GCU PATHOPHYSIOLOGY MIDTERM EXAM: ACID-BASE
BALANCE, ELECTROLYTE DISORDERS, AND ANION GAP
- 200 QUESTIONS WITH COMPLETE SOLUTIONS
1. A patient presents with a serum sodium level of 152 mEq/L. This condition is
classified as:
A. Hyponatremia
B. Hypernatremia
C. Pseudohyponatremia
D. Normal sodium level
Answer: B. Hypernatremia
Explanation: Hypernatremia is defined as a serum sodium level greater than 145
mEq/L. A level of 152 mEq/L clearly indicates hypernatremia, which reflects an
excess of sodium relative to total body water.
2. What is the normal serum osmolarity range?
A. 275-285 mOsm/L
B. 285-295 mOsm/L
C. 295-305 mOsm/L
D. 305-315 mOsm/L
Answer: B. 285-295 mOsm/L
Explanation: Normal serum osmolarity ranges from 285 to 295 mOsm/L. This
measurement reflects the concentration of dissolved particles in the blood and is
crucial for maintaining fluid balance.
,3. A patient with hyponatremia but normal serum osmolality (290 mOsm/L) has:
A. True hyponatremia
B. Hypernatremia
C. Pseudohyponatremia
D. Isotonic hyponatremia
Answer: C. Pseudohyponatremia
Explanation: Pseudohyponatremia occurs when hyponatremia is present with
normal serum osmolality (285-295 mOsm/L). This is typically caused by elevated
lipids or proteins that displace the aqueous phase of plasma, falsely lowering
sodium measurements.
4. Under physiologic conditions, what percentage of total plasma volume is the
aqueous phase?
A. 7%
B. 93%
C. 50%
D. 75%
Answer: B. 93%
Explanation: Under normal physiologic conditions, 93% of total plasma volume is
an aqueous phase containing electrolytes. The remaining 7% is a solid phase
primarily composed of lipids and proteins.
5. Acidosis is defined as a blood pH:
A. Above 7.45
B. Between 7.35-7.45
C. Below 7.35
D. Exactly 7.40
,Answer: C. Below 7.35
Explanation: Acidosis is characterized by excessive acidity of body fluids, resulting
in a blood pH below 7.35. This represents an accumulation of hydrogen ions or
loss of bicarbonate.
6. What pH range represents normal blood?
A. 7.25-7.35
B. 7.35-7.45
C. 7.45-7.55
D. 7.55-7.65
Answer: B. 7.35-7.45
Explanation: Normal blood pH is maintained within a narrow range of 7.35 to
7.45. This tight regulation is essential for proper cellular function and enzyme
activity.
7. Alkalosis is characterized by a blood pH:
A. Below 7.35
B. Between 7.35-7.45
C. Above 7.45
D. Exactly 7.40
Answer: C. Above 7.45
Explanation: Alkalosis occurs when there is an excess of base or lack of acids in
body fluids, resulting in a blood pH above 7.45.
8. In compensated respiratory acidosis, which laboratory finding is expected?
A. Low pH, low CO2, low HCO3
B. Normal pH, high CO2, high HCO3
C. High pH, low CO2, low HCO3
D. Normal pH, normal CO2, normal HCO3
, Answer: B. Normal pH, high CO2, high HCO3
Explanation: In compensated respiratory acidosis, the body has partially corrected
the acid-base disturbance. The pH returns to normal, but CO2 remains elevated
(respiratory cause) and HCO3 is elevated (metabolic compensation).
9. Compensated metabolic acidosis is characterized by:
A. Low pH, high CO2, high HCO3
B. Normal pH, low CO2, low HCO3
C. High pH, low CO2, high HCO3
D. Normal pH, high CO2, high HCO3
Answer: B. Normal pH, low CO2, low HCO3
Explanation: In compensated metabolic acidosis, the pH returns to normal. The
HCO3 remains low (metabolic cause) and the CO2 is low (respiratory
compensation through hyperventilation).
10. What is the normal PaCO2 range?
A. 25-35 mmHg
B. 35-45 mmHg
C. 45-55 mmHg
D. 55-65 mmHg
Answer: B. 35-45 mmHg
Explanation: Normal PaCO2 (partial pressure of carbon dioxide) ranges from 35 to
45 mmHg. This parameter reflects respiratory function and carbon dioxide
elimination.
11. The normal bicarbonate (HCO3) level is:
A. 16-20 mEq/L
B. 22-26 mEq/L
BALANCE, ELECTROLYTE DISORDERS, AND ANION GAP
- 200 QUESTIONS WITH COMPLETE SOLUTIONS
1. A patient presents with a serum sodium level of 152 mEq/L. This condition is
classified as:
A. Hyponatremia
B. Hypernatremia
C. Pseudohyponatremia
D. Normal sodium level
Answer: B. Hypernatremia
Explanation: Hypernatremia is defined as a serum sodium level greater than 145
mEq/L. A level of 152 mEq/L clearly indicates hypernatremia, which reflects an
excess of sodium relative to total body water.
2. What is the normal serum osmolarity range?
A. 275-285 mOsm/L
B. 285-295 mOsm/L
C. 295-305 mOsm/L
D. 305-315 mOsm/L
Answer: B. 285-295 mOsm/L
Explanation: Normal serum osmolarity ranges from 285 to 295 mOsm/L. This
measurement reflects the concentration of dissolved particles in the blood and is
crucial for maintaining fluid balance.
,3. A patient with hyponatremia but normal serum osmolality (290 mOsm/L) has:
A. True hyponatremia
B. Hypernatremia
C. Pseudohyponatremia
D. Isotonic hyponatremia
Answer: C. Pseudohyponatremia
Explanation: Pseudohyponatremia occurs when hyponatremia is present with
normal serum osmolality (285-295 mOsm/L). This is typically caused by elevated
lipids or proteins that displace the aqueous phase of plasma, falsely lowering
sodium measurements.
4. Under physiologic conditions, what percentage of total plasma volume is the
aqueous phase?
A. 7%
B. 93%
C. 50%
D. 75%
Answer: B. 93%
Explanation: Under normal physiologic conditions, 93% of total plasma volume is
an aqueous phase containing electrolytes. The remaining 7% is a solid phase
primarily composed of lipids and proteins.
5. Acidosis is defined as a blood pH:
A. Above 7.45
B. Between 7.35-7.45
C. Below 7.35
D. Exactly 7.40
,Answer: C. Below 7.35
Explanation: Acidosis is characterized by excessive acidity of body fluids, resulting
in a blood pH below 7.35. This represents an accumulation of hydrogen ions or
loss of bicarbonate.
6. What pH range represents normal blood?
A. 7.25-7.35
B. 7.35-7.45
C. 7.45-7.55
D. 7.55-7.65
Answer: B. 7.35-7.45
Explanation: Normal blood pH is maintained within a narrow range of 7.35 to
7.45. This tight regulation is essential for proper cellular function and enzyme
activity.
7. Alkalosis is characterized by a blood pH:
A. Below 7.35
B. Between 7.35-7.45
C. Above 7.45
D. Exactly 7.40
Answer: C. Above 7.45
Explanation: Alkalosis occurs when there is an excess of base or lack of acids in
body fluids, resulting in a blood pH above 7.45.
8. In compensated respiratory acidosis, which laboratory finding is expected?
A. Low pH, low CO2, low HCO3
B. Normal pH, high CO2, high HCO3
C. High pH, low CO2, low HCO3
D. Normal pH, normal CO2, normal HCO3
, Answer: B. Normal pH, high CO2, high HCO3
Explanation: In compensated respiratory acidosis, the body has partially corrected
the acid-base disturbance. The pH returns to normal, but CO2 remains elevated
(respiratory cause) and HCO3 is elevated (metabolic compensation).
9. Compensated metabolic acidosis is characterized by:
A. Low pH, high CO2, high HCO3
B. Normal pH, low CO2, low HCO3
C. High pH, low CO2, high HCO3
D. Normal pH, high CO2, high HCO3
Answer: B. Normal pH, low CO2, low HCO3
Explanation: In compensated metabolic acidosis, the pH returns to normal. The
HCO3 remains low (metabolic cause) and the CO2 is low (respiratory
compensation through hyperventilation).
10. What is the normal PaCO2 range?
A. 25-35 mmHg
B. 35-45 mmHg
C. 45-55 mmHg
D. 55-65 mmHg
Answer: B. 35-45 mmHg
Explanation: Normal PaCO2 (partial pressure of carbon dioxide) ranges from 35 to
45 mmHg. This parameter reflects respiratory function and carbon dioxide
elimination.
11. The normal bicarbonate (HCO3) level is:
A. 16-20 mEq/L
B. 22-26 mEq/L
