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BIO 202L LAB 15 WORKSHEET 2026/2027 | Electrolytes,
Water, Acid & Bases - Fluid Balance & ABG Interpretation |
Complete Answers | Pass Guaranteed - A+ Graded
[Section 1: Body Fluid Compartments & Water Balance (Q1-12)]
Q1. A 70-kg adult male has approximately what volume of total body water (TBW)?
A. 28 L B. 42 L C. 56 L D. 84 L
C. 42 L [CORRECT]
Rationale: Total body water equals approximately 60% of body weight. For a 70-kg
individual, 70 kg × 0.60 = 42 L. This represents the sum of all fluid compartments (ICF
+ ECF). Correct Answer: C
Q2. Which of the following correctly describes the distribution of extracellular fluid
(ECF)? A. Plasma constitutes 75% of ECF and interstitial fluid constitutes 25% of ECF
B. Plasma constitutes 25% of ECF and interstitial fluid constitutes 75% of ECF C.
Plasma and interstitial fluid each constitute 50% of ECF D. Plasma constitutes 5% of
ECF and interstitial fluid constitutes 95% of ECF
B. Plasma constitutes 25% of ECF and interstitial fluid constitutes 75% of ECF
[CORRECT]
Rationale: ECF represents 20% of body weight (1/3 of TBW). Of this ECF, plasma
accounts for 5% of body weight (25% of ECF) and interstitial fluid accounts for 15%
of body weight (75% of ECF). This 1:3 ratio is critical for understanding capillary
exchange dynamics. Correct Answer: B
Q3. Transcellular fluid includes all of the following EXCEPT: A. Cerebrospinal fluid B.
Synovial fluid C. Intracellular fluid D. Peritoneal fluid
C. Intracellular fluid [CORRECT]
,2
Rationale: Transcellular fluid is a specialized subdivision of ECF that includes CSF,
synovial fluid, pleural fluid, peritoneal fluid, and ocular fluid. Intracellular fluid (ICF) is
a separate major compartment (40% body weight, 2/3 TBW) and is not classified as
transcellular. Correct Answer: C
Q4. A patient in the desert becomes dehydrated after 24 hours without water. Which
receptor mechanism is primarily responsible for triggering the thirst response? A.
Baroreceptors in the carotid sinus detecting decreased blood pressure B.
Osmoreceptors in the hypothalamus detecting increased plasma osmolality C.
Chemoreceptors in the medulla detecting decreased PaCO2 D. Stretch receptors in
the atria detecting decreased blood volume
B. Osmoreceptors in the hypothalamus detecting increased plasma osmolality
[CORRECT]
Rationale: The primary thirst mechanism is mediated by osmoreceptors in the
anterolateral hypothalamus, which are stimulated by increased plasma osmolality (as
little as 1-2%). While baroreceptor-mediated thirst occurs with significant volume
depletion (>10% blood volume loss), osmoreceptor stimulation is the dominant
trigger in dehydration. Correct Answer: B
Q5. Antidiuretic hormone (ADH/vasopressin) exerts its primary effect on water
reabsorption by: A. Increasing Na+ reabsorption in the proximal convoluted tubule B.
Inserting aquaporin-2 channels into the apical membrane of collecting duct principal
cells C. Stimulating aldosterone secretion from the adrenal cortex D. Inhibiting
carbonic anhydrase in the proximal tubule
B. Inserting aquaporin-2 channels into the apical membrane of collecting duct
principal cells [CORRECT]
Rationale: ADH binds to V2 receptors on collecting duct principal cells, triggering
cAMP-mediated insertion of aquaporin-2 water channels into the apical membrane.
This increases water reabsorption from the tubular lumen, decreases urine volume,
, 3
and increases urine osmolality. Aldosterone and carbonic anhydrase are not directly
involved in ADH-mediated water reabsorption. Correct Answer: B
Q6. A patient with diabetes insipidus presents with polyuria and diluted urine. Which
laboratory finding would be MOST consistent with this diagnosis? A. Decreased
plasma osmolality with increased urine osmolality B. Increased plasma osmolality
with decreased urine osmolality C. Normal plasma osmolality with normal urine
osmolality D. Decreased plasma osmolality with decreased urine osmolality
B. Increased plasma osmolality with decreased urine osmolality [CORRECT]
Rationale: Diabetes insipidus results from ADH deficiency or renal resistance to ADH.
Without functional ADH, aquaporin-2 channels remain internalized, preventing water
reabsorption in collecting ducts. This produces large volumes of dilute urine
(decreased urine osmolality) and progressive free water loss leading to increased
plasma osmolality and hypernatremia. Correct Answer: B
Q7. Which of the following represents the LARGEST daily route of water loss under
normal conditions? A. Insensible perspiration through the skin B. Water vapor from
the lungs C. Obligatory and facultative urine output D. Fecal water loss
C. Obligatory and facultative urine output [CORRECT]
Rationale: Under normal conditions, the kidneys excrete 1500-2000 mL/day
(obligatory + facultative urine output), which exceeds insensible skin loss (~500 mL),
pulmonary water loss (~400 mL), and fecal loss (~200 mL). The kidneys are the
primary regulator of water balance because they can adjust urine volume
dramatically (from 0.5 L to >20 L/day) in response to hydration status. Correct
Answer: C
BIO 202L LAB 15 WORKSHEET 2026/2027 | Electrolytes,
Water, Acid & Bases - Fluid Balance & ABG Interpretation |
Complete Answers | Pass Guaranteed - A+ Graded
[Section 1: Body Fluid Compartments & Water Balance (Q1-12)]
Q1. A 70-kg adult male has approximately what volume of total body water (TBW)?
A. 28 L B. 42 L C. 56 L D. 84 L
C. 42 L [CORRECT]
Rationale: Total body water equals approximately 60% of body weight. For a 70-kg
individual, 70 kg × 0.60 = 42 L. This represents the sum of all fluid compartments (ICF
+ ECF). Correct Answer: C
Q2. Which of the following correctly describes the distribution of extracellular fluid
(ECF)? A. Plasma constitutes 75% of ECF and interstitial fluid constitutes 25% of ECF
B. Plasma constitutes 25% of ECF and interstitial fluid constitutes 75% of ECF C.
Plasma and interstitial fluid each constitute 50% of ECF D. Plasma constitutes 5% of
ECF and interstitial fluid constitutes 95% of ECF
B. Plasma constitutes 25% of ECF and interstitial fluid constitutes 75% of ECF
[CORRECT]
Rationale: ECF represents 20% of body weight (1/3 of TBW). Of this ECF, plasma
accounts for 5% of body weight (25% of ECF) and interstitial fluid accounts for 15%
of body weight (75% of ECF). This 1:3 ratio is critical for understanding capillary
exchange dynamics. Correct Answer: B
Q3. Transcellular fluid includes all of the following EXCEPT: A. Cerebrospinal fluid B.
Synovial fluid C. Intracellular fluid D. Peritoneal fluid
C. Intracellular fluid [CORRECT]
,2
Rationale: Transcellular fluid is a specialized subdivision of ECF that includes CSF,
synovial fluid, pleural fluid, peritoneal fluid, and ocular fluid. Intracellular fluid (ICF) is
a separate major compartment (40% body weight, 2/3 TBW) and is not classified as
transcellular. Correct Answer: C
Q4. A patient in the desert becomes dehydrated after 24 hours without water. Which
receptor mechanism is primarily responsible for triggering the thirst response? A.
Baroreceptors in the carotid sinus detecting decreased blood pressure B.
Osmoreceptors in the hypothalamus detecting increased plasma osmolality C.
Chemoreceptors in the medulla detecting decreased PaCO2 D. Stretch receptors in
the atria detecting decreased blood volume
B. Osmoreceptors in the hypothalamus detecting increased plasma osmolality
[CORRECT]
Rationale: The primary thirst mechanism is mediated by osmoreceptors in the
anterolateral hypothalamus, which are stimulated by increased plasma osmolality (as
little as 1-2%). While baroreceptor-mediated thirst occurs with significant volume
depletion (>10% blood volume loss), osmoreceptor stimulation is the dominant
trigger in dehydration. Correct Answer: B
Q5. Antidiuretic hormone (ADH/vasopressin) exerts its primary effect on water
reabsorption by: A. Increasing Na+ reabsorption in the proximal convoluted tubule B.
Inserting aquaporin-2 channels into the apical membrane of collecting duct principal
cells C. Stimulating aldosterone secretion from the adrenal cortex D. Inhibiting
carbonic anhydrase in the proximal tubule
B. Inserting aquaporin-2 channels into the apical membrane of collecting duct
principal cells [CORRECT]
Rationale: ADH binds to V2 receptors on collecting duct principal cells, triggering
cAMP-mediated insertion of aquaporin-2 water channels into the apical membrane.
This increases water reabsorption from the tubular lumen, decreases urine volume,
, 3
and increases urine osmolality. Aldosterone and carbonic anhydrase are not directly
involved in ADH-mediated water reabsorption. Correct Answer: B
Q6. A patient with diabetes insipidus presents with polyuria and diluted urine. Which
laboratory finding would be MOST consistent with this diagnosis? A. Decreased
plasma osmolality with increased urine osmolality B. Increased plasma osmolality
with decreased urine osmolality C. Normal plasma osmolality with normal urine
osmolality D. Decreased plasma osmolality with decreased urine osmolality
B. Increased plasma osmolality with decreased urine osmolality [CORRECT]
Rationale: Diabetes insipidus results from ADH deficiency or renal resistance to ADH.
Without functional ADH, aquaporin-2 channels remain internalized, preventing water
reabsorption in collecting ducts. This produces large volumes of dilute urine
(decreased urine osmolality) and progressive free water loss leading to increased
plasma osmolality and hypernatremia. Correct Answer: B
Q7. Which of the following represents the LARGEST daily route of water loss under
normal conditions? A. Insensible perspiration through the skin B. Water vapor from
the lungs C. Obligatory and facultative urine output D. Fecal water loss
C. Obligatory and facultative urine output [CORRECT]
Rationale: Under normal conditions, the kidneys excrete 1500-2000 mL/day
(obligatory + facultative urine output), which exceeds insensible skin loss (~500 mL),
pulmonary water loss (~400 mL), and fecal loss (~200 mL). The kidneys are the
primary regulator of water balance because they can adjust urine volume
dramatically (from 0.5 L to >20 L/day) in response to hydration status. Correct
Answer: C
