Comprehensive Basic Science Test 1 — Questions and Answers
Question 1: In a steady state, the difference in CO2 content between the venous blood leaving a tissue and the arterial blood entering the tissue is determined by which of the following ratios?
- Alveolar ventilation to tissue blood flow
- Alveolar ventilation to tissue O2 consumption
- Tissue CO2 production to tissue blood flow (Correct answer)
- Tissue CO2 production to tissue O2 consumption
- Tissue CO2 production to venous PCO2
Correct answer: Tissue CO2 production to tissue blood flow
The difference in CO2 content between venous blood leaving a tissue and arterial blood entering it reflects the amount of CO2 added to the blood as it passes through that tissue. This CO2 is produced by the tissue's metabolic activity. According to the Fick principle, this difference is determined by the ratio of the tissue's CO2 production rate to the rate of blood flow through that tissue.
Question 2: A 16-month-old boy is brought to the physician by his mother for a well-child examination. His mother expresses concern that he did not walk until the age of 14 months, whereas his older sister walked at the age of 10 months. Physical examination shows no abnormalities. Which of the following best explains this patient’s condition?
- Autistic disorder
- Child abuse
- Oppositional defiant disorder
- Sensory integration disorder
- Normal development (Correct answer)
Correct answer: Normal development
The normal range for independent walking is typically between 9 and 18 months of age. Walking at 14 months falls well within this normal developmental window. While his older sister walked earlier, individual variations in developmental milestones are common and do not indicate a problem unless they fall outside established normal ranges or are accompanied by other concerning signs.
Question 3: A 77-year-old woman is visited by the home care nurse who notes that the patient is more lethargic than usual. Her skin and mucous membranes are dry. An increase in the serum concentration or activity of which of the following provides the strongest indication that the patient is dehydrated?
- Albumin (Correct answer)
- Alkaline phosphatase
- Bilirubin
- Calcium
- Uric acid
Correct answer: Albumin
Dehydration causes a reduction in plasma volume, leading to hemoconcentration. Albumin is a large protein that remains within the intravascular space. When plasma volume decreases due to dehydration, the concentration of albumin in the serum increases because the same amount of albumin is now dissolved in a smaller volume of fluid, making it a strong indicator of dehydration.
Question 4: A male newborn delivered at 26 weeks’ gestation develops respiratory distress immediately after a spontaneous vaginal delivery. His respirations are 40/min. Physical examination shows cyanosis and lower rib retractions with respiration. Heart sounds are normal. Bilateral breath sounds are heard on auscultation. A chest x-ray shows bilateral lung opacities. The most likely cause of this patient’s breathing difficulties is insufficient production of which of the following substances?
- Collagen, type III
- α-Fetoprotein
- Meconium
- Retinoic acid
- Surfactant (Correct answer)
Correct answer: Surfactant
The newborn's prematurity (26 weeks' gestation) is the key factor. Premature infants often have immature lungs and insufficient production of pulmonary surfactant. Surfactant reduces alveolar surface tension, preventing alveolar collapse during expiration and ensuring adequate gas exchange, so its deficiency leads to respiratory distress syndrome (RDS), characterized by the described symptoms and diffuse lung opacities.
Question 5: A 28-year-old woman, gravida 1, para 1, comes to the physician because of progressive fatigue since delivering a male newborn 6 months ago. She is sleeping 8 to 10 hours nightly, but she is still tired during the day. She also has not had a menstrual period since her pregnancy. Pregnancy was complicated during the third trimester by severe bleeding from placenta previa. She required multiple blood transfusions during the cesarean delivery, but she did well after the delivery. She was unable to breast-feed her newborn because of poor milk production. Which of the following is the most likely diagnosis?
- Anemia
- Cardiomyopathy
- Major depressive disorder
- Postpartum pituitary infarction (Correct answer)
- Thyroiditis
Correct answer: Postpartum pituitary infarction
The patient's history of severe postpartum hemorrhage, followed by symptoms of hypopituitarism (progressive fatigue, amenorrhea since pregnancy, poor milk production), is classic for Sheehan syndrome. This condition involves ischemic necrosis of the pituitary gland due to massive blood loss during or after childbirth. The enlarged pituitary gland during pregnancy is particularly vulnerable to ischemia, leading to a deficiency in various pituitary hormones.
Question 6: A 12-year-old African American boy is brought to the physician by his mother because of a swollen right earlobe for 3 weeks. He had the ear pierced at a local mall 6 weeks ago. The swelling has persisted despite removal of the earring 3 weeks ago. The mother developed a thick rubbery scar on her abdomen after a cesarean delivery 12 years ago. His temperature is 37°C (98.6°F). Physical examination shows a nontender, flesh-colored swelling of the right earlobe. The skin is intact over the swelling, and it is soft and nontender. There is no cervical lymphadenopathy. Which of the following is the most likely cause of the swelling in this patient?
- Bacterial infection
- Contact dermatitis
- Foreign body
- Keloid (Correct answer)
- Lipoma
Correct answer: Keloid
Keloids are excessive scar tissue formations that extend beyond the original wound boundaries, often triggered by skin trauma like piercings. The patient's African American ethnicity and his mother's history of a thick, rubbery scar (suggestive of keloid) indicate a genetic predisposition. The persistent, nontender, flesh-colored swelling of the earlobe after piercing is characteristic of a keloid.
Question 7: A 5-year-old boy is brought to the physician by his parents because of an 8-month history of difficulty walking. His parents say that he limps when he walks and has a waddling gait; he also has difficulty standing. When getting up from a sitting position, he uses his hands to walk up his thighs and push his body into a standing position. His parents have not noticed any weakness of his arms. His mother is an only child, but she has an uncle who became bedridden as a child and died of respiratory arrest. Physical examination shows prominent calf muscles. Muscle strength is 4/5 at both hips but normal elsewhere. This patient most likely has a mutation in the gene coding for which of the following proteins?
- Actin
- Dystrophin (Correct answer)
- Frataxin
- Myelin
- Myosin
Correct answer: Dystrophin
The clinical presentation, including progressive muscle weakness, waddling gait, difficulty standing, Gowers sign (using hands to walk up thighs), and pseudohypertrophy of the calves, is highly suggestive of Duchenne muscular dystrophy (DMD). DMD is an X-linked recessive disorder caused by mutations in the DMD gene, which codes for the protein dystrophin. Dystrophin is crucial for maintaining the structural integrity of muscle fibers, and its absence leads to muscle degeneration, as seen in this patient and his maternal uncle.
Question 8: A 27-year-old man comes to the physician because of pain with urination for 3 days. He has had no fever or chills. He is sexually active with three partners and does not use condoms consistently. He began having sexual relations with his most recent partner 1 week ago. His temperature is 37°C (98.6°F). Physical examination shows no abnormalities except for a clear, watery urethral discharge. Urinalysis shows 10–20 WBC/hpf but no bacteria. Which of the following is the most likely causal organism?
- Chlamydia trachomatis (Correct answer)
- Entamoeba histolytica
- Escherichia coli
- Helicobacter pylori
- Shigella flexneri
Correct answer: Chlamydia trachomatis
The patient presents with symptoms of urethritis (dysuria, clear watery discharge) and a urinalysis showing pyuria without bacteriuria, which is characteristic of non-gonococcal urethritis. Given his sexual history with multiple partners and inconsistent condom use, Chlamydia trachomatis is the most common cause of non-gonococcal urethritis. Unlike Neisseria gonorrhoeae, chlamydial infections often cause a less purulent discharge and can be milder.
Question 9: A 20-year-old college student develops fever, severe pharyngitis, hepatosplenomegaly, and lymphadenopathy. The pathogenesis of this syndrome most likely involves a double-stranded DNA virus infection of which of the following cells?
- B lymphocytes (Correct answer)
- Kupffer cells
- Macrophages
- Neutrophils
- T lymphocytes
Correct answer: B lymphocytes
The constellation of symptoms (fever, severe pharyngitis, hepatosplenomegaly, and lymphadenopathy) in a young adult is classic for infectious mononucleosis. This syndrome is most commonly caused by the Epstein-Barr virus (EBV), which is a double-stranded DNA virus. EBV primarily infects and replicates within B lymphocytes, leading to their proliferation and the characteristic immune response involving atypical T lymphocytes.
Question 10: A 2-year-old boy with Down syndrome is brought to the physician by his mother for a follow-up examination. His blood pressure is increased in the upper extremities and decreased in the lower extremities. Physical examination shows cyanosis of the lower extremities. An AP x-ray of the chest shows notching of the inferior surfaces of the 3rd through 8th ribs. The diagnosis of left ventricular hypertrophy is suspected. Which of the following is the most likely underlying abnormality in this patient?
- Atrial septal defect
- Coarctation of the aorta (Correct answer)
- Persistent truncus arteriosus
- Tetralogy of Fallot
- Transposition of the great arteries
Correct answer: Coarctation of the aorta
The classic findings of coarctation of the aorta include a blood pressure differential between the upper and lower extremities (increased in upper, decreased in lower) and rib notching on chest X-ray, caused by collateral circulation development. Cyanosis of the lower extremities suggests severe coarctation with differential cyanosis, where deoxygenated blood from the pulmonary artery shunts through a patent ductus arteriosus to supply the lower body. Left ventricular hypertrophy is a compensatory response to the increased afterload.
Question 11: A 1-day-old neonate has hemolytic disease of the newborn. The parents are both Rh-positive, but IgG isohemagglutinins are found in the mother’s blood. Which of the following parental blood types is most likely to cause this condition?
- Mother A, Father O
- Mother AB, Father O
- Mother B, Father O
- Mother B, Father A
- Mother O, Father AB (Correct answer)
Correct answer: Mother O, Father AB
Hemolytic disease of the newborn (HDN) in Rh-positive parents, with IgG isohemagglutinins in the mother's blood, points to ABO incompatibility. This occurs when the mother is blood type O and the father is A, B, or AB. Type O mothers naturally produce anti-A and anti-B IgG antibodies, which can cross the placenta and hemolyze fetal red blood cells if the fetus has A or B antigens. The combination of Mother O and Father AB ensures the fetus will inherit either A or B antigens, making ABO incompatibility the most likely cause.
Question 12: A previously healthy 42-year-old woman comes to the emergency department because of progressive shortness of breath and intermittent cough productive of blood-tinged sputum for 10 days. She has no history of major medical illness and takes no medications. Her respirations are 24/min. Diffuse rhonchi are heard in both lung fields on auscultation. A chest x-ray shows patchy opacities bilaterally. Laboratory studies show: Serum creatinine 2.5 mg/dL Urine Protein 3+ RBC 3+ RBC casts numerous A serum anti-glomerular basement membrane autoantibody assay is positive. Which of the following is the most likely diagnosis?
- Goodpasture syndrome (Correct answer)
- Hemolytic uremic syndrome
- Löffler syndrome
- Mucocutaneous lymph node syndrome (Kawasaki disease)
- Granulomatosis with polyangiitis
Correct answer: Goodpasture syndrome
This patient presents with a classic triad of rapidly progressive glomerulonephritis (elevated creatinine, proteinuria, hematuria with RBC casts) and pulmonary hemorrhage (shortness of breath, hemoptysis, lung opacities). The positive anti-glomerular basement membrane (anti-GBM) autoantibody assay is pathognomonic for Goodpasture syndrome. This autoimmune disease involves antibodies targeting type IV collagen in the basement membranes of both the glomeruli in the kidneys and the alveoli in the lungs.
Question 13: A 10-year-old boy is found to have mild iron deficiency anemia. His mother informs the physician that the family members belong to a religious denomination that does not consume meat. Her son refuses to eat dark green vegetables or to take vitamin pills, stating that they make him feel nauseated. It is most appropriate for the physician to ask the mother which of the following questions next?
- “Are you concerned that if you let him get away with not eating right when he’s 10, he’ll be more likely to give you trouble when he’s a teenager?”
- “Can you tell me exactly why your religion prohibits meat?”
- “Would you like information on other iron rich foods consistent with a vegetarian diet?” (Correct answer)
- “Would you like me to write a note to your religious leader requesting a medical exemption from your dietary requirements?”
- “Wouldn’t your son rather eat spinach than get an iron shot every week?”
Correct answer: “Would you like information on other iron rich foods consistent with a vegetarian diet?”
The physician's role is to provide patient-centered care and address the medical issue within the family's cultural and religious context. The boy has iron deficiency anemia and a vegetarian diet. Offering information on alternative iron-rich foods that align with their religious beliefs and the boy's preferences is a supportive, practical, and non-judgmental approach to improve his health, respecting their values while addressing the medical problem.
Question 14: A 64-year-old man comes to the physician because of a 3-day history of painful rash over his right flank. Three days before the rash appeared, he had pain in the same area. His temperature is 37.4°C (99.3°F), pulse is 78/min, respirations are 17/min, and blood pressure is 130/70 mm Hg. Physical examination shows clustered lesions in a band-like area over the right flank. The lesions have an erythematous base and are crusted. Which of the following is the most likely causal virus?
- Cytomegalovirus
- Epstein-Barr virus
- Human papillomavirus
- Kaposi sarcoma virus
- Varicella-zoster virus (Correct answer)
Correct answer: Varicella-zoster virus
The patient's symptoms are highly characteristic of herpes zoster, also known as shingles. This condition is caused by the reactivation of the latent varicella-zoster virus (VZV) from sensory ganglia. The classic presentation involves a prodrome of pain or tingling, followed by a vesicular rash that erupts in a dermatomal distribution (band-like pattern), often unilateral, and is typically painful.
Question 15: A 27-year-old man with AIDS is brought to the hospital 30 minutes after having a seizure. He currently takes no medications. A CT scan of the head shows multiple ring-enhancing lesions. Which of the following is the most likely diagnosis?
- Amoebiasis
- Cysticercosis
- Echinococcosis
- Schistosomiasis
- Toxoplasmosis (Correct answer)
- Trichinosis
Correct answer: Toxoplasmosis
In an HIV-positive patient with AIDS, the presence of multiple ring-enhancing lesions on brain imaging, especially with a seizure, is highly suggestive of cerebral toxoplasmosis. This opportunistic infection, caused by Toxoplasma gondii, is the most common cause of focal brain lesions in AIDS patients, particularly when the CD4 count is low.
Question 16: An investigator has conducted an experiment to determine whether certain environmental exposure morbidity is eliminated if a person carries a specific allele of three different genes on three separate chromosomes. The frequencies of an individual having the allele for these respective genes are 0.6, 0.2, and 0.1. All three alleles are necessary to confer protection. The probability that a randomly selected individual will have all three alleles is closest to which of the following?
- 0.900
- 0.600
- 0.200
- 0.100
- 0.012 (Correct answer)
Correct answer: 0.012
Since the three genes are on separate chromosomes, the presence of each allele is an independent event. To find the probability that an individual will have all three alleles, we multiply the probabilities of each independent event. Therefore, the probability is 0.6 * 0.2 * 0.1 = 0.012.
Question 17: A health inspector confiscates chickens smuggled into Taiwan from mainland China after she discovers them in the hold of a ship. Testing shows that, although the chickens appear healthy, they are infected with the H5N1 subtype of the influenza A virus. Which of the following is the primary concern for human health from these virus-infected chickens?
- Mutation of the virus to a form that causes fatal encephalitis
- Mutation of the virus to a form that causes fatal renal disease
- Mutation of the virus to a form that is highly infectious among humans (Correct answer)
- Secretion of a product that will cause immunosuppression in those that eat the meat
- Secretion of a product that will cause mutations of the virus in the fetuses of mothers that eat the meat
- Secretion of a product that will make the meat of the chicken poisonous to eat
Correct answer: Mutation of the virus to a form that is highly infectious among humans
H5N1 avian influenza is highly pathogenic in humans but typically has limited human-to-human transmission. The primary concern with infected animals, especially those in close contact with humans, is the potential for the virus to undergo genetic reassortment or mutation. This could lead to a new strain that retains its virulence but gains the ability to spread efficiently among humans, potentially triggering a pandemic.
Question 18: A 35-year-old woman has hypertension and truncal obesity. Serum studies show: Cortisol (AM) 100 µg/dL (N=5–20) Cortisol (PM) 100 µg/dL (N=2.5–10) ACTH (AM) 100 µg/dL (N=20–100) Cortisol 8 h after 1 mg dexamethasone 95 µg/dL Cortisol 8 h after 8 mg dexamethasone 30 µg/dL (N=5–20) Which of the following is the most likely cause of this woman’s increased serum cortisol concentration?
- Adrenocortical adenoma
- Ectopic corticotropin-releasing hormone producing neoplasm
- Ectopic corticotropin-secreting neoplasm
- Pituitary microadenoma (Correct answer)
- Self-administration ofsynthetic glucocorticoids
Correct answer: Pituitary microadenoma
The patient's symptoms (hypertension, truncal obesity) and lab results (elevated cortisol with loss of diurnal variation, lack of suppression by low-dose dexamethasone, but partial suppression by high-dose dexamethasone) are classic for Cushing disease. Cushing disease is caused by an ACTH-secreting pituitary adenoma, often a microadenoma. The high-dose dexamethasone test typically suppresses ACTH and cortisol production in pituitary-dependent Cushing disease, but not in ectopic ACTH production or adrenal tumors.
Question 19: A 42-year-old woman comes to the physician for a routine health maintenance examination. She says that she feels fine. She is 170 cm (5 ft 7 in) tall and weighs 86 kg (190 lb); BMI is 30 kg/m2 . Her blood pressure is 131/82 mm Hg. Physical examination shows no other abnormalities. Fasting serum studies show: Glucose 105 mg/dL Cholesterol, total 210 mg/dL Triglycerides 185 mg/dL C-reactive protein 0.35 mg/L (N=20–100) This patient is at increased risk for developing which of the following conditions?
- Atherosclerosis (Correct answer)
- Systemic lupus erythematosus
- Systemic sclerosis (scleroderma)
- Type 1 diabetes mellitus
Correct answer: Atherosclerosis
The patient exhibits several risk factors for metabolic syndrome and cardiovascular disease: obesity (BMI 30), prehypertension (BP 131/82), impaired fasting glucose (105 mg/dL), and dyslipidemia (total cholesterol 210, triglycerides 185). Individually and collectively, these factors significantly increase the risk for developing atherosclerosis, which is the underlying cause of many cardiovascular events like heart attacks and strokes.
Comprehensive Basic Science Test 1
In a steady state, the difference in CO2 content between the venous blood leaving a tissue and the arterial blood entering the tissue is determined by which of the following ratios?