USMLE Step 1 Sample Test Questions PDF

USMLE STEP 1 SAMPLE TEST QUESTIONS BLOCK 1, ITEMS 1-40 1. A 67-year-old woman with congenital bicuspid aortic valve is admitted to the hospital because of a 2-day history of fever and chills. Current medication is lisinopril. Temperature is 38.0°...

USMLE STEP 1 SAMPLE TEST QUESTIONS BLOCK 1, ITEMS 1-40 1. A 67-year-old woman with congenital bicuspid aortic valve is admitted to the hospital because of a 2-day history of fever and chills. Current medication is lisinopril. Temperature is 38.0°C (100.4°F), pulse is 90/min, respirations are 20/min, and blood pressure is 110/70 mm Hg. Cardiac examination shows a grade 3/6 systolic murmur that is best heard over the second right intercostal space. Blood culture grows viridans streptococci susceptible to penicillin. In addition to penicillin, an antibiotic synergistic to penicillin is administered that may help shorten the duration of this patient's drug treatment. Which of the following is the most likely mechanism of action of this additional antibiotic on bacteria? (A) Binding to DNA-dependent RNA polymerase (B) Binding to the 30S ribosomal protein (C) Competition with p-aminobenzoic acid (D) Inhibition of dihydrofolate reductase (E) Inhibition of DNA gyrase 2. A 12-year-old girl is brought to the physician because of a 2-month history of intermittent yellowing of the eyes and skin. Physical examination shows no abnormalities except for jaundice. Her serum total bilirubin concentration is 3 mg/dL, with a direct component of 1 mg/dL. Serum studies show a haptoglobin concentration and AST and ALT activities that are within the reference ranges. There is no evidence of injury or exposure to toxins. Which of the following additional findings is most likely in this patient? (A) Decreased activity of UDP glucuronosyltransferase (B) Gallstones (C) Increased hemolysis (D) Increased serum alkaline phosphatase activity (E) Ineffective erythropoiesis 3. During an experiment, drug X is added to a muscle bath containing a strip of guinea pig intestinal smooth muscle. Agonists are added to the bath, and the resultant effects on muscle tension are shown in the table. Agonist Muscle Tension Before Drug X (g) Muscle Tension After Drug X (g) Vehicle 6.0 6.1 Acetylcholine 11.3 18.5 Norepinephrine 4.1 4.2 Which of the following types of drugs is most likely to produce effects most similar to those of drug X? (A) α1-Adrenergic antagonist (B) β-Adrenergic antagonist (C) Cholinesterase inhibitor (D) Monoamine oxidase inhibitor (E) Muscarinic antagonist 8 4. A 30-year-old woman, gravida 2, para 0, aborta 1, at 28 weeks' gestation comes to the office for a prenatal visit. She has had one previous pregnancy resulting in a spontaneous abortion at 12 weeks' gestation. Today, her vital signs are within normal limits. Physical examination shows a uterus consistent in size with a 28-week gestation. Fetal ultrasonography shows a male fetus with no abnormalities. Her blood group is O, Rh-negative. The father's blood group is B, Rh-positive. The physician recommends administration of Rho(D) immune globulin to the patient. This treatment is most likely to prevent which of the following in this mother? (A) Development of natural killer cells (B) Development of polycythemia (C) Formation of antibodies to RhD (D) Generation of IgM antibodies from fixing complement in the fetus (E) Immunosuppression caused by RhD on erythrocytes from the fetus 5. A 55-year-old man is brought to the emergency department because of shortness of breath and confusion for 4 hours. He has hypertension and chronic kidney disease requiring hemodialysis. An ECG shows low voltage with electrical alternans. Physical examination is most likely to show which of the following findings? Blood Pressure Jugular Venous Pulsus (mm Hg) Pulse (/min) Pressure Paradoxus (A) 85/60 120 increased increased (B) 85/60 120 increased normal (C) 85/60 120 normal normal (D) 120/80 80 increased increased (E) 120/80 80 normal increased (F) 120/80 80 normal normal 6. A 52-year-old woman begins pharmacotherapy after being diagnosed with type 2 diabetes mellitus. Four weeks later, her hepatic glucose output is decreased, and target tissue glucose uptake and utilization are increased. Which of the following drugs was most likely prescribed for this patient? (A) Acarbose (B) Glyburide (C) Metformin (D) Nateglinide (E) Repaglinide 9 7. An asymptomatic 44-year-old man is found to have HIV infection during routine screening prior to donating blood. A complete blood count done at the time of the screening shows: Hemoglobin 10 g/dL Hematocrit 30% Leukocyte count 4600/mm3 Platelet count 15,000/mm3 Prothrombin time 12 sec (INR=1.1) Partial thromboplastin time 23 sec Which of the following physical findings is most likely in this patient? (A) Deep venous thrombosis (B) Hemarthrosis (C) Petechiae (D) Subungual hemorrhage (E) Visceral hematoma 8. A 23-year-old woman with bone marrow failure is treated with a large dose of rabbit antithymocyte globulin. Ten days later, she develops fever, lymphadenopathy, arthralgias, and erythema on her hands and feet. Which of the following is the most likely cause of these symptoms? (A) Cytokine secretion by natural killer cells (B) Eosinophil degranulation (C) Immune complex deposition in tissues (D) Polyclonal T-lymphocyte activation (E) Widespread apoptosis of B lymphocytes 9. After being severely beaten and sustaining a gunshot wound to the abdomen, a 42-year-old woman undergoes resection of a perforated small bowel. During the operation, plastic reconstruction of facial fractures, and open reduction and internal fixation of the left femur are also done. Thirty-six hours postoperatively, she is awake but not completely alert. She is receiving intravenous morphine via a patient-controlled pump. She says that she needs the morphine to treat her pain, but she is worried that she is becoming addicted. She has no history of substance use disorder. She drinks one to two glasses of wine weekly. Which of the following initial actions by the physician is most appropriate? (A) Reassure the patient that her chance of becoming addicted to narcotics is minuscule (B) Maintain the morphine, but periodically administer intravenous naloxone (C) Switch the patient to oral acetaminophen as soon as she can take medication orally (D) Switch the patient to intramuscular lorazepam (E) Switch the patient to intravenous phenobarbital 10 10. A 22-year-old woman comes to the office because of a 4-day history of an itchy, red rash on her right arm. She has no history of major medical illness and takes no medications. She says she has recently used a new hair dye. She is 165 cm (5 ft 5 in) tall and weighs 61 kg (135 lb); BMI is 23 kg/m2. Her temperature is 37.0°C (98.6°F), pulse is 70/min. respirations are 22/min, and blood pressure is 115/70 mm Hg. Examination of the right forearm shows the findings in the photograph. Which of the following ligand → receptor pairs most likely played a primary role in the proliferation of the T lymphocytes present at the site of the rash in this patient? (A) CD2 on T lymphocytes → intercellular adhesion molecule (ICAM)-3 on epidermal Langerhans cells (B) CD28 on T lymphocytes → CD80 on epidermal Langerhans cells (C) CD40L on T lymphocytes → CD40 on epidermal Langerhans cells (D) CD45 on T lymphocytes → CD28 on epidermal Langerhans cells (E) Lymphocyte function-associated antigen-1 on T lymphocytes → ICAM1 on epidermal Langerhans cells 11. Six healthy subjects participate in a study of muscle metabolism during which hyperglycemia and hyperinsulinemia is induced. Muscle biopsy specimens obtained from the subjects during the resting state show significantly increased concentrations of malonyl-CoA. The increased malonyl-CoA concentration most likely directly inhibits which of the following processes in these subjects? (A) Fatty acid oxidation (B) Fatty acid synthesis (C) Gluconeogenesis (D) Glycogenolysis (E) Glycolysis (F) Oxidative phosphorylation 12. Over 1 year, a study is conducted to assess the antileukemic activity of a new tyrosine kinase inhibitor in patients with chronic myeloid leukemia in blast crisis. All patients enrolled in the study are informed that they would be treated with the tyrosine kinase inhibitor. They are assigned to successive dose cohorts of 300 to 1000 mg/day of the drug. Six to eight patients are assigned to each dose. Treatment efficacy is determined based on the results of complete blood counts and bone marrow assessments conducted regularly throughout the study. This study is best described as which of the following? (A) Case-control study (B) Crossover study (C) Open-labeled clinical trial (D) Randomized clinical trial (E) Single-blind, randomized, controlled trial 11 13. A 63-year-old man is brought to the emergency department because of a 4-day history of increasingly severe left leg pain and swelling of his left calf. He also has a 1-month history of increasingly severe upper midthoracic back pain. During this time, he has had a 9-kg (20-lb) weight loss despite no change in appetite. He has no history of major medical illness. His only medication is ibuprofen. He is 180 cm (5 ft 11 in) tall and weighs 82 kg (180 lb); BMI is 25 kg/m2. His vital signs are within normal limits. On examination, lower extremity pulses are palpable bilaterally. The remainder of the physical examination shows no abnormalities. An x-ray of the thoracic spine shows no abnormalities. A CT scan of the abdomen shows a 3-cm mass in the body of the pancreas; there are liver metastases and encasement of the superior mesenteric artery. Ultrasonography of the left lower extremity shows a femoropopliteal venous clot. Which of the following is the most likely cause of this patient’s symptoms? (A) Carcinoid syndrome (B) Hypercoagulability from advanced malignancy (C) Multiple endocrine neoplasia (D) Splenic artery aneurysm and embolic disease of the left lower extremity (E) Superior mesenteric artery syndrome 14. A 40-year-old woman comes to the physician because of a 6-month history of increased facial hair growth. Her last menstrual period was 4 months ago. She is 165 cm (5 ft 5 in) tall and weighs 70 kg (154 lb); BMI is 26 kg/m2. Her pulse is 80/min, and blood pressure is 130/82 mm Hg. Physical examination shows temporal balding and coarse dark hair on the upper lip and chin. Pelvic examination shows clitoral enlargement. Her serum testosterone concentration is increased. Serum concentrations of androstenedione, dehydroepiandrosterone, and urinary 17-ketosteroids are within the reference ranges. Ultrasonography of the pelvis shows a 12-cm ovarian mass. Which of the following best describes this mass? (A) Granulosa tumor (B) Ovarian carcinoid (C) Sertoli-Leydig tumor (D) Teratoma (E) Thecoma 15. A 35-year-old man comes to the physician because of pain and swelling of his right arm where he scraped it on a tree branch 2 days ago. His temperature is 38.3°C (101°F). Examination of the right forearm shows edema around a fluctuant erythematous lesion at the site of trauma. The area is extremely tender to palpation. Which of the following is most likely the primary mechanism of the development of edema in this patient? (A) Degranulation of eosinophils (B) Disruption of vascular basement membranes (C) Increased hydrostatic pressure (D) Release of thromboxane (E) Separation of endothelial junctions 16. A 12-year-old boy is brought to the physician because of a 2-month history of headaches and a 6-day history of nausea and vomiting. Funduscopic examination shows bilateral papilledema. He walks with a broad-based gait. An MRI of the brain shows a tumor in the pineal region compressing the brain stem and leading to hydrocephalus. This patient most likely has impairment of which of the following oculomotor functions? (A) Abduction (B) Horizontal pursuit (C) Optokinetic nystagmus (D) Upward gaze (E) Vestibulo-ocular reflex 12 17. A 52-year-old man comes to the emergency department because of a 1-day history of nausea, vomiting, and right- sided abdominal pain that radiates to his back. He has not had fever or increased urinary frequency. He has a history of type 2 diabetes mellitus, hyperlipidemia, hypertension, and atrial fibrillation. Current medications are atorvastatin, glyburide, hydrochlorothiazide, lisinopril, and warfarin. He smoked 1½ packs of cigarettes daily for 35 years until he quit 6 months ago. He has had no recent alcoholic beverage or illicit drug use. He is 188 cm (6 ft 2 in) tall and weighs 109 kg (240 lb); BMI is 31 kg/m2. Temperature is 36.4°C (97.6°F), pulse is 88/min, respirations are 20/min, and blood pressure is 165/92 mm Hg. Pulse oximetry on room air shows an oxygen saturation of 96%. Physical examination discloses right upper quadrant and flank tenderness but no rebound tenderness or guarding. CT scan of the abdomen with and without contrast shows an enlarged right kidney and wedge-shaped areas of hypodensity; there is no evidence of nephrolithiasis. Which of the following is the strongest predisposing risk factor for this patient's condition? (A) Atrial fibrillation (B) Hyperlipidemia (C) Hypertension (D) Past smoking history (E) Type 2 diabetes mellitus 18. A 24-year-old man comes to the office because of a 2-day history of a red, itchy rash on his buttocks and legs. Four days ago, he returned from a cruise to the Caribbean, during which he swam in the ship’s pool and used the hot tub. He appears well. His vital signs are within normal limits. Physical examination shows the findings in the photograph. The infectious agent causing these findings most likely began to proliferate in which of the following locations? (A) Apocrine gland (B) Dermis (C) Eccrine gland (D) Hair follicle (E) Sebaceous gland 13 19. An otherwise healthy 45-year-old man comes to the physician because of a 3-week history of progressive epigastric heartburn and a 4.5-kg (10-lb) weight loss. The pain tends to be more severe at night and occurs 1 to 3 hours after meals during the day. He has had similar episodes with lesser intensity during the past year. Abdominal examination shows tenderness to deep palpation. Test of the stool for occult blood is positive. Endoscopy shows a bleeding 3-cm ulcer in the antrum of the stomach. A photomicrograph of Steiner silver-stained tissue (400x) from a biopsy of the gastric mucosa adjacent to the ulcer is shown. Which of the following processes is most likely to be involved? (A) Elaboration of proteases and urease with local tissue destruction (B) Hyperacidity and gastric ulcer development (C) Ingestion of preformed toxins in contaminated well water (D) Spirochete invasion of gastric cells 20. A 14-year-old boy is brought to the emergency department after being hit with a baseball bat on the lateral side of his leg immediately below the knee. He is unable to dorsiflex his foot. Which of the following nerves is most likely injured? (A) Common fibular (peroneal) (B) Femoral (C) Obturator (D) Sural (E) Tibial 21. A 26-year-old woman is brought to the emergency department because of an 8-hour history of severe back and abdominal pain and mild but persistent vaginal bleeding. Ultrasonography of the abdomen shows a 2-cm ectopic pregnancy in the ampulla. The ampulla has ruptured into the surrounding tissue. Fluid from this rupture will most likely be found in which of the following locations? (A) Lesser peritoneal cavity (B) Mesometrium (C) Pouch of Douglas (D) Uterine cavity (E) Vagina 14 22. A 46-year-old woman with active ankylosing spondylitis comes to the office for a follow-up examination. The use of various conventional nonsteroidal anti-inflammatory drugs has been ineffective. Sulfasalazine treatment also has not resulted in improvement. The most appropriate next step in treatment is administration of a drug that inhibits which of the following? (A) CD20 (B) Cyclooxygenase-2 (C) Cytotoxic T-lymphocyte antigen 4 (D) Epidermal growth factor (E) Interleukin-1 (IL-1) (F) Tumor necrosis factor α 23. A 55-year-old man comes to the physician because of a 2-week history of recurrent, widespread blister formation. Physical examination shows lesions that are most numerous in the flexural areas including the axillae and groin. The blisters do not break easily, and there are no oral lesions. These blisters are most likely the result of adhesion failure involving which of the following? (A) Basement membrane (B) Dermal papillae (C) Langerhans cells (D) Melanocytes (E) Merkel cells 24. A 17-year-old girl is brought to the emergency department 30 minutes after her boyfriend found her unconscious next to an empty bottle of acetaminophen. It is suspected that she ingested the tablets approximately 12 hours ago. Her serum acetaminophen concentration is markedly increased. Treatment with activated charcoal and acetylcysteine is initiated. Approximately 48 hours later, the patient develops jaundice, and her serum AST activity is 3000 U/L. Which of the following best explains the jaundice in this patient? (A) Activation of biliverdin reductase (B) Decreased bilirubin conjugation (C) Decreased generation of urobilinogen (D) Increased hemolysis (E) Increased serum glutathione concentration 25. A 72-year-old woman comes to the physician because of a 3-day history of fever, shortness of breath, difficulty swallowing, chest pain, and cough. She is frail. Physical examination shows tachypnea and equal pulses bilaterally. Percussion of the chest shows dullness over the right lower lung field. Laboratory studies show arterial hypoxemia and decreased PCO2. A chest x-ray shows an area of opacification in the lower region of the right lung. Which of the following is the most likely cause of this patient's condition? (A) Alveolar proteinosis (B) Aspiration (C) Cigarette smoking (D) Emphysema (E) Vasculitis 15 26. A 62-year-old man is admitted to the hospital for evaluation of abdominal pain. During the interview, he responds to the questions with a single word and sometimes with sarcastic answers. He does not engage in eye contact, and he frowns as he tells the physician that this is the third time he has been asked these questions. Which of the following is the most appropriate response by the physician? (A) "Can you tell me more about your abdominal pain?" (B) "I understand that you do not feel well, but I need to get a history here." (C) "I'll come back once you've calmed down, and we can talk more then." (D) "Listen, if you choose not to cooperate, I'm not going to be able to help you." (E) "You sound upset. Tell me a little more about that." 27. A 54-year-old man comes to the physician because of episodes of fainting for 3 months. He also has had difficulty performing daily tasks because he is easily fatigued. He had a myocardial infarction 12 years ago. His pulse is 40/min, respirations are 18/min, and blood pressure is 138/85 mm Hg. Physical examination shows evidence of cannon a waves. An ECG shows a P-wave rate of 90/min, and an R-wave rate of 40/min, with no apparent relation between the two. Which of the following is the most likely diagnosis? (A) First-degree atrioventricular block (B) Right bundle branch block (C) Second-degree atrioventricular block, type I (D) Second-degree atrioventricular block, type II (E) Third-degree atrioventricular block 28. A 42-year-old woman comes to the physician for a routine examination. She says that she has felt well except for occasional episodes of constipation, abdominal discomfort, and mild fatigue. She was treated for a renal calculus 10 years ago and was told she had a "lazy gallbladder." Her pulse is 82/min, and blood pressure is 150/80 mm Hg. Physical examination shows no other abnormalities. Laboratory studies show: Erythrocyte count 3 million/mm3 Serum K+ 4.5 mEq/L Cl– 107 mEq/L Ca2+ 12 mg/dL Phosphorus 2.2 mg/dL Alkaline phosphatase 95 U/L The most likely cause of this patient's condition is a small, well-defined nodule in which of the following locations? (A) Adrenal gland (B) Anterior pituitary gland (C) Gallbladder (D) Kidney (E) Parathyroid gland (F) Thymus 16 29. A 72-year-old woman is brought to the emergency department by her husband because of a 1-hour history of difficulty walking and speaking. The husband says that she was well last night but when she awoke this morning, she had difficulty getting out of bed and her speech was slurred. She has a 20-year history of type 2 diabetes mellitus well controlled with medication and diet. She is alert and oriented and is able to follow commands and respond verbally, but she has impaired speech. Her pulse is 80/min, respirations are 16/min, and blood pressure is 142/88 mm Hg. Physical examination shows left-sided hemiparesis. The tongue deviates to the right when protruded. Sensation to pinprick and temperature is normal, and proprioception and sensation to light touch are absent over the left upper and lower extremities. Which of the following labeled sites in the photograph of a cross section of a normal brain stem is most likely damaged in this patient? 30. A 68-year-old woman with end-stage renal disease comes to the office for a follow-up examination. She has required hemodialysis for the past year. Initially, she did well, but within the past 3 months, she has been admitted to the hospital for fluid overload because of poor adherence to fluid and salt restrictions. She says, "I'm so sick of being on dialysis. Following the restrictions is really hard." Which of the following is the most appropriate initial response by the physician? (A) "I imagine being on dialysis is frustrating, but you don't want to die from kidney disease, do you?" (B) "I know that this is challenging, but do you remember how difficult it is to be hospitalized?" (C) "It is tough to change your diet and fluid intake, but what sorts of things were you doing at first when you were following the recommendations?" (D) "Making these changes is so difficult. Can you imagine how good you will feel once you make the changes again?" (E) "This is very hard to do, but you may have an easier time if you met with the dietician again." 17 31. During an experiment, a Southern blot analysis is done by digesting DNA samples with a single restriction endonuclease, separating the digestion products by gel electrophoresis, and transferring them to a filter. The investigator probes the filter by exposing it to a cDNA clone that encodes a single immunoglobulin-constant region. The figure shows the resulting pattern with DNA samples isolated from different organs. Assuming there were no technical errors, the Southern blot analysis results demonstrate which of the following processes? (A) Affinity maturation (B) Apoptosis (C) Gene rearrangement (D) RNA splicing (E) Somatic hypermutation 32. A 17-year-old girl has never had a menstrual period. Physical examination shows a normal female body habitus, normal breast development, and normal appearing external genitalia. She has no axillary or pubic hair. The patient refuses to have a pelvic or rectal examination. Which of the following is the most likely explanation for the clinical presentation? (A) Androgen insensitivity (B) Congenital adrenal hyperplasia (C) Ectodermal dysplasia (D) A psychiatric disorder (E) A sex chromosome mosaicism 18 33. A 16-year-old boy is brought to the physician because of a 3-day history of abdominal pain and vomiting; he also has had decreased appetite during this period. The pain was initially on the right but now has become generalized. His temperature is 38.8°C (101.8°F), pulse is 100/min, respirations are 20/min, and blood pressure is 143/83 mm Hg. Abdominal examination shows guarding with diffuse rebound tenderness. There are no palpable masses. A CT scan of the abdomen shows a perforated appendix. Examination of peritoneal fluid from this patient will most likely show which of the following organisms? (A) Candida albicans (B) Citrobacter freundii (C) Escherichia coli (D) Staphylococcus aureus (E) Streptococcus pneumoniae 34. A 45-year-old woman comes to the office because of a 6-month history of hot flashes, night sweats, and insomnia. She has not had a menstrual period during this time. She thinks she is going through menopause and asks the physician if there are any medications that will alleviate her symptoms. Physical examination shows no abnormalities. The result of a urine pregnancy test is negative. The physician explains that hormone therapy likely will help and explains the risks to the patient. Which of the following is the next most appropriate physician statement? (A) "Could you tell me your thoughts about the hormone treatment option we have discussed?" (B) "I have many patients with similar symptoms, and everyone responds to hormone therapy differently." (C) "I will give you some written information to review, and then I can answer any remaining questions." (D) "If your symptoms are really severe, the risk of hormone therapy may be worth it.” (E) "Would you like me to tell you what I think you should do?" 35. A randomized controlled trial is conducted to assess the risk for development of gastrointestinal adverse effects using azithromycin compared with erythromycin in the treatment of pertussis in children. Of the 100 children with pertussis enrolled, 50 receive azithromycin, and 50 receive erythromycin. Results show vomiting among 5 patients in the azithromycin group, compared with 15 patients in the erythromycin group. Which of the following best represents the absolute risk reduction for vomiting among patients in the azithromycin group? (A) 0.1 (B) 0.2 (C) 0.33 (D) 0.67 (E) 0.8 19 36. A 34-year-old woman with a 10-year history of hepatitis C comes to the physician because of progressive fatigue during the past month. Her vital signs are within normal limits. Physical examination shows that the liver is not palpable. Serum studies show: Albumin 3 g/dL Total bilirubin 1.8 mg/dL Alkaline phosphatase 115 U/L AST 53 U/L ALT 48 U/L A liver biopsy specimen shows focal areas of hepatocellular injury with infiltration of lymphocytes and early fibrosis. Which of the following mechanisms is the most likely cause of the ongoing hepatocyte injury in this patient? (A) Foreign peptides bound to class I MHC molecules are recognized by CD4+ T lymphocytes (B) Foreign peptides bound to class I MHC molecules are recognized by CD8+ T lymphocytes (C) Foreign peptides bound to class II MHC molecules are recognized by CD8+ T lymphocytes (D) Self-peptides bound to class I MHC molecules are recognized by CD8+ T lymphocytes (E) Self-peptides bound to class II MHC molecules are recognized by CD4+ T lymphocytes 37. A 50-year-old woman comes to the physician for a follow-up examination. Her blood pressure was 145/100 mm Hg and 145/95 mm Hg, respectively, at two previous visits. Today, her pulse is 75/min, respirations are 15/min, and blood pressure is 150/95 mm Hg. Physical examination shows no other abnormalities. If left untreated, which of the following is most likely to decrease in this patient? (A) Baroreceptor output (B) Left ventricular stiffness during diastole (C) Left ventricular stroke work (D) Left ventricular wall thickness (E) Myocardial oxygen consumption 38. A 62-year-old man comes to the physician for a follow-up examination after he was diagnosed with chronic inflammatory interstitial pneumonitis. Following pulmonary function testing, a biopsy specimen of the affected area of the lungs is obtained. Compared with a healthy man, analysis of this patient's biopsy specimen is most likely to show which of the following patterns of changes in the cell populations of alveoli? Type I Pneumocytes Type II Pneumocytes Fibroblasts (A) ↑ ↑ ↑ (B) ↑ ↑ ↓ (C) ↑ ↓ ↑ (D) ↑ ↓ ↓ (E) ↓ ↑ ↑ (F) ↓ ↑ ↓ (G) ↓ ↓ ↑ (H) ↓ ↓ ↓ 20 39. A 31-year-old woman with type 2 diabetes mellitus comes to the physician because of an oozing, foul-smelling wound on her foot for 2 days. Physical examination shows a 4-cm, necrotizing wound with a purplish black discoloration over the heel. Crepitant bullae producing profuse amounts of serous drainage are seen. A Gram stain of a tissue biopsy specimen shows gram-positive rods. The causal organism most likely produces which of the following virulence factors? (A) Endotoxin (B) Fimbriae (C) Pneumolysin (D) Polysaccharide capsule (E) α-Toxin 40. A 4-month-old boy with severe combined immunodeficiency receives a bone marrow transplant. Six days later, he develops a widespread, erythematous, maculopapular rash over the trunk. Examination of a skin biopsy specimen shows diffuse vacuolar degeneration of basal epidermal cells with a mononuclear inflammatory cell infiltrate. Which of the following is the most likely cause of this patient’s rash? (A) Fixed drug eruption (B) Graft-versus-host disease (C) Immune complex deposition (D) Mast cell degranulation (E) Staphylococcal folliculitis 21