COMSAE Phase 1 Practice Exam: 176
Original Questions With Detailed Answers
& Rationales
Question 1 — Cardiovascular Physiology
A 22-year-old medical student undergoes a sudden increase in sympathetic activity during
exercise. Which change most directly contributes to the increase in cardiac output?
A. Decreased heart rate
B. Increased vagal stimulation
C. Increased myocardial contractility
D. Decreased venous return
E. Increased systemic vascular resistance
Answer: C. Increased myocardial contractility
Rationale: Sympathetic stimulation increases heart rate and myocardial contractility through β₁-
adrenergic receptors. Increased contractility raises stroke volume, contributing to increased
cardiac output.
Question 2 — Microbiology
A patient develops watery diarrhea after receiving clindamycin for a dental infection. Testing
demonstrates toxin-producing Clostridioides difficile. Which mechanism is primarily responsible
for the patient's intestinal injury?
A. Inhibition of protein synthesis
B. Activation of adenylate cyclase
C. Inactivation of Rho GTPases
D. Destruction of enterocyte DNA
E. Blockade of acetylcholine receptors
Answer: C. Inactivation of Rho GTPases
Rationale: C. difficile toxins disrupt Rho-family GTPases, causing cytoskeletal disruption,
impaired tight junctions, inflammation, and mucosal injury. Antibiotic exposure is a major risk
factor.
,Question 3 — Pharmacology
A patient with hypertension is prescribed lisinopril. Which adverse effect is most characteristic
of this medication?
A. Hypokalemia
B. Persistent dry cough
C. Severe constipation
D. Gingival hyperplasia
E. Bradycardia
Answer: B. Persistent dry cough
Rationale: ACE inhibitors decrease conversion of angiotensin I to angiotensin II and also reduce
bradykinin degradation. Increased bradykinin can produce a persistent dry cough. ACE inhibitors
can also cause hyperkalemia and angioedema.
Question 4 — Renal Physiology
A patient becomes severely dehydrated after several days of vomiting. Which renal response
would be expected?
A. Decreased ADH secretion
B. Increased urine volume
C. Increased collecting-duct water permeability
D. Decreased renin secretion
E. Decreased sodium reabsorption
Answer: C. Increased collecting-duct water permeability
Rationale: Dehydration increases ADH secretion. ADH promotes insertion of aquaporin-2
channels into collecting-duct cells, increasing water reabsorption and producing concentrated
urine.
Question 5 — Osteopathic Principles
A patient presents with restricted thoracic cage motion and decreased rib excursion. Which
osteopathic principle best describes the relationship between structure and physiologic
function?
,A. The body is a unit
B. Structure and function are reciprocally interrelated
C. The body possesses self-regulatory mechanisms
D. Rational treatment is based on understanding the body's mechanisms
E. The lymphatic system is the primary regulatory mechanism
Answer: B. Structure and function are reciprocally interrelated
Rationale: Osteopathic medicine recognizes that structural abnormalities can influence
physiologic function and that altered function can affect structure.
Question 6 — Immunology
A child develops recurrent bacterial infections involving the respiratory and gastrointestinal
tracts. Laboratory testing reveals markedly decreased immunoglobulin levels with normal T-cell
function. Which condition is most likely?
A. DiGeorge syndrome
B. Severe combined immunodeficiency
C. X-linked agammaglobulinemia
D. Chronic granulomatous disease
E. Chediak-Higashi syndrome
Answer: C. X-linked agammaglobulinemia
Rationale: X-linked agammaglobulinemia results from a mutation in Bruton tyrosine kinase,
causing impaired B-cell maturation and markedly decreased immunoglobulins. Patients are
particularly susceptible to recurrent bacterial infections.
Question 7 — Pathology
A 65-year-old smoker has progressive cough, weight loss, and hemoptysis. Imaging reveals a
central lung mass. Biopsy demonstrates malignant cells with keratin pearls. Which diagnosis is
most likely?
A. Adenocarcinoma
B. Small-cell carcinoma
C. Squamous cell carcinoma
D. Large-cell carcinoma
E. Carcinoid tumor
, Answer: C. Squamous cell carcinoma
Rationale: Squamous cell carcinoma is strongly associated with smoking and commonly occurs
centrally near the bronchi. Histologically, keratin pearls and intercellular bridges are
characteristic.
Question 8 — Biochemistry
A patient with prolonged fasting develops increased production of ketone bodies. Which organ
is primarily responsible for ketogenesis?
A. Brain
B. Skeletal muscle
C. Liver
D. Kidney
E. Adipose tissue
Answer: C. Liver
Rationale: During prolonged fasting, fatty acids undergo β-oxidation in the liver, producing
acetyl-CoA. Excess acetyl-CoA is converted into ketone bodies. The liver produces ketones but
cannot utilize them because it lacks thiophorase.
Question 9 — Neurology
A patient develops sudden weakness of the right face, arm, and leg. The weakness is
accompanied by expressive aphasia. Which cerebral artery is most likely affected?
A. Right anterior cerebral artery
B. Left middle cerebral artery
C. Right middle cerebral artery
D. Left posterior cerebral artery
E. Basilar artery
Answer: B. Left middle cerebral artery
Rationale: The left cerebral hemisphere is typically dominant for language. The middle cerebral
artery supplies the lateral frontal and parietal regions, including areas responsible for language
and motor control of the contralateral face and upper extremity.
Original Questions With Detailed Answers
& Rationales
Question 1 — Cardiovascular Physiology
A 22-year-old medical student undergoes a sudden increase in sympathetic activity during
exercise. Which change most directly contributes to the increase in cardiac output?
A. Decreased heart rate
B. Increased vagal stimulation
C. Increased myocardial contractility
D. Decreased venous return
E. Increased systemic vascular resistance
Answer: C. Increased myocardial contractility
Rationale: Sympathetic stimulation increases heart rate and myocardial contractility through β₁-
adrenergic receptors. Increased contractility raises stroke volume, contributing to increased
cardiac output.
Question 2 — Microbiology
A patient develops watery diarrhea after receiving clindamycin for a dental infection. Testing
demonstrates toxin-producing Clostridioides difficile. Which mechanism is primarily responsible
for the patient's intestinal injury?
A. Inhibition of protein synthesis
B. Activation of adenylate cyclase
C. Inactivation of Rho GTPases
D. Destruction of enterocyte DNA
E. Blockade of acetylcholine receptors
Answer: C. Inactivation of Rho GTPases
Rationale: C. difficile toxins disrupt Rho-family GTPases, causing cytoskeletal disruption,
impaired tight junctions, inflammation, and mucosal injury. Antibiotic exposure is a major risk
factor.
,Question 3 — Pharmacology
A patient with hypertension is prescribed lisinopril. Which adverse effect is most characteristic
of this medication?
A. Hypokalemia
B. Persistent dry cough
C. Severe constipation
D. Gingival hyperplasia
E. Bradycardia
Answer: B. Persistent dry cough
Rationale: ACE inhibitors decrease conversion of angiotensin I to angiotensin II and also reduce
bradykinin degradation. Increased bradykinin can produce a persistent dry cough. ACE inhibitors
can also cause hyperkalemia and angioedema.
Question 4 — Renal Physiology
A patient becomes severely dehydrated after several days of vomiting. Which renal response
would be expected?
A. Decreased ADH secretion
B. Increased urine volume
C. Increased collecting-duct water permeability
D. Decreased renin secretion
E. Decreased sodium reabsorption
Answer: C. Increased collecting-duct water permeability
Rationale: Dehydration increases ADH secretion. ADH promotes insertion of aquaporin-2
channels into collecting-duct cells, increasing water reabsorption and producing concentrated
urine.
Question 5 — Osteopathic Principles
A patient presents with restricted thoracic cage motion and decreased rib excursion. Which
osteopathic principle best describes the relationship between structure and physiologic
function?
,A. The body is a unit
B. Structure and function are reciprocally interrelated
C. The body possesses self-regulatory mechanisms
D. Rational treatment is based on understanding the body's mechanisms
E. The lymphatic system is the primary regulatory mechanism
Answer: B. Structure and function are reciprocally interrelated
Rationale: Osteopathic medicine recognizes that structural abnormalities can influence
physiologic function and that altered function can affect structure.
Question 6 — Immunology
A child develops recurrent bacterial infections involving the respiratory and gastrointestinal
tracts. Laboratory testing reveals markedly decreased immunoglobulin levels with normal T-cell
function. Which condition is most likely?
A. DiGeorge syndrome
B. Severe combined immunodeficiency
C. X-linked agammaglobulinemia
D. Chronic granulomatous disease
E. Chediak-Higashi syndrome
Answer: C. X-linked agammaglobulinemia
Rationale: X-linked agammaglobulinemia results from a mutation in Bruton tyrosine kinase,
causing impaired B-cell maturation and markedly decreased immunoglobulins. Patients are
particularly susceptible to recurrent bacterial infections.
Question 7 — Pathology
A 65-year-old smoker has progressive cough, weight loss, and hemoptysis. Imaging reveals a
central lung mass. Biopsy demonstrates malignant cells with keratin pearls. Which diagnosis is
most likely?
A. Adenocarcinoma
B. Small-cell carcinoma
C. Squamous cell carcinoma
D. Large-cell carcinoma
E. Carcinoid tumor
, Answer: C. Squamous cell carcinoma
Rationale: Squamous cell carcinoma is strongly associated with smoking and commonly occurs
centrally near the bronchi. Histologically, keratin pearls and intercellular bridges are
characteristic.
Question 8 — Biochemistry
A patient with prolonged fasting develops increased production of ketone bodies. Which organ
is primarily responsible for ketogenesis?
A. Brain
B. Skeletal muscle
C. Liver
D. Kidney
E. Adipose tissue
Answer: C. Liver
Rationale: During prolonged fasting, fatty acids undergo β-oxidation in the liver, producing
acetyl-CoA. Excess acetyl-CoA is converted into ketone bodies. The liver produces ketones but
cannot utilize them because it lacks thiophorase.
Question 9 — Neurology
A patient develops sudden weakness of the right face, arm, and leg. The weakness is
accompanied by expressive aphasia. Which cerebral artery is most likely affected?
A. Right anterior cerebral artery
B. Left middle cerebral artery
C. Right middle cerebral artery
D. Left posterior cerebral artery
E. Basilar artery
Answer: B. Left middle cerebral artery
Rationale: The left cerebral hemisphere is typically dominant for language. The middle cerebral
artery supplies the lateral frontal and parietal regions, including areas responsible for language
and motor control of the contralateral face and upper extremity.
