COMPREHENSIVE OSTEOPATHIC MEDICAL SELF-ASSESSMENT EXAMINATION
(COMSAE) PHASE 1 FORM 115 COMPLETE PRACTICE EXAM QUESTIONS AND
ANSWERS | VERIFIED SOLUTIONS | UPDATED 2026/2027 STUDY GUIDE
Examiner/Administrator: National Board of Osteopathic Medical Examiners (NBOME)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━
COMPREHENSIVE OSTEOPATHIC MEDICAL
SELF-ASSESSMENT EXAMINATION
COMSAE PHASE 1 FORM 115
2026/2027 EDITION
━━━━━━━━━━━━━━━━━━━━━━━━━━━━
COMPLETE PRACTICE EXAM
100 MULTIPLE-CHOICE QUESTIONS
EXACT OFFICIAL COUNT: 100 QUESTIONS
PASSING SCORE: 70%
TESTING TIME: 120 MINUTES
━━━━━━━━━━━━━━━━━━━━━━━━━━━━
NBOME || ALIGNED WITH CURRENT OSTEOPATHIC LICENSING BLUEPRINTS ||
BIOMEDICAL SCIENCES || SYSTEMS-BASED CLINICAL INTEGRATION || OSTEOPATHIC
PRINCIPLES & PRACTICE || PROFESSIONAL STUDY GUIDE || 100% VERIFIED | GRADED
A+ || COMPREHENSIVE BOARD PREPARATION || PREPARED FOR MEDICAL LICENSING
& CERTIFICATION || PROFESSIONAL EXAMINATION USE
━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Questions 1–10 → Foundational Biomedical Sciences & Physiology
Q1. A 24-year-old medical student participating in a physiology laboratory undergoes
arterial blood gas analysis after intentionally hyperventilating for 3 minutes. Which of
,the following compensatory responses is most likely to occur if the respiratory
disturbance persists for several hours?
A. Increased renal bicarbonate reabsorption
B. Increased hydrogen ion secretion by intercalated cells
C. Decreased renal ammonium production
D. Increased distal tubular bicarbonate secretion
Correct Answer: 🔴 D. Increased distal tubular bicarbonate secretion
Explanation: 🔹 Acute hyperventilation produces respiratory alkalosis due to excessive
carbon dioxide elimination. If the condition persists, renal compensation occurs by
reducing bicarbonate reabsorption and increasing bicarbonate excretion in the distal
nephron. This lowers serum bicarbonate concentration and helps normalize pH. Option A
would worsen alkalosis. Option B is a compensatory response to acidosis, not alkalosis.
Option C may occur indirectly but is not the principal compensatory mechanism
emphasized in respiratory alkalosis physiology.
Q2. A 67-year-old man with long-standing hypertension develops concentric left
ventricular hypertrophy. Which molecular adaptation is most responsible for the
increase in myocardial wall thickness?
A. Hyperplasia mediated by satellite cells
B. Increased synthesis of sarcomeres in parallel
C. Increased apoptosis of ventricular myocytes
D. Deposition of amyloid within the myocardium
Correct Answer: 🔴 B. Increased synthesis of sarcomeres in parallel
Explanation: 🔹 Pressure overload states such as chronic hypertension lead to concentric
hypertrophy through the addition of sarcomeres in parallel, increasing myocyte width
and ventricular wall thickness. Cardiac myocytes have limited regenerative capability,
making hyperplasia unlikely. Apoptosis would reduce myocardial mass. Amyloid
deposition may cause restrictive cardiomyopathy rather than adaptive concentric
hypertrophy.
,Q3. A researcher administers a drug that selectively blocks voltage-gated sodium
channels in peripheral nerves. Which phase of the neuronal action potential will be
most directly impaired?
A. Resting membrane stabilization
B. Repolarization
C. Rapid depolarization
D. Hyperpolarization
Correct Answer: 🔴 C. Rapid depolarization
Explanation: 🔹 Voltage-gated sodium channels are responsible for the rapid influx of
sodium ions during phase 0 depolarization of excitable cells. Blocking these channels
prevents propagation of action potentials. Repolarization is primarily mediated by
potassium efflux. Hyperpolarization occurs after potassium channel activity. Resting
membrane potential depends predominantly on potassium permeability and the sodium-
potassium ATPase.
Q4. A 3-year-old child is brought to the emergency department after accidental
ingestion of an unknown medication. Laboratory studies reveal an elevated anion gap
metabolic acidosis and calcium oxalate crystals in the urine. Which toxin is the most
likely cause?
A. Methanol
B. Ethylene glycol
C. Salicylates
D. Isopropyl alcohol
Correct Answer: 🔴 B. Ethylene glycol
Explanation: 🔹 Ethylene glycol intoxication classically produces high anion gap
metabolic acidosis with calcium oxalate crystal deposition in urine due to metabolism
into oxalic acid. Methanol primarily causes visual disturbances and formic acid toxicity.
Salicylates cause mixed respiratory alkalosis and metabolic acidosis. Isopropyl alcohol
leads to ketosis without metabolic acidosis.
, Q5. A patient with severe dehydration secondary to gastroenteritis demonstrates
increased secretion of antidiuretic hormone (ADH). ADH primarily acts on which
nephron segment to increase water reabsorption?
A. Proximal convoluted tubule
B. Thin descending limb
C. Thick ascending limb
D. Collecting duct principal cells
Correct Answer: 🔴 D. Collecting duct principal cells
Explanation: 🔹 ADH acts on V2 receptors in principal cells of the collecting duct,
increasing insertion of aquaporin-2 channels into the luminal membrane and enhancing
water reabsorption. The proximal tubule and descending limb are intrinsically water
permeable but not primarily regulated by ADH. The thick ascending limb is impermeable
to water and functions in sodium-potassium-chloride transport.
Q6. A 52-year-old woman develops fatigue and glossitis. Laboratory evaluation reveals
macrocytic anemia and elevated methylmalonic acid levels. Deficiency of which vitamin
is most likely responsible?
A. Folate
B. Vitamin B12
C. Vitamin B6
D. Riboflavin
Correct Answer: 🔴 B. Vitamin B12
Explanation: 🔹 Vitamin B12 deficiency produces megaloblastic anemia with elevated
methylmalonic acid due to impaired methylmalonyl-CoA mutase activity. Neurologic
symptoms may also occur. Folate deficiency also causes macrocytic anemia but does not
elevate methylmalonic acid. Vitamin B6 deficiency is associated with sideroblastic
anemia, while riboflavin deficiency causes cheilosis and corneal vascularization.
Q7. During strenuous exercise, skeletal muscle oxygen demand increases substantially.
Which factor most strongly shifts the oxyhemoglobin dissociation curve to the right?
(COMSAE) PHASE 1 FORM 115 COMPLETE PRACTICE EXAM QUESTIONS AND
ANSWERS | VERIFIED SOLUTIONS | UPDATED 2026/2027 STUDY GUIDE
Examiner/Administrator: National Board of Osteopathic Medical Examiners (NBOME)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━
COMPREHENSIVE OSTEOPATHIC MEDICAL
SELF-ASSESSMENT EXAMINATION
COMSAE PHASE 1 FORM 115
2026/2027 EDITION
━━━━━━━━━━━━━━━━━━━━━━━━━━━━
COMPLETE PRACTICE EXAM
100 MULTIPLE-CHOICE QUESTIONS
EXACT OFFICIAL COUNT: 100 QUESTIONS
PASSING SCORE: 70%
TESTING TIME: 120 MINUTES
━━━━━━━━━━━━━━━━━━━━━━━━━━━━
NBOME || ALIGNED WITH CURRENT OSTEOPATHIC LICENSING BLUEPRINTS ||
BIOMEDICAL SCIENCES || SYSTEMS-BASED CLINICAL INTEGRATION || OSTEOPATHIC
PRINCIPLES & PRACTICE || PROFESSIONAL STUDY GUIDE || 100% VERIFIED | GRADED
A+ || COMPREHENSIVE BOARD PREPARATION || PREPARED FOR MEDICAL LICENSING
& CERTIFICATION || PROFESSIONAL EXAMINATION USE
━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Questions 1–10 → Foundational Biomedical Sciences & Physiology
Q1. A 24-year-old medical student participating in a physiology laboratory undergoes
arterial blood gas analysis after intentionally hyperventilating for 3 minutes. Which of
,the following compensatory responses is most likely to occur if the respiratory
disturbance persists for several hours?
A. Increased renal bicarbonate reabsorption
B. Increased hydrogen ion secretion by intercalated cells
C. Decreased renal ammonium production
D. Increased distal tubular bicarbonate secretion
Correct Answer: 🔴 D. Increased distal tubular bicarbonate secretion
Explanation: 🔹 Acute hyperventilation produces respiratory alkalosis due to excessive
carbon dioxide elimination. If the condition persists, renal compensation occurs by
reducing bicarbonate reabsorption and increasing bicarbonate excretion in the distal
nephron. This lowers serum bicarbonate concentration and helps normalize pH. Option A
would worsen alkalosis. Option B is a compensatory response to acidosis, not alkalosis.
Option C may occur indirectly but is not the principal compensatory mechanism
emphasized in respiratory alkalosis physiology.
Q2. A 67-year-old man with long-standing hypertension develops concentric left
ventricular hypertrophy. Which molecular adaptation is most responsible for the
increase in myocardial wall thickness?
A. Hyperplasia mediated by satellite cells
B. Increased synthesis of sarcomeres in parallel
C. Increased apoptosis of ventricular myocytes
D. Deposition of amyloid within the myocardium
Correct Answer: 🔴 B. Increased synthesis of sarcomeres in parallel
Explanation: 🔹 Pressure overload states such as chronic hypertension lead to concentric
hypertrophy through the addition of sarcomeres in parallel, increasing myocyte width
and ventricular wall thickness. Cardiac myocytes have limited regenerative capability,
making hyperplasia unlikely. Apoptosis would reduce myocardial mass. Amyloid
deposition may cause restrictive cardiomyopathy rather than adaptive concentric
hypertrophy.
,Q3. A researcher administers a drug that selectively blocks voltage-gated sodium
channels in peripheral nerves. Which phase of the neuronal action potential will be
most directly impaired?
A. Resting membrane stabilization
B. Repolarization
C. Rapid depolarization
D. Hyperpolarization
Correct Answer: 🔴 C. Rapid depolarization
Explanation: 🔹 Voltage-gated sodium channels are responsible for the rapid influx of
sodium ions during phase 0 depolarization of excitable cells. Blocking these channels
prevents propagation of action potentials. Repolarization is primarily mediated by
potassium efflux. Hyperpolarization occurs after potassium channel activity. Resting
membrane potential depends predominantly on potassium permeability and the sodium-
potassium ATPase.
Q4. A 3-year-old child is brought to the emergency department after accidental
ingestion of an unknown medication. Laboratory studies reveal an elevated anion gap
metabolic acidosis and calcium oxalate crystals in the urine. Which toxin is the most
likely cause?
A. Methanol
B. Ethylene glycol
C. Salicylates
D. Isopropyl alcohol
Correct Answer: 🔴 B. Ethylene glycol
Explanation: 🔹 Ethylene glycol intoxication classically produces high anion gap
metabolic acidosis with calcium oxalate crystal deposition in urine due to metabolism
into oxalic acid. Methanol primarily causes visual disturbances and formic acid toxicity.
Salicylates cause mixed respiratory alkalosis and metabolic acidosis. Isopropyl alcohol
leads to ketosis without metabolic acidosis.
, Q5. A patient with severe dehydration secondary to gastroenteritis demonstrates
increased secretion of antidiuretic hormone (ADH). ADH primarily acts on which
nephron segment to increase water reabsorption?
A. Proximal convoluted tubule
B. Thin descending limb
C. Thick ascending limb
D. Collecting duct principal cells
Correct Answer: 🔴 D. Collecting duct principal cells
Explanation: 🔹 ADH acts on V2 receptors in principal cells of the collecting duct,
increasing insertion of aquaporin-2 channels into the luminal membrane and enhancing
water reabsorption. The proximal tubule and descending limb are intrinsically water
permeable but not primarily regulated by ADH. The thick ascending limb is impermeable
to water and functions in sodium-potassium-chloride transport.
Q6. A 52-year-old woman develops fatigue and glossitis. Laboratory evaluation reveals
macrocytic anemia and elevated methylmalonic acid levels. Deficiency of which vitamin
is most likely responsible?
A. Folate
B. Vitamin B12
C. Vitamin B6
D. Riboflavin
Correct Answer: 🔴 B. Vitamin B12
Explanation: 🔹 Vitamin B12 deficiency produces megaloblastic anemia with elevated
methylmalonic acid due to impaired methylmalonyl-CoA mutase activity. Neurologic
symptoms may also occur. Folate deficiency also causes macrocytic anemia but does not
elevate methylmalonic acid. Vitamin B6 deficiency is associated with sideroblastic
anemia, while riboflavin deficiency causes cheilosis and corneal vascularization.
Q7. During strenuous exercise, skeletal muscle oxygen demand increases substantially.
Which factor most strongly shifts the oxyhemoglobin dissociation curve to the right?
