BIOD 152 MODULE 5 EXAM (KIDNEY) ACTUAL EXAM 2026/2027 |
Portage Learning | 26 Questions with Rationales | Complete Answer
Key | Updated Edition | Pass Guaranteed - A+ Graded
Q1 (Multiple Choice): Which structure of the nephron is responsible for the majority of
water reabsorption (approximately 65%) and is therefore considered the "obligatory
water reabsorption" segment that occurs regardless of hydration status?
A. Descending limb of the loop of Henle
B. Proximal convoluted tubule (PCT) [CORRECT]
C. Collecting duct
D. Distal convoluted tubule (DCT)
Correct Answer: B
Rationale: The proximal convoluted tubule (PCT) reabsorbs approximately 65% of
filtered water along with 65% of sodium and chloride. This is termed "obligatory" or
"constitutive" reabsorption because it occurs constantly through both transcellular and
paracellular pathways, driven by the osmotic gradient created by solute transport. The
PCT is highly permeable to water due to abundant aquaporin-1 (AQP1) channels.
● A (Descending limb) does reabsorb water (20% of filtered load), but this is part of
the countercurrent mechanism and is less than the PCT contribution.
● C (Collecting duct) performs "facultative" water reabsorption (variable,
ADH-dependent), accounting for final urine concentration adjustments (5-10% of
filtered water).
● D (DCT) reabsorbs only about 5% of filtered water and is relatively impermeable
to water compared to PCT.
,Q2 (Diagram Labeling): Image description: Longitudinal section of the nephron showing
renal corpuscle and tubular segments with numbered structures.
Label the following structures:
1. Capillary network where filtration occurs; surrounded by Bowman's capsule
2. Structure that monitors filtrate composition and controls renin release
3. Segment with simple cuboidal cells with dense microvilli (brush border) for
reabsorption
4. Segment impermeable to water but actively transports NaCl out, creating
hypertonic medulla
5. Final site where urine concentration is hormonally regulated
Correct Answer:
1. Glomerulus [CORRECT]
2. Macula densa (of juxtaglomerular apparatus) [CORRECT]
3. Proximal convoluted tubule (PCT) [CORRECT]
4. Ascending limb of loop of Henle (thick ascending limb) [CORRECT]
5. Collecting duct [CORRECT]
Rationale:
1. Glomerulus: A tuft of fenestrated capillaries where blood is filtered under
hydrostatic pressure. The filtration barrier includes fenestrated endothelium,
basement membrane, and podocyte foot processes.
2. Macula densa: Specialized distal convoluted tubule cells that sense NaCl
concentration in tubular fluid. Low NaCl triggers release of renin from
juxtaglomerular cells, activating the RAAS system.
3. PCT: Characterized by extensive microvilli forming a brush border that increases
surface area 20-fold for massive reabsorption of glucose, amino acids, ions, and
water.
4. Thick ascending limb: Contains Na+-K+-2Cl- cotransporters (NKCC2) that actively
transport solutes out without water following, diluting tubular fluid and creating
medullary hypertonicity essential for countercurrent concentration.
5. Collecting duct: Final regulator of urine concentration; principal cells contain
aquaporin-2 (AQP2) channels inserted under ADH stimulation, allowing variable
water reabsorption from 5% to maximum concentration.
, Q3 (Short Answer): Explain the three mechanisms that regulate glomerular filtration rate
(GFR): autoregulation, neural regulation, and hormonal regulation. Include the specific
sensors, effectors, and physiological outcomes for each.
Correct Answer:
Autoregulation: [1] Myogenic mechanism—vascular smooth muscle of afferent arteriole
responds to stretch (increased BP causes constriction, decreased BP causes dilation).
[2] Tubuloglomerular feedback—macula densa senses distal NaCl delivery; high delivery
causes afferent arteriole constriction (adenosine, ATP) and efferent dilation, reducing
GFR. Low delivery causes afferent dilation (prostaglandins, NO), increasing GFR.
Maintains constant GFR across MAP 80-180 mmHg.
Neural regulation: Sympathetic nervous system innervation of afferent and efferent
arterioles. Strong stimulation (exercise, stress, hemorrhage) causes vasoconstriction,
reducing renal blood flow and GFR to preserve blood pressure and redirect flow to vital
organs.
Hormonal regulation: [1] Angiotensin II—constricts efferent > afferent arteriole,
maintaining GFR despite reduced renal perfusion. [2] Atrial natriuretic peptide
(ANP)—dilates afferent, constricts efferent, increasing GFR and promoting natriuresis.
[CORRECT]
Rationale: These three mechanisms operate on different time scales and for different
physiological purposes. Autoregulation is intrinsic, local, and rapid (seconds), protecting
glomerular capillaries from pressure damage. Neural regulation provides systemic
integration for emergencies. Hormonal regulation (RAAS, ANP) provides
intermediate-term adjustment for volume and pressure homeostasis. Understanding
these mechanisms is essential for comprehending how the kidney maintains stable
Portage Learning | 26 Questions with Rationales | Complete Answer
Key | Updated Edition | Pass Guaranteed - A+ Graded
Q1 (Multiple Choice): Which structure of the nephron is responsible for the majority of
water reabsorption (approximately 65%) and is therefore considered the "obligatory
water reabsorption" segment that occurs regardless of hydration status?
A. Descending limb of the loop of Henle
B. Proximal convoluted tubule (PCT) [CORRECT]
C. Collecting duct
D. Distal convoluted tubule (DCT)
Correct Answer: B
Rationale: The proximal convoluted tubule (PCT) reabsorbs approximately 65% of
filtered water along with 65% of sodium and chloride. This is termed "obligatory" or
"constitutive" reabsorption because it occurs constantly through both transcellular and
paracellular pathways, driven by the osmotic gradient created by solute transport. The
PCT is highly permeable to water due to abundant aquaporin-1 (AQP1) channels.
● A (Descending limb) does reabsorb water (20% of filtered load), but this is part of
the countercurrent mechanism and is less than the PCT contribution.
● C (Collecting duct) performs "facultative" water reabsorption (variable,
ADH-dependent), accounting for final urine concentration adjustments (5-10% of
filtered water).
● D (DCT) reabsorbs only about 5% of filtered water and is relatively impermeable
to water compared to PCT.
,Q2 (Diagram Labeling): Image description: Longitudinal section of the nephron showing
renal corpuscle and tubular segments with numbered structures.
Label the following structures:
1. Capillary network where filtration occurs; surrounded by Bowman's capsule
2. Structure that monitors filtrate composition and controls renin release
3. Segment with simple cuboidal cells with dense microvilli (brush border) for
reabsorption
4. Segment impermeable to water but actively transports NaCl out, creating
hypertonic medulla
5. Final site where urine concentration is hormonally regulated
Correct Answer:
1. Glomerulus [CORRECT]
2. Macula densa (of juxtaglomerular apparatus) [CORRECT]
3. Proximal convoluted tubule (PCT) [CORRECT]
4. Ascending limb of loop of Henle (thick ascending limb) [CORRECT]
5. Collecting duct [CORRECT]
Rationale:
1. Glomerulus: A tuft of fenestrated capillaries where blood is filtered under
hydrostatic pressure. The filtration barrier includes fenestrated endothelium,
basement membrane, and podocyte foot processes.
2. Macula densa: Specialized distal convoluted tubule cells that sense NaCl
concentration in tubular fluid. Low NaCl triggers release of renin from
juxtaglomerular cells, activating the RAAS system.
3. PCT: Characterized by extensive microvilli forming a brush border that increases
surface area 20-fold for massive reabsorption of glucose, amino acids, ions, and
water.
4. Thick ascending limb: Contains Na+-K+-2Cl- cotransporters (NKCC2) that actively
transport solutes out without water following, diluting tubular fluid and creating
medullary hypertonicity essential for countercurrent concentration.
5. Collecting duct: Final regulator of urine concentration; principal cells contain
aquaporin-2 (AQP2) channels inserted under ADH stimulation, allowing variable
water reabsorption from 5% to maximum concentration.
, Q3 (Short Answer): Explain the three mechanisms that regulate glomerular filtration rate
(GFR): autoregulation, neural regulation, and hormonal regulation. Include the specific
sensors, effectors, and physiological outcomes for each.
Correct Answer:
Autoregulation: [1] Myogenic mechanism—vascular smooth muscle of afferent arteriole
responds to stretch (increased BP causes constriction, decreased BP causes dilation).
[2] Tubuloglomerular feedback—macula densa senses distal NaCl delivery; high delivery
causes afferent arteriole constriction (adenosine, ATP) and efferent dilation, reducing
GFR. Low delivery causes afferent dilation (prostaglandins, NO), increasing GFR.
Maintains constant GFR across MAP 80-180 mmHg.
Neural regulation: Sympathetic nervous system innervation of afferent and efferent
arterioles. Strong stimulation (exercise, stress, hemorrhage) causes vasoconstriction,
reducing renal blood flow and GFR to preserve blood pressure and redirect flow to vital
organs.
Hormonal regulation: [1] Angiotensin II—constricts efferent > afferent arteriole,
maintaining GFR despite reduced renal perfusion. [2] Atrial natriuretic peptide
(ANP)—dilates afferent, constricts efferent, increasing GFR and promoting natriuresis.
[CORRECT]
Rationale: These three mechanisms operate on different time scales and for different
physiological purposes. Autoregulation is intrinsic, local, and rapid (seconds), protecting
glomerular capillaries from pressure damage. Neural regulation provides systemic
integration for emergencies. Hormonal regulation (RAAS, ANP) provides
intermediate-term adjustment for volume and pressure homeostasis. Understanding
these mechanisms is essential for comprehending how the kidney maintains stable
