Comprehensive Basic Science Examination
(CBSE) Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. A 45-year-old man with a history of chronic alcohol use presents with
fatigue, jaundice, and ascites. Laboratory studies reveal elevated serum
aminotransferases and a prolonged prothrombin time. A liver biopsy shows
hepatocytes with large, pale-staining cytoplasmic vacuoles that displace the
nucleus to the periphery. Which of the following is the most likely
mechanism of this cellular change?
A. Accumulation of cholesterol esters due to lysosomal enzyme deficiency
B. Deposition of amyloid fibrils due to protein misfolding
C. Intracellular accumulation of triglycerides due to impaired lipoprotein
secretion
D. Glycogen accumulation due to deficient glucose-6-phosphatase activity
Answer: C
*Rationale: The biopsy finding of hepatocytes with large, pale-staining
cytoplasmic vacuoles displacing the nucleus is characteristic of macrovesicular
steatosis, which is a common finding in alcoholic liver disease. The primary
mechanism is the accumulation of triglycerides within hepatocytes. This occurs
due to multiple factors including increased fatty acid synthesis, decreased fatty
acid oxidation, and, critically, impaired assembly and secretion of very-low-density
lipoproteins (VLDL). The impaired secretion results from damage to the
microtubular apparatus and the Golgi complex, which are essential for lipoprotein
export.
2. A 28-year-old woman is brought to the emergency department after a
motor vehicle accident. She has multiple fractures and significant blood
loss. Her blood pressure is 85/50 mm Hg, and heart rate is 125 bpm.
, Laboratory tests show a hematocrit of 25%. Which of the following
physiological responses is most directly responsible for maintaining her
mean arterial pressure at this stage?
A. Increased systemic vascular resistance due to alpha-1 adrenergic
receptor activation
B. Increased cardiac output due to beta-1 adrenergic receptor activation
C. Increased venous return due to alpha-2 adrenergic receptor activation
D. Increased stroke volume due to increased end-diastolic volume
Answer: A
*Rationale: In the setting of acute hemorrhage and hypovolemic shock, the body's
primary compensatory mechanism to maintain mean arterial pressure (MAP) is to
increase systemic vascular resistance (SVR). This is achieved through baroreceptor-
mediated activation of the sympathetic nervous system, leading to alpha-1
adrenergic receptor stimulation on vascular smooth muscle. This causes
widespread vasoconstriction of arterioles and veins, increasing SVR and thus MAP.
While beta-1 activation increases heart rate (tachycardia), the primary
determinant of MAP in this hypovolemic state is SVR, as stroke volume is reduced.
3. A 6-year-old boy is brought to the clinic due to recurrent respiratory
infections. A sweat test shows elevated chloride levels. Genetic testing
reveals a mutation in a gene encoding a chloride channel. Which of the
following additional findings is most likely to be present in this patient?
A. Increased viscosity of pancreatic secretions
B. Decreased sodium reabsorption in the distal convoluted tubule
C. Increased activity of the Na+/K+ ATPase pump in respiratory epithelial
cells
D. Decreased production of surfactant by type II pneumocytes
Answer: A
*Rationale: The patient's presentation is classic for cystic fibrosis, caused by a
mutation in the CFTR gene encoding a cAMP-regulated chloride channel. The
defect in CFTR leads to decreased chloride secretion and increased sodium and
water reabsorption across epithelial surfaces, resulting in thick, viscous secretions.
,In the pancreas, this viscosity leads to ductal obstruction, enzyme insufficiency,
and malabsorption. The other options are not characteristic of CFTR dysfunction.
4. A researcher is studying the transport of a novel amino acid across the
intestinal epithelium. She finds that the transport is dependent on the
presence of a sodium gradient, is saturable, and can be inhibited by
chemically similar amino acids. Which of the following best describes this
transport mechanism?
A. Primary active transport
B. Secondary active transport (symport)
C. Facilitated diffusion
D. Simple diffusion
Answer: B
*Rationale: The characteristics described—dependence on a sodium gradient
(energy from the Na+/K+ ATPase), saturability (carrier-mediated), and inhibition by
similar substrates (specificity)—are hallmarks of secondary active transport.
Specifically, a symporter couples the movement of sodium down its
electrochemical gradient to the movement of the amino acid against its
concentration gradient in the same direction. Primary active transport would
directly use ATP, facilitated diffusion would not require an energy source like the
sodium gradient, and simple diffusion does not exhibit saturability.
5. A 55-year-old man with a history of hypertension is started on a new
medication. The drug inhibits the conversion of a decapeptide to an
octapeptide in the pulmonary circulation. Which of the following
physiologic effects is most directly associated with the action of this drug?
A. Decreased sodium reabsorption in the proximal convoluted tubule
B. Increased synthesis of aldosterone from the adrenal cortex
C. Decreased degradation of bradykinin in the lungs
D. Increased release of renin from the juxtaglomerular apparatus
Answer: C
*Rationale: The drug is an ACE inhibitor, which blocks the angiotensin-converting
enzyme (ACE) that converts angiotensin I (a decapeptide) to angiotensin II (an
, octapeptide). ACE is also responsible for the degradation of bradykinin. Therefore,
inhibition of ACE leads to decreased degradation and thus increased levels of
bradykinin. The other options are incorrect: ACE inhibitors decrease aldosterone
synthesis, decrease sodium reabsorption (indirectly), and can lead to increased
renin release as a compensatory response, but the most direct action related to
the described conversion is the effect on bradykinin.
6. A 32-year-old woman presents with amenorrhea and galactorrhea. An MRI
of her pituitary gland reveals a microadenoma. Laboratory tests show an
elevated serum level of a single-chain polypeptide hormone. Which of the
following mechanisms best explains the galactorrhea?
A. Direct stimulation of mammary gland prolactin receptors
B. Inhibition of hypothalamic dopamine release
C. Increased sensitivity of ovarian follicles to FSH
D. Enhanced release of thyrotropin-releasing hormone (TRH)
Answer: A
*Rationale: The patient has a prolactinoma, a pituitary adenoma secreting
prolactin. Prolactin is a single-chain polypeptide hormone that directly binds to its
receptors on mammary alveolar epithelial cells, stimulating milk production
(galactorrhea). Prolactin does not stimulate TRH release; rather, TRH can stimulate
prolactin. Prolactin inhibits gonadotropin-releasing hormone (GnRH) secretion,
leading to decreased FSH and LH, not increased sensitivity of follicles. While
dopamine inhibits prolactin, it is the loss of this inhibition that may contribute, but
the galactorrhea is caused by the direct action of prolactin on the breast.
7. A 19-year-old man with sickle cell disease is admitted with severe pain in his
chest, back, and abdomen. His oxygen saturation is 88% on room air. A
chest X-ray shows a new infiltrate in the right lower lobe. Which of the
following pathophysiological mechanisms is most directly responsible for
this patient's acute pulmonary event?
A. Fat emboli from bone marrow infarction
B. In situ thrombosis of pulmonary arterioles
(CBSE) Questions And Correct Answers
(Verified Answers) Plus Rationales 2026
Q&A | Instant Download Pdf
1. A 45-year-old man with a history of chronic alcohol use presents with
fatigue, jaundice, and ascites. Laboratory studies reveal elevated serum
aminotransferases and a prolonged prothrombin time. A liver biopsy shows
hepatocytes with large, pale-staining cytoplasmic vacuoles that displace the
nucleus to the periphery. Which of the following is the most likely
mechanism of this cellular change?
A. Accumulation of cholesterol esters due to lysosomal enzyme deficiency
B. Deposition of amyloid fibrils due to protein misfolding
C. Intracellular accumulation of triglycerides due to impaired lipoprotein
secretion
D. Glycogen accumulation due to deficient glucose-6-phosphatase activity
Answer: C
*Rationale: The biopsy finding of hepatocytes with large, pale-staining
cytoplasmic vacuoles displacing the nucleus is characteristic of macrovesicular
steatosis, which is a common finding in alcoholic liver disease. The primary
mechanism is the accumulation of triglycerides within hepatocytes. This occurs
due to multiple factors including increased fatty acid synthesis, decreased fatty
acid oxidation, and, critically, impaired assembly and secretion of very-low-density
lipoproteins (VLDL). The impaired secretion results from damage to the
microtubular apparatus and the Golgi complex, which are essential for lipoprotein
export.
2. A 28-year-old woman is brought to the emergency department after a
motor vehicle accident. She has multiple fractures and significant blood
loss. Her blood pressure is 85/50 mm Hg, and heart rate is 125 bpm.
, Laboratory tests show a hematocrit of 25%. Which of the following
physiological responses is most directly responsible for maintaining her
mean arterial pressure at this stage?
A. Increased systemic vascular resistance due to alpha-1 adrenergic
receptor activation
B. Increased cardiac output due to beta-1 adrenergic receptor activation
C. Increased venous return due to alpha-2 adrenergic receptor activation
D. Increased stroke volume due to increased end-diastolic volume
Answer: A
*Rationale: In the setting of acute hemorrhage and hypovolemic shock, the body's
primary compensatory mechanism to maintain mean arterial pressure (MAP) is to
increase systemic vascular resistance (SVR). This is achieved through baroreceptor-
mediated activation of the sympathetic nervous system, leading to alpha-1
adrenergic receptor stimulation on vascular smooth muscle. This causes
widespread vasoconstriction of arterioles and veins, increasing SVR and thus MAP.
While beta-1 activation increases heart rate (tachycardia), the primary
determinant of MAP in this hypovolemic state is SVR, as stroke volume is reduced.
3. A 6-year-old boy is brought to the clinic due to recurrent respiratory
infections. A sweat test shows elevated chloride levels. Genetic testing
reveals a mutation in a gene encoding a chloride channel. Which of the
following additional findings is most likely to be present in this patient?
A. Increased viscosity of pancreatic secretions
B. Decreased sodium reabsorption in the distal convoluted tubule
C. Increased activity of the Na+/K+ ATPase pump in respiratory epithelial
cells
D. Decreased production of surfactant by type II pneumocytes
Answer: A
*Rationale: The patient's presentation is classic for cystic fibrosis, caused by a
mutation in the CFTR gene encoding a cAMP-regulated chloride channel. The
defect in CFTR leads to decreased chloride secretion and increased sodium and
water reabsorption across epithelial surfaces, resulting in thick, viscous secretions.
,In the pancreas, this viscosity leads to ductal obstruction, enzyme insufficiency,
and malabsorption. The other options are not characteristic of CFTR dysfunction.
4. A researcher is studying the transport of a novel amino acid across the
intestinal epithelium. She finds that the transport is dependent on the
presence of a sodium gradient, is saturable, and can be inhibited by
chemically similar amino acids. Which of the following best describes this
transport mechanism?
A. Primary active transport
B. Secondary active transport (symport)
C. Facilitated diffusion
D. Simple diffusion
Answer: B
*Rationale: The characteristics described—dependence on a sodium gradient
(energy from the Na+/K+ ATPase), saturability (carrier-mediated), and inhibition by
similar substrates (specificity)—are hallmarks of secondary active transport.
Specifically, a symporter couples the movement of sodium down its
electrochemical gradient to the movement of the amino acid against its
concentration gradient in the same direction. Primary active transport would
directly use ATP, facilitated diffusion would not require an energy source like the
sodium gradient, and simple diffusion does not exhibit saturability.
5. A 55-year-old man with a history of hypertension is started on a new
medication. The drug inhibits the conversion of a decapeptide to an
octapeptide in the pulmonary circulation. Which of the following
physiologic effects is most directly associated with the action of this drug?
A. Decreased sodium reabsorption in the proximal convoluted tubule
B. Increased synthesis of aldosterone from the adrenal cortex
C. Decreased degradation of bradykinin in the lungs
D. Increased release of renin from the juxtaglomerular apparatus
Answer: C
*Rationale: The drug is an ACE inhibitor, which blocks the angiotensin-converting
enzyme (ACE) that converts angiotensin I (a decapeptide) to angiotensin II (an
, octapeptide). ACE is also responsible for the degradation of bradykinin. Therefore,
inhibition of ACE leads to decreased degradation and thus increased levels of
bradykinin. The other options are incorrect: ACE inhibitors decrease aldosterone
synthesis, decrease sodium reabsorption (indirectly), and can lead to increased
renin release as a compensatory response, but the most direct action related to
the described conversion is the effect on bradykinin.
6. A 32-year-old woman presents with amenorrhea and galactorrhea. An MRI
of her pituitary gland reveals a microadenoma. Laboratory tests show an
elevated serum level of a single-chain polypeptide hormone. Which of the
following mechanisms best explains the galactorrhea?
A. Direct stimulation of mammary gland prolactin receptors
B. Inhibition of hypothalamic dopamine release
C. Increased sensitivity of ovarian follicles to FSH
D. Enhanced release of thyrotropin-releasing hormone (TRH)
Answer: A
*Rationale: The patient has a prolactinoma, a pituitary adenoma secreting
prolactin. Prolactin is a single-chain polypeptide hormone that directly binds to its
receptors on mammary alveolar epithelial cells, stimulating milk production
(galactorrhea). Prolactin does not stimulate TRH release; rather, TRH can stimulate
prolactin. Prolactin inhibits gonadotropin-releasing hormone (GnRH) secretion,
leading to decreased FSH and LH, not increased sensitivity of follicles. While
dopamine inhibits prolactin, it is the loss of this inhibition that may contribute, but
the galactorrhea is caused by the direct action of prolactin on the breast.
7. A 19-year-old man with sickle cell disease is admitted with severe pain in his
chest, back, and abdomen. His oxygen saturation is 88% on room air. A
chest X-ray shows a new infiltrate in the right lower lobe. Which of the
following pathophysiological mechanisms is most directly responsible for
this patient's acute pulmonary event?
A. Fat emboli from bone marrow infarction
B. In situ thrombosis of pulmonary arterioles
