route in all age groups. 90% of patients present with involvement of a single joint, usually the knee. The usual presentation is moderate-to-severe pain, effusion, muscle spasm, and decreased range of motion. Peripheral leukocytosis and a left shift are common. Disseminated gonococcal infections present as fever, chills, rash, and articular symptoms. Papules progressing to hemorrhagic pustules develop on the trunk and extensor surfaces of the distal extremities. Migratory arthritis and tenosynovitis of multiple joints is common.
    --------------------------------------------------------------------------------16>The correct answer is D. Many people who request physician-assisted suicide have one of two conditions present: either a poorly controlled painful condition or severe depression. If the painful condition is adequately treated or the depression is brought under good medical control, the request for physician assistance in terminating the situation is typically withdrawn. It is important to note that bringing these conditions under control requires the intervention of caregivers who are specifically trained in the management of these two conditions; primary care physicians usually are not adequately trained to address these difficult presentations.
    While patients who are diagnosed as bipolar disorder (choice A), borderline personality disorder (choice B), and schizophrenic disorder (choice E) often make suicide attempts (and frequently complete those attempts), they do not generally ask their physician for assistance in the suicide.
    Persons with factitious disorder (choice C) are seeking primary gain, often for dependency needs, and are seeking to enter the "sick role" not the "dead role."
    --------------------------------------------------------------------------------17>The correct answer is E. The patient has bilateral acoustic neuromas, probably due to neurofibromatosis type II (over 90% of patients with NF-2 develop bilateral acoustic neuromas). This condition is a associated with the NF-2, gene, located on 22q (note all the 2's). Patients often develop meningiomas, gliomas, and schwannomas of cranial and spinal nerves.
    5q (choice A) contains the APC tumor suppressor gene, which is associated with familial and sporadic colorectal cancers.
    13q (choice B) contains the Rb tumor suppressor gene, which is associated with retinoblastoma and osteosarcoma.
    17q (choice C) contains both the NF-1 tumor suppressor gene, which is associated with neurofibromatosis type I, and the p53 tumor suppressor gene, associated with many human cancers.
    18q (choice D) contains both the DCC gene, which is associated with colon and gastric carcinomas and the DPC gene, associated with pancreatic cancer.

    The correct answer is D. Perforation of a peptic ulcer is potentially fatal, because of either peritonitis with sepsis or sudden exsanguination (if the perforation damages one of the many arteries of the stomach). Peptic ulcer disease, gastritis, and possibly gastric carcinoma and gastric lymphoma have been strongly associated with Helicobacter pylori colonization of the mucus layer covering the gastric mucosa. Colonization is associated with destruction of the mucus layer, thereby destroying its protective function.
    Cryptosporidium parvum (choice A) causes diarrhea that is severe in immunocompromised patients.
    Entamoeba histolytica (choice B) produces dysentery-like symptoms or can cause liver abscess.
    Escherichia coli (choice C) causes a variety of diarrheal diseases and can infect the bladder and soft tissues.
    Mycobacterium tuberculosis (choice E) causes tuberculosis, characterized by granuloma formation, especially in the lungs.
    --------------------------------------------------------------------------------19>The correct answer is E. By the third week of development, hematopoiesis begins in the blood islands of the yolk sac. Beginning at 1 month of age and continuing until 7 months of age, blood elements are also formed in the liver. Hematopoiesis occurs in the spleen and lymphatic organs between 2 and 4 months, and in the bone marrow after 4 months.
    15>The correct answer is C. The patient is suffering from schizophrenia. The key to the diagnosis of psychosis is that there has been a marked decline in the level of functioning (i.e., the man is homeless and cannot care for himself). Although hallucinations or delusions are not mentioned in the case history, the presence of disorganized speech, grossly disorganized behavior, and the duration of symptoms (longer than six months) suggest a diagnosis of schizophrenia.
    In schizoaffective disorder (choice A), alterations in mood are present during a substantial portion of the illness.
    Although schizoid personality disorder (choice B) produces detachment from social relationships and is characterized by restriction of emotional expression, it is not accompanied by a marked decline in occupational functioning.
    Schizophreniform disorder (choice D) is characterized by schizophrenic-like symptoms, but the duration of symptoms is, by definition, less than six months.
    Schizotypal personality disorder (choice E) is characterized by eccentricities of behavior, odd beliefs or magical thinking, and difficulties with social and interpersonal relationships. Unlike schizophrenia, schizotypal personality disorder is not characterized by a formal thought disorder.

    --------------------------------------------------------------------------------21>The correct answer is E. Familial hypercholesterolemia, which is due to defective function of the LDL receptor, is an area of intense research. The molecular basis of LDL receptor abnormalities is becoming better understood, and more than 200 mutations in the gene for the LDL receptor have been identified. The gene has 5 general domains and 18 exons. Defects near exons 7 to 14 (including this case) are in the region of homology with epidermal growth factor receptor precursor. This region of the molecule is needed for dissociation of LDL from the receptor in the endosome. Receptors with a defect in this area (sometimes called class II mutations) also have trouble being initially transported to the Golgi complex (transport-deficiency alleles) and become trapped in endoplasmic reticulum.
    Decreased transcription of the LDL receptor gene (choice A) is considered a class I mutation and involves the signal sequence domain near exon 1.
    Poor internalization of LDL bound to LDL receptor (choice B) is considered a class IV mutation. Such mutations are associated with the membrane-spanning/cytoplasmic domain, specifically near exon 18.
    Poor retention of the LDL receptor in the membrane (choice C) is considered a class IV mutation and is associated with the membrane-spanning/cytoplasmic domain, specifically near exons 2-6.
    Reduced binding of LDL (choice D) is considered a class III mutation and involves the LDL binding domain near exons 2-6.
    --------------------------------------------------------------------------------22>The correct answer is D. Respiratory distress immediately follows amniotic fluid embolism as the emboli consisting of squamous cells, lanugo, and mucus deposit in the pulmonary microcirculation, producing numerous tiny pulmonary infarcts. The dramatic respiratory distress may also reflect the action of prostaglandins and other bioactive compounds present in high concentrations in the amniotic fluid embolus.
    Hemiplegia (choice A) would reflect an ischemic injury to one hemisphere of the cerebrum or the brainstem. A venous embolus would not produce such an insult.
    Placental abruption (choice B) is partial, premature separation of the placental disc from the endometrium. Although abruption may occur in this setting, it is not a result of an amniotic fluid embolism.
    There are numerous causes of renal failure (choice C); the most likely ones in the peripartum interval include eclampsia, hypovolemic shock, and ascending infections. Amniotic fluid embolism would be expected to produce severe dyspnea well before shock and renal failure might arise.
    Splinter hemorrhages (choice E) are small hemorrhages seen on toes and fingers due to a shower of microemboli arising in the arterial circulation. Amniotic fluid emboli arise in the veins and deposit in the lungs.
    --------------------------------------------------------------------------------23>The correct answer is D. The patient has a megaloblastic anemia, which can be due to deficiency of folate or B12. Pregnancy increases the need for folate and other nutrients used by both baby and mother, and may "unmask" a borderline dietary deficiency. For this reason, most obstetricians recommend vitamin supplements for pregnant women.
    Ascorbic acid (choice A) is vitamin C, and its deficiency predisposes for capillary fragility and oral lesions.
    Calcium deficiency (choice B) predisposes for osteoporosis/osteopenia.
    Copper deficiency (choice C) is rare; when it occurs, it may cause a hypochromic anemia, neutropenia, osteoporosis, or hypotonia.
    Iron deficiency (choice E) causes a microcytic, hypochromic anemia, with reduced mental and physical performance.
    --------------------------------------------------------------------------------24>The correct answer is D. The lesions are characteristic of molluscum contagiosum, which is a typically benign and self-limited condition caused by a poxvirus. The disease can be transmitted either venereally or through non-venereal contact. The other viruses listed do not cause similar skin lesions. Patients with advanced HIV infection may develop a severe, generalized, and persistent eruption, often involving the face and upper body.
    Cytomegalovirus (choice A) causes congenital infections and disseminated infections in immunosuppressed patients.
    Herpesvirus 6 (choice B)causes roseola (exanthem subitum).
    Parvovirus (choice C) causes aplastic crises in patients with hemolytic anemia.
    Variola (choice E) is the smallpox virus.
    --------------------------------------------------------------------------------25>The correct answer is D. This is a relatively simple question that requires you to visualize the relationship among the key parts of the kidney and to identify the one that lies most medially. If you think about it for a second, since the kidneys ultimately drain into the ureter at their medial poles, you are looking for the structure that is closest to the ureter. The correct answer is the renal pelvis. The renal pelvis is the dilated upper portion of the ureter that receives the major calyces.
    In terms of the other answer choices, the order from most lateral to most medial is: renal cortex (choice C), renal pyramid (choice E), minor calyx (choice B), major calyx (choice A), and then the renal pelvis (choice D).
    The correct answer is A. Cyclophosphamide is metabolized to acrolein, which is excreted in the urine. If the patient's urine is concentrated, the toxic metabolite may cause severe bladder damage. Early symptoms of bladder toxicity include dysuria and frequency. This can be distinguished from a urinary tract infection, since there is no bacteriuria with cyclophosphamide-induced bladder toxicity. However, microscopic hematuria is often present on urinalysis. In severe hemorrhagic cystitis, large segments of the bladder mucosa may be shed which can lead to prolonged, gross hematuria. The incidence of cyclophosphamide-induced hemorrhagic cystitis can be decreased by ensuring that the patient maintains a high fluid intake. Cyclophosphamide is an alkylating agent used in the treatment of breast carcinoma, malignant lymphoma, multiple myeloma, and adenocarcinoma of the ovary, as well as various other forms of cancer. The major toxic reactions commonly seen with this agent include mucositis, nausea, hepatotoxicity, sterile hemorrhagic and non-hemorrhagic cystitis, leukopenia, neutropenia, and interstitial pulmonary fibrosis.
    Mitomycin (choice B) is an antibiotic antineoplastic agent used in the treatment of breast carcinoma, adenocarcinoma of the pancreas and stomach, as well as various other forms of cancer. The major toxic reactions commonly seen with this agent include bone marrow depression, nausea, hepatotoxicity, acute bronchospasm, thrombocytopenia, and interstitial pneumonitis.
    Paclitaxel (choice C) is an antineoplastic agent primarily used in the treatment of ovarian and breast cancer. The major toxic reactions commonly seen with this agent include bone marrow depression, nausea, hepatotoxicity, bronchospasm, thrombocytopenia, and neutropenia.
    Tamoxifen (choice D) is an antineoplastic hormone primarily used in the palliative treatment of estrogen-receptor positive breast cancer patients. The major toxic reactions commonly seen with this agent include depression, dizziness, thrombosis, mild leukopenia or thrombocytopenia.
    Vincristine (choice E) is a mitotic inhibitor antineoplastic agent used in the treatment of breast cancer, Hodgkin's disease, non-Hodgkin's lymphoma, advanced testicular cancer and various other types of cancer. The major toxic reactions commonly seen with this agent include mental depression, hemorrhagic enterocolitis, bone marrow depression, nausea, thrombocytopenia, and leukopenia
    --------------------------------------------------------------------------------27>The correct answer is A. In a syndrome called cleidocranial dysostosis, absence of part of the clavicles accompanies a broad skull, and facial and dental anomalies. Note that you could also have answered this question by noting that of the bones listed, only the clavicles form by intramembranous ossification.
    The femurs (choice B), metatarsals (choice C), phalanges (choice D), and tibias (choice E) are cartilaginous (formed by endochondral ossification) rather than membranous bones.
    --------------------------------------------------------------------------------28>The correct answer is D. The tumor is a neuroblastoma, which is one of the principal forms of cancer in children. Neuroblastoma typically occurs before age 5, with many presenting before age 2. Neuroblastoma can arise from neural crest cells throughout the body, but the adrenal medulla is the most common site. Homer-Wright pseudorosettes are circles of tumor cells with central young nerve fibers arising from the tumor cells. The oncogene associated with neuroblastoma is N-myc.
    erb-B2 (choice A) is associated with breast, ovarian, and gastric carcinomas.
    c-myc (choice B) is associated with Burkitt's lymphoma.
    L-myc (choice C) is associated with small cell carcinoma of the lung.
    ret (choice E) is associated with multiple endocrine neoplasia, types II and III.
    --------------------------------------------------------------------------------29>The correct answer is B. The disease is von Hippel-Landau disease, which is associated with a deletion involving the VHL gene on chromosome 3 (3p). Affected individuals develop vascular tumors (hemangioblastomas) of the retina, cerebellum, and/or medulla. Roughly half of the affected individuals later develop multiple, bilateral renal cell carcinomas.
    Berry aneurysms (choice A) are unrelated to hemangioblastomas, but are instead associated with adult polycystic disease.
    Peripheral nerve cancers (choice C) are a feature of von Recklinghausen's disease (neurofibromatosis type I).
    Choreiform movements, related to decreased GABA and acetylcholine (choice D), are a feature of Huntington's disease.
    Extremely high serum cholesterol (choice E) suggests the homozygous form of familial hypercholesterolemia.
    --------------------------------------------------------------------------------30>The correct answer is A. The space constant of an axon reflects the amount of passive or electrotonic spread of current within an axon. The larger the space constant, the further the current can spread, allowing action potentials to propagate faster. This is why myelin increases the conduction velocity of action potentials down an axon. Conversely, demyelination decreases the space constant and slows action potential conduction.
    --------------------------------------------------------------------------------31>The correct answer is A. Coarctation of the aorta occurs in two patterns. In the infantile type, the stenosis is proximal to the insertion of the ductus arteriosus (preductal); this pattern is associated with Turner's syndrome. In the adult form, the stenosis is distal to the ductus arteriosus (postductal) and is associated with notching of the ribs (secondary to continued pressure from the aorta on them), hypertension in the upper extremities, and weak pulses in the lower extremities. Headache, cold extremities, and lower extremity claudication with exercise are typical if the patient is symptomatic (many adults with mild distal coarctation may remain asymptomatic for years). Upper extremity hypertension with weak pulses in the lower extremities, and a midsystolic (or continuous) murmur over the chest or back may be the only obvious signs in some. Note that the chronic cough is probably related to the man's smoking, and is not caused by the coarctation.
    Eisenmenger's syndrome (choice B) is a shift from a left-to-right shunt to a right-to-left shunt secondary to pulmonary hypertension.
    Tetralogy of Fallot (choice C) and transposition of great arteries (choice D) cause cyanosis and are usually diagnosed in infancy.
    Ventricular septal defect (choice E) might remain undiagnosed until adulthood, but would not cause notching of the ribs.
    --------------------------------------------------------------------------------32>The correct answer is C. The muscularis of the upper third of the esophagus (choice E) is composed entirely of striated muscle. The middle third (choice C) contains both striated and smooth muscle. The lower third (choice B) and lower esophageal sphincter (choice A) contain only smooth muscle. There is no such thing as the upper esophageal sphincter (choice D).
    --------------------------------------------------------------------------------33>The correct answer is A. Bilirubin is a degradative product of hemoglobin metabolism. Bilirubin (pigment) stones are specifically associated with excessive bilirubin production in hemolytic anemias, including sickle cell anemia. Bilirubin stones can also be seen in hepatic cirrhosis and liver fluke infestation.
    Calcium oxalate stones (choice B) and cystine stones (choice E) are found in the kidney, rather than the gallbladder.
    Pure cholesterol stones (choice C) are less common than mixed gallstones, but have the same risk factors, including obesity and multiple pregnancies.
    Mixed stones (choice D) are the common "garden variety" gallstones, found especially in obese, middle aged patients, with a female predominance
    The correct answer is A. Malnutrition associated with chronic alcoholism can lead to a severe magnesium deficiency. The effect of low serum magnesium on parathyroid hormone secretion (PTH) depends on severity and duration. An acute decrease in serum magnesium will increase PTH secretion, while a prolonged severe deficiency results in decreased PTH secretion. There is also evidence that the action of PTH is decreased with chronic magnesium deficiency. Hence, this patient is suffering from "functional" hypoparathyroidism. The low serum calcium can produce weakness, tremors, muscle fasciculations, and seizures. A positive Trousseau's sign indicates the presence of latent tetany. It is observed by inflating a blood pressure cuff above systolic blood pressure for at least 2 minutes. A positive reaction consists of the development of carpal spasm, with relaxation occurring within seconds after deflating the cuff. In patients with magnesium deficiency, magnesium administration will produce a prompt rise in plasma PTH with subsequent restoration of serum calcium concentration to normal.
    With functional hypoparathyroidism bone density would be decreased (not increased, choice C).
    The combination of decreased PTH secretion (not increased, choice D) and decreased effectiveness of PTH produce hypocalcemia and hyperphosphatemia (not hypophosphatemia, choice B).
    Urinary cAMP would probably be decreased (not increased, choice E), given the low PTH.
    --------------------------------------------------------------------------------35>The correct answer is E. Enteropeptidase, formerly called enterokinase, activates trypsinogen by limited proteolytic digestion to give trypsin. Trypsin is itself capable of activating trypsinogen, which produces a positive feedback effect. Trypsin also activates chymotrypsinogen (and several other proteolytic enzymes), so deficiency of enteropeptidase results in a severe deficiency of enzymes that digest protein.
    Amylase (choice A) aids in the breakdown of starches to oligosaccharides, maltose, and maltotriose.
    Colipase (choice B), along with other lipases, functions to digest fats.
    Lactase (choice C) is a brush-border disaccharidase that hydrolyzes the bond between galactose and glucose in lactose.
    Pepsin (choice D) is a proteolytic enzyme secreted in an inactive form (pepsinogen) by the chief cells of the stomach. Pepsinogen is activated by stomach acid, and so is not dependent on enteropeptidase. Pepsin alone will not replace the activities of other proteolytic enzymes, partly because food does not remain in the stomach for an extended period of time.
    --------------------------------------------------------------------------------36>The correct answer is E. The child is likely suffering from cystic fibrosis. In this disorder, an abnormality of chloride channels causes all exocrine secretions to be much thicker, and more viscous than normal. Pancreatic secretion of digestive enzymes is often severely impaired, with consequent steatorrhea and deficiency of fat-soluble vitamins, including vitamin A.
    Cystinuria (choice A) is a relatively common disorder in which a defective transporter for dibasic amino acids (cystine, ornithine, lysine, arginine; COLA) leads to saturation of the urine with cystine, which is not very soluble in urine, and precipitates out to form stones.
    Hypoglycemia (choice B) is not a prominent feature of children with cystic fibrosis who are on a normal diet. Hyperglycemia may occur late in the course of the disease.
    Iron deficiency anemia (choice C) is not found with any regularity in children with cystic fibrosis.
    Sphingomyelin accumulation (choice D) is generally associated with deficiency of sphingomyelinase, as seen in Niemann-Pick disease.

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