PHGY 216 FINAL EXAM 2026/2027
Comprehensive Practice Examination
150 Questions with Detailed Rationales in Italics
SECTION 1: BODY FLUID COMPARTMENTS & HOMEOSTASIS
(Questions 1-15)
1. What is the major cation in the intracellular fluid (ICF)?
A. Sodium
B. Chloride
C. Potassium
D. Bicarbonate
Correct Answer: C
Rationale: Potassium is the predominant intracellular cation, maintained by the Na+/K+
ATPase pump which actively transports potassium into cells. Sodium is the primary
extracellular cation. This concentration gradient is essential for cellular function,
particularly in excitable tissues like neurons and muscle cells .
2. A 70 kg male has total body water of approximately 42 liters. This represents
what percentage of his body weight?
A. 50%
B. 60%
C. 70%
D. 80%
Correct Answer: B
,Rationale: Total body water averages approximately 60% of body weight in adult males.
This percentage is lower in females due to higher body fat content. The calculation 42 L /
70 kg = 0.6 = 60% .
3. Approximately what percentage of total body water is contained in the
intracellular fluid compartment?
A. One-third
B. One-half
C. Two-thirds
D. Three-quarters
Correct Answer: C
Rationale: The ICF contains approximately two-thirds of total body water, while the ECF
contains the remaining one-third. The ECF is further subdivided into plasma (one-fifth of
ECF) and interstitial fluid (four-fifths of ECF) .
4. Which statement about the composition of plasma and interstitial fluid is TRUE?
A. Plasma has lower protein concentration than interstitial fluid
B. They are identical except that plasma contains more protein
C. Interstitial fluid contains more sodium than plasma
D. They are completely identical in composition
Correct Answer: B
Rationale: At the capillary level, water and small solutes exchange freely, but plasma
proteins are too large to pass through the capillary wall. Therefore, plasma and interstitial
fluid are chemically identical EXCEPT that plasma contains significantly more protein,
creating the colloid oncotic pressure that helps regulate fluid movement .
,5. A patient presents with severe vomiting over 24 hours. Which fluid
compartment shows the most immediate change in volume?
A. Intracellular fluid
B. Extracellular fluid
C. Transcellular fluid
D. Cerebrospinal fluid
Correct Answer: B
Rationale: Fluid losses from vomiting originate from the ECF (plasma and interstitial fluid).
The ICF is not directly affected initially because the cell membrane is not freely permeable
to water. After ECF volume decreases, osmotic gradients may cause water shifts from ICF
to ECF .
6. Which of the following is an example of a transcellular fluid?
A. Blood plasma
B. Interstitial fluid
C. Cerebrospinal fluid
D. Lymph
Correct Answer: C
Rationale: Transcellular fluids are specialized fluids contained within epithelial-lined
spaces. Examples include cerebrospinal fluid, synovial fluid, pleural fluid, peritoneal fluid,
and the aqueous humor of the eye. These are considered part of the ECF but are distinct
from plasma and interstitial fluid .
7. A patient is diagnosed with SIADH (Syndrome of Inappropriate Antidiuretic
Hormone), leading to excessive water retention without proportional sodium
retention. What results?
A. ECF becomes hypotonic (dilute)
B. ECF becomes hypertonic (concentrated)
, C. Red blood cells shrink
D. No change in ECF osmolarity
Correct Answer: A
Rationale: In SIADH, excessive ADH/vasopressin causes water retention without
corresponding sodium retention. Since water is retained but sodium is not, the ECF
becomes dilute (hypotonic). Water then moves into cells down the osmotic gradient,
causing cellular swelling, which can lead to hyponatremia and cerebral edema .
8. What is the primary regulator of ECF osmolarity?
A. Sodium balance only
B. Water balance
C. Potassium balance
D. Calcium balance
Correct Answer: B
Rationale: ECF osmolarity is primarily regulated by water balance, not salt balance. While
salt balance affects ECF volume, water balance determines osmolarity. The body has
sensitive osmoreceptors in the hypothalamus that detect changes in ECF osmolarity and
trigger thirst and ADH release to maintain homeostasis .
9. Which would be the MOST effective way to increase ECF volume?
A. Drink distilled water
B. Consume sodium-containing (isotonic) fluids
C. Consume a high-potassium meal
D. Increase protein intake
Correct Answer: B
Rationale: Sodium is the primary determinant of ECF volume because it is the major
extracellular cation and is osmotically active. Consuming sodium-containing fluids
Comprehensive Practice Examination
150 Questions with Detailed Rationales in Italics
SECTION 1: BODY FLUID COMPARTMENTS & HOMEOSTASIS
(Questions 1-15)
1. What is the major cation in the intracellular fluid (ICF)?
A. Sodium
B. Chloride
C. Potassium
D. Bicarbonate
Correct Answer: C
Rationale: Potassium is the predominant intracellular cation, maintained by the Na+/K+
ATPase pump which actively transports potassium into cells. Sodium is the primary
extracellular cation. This concentration gradient is essential for cellular function,
particularly in excitable tissues like neurons and muscle cells .
2. A 70 kg male has total body water of approximately 42 liters. This represents
what percentage of his body weight?
A. 50%
B. 60%
C. 70%
D. 80%
Correct Answer: B
,Rationale: Total body water averages approximately 60% of body weight in adult males.
This percentage is lower in females due to higher body fat content. The calculation 42 L /
70 kg = 0.6 = 60% .
3. Approximately what percentage of total body water is contained in the
intracellular fluid compartment?
A. One-third
B. One-half
C. Two-thirds
D. Three-quarters
Correct Answer: C
Rationale: The ICF contains approximately two-thirds of total body water, while the ECF
contains the remaining one-third. The ECF is further subdivided into plasma (one-fifth of
ECF) and interstitial fluid (four-fifths of ECF) .
4. Which statement about the composition of plasma and interstitial fluid is TRUE?
A. Plasma has lower protein concentration than interstitial fluid
B. They are identical except that plasma contains more protein
C. Interstitial fluid contains more sodium than plasma
D. They are completely identical in composition
Correct Answer: B
Rationale: At the capillary level, water and small solutes exchange freely, but plasma
proteins are too large to pass through the capillary wall. Therefore, plasma and interstitial
fluid are chemically identical EXCEPT that plasma contains significantly more protein,
creating the colloid oncotic pressure that helps regulate fluid movement .
,5. A patient presents with severe vomiting over 24 hours. Which fluid
compartment shows the most immediate change in volume?
A. Intracellular fluid
B. Extracellular fluid
C. Transcellular fluid
D. Cerebrospinal fluid
Correct Answer: B
Rationale: Fluid losses from vomiting originate from the ECF (plasma and interstitial fluid).
The ICF is not directly affected initially because the cell membrane is not freely permeable
to water. After ECF volume decreases, osmotic gradients may cause water shifts from ICF
to ECF .
6. Which of the following is an example of a transcellular fluid?
A. Blood plasma
B. Interstitial fluid
C. Cerebrospinal fluid
D. Lymph
Correct Answer: C
Rationale: Transcellular fluids are specialized fluids contained within epithelial-lined
spaces. Examples include cerebrospinal fluid, synovial fluid, pleural fluid, peritoneal fluid,
and the aqueous humor of the eye. These are considered part of the ECF but are distinct
from plasma and interstitial fluid .
7. A patient is diagnosed with SIADH (Syndrome of Inappropriate Antidiuretic
Hormone), leading to excessive water retention without proportional sodium
retention. What results?
A. ECF becomes hypotonic (dilute)
B. ECF becomes hypertonic (concentrated)
, C. Red blood cells shrink
D. No change in ECF osmolarity
Correct Answer: A
Rationale: In SIADH, excessive ADH/vasopressin causes water retention without
corresponding sodium retention. Since water is retained but sodium is not, the ECF
becomes dilute (hypotonic). Water then moves into cells down the osmotic gradient,
causing cellular swelling, which can lead to hyponatremia and cerebral edema .
8. What is the primary regulator of ECF osmolarity?
A. Sodium balance only
B. Water balance
C. Potassium balance
D. Calcium balance
Correct Answer: B
Rationale: ECF osmolarity is primarily regulated by water balance, not salt balance. While
salt balance affects ECF volume, water balance determines osmolarity. The body has
sensitive osmoreceptors in the hypothalamus that detect changes in ECF osmolarity and
trigger thirst and ADH release to maintain homeostasis .
9. Which would be the MOST effective way to increase ECF volume?
A. Drink distilled water
B. Consume sodium-containing (isotonic) fluids
C. Consume a high-potassium meal
D. Increase protein intake
Correct Answer: B
Rationale: Sodium is the primary determinant of ECF volume because it is the major
extracellular cation and is osmotically active. Consuming sodium-containing fluids
