Human Physiology Advanced Prep:
Master Organ System Physiology
Practice Questions
Subject: Organ System Physiology
Question 1: In the context of the Frank-Starling mechanism, which of the following molecular
events primarily accounts for the increase in contractile force following an increase in end-
diastolic volume?
A) Increased phosphorylation of phospholamban by PKA.
B) Increased sensitivity of Troponin C to calcium due to increased sarcomere stretch.
C) Activation of L-type calcium channels via cyclic AMP.
D) Decreased activity of the SERCA pump.
Correct Answer: B) Increased sensitivity of Troponin C to calcium due to increased
sarcomere stretch.
Explanation: The Frank-Starling law describes the heart's ability to adapt to increasing volumes
of inflowing blood. At the molecular level, stretching the cardiac myocytes increases the
myofilament lattice spacing and enhances the affinity of Troponin C for calcium. This makes the
contractile apparatus more sensitive to the existing calcium, increasing force development
without requiring an increase in intracellular calcium concentration. Options A and C describe
extrinsic regulation (sympathetic), not the intrinsic Frank-Starling mechanism.
Question 2: A patient presents with metabolic alkalosis and hypokalemia. Urinalysis reveals high
urinary chloride concentration. Which of the following is the most likely diagnosis?
A) Gitelman Syndrome
B) Bartter Syndrome
C) Laxative abuse
D) Primary hyperaldosteronism
Correct Answer: D) Primary hyperaldosteronism
,Explanation: In metabolic alkalosis with hypokalemia, the urinary chloride level differentiates
the etiology. High urinary chloride (>20 mEq/L) suggests an aldosterone-excess state (like
Conn’s syndrome/primary hyperaldosteronism). Low urinary chloride (<10 mEq/L) is seen in
vomiting or diuretic use. Gitelman and Bartter syndromes are characterized by salt-wasting and
usually present with normal or low blood pressure, whereas hyperaldosteronism is characterized
by hypertension.
Question 3: During the renal handling of glucose, the transport maximum (Tm) is exceeded
when plasma glucose levels reach approximately 200 mg/dL. At this threshold, what is the
primary reason for glucose appearing in the urine?
A) The SGLT2 transporters in the proximal tubule become saturated.
B) The Glomerular Filtration Rate (GFR) increases beyond the capacity of the kidney to filter
glucose.
C) The renal threshold for glucose transport is reached due to the down-regulation of GLUT2 on
the basolateral membrane.
D) Competitive inhibition by sodium ions at the apical membrane.
Correct Answer: A) The SGLT2 transporters in the proximal tubule become saturated.
Explanation: *Glucose is freely filtered at the glomerulus and reabsorbed in the proximal tubule
via sodium-glucose linked transporters (SGLT1 and SGLT2). Once the filtered load of glucose
exceeds the combined transport capacity (Tm) of these carriers, the transporters become
saturated, and any excess glucose remains in the tubular lumen to be excreted.
*
Question 4: Which of the following best describes the physiological effect of Atrial Natriuretic
Peptide (ANP) on the renal vasculature?
A) Afferent arteriolar constriction and efferent arteriolar dilation.
B) Afferent arteriolar dilation and efferent arteriolar constriction.
C) Vasoconstriction of both arterioles.
D) Vasodilation of both arterioles.
Correct Answer: B) Afferent arteriolar dilation and efferent arteriolar constriction.
Explanation: ANP is released in response to atrial stretch. To increase sodium and water
excretion, it increases the GFR. It achieves this by dilating the afferent arteriole (increasing
,glomerular hydrostatic pressure) and constricting the efferent arteriole (further increasing
pressure). This dual action significantly boosts the glomerular filtration fraction.
Question 5: A patient with chronic obstructive pulmonary disease (COPD) has a blood gas
showing a pH of 7.25, $PaCO_2$ of 65 mmHg, and $HCO_3^-$ of 28 mEq/L. What is the status
of the renal compensation in this patient?
A) Acute respiratory acidosis; kidneys have not yet compensated.
B) Chronic respiratory acidosis; partial renal compensation.
C) Fully compensated respiratory acidosis.
D) Metabolic alkalosis superimposed on respiratory acidosis.
Correct Answer: B) Chronic respiratory acidosis; partial renal compensation.
Explanation: In acute respiratory acidosis, the $HCO_3^-$ rises approximately 1 mEq/L for
every 10 mmHg rise in $PaCO_2$. Here, $PaCO_2$ has risen from 40 to 65 (an increase of 25
mmHg). An acute response would be $HCO_3^-$ around 26.5. A value of 28 indicates the
kidneys are actively retaining bicarbonate to buffer the excess acid, indicating a chronic state,
though the pH remains low (partial compensation).
Question 6: In the gastric phase of digestion, which cell type is responsible for the secretion of
intrinsic factor?
A) G cells
, B) Parietal cells
C) Chief cells
D) Mucous neck cells
Correct Answer: B) Parietal cells
Explanation: Parietal cells (oxyntic cells) are located primarily in the body and fundus of the
stomach. They secrete hydrochloric acid (HCl) for digestion and intrinsic factor, which is
essential for the absorption of Vitamin B12 in the terminal ileum. G cells secrete gastrin, and
chief cells secrete pepsinogen.
Question 7: The rapid depolarization phase of the cardiac pacemaker potential in the Sinoatrial
(SA) node is primarily mediated by which ion current?
A) Fast voltage-gated $Na^+$ channels
B) L-type $Ca^{2+}$ channels
C) T-type $Ca^{2+}$ channels
D) $K^+$ rectifier channels
Correct Answer: B) L-type $Ca^{2+}$ channels
Explanation: Unlike the ventricular myocytes which rely on $Na^+$ for rapid depolarization, SA
node cells have a resting potential that never reaches a stable value. The "upstroke" or
depolarization of the action potential in nodal tissue is mediated by the influx of calcium through
L-type (long-lasting) channels. T-type (transient) channels contribute to the final part of the
pacemaker prepotential.
Question 8: Which hormone is primarily responsible for the contraction of the gallbladder and
the relaxation of the Sphincter of Oddi during fat digestion?
A) Secretin
B) Cholecystokinin (CCK)
C) Gastrin
D) Somatostatin
Correct Answer: B) Cholecystokinin (CCK)
Master Organ System Physiology
Practice Questions
Subject: Organ System Physiology
Question 1: In the context of the Frank-Starling mechanism, which of the following molecular
events primarily accounts for the increase in contractile force following an increase in end-
diastolic volume?
A) Increased phosphorylation of phospholamban by PKA.
B) Increased sensitivity of Troponin C to calcium due to increased sarcomere stretch.
C) Activation of L-type calcium channels via cyclic AMP.
D) Decreased activity of the SERCA pump.
Correct Answer: B) Increased sensitivity of Troponin C to calcium due to increased
sarcomere stretch.
Explanation: The Frank-Starling law describes the heart's ability to adapt to increasing volumes
of inflowing blood. At the molecular level, stretching the cardiac myocytes increases the
myofilament lattice spacing and enhances the affinity of Troponin C for calcium. This makes the
contractile apparatus more sensitive to the existing calcium, increasing force development
without requiring an increase in intracellular calcium concentration. Options A and C describe
extrinsic regulation (sympathetic), not the intrinsic Frank-Starling mechanism.
Question 2: A patient presents with metabolic alkalosis and hypokalemia. Urinalysis reveals high
urinary chloride concentration. Which of the following is the most likely diagnosis?
A) Gitelman Syndrome
B) Bartter Syndrome
C) Laxative abuse
D) Primary hyperaldosteronism
Correct Answer: D) Primary hyperaldosteronism
,Explanation: In metabolic alkalosis with hypokalemia, the urinary chloride level differentiates
the etiology. High urinary chloride (>20 mEq/L) suggests an aldosterone-excess state (like
Conn’s syndrome/primary hyperaldosteronism). Low urinary chloride (<10 mEq/L) is seen in
vomiting or diuretic use. Gitelman and Bartter syndromes are characterized by salt-wasting and
usually present with normal or low blood pressure, whereas hyperaldosteronism is characterized
by hypertension.
Question 3: During the renal handling of glucose, the transport maximum (Tm) is exceeded
when plasma glucose levels reach approximately 200 mg/dL. At this threshold, what is the
primary reason for glucose appearing in the urine?
A) The SGLT2 transporters in the proximal tubule become saturated.
B) The Glomerular Filtration Rate (GFR) increases beyond the capacity of the kidney to filter
glucose.
C) The renal threshold for glucose transport is reached due to the down-regulation of GLUT2 on
the basolateral membrane.
D) Competitive inhibition by sodium ions at the apical membrane.
Correct Answer: A) The SGLT2 transporters in the proximal tubule become saturated.
Explanation: *Glucose is freely filtered at the glomerulus and reabsorbed in the proximal tubule
via sodium-glucose linked transporters (SGLT1 and SGLT2). Once the filtered load of glucose
exceeds the combined transport capacity (Tm) of these carriers, the transporters become
saturated, and any excess glucose remains in the tubular lumen to be excreted.
*
Question 4: Which of the following best describes the physiological effect of Atrial Natriuretic
Peptide (ANP) on the renal vasculature?
A) Afferent arteriolar constriction and efferent arteriolar dilation.
B) Afferent arteriolar dilation and efferent arteriolar constriction.
C) Vasoconstriction of both arterioles.
D) Vasodilation of both arterioles.
Correct Answer: B) Afferent arteriolar dilation and efferent arteriolar constriction.
Explanation: ANP is released in response to atrial stretch. To increase sodium and water
excretion, it increases the GFR. It achieves this by dilating the afferent arteriole (increasing
,glomerular hydrostatic pressure) and constricting the efferent arteriole (further increasing
pressure). This dual action significantly boosts the glomerular filtration fraction.
Question 5: A patient with chronic obstructive pulmonary disease (COPD) has a blood gas
showing a pH of 7.25, $PaCO_2$ of 65 mmHg, and $HCO_3^-$ of 28 mEq/L. What is the status
of the renal compensation in this patient?
A) Acute respiratory acidosis; kidneys have not yet compensated.
B) Chronic respiratory acidosis; partial renal compensation.
C) Fully compensated respiratory acidosis.
D) Metabolic alkalosis superimposed on respiratory acidosis.
Correct Answer: B) Chronic respiratory acidosis; partial renal compensation.
Explanation: In acute respiratory acidosis, the $HCO_3^-$ rises approximately 1 mEq/L for
every 10 mmHg rise in $PaCO_2$. Here, $PaCO_2$ has risen from 40 to 65 (an increase of 25
mmHg). An acute response would be $HCO_3^-$ around 26.5. A value of 28 indicates the
kidneys are actively retaining bicarbonate to buffer the excess acid, indicating a chronic state,
though the pH remains low (partial compensation).
Question 6: In the gastric phase of digestion, which cell type is responsible for the secretion of
intrinsic factor?
A) G cells
, B) Parietal cells
C) Chief cells
D) Mucous neck cells
Correct Answer: B) Parietal cells
Explanation: Parietal cells (oxyntic cells) are located primarily in the body and fundus of the
stomach. They secrete hydrochloric acid (HCl) for digestion and intrinsic factor, which is
essential for the absorption of Vitamin B12 in the terminal ileum. G cells secrete gastrin, and
chief cells secrete pepsinogen.
Question 7: The rapid depolarization phase of the cardiac pacemaker potential in the Sinoatrial
(SA) node is primarily mediated by which ion current?
A) Fast voltage-gated $Na^+$ channels
B) L-type $Ca^{2+}$ channels
C) T-type $Ca^{2+}$ channels
D) $K^+$ rectifier channels
Correct Answer: B) L-type $Ca^{2+}$ channels
Explanation: Unlike the ventricular myocytes which rely on $Na^+$ for rapid depolarization, SA
node cells have a resting potential that never reaches a stable value. The "upstroke" or
depolarization of the action potential in nodal tissue is mediated by the influx of calcium through
L-type (long-lasting) channels. T-type (transient) channels contribute to the final part of the
pacemaker prepotential.
Question 8: Which hormone is primarily responsible for the contraction of the gallbladder and
the relaxation of the Sphincter of Oddi during fat digestion?
A) Secretin
B) Cholecystokinin (CCK)
C) Gastrin
D) Somatostatin
Correct Answer: B) Cholecystokinin (CCK)
