, Question 1
In the ischemic penumbra, which molecular event most directly triggers the
mitochondrial permeability transition pore (mPTP) opening that commits
neurons to irreversible necrosis?
A. Excessive glutamate reuptake by astrocytes
B. Calcium overload and reactive oxygen species burst
C. Upregulation of Bcl-2 anti-apoptotic proteins
D. Activation of caspase-3 via cytochrome c release
Correct Answer: B - Calcium overload and reactive oxygen
species burst
RATIONALE
During ischemia, ATP depletion leads to failure of ion pumps, causing
intracellular Ca2+ overload and ROS generation, which are the
primary triggers for mPTP opening and necrosis. Bcl-2 upregulation
and caspase-3 activation are features of apoptosis, not necrosis.
Glutamate reuptake would be protective, not triggering.
Question 2
A patient with chronic kidney disease has an eGFR of 28 mL/min/1.73m² and
a serum potassium of 5.8 mEq/L. Which ECG finding is most consistent with
this electrolyte disturbance?
A. Prominent U waves
B. Prolonged QT interval
C. Peaked T waves and widened QRS
D. ST segment depression with T wave inversion
Correct Answer: C - Peaked T waves and widened QRS
Page 2
, RATIONALE
Hyperkalemia (>5.5 mEq/L) classically causes peaked T waves,
widened QRS, and ultimately a sine wave pattern. U waves and
prolonged QT are associated with hypokalemia and hypocalcemia,
respectively. ST depression with T inversion is typical of ischemia,
not hyperkalemia.
Question 3
Which epigenetic mechanism best explains the silencing of a tumor suppressor
gene in a subset of hereditary breast cancers lacking a coding mutation?
A. Histone acetylation at promoter regions
B. DNA hypermethylation of CpG islands
C. Chromosomal translocation
D. Gain-of-function mutation in oncogenes
Correct Answer: B - DNA hypermethylation of CpG islands
RATIONALE
DNA hypermethylation of CpG islands in promoter regions leads to
transcriptional silencing of tumor suppressor genes, a common
epigenetic mechanism in cancer. Histone acetylation typically
promotes gene expression, and translocations or oncogene mutations
are genetic, not epigenetic, changes.
Question 4
Which pathophysiologic alteration is most directly responsible for the
hypoxemia seen in a patient with acute respiratory distress syndrome (ARDS)?
A. Increased alveolar dead space
B. Intrapulmonary shunt due to alveolar flooding
C. Hypoventilation from respiratory muscle fatigue
D. Diffusion limitation from thickened alveolar membrane
Correct Answer: B - Intrapulmonary shunt due to alveolar
flooding
Page 3
, RATIONALE
ARDS is characterized by increased permeability pulmonary edema,
leading to alveolar flooding and intrapulmonary shunting, which
causes severe hypoxemia refractory to oxygen therapy. Dead space,
hypoventilation, and diffusion limitation contribute but are not the
primary mechanisms.
Question 5
A patient with type 1 diabetes presents with polyuria, polydipsia, and a blood
glucose of 520 mg/dL. Which pathophysiologic mechanism best explains the
polyuria?
A. Osmotic diuresis from glucose exceeding renal threshold
B. Increased ADH secretion due to hyperglycemia
C. Direct tubular damage from ketone bodies
D. Activation of the renin-angiotensin-aldosterone system
Correct Answer: A - Osmotic diuresis from glucose exceeding
renal threshold
RATIONALE
When blood glucose exceeds the renal threshold (~180 mg/dL),
glucose spills into the urine, creating an osmotic gradient that draws
water into the tubules, causing osmotic diuresis and polyuria. ADH
secretion is not the primary driver, and ketones do not directly damage
tubules in the acute setting.
Question 6
Which statement best describes the role of tumor necrosis factor-alpha (TNF-)
in the pathogenesis of rheumatoid arthritis?
A. It promotes osteoclastogenesis and synovial inflammation.
B. It inhibits matrix metalloproteinases (MMPs).
C. It downregulates adhesion molecules on endothelial cells.
D. It induces regulatory T cell differentiation.
Page 4
In the ischemic penumbra, which molecular event most directly triggers the
mitochondrial permeability transition pore (mPTP) opening that commits
neurons to irreversible necrosis?
A. Excessive glutamate reuptake by astrocytes
B. Calcium overload and reactive oxygen species burst
C. Upregulation of Bcl-2 anti-apoptotic proteins
D. Activation of caspase-3 via cytochrome c release
Correct Answer: B - Calcium overload and reactive oxygen
species burst
RATIONALE
During ischemia, ATP depletion leads to failure of ion pumps, causing
intracellular Ca2+ overload and ROS generation, which are the
primary triggers for mPTP opening and necrosis. Bcl-2 upregulation
and caspase-3 activation are features of apoptosis, not necrosis.
Glutamate reuptake would be protective, not triggering.
Question 2
A patient with chronic kidney disease has an eGFR of 28 mL/min/1.73m² and
a serum potassium of 5.8 mEq/L. Which ECG finding is most consistent with
this electrolyte disturbance?
A. Prominent U waves
B. Prolonged QT interval
C. Peaked T waves and widened QRS
D. ST segment depression with T wave inversion
Correct Answer: C - Peaked T waves and widened QRS
Page 2
, RATIONALE
Hyperkalemia (>5.5 mEq/L) classically causes peaked T waves,
widened QRS, and ultimately a sine wave pattern. U waves and
prolonged QT are associated with hypokalemia and hypocalcemia,
respectively. ST depression with T inversion is typical of ischemia,
not hyperkalemia.
Question 3
Which epigenetic mechanism best explains the silencing of a tumor suppressor
gene in a subset of hereditary breast cancers lacking a coding mutation?
A. Histone acetylation at promoter regions
B. DNA hypermethylation of CpG islands
C. Chromosomal translocation
D. Gain-of-function mutation in oncogenes
Correct Answer: B - DNA hypermethylation of CpG islands
RATIONALE
DNA hypermethylation of CpG islands in promoter regions leads to
transcriptional silencing of tumor suppressor genes, a common
epigenetic mechanism in cancer. Histone acetylation typically
promotes gene expression, and translocations or oncogene mutations
are genetic, not epigenetic, changes.
Question 4
Which pathophysiologic alteration is most directly responsible for the
hypoxemia seen in a patient with acute respiratory distress syndrome (ARDS)?
A. Increased alveolar dead space
B. Intrapulmonary shunt due to alveolar flooding
C. Hypoventilation from respiratory muscle fatigue
D. Diffusion limitation from thickened alveolar membrane
Correct Answer: B - Intrapulmonary shunt due to alveolar
flooding
Page 3
, RATIONALE
ARDS is characterized by increased permeability pulmonary edema,
leading to alveolar flooding and intrapulmonary shunting, which
causes severe hypoxemia refractory to oxygen therapy. Dead space,
hypoventilation, and diffusion limitation contribute but are not the
primary mechanisms.
Question 5
A patient with type 1 diabetes presents with polyuria, polydipsia, and a blood
glucose of 520 mg/dL. Which pathophysiologic mechanism best explains the
polyuria?
A. Osmotic diuresis from glucose exceeding renal threshold
B. Increased ADH secretion due to hyperglycemia
C. Direct tubular damage from ketone bodies
D. Activation of the renin-angiotensin-aldosterone system
Correct Answer: A - Osmotic diuresis from glucose exceeding
renal threshold
RATIONALE
When blood glucose exceeds the renal threshold (~180 mg/dL),
glucose spills into the urine, creating an osmotic gradient that draws
water into the tubules, causing osmotic diuresis and polyuria. ADH
secretion is not the primary driver, and ketones do not directly damage
tubules in the acute setting.
Question 6
Which statement best describes the role of tumor necrosis factor-alpha (TNF-)
in the pathogenesis of rheumatoid arthritis?
A. It promotes osteoclastogenesis and synovial inflammation.
B. It inhibits matrix metalloproteinases (MMPs).
C. It downregulates adhesion molecules on endothelial cells.
D. It induces regulatory T cell differentiation.
Page 4
