FLUID AND ELECTROLYTE IMBALANCES EXAM
ACTUAL QUESTIONS AND ANSWERS|GRADED A+
SECTION 1: FLUID COMPARTMENTS & OSMOLALITY
1. Total body water (TBW) constitutes approximately what percentage of body
weight in an average adult male?
• A) 40%
• B) 50%
• C) 60%
• D) 70%
Correct Answer: C
Rationale: Total body water accounts for approximately 60% of body weight in
adult males (50–55% in females due to higher body fat). It is divided into
intracellular fluid (ICF, ~40% of body weight) and extracellular fluid (ECF, ~20% of
body weight).
2. The intracellular fluid (ICF) compartment contains approximately what
percentage of total body water?
• A) 20%
• B) 33%
• C) 67%
• D) 80%
Correct Answer: C
*Rationale: The ICF contains approximately two-thirds (67%) of total body water.
,The ECF contains the remaining one-third. The ICF is the larger of the two
compartments and is where most cellular metabolic activity occurs.*
3. The primary cation in the intracellular fluid is:
• A) Sodium (Na+)
• B) Potassium (K+)
• C) Calcium (Ca2+)
• D) Magnesium (Mg2+)
Correct Answer: B
*Rationale: Potassium is the primary intracellular cation (approx. 140 mEq/L).
Sodium is the primary extracellular cation. The Na+/K+ ATPase pump maintains
this gradient by actively pumping Na+ out of cells and K+ into cells.*
4. The primary cation in the extracellular fluid is:
• A) Potassium (K+)
• B) Sodium (Na+)
• C) Magnesium (Mg2+)
• D) Calcium (Ca2+)
Correct Answer: B
*Rationale: Sodium is the dominant cation in the ECF (approx. 135–145 mEq/L). It
is the primary determinant of serum osmolality and plays a critical role in fluid
balance, nerve impulse transmission, and muscle contraction.*
5. Serum osmolality is primarily determined by which electrolyte?
• A) Potassium
, • B) Chloride
• C) Sodium
• D) Bicarbonate
Correct Answer: C
*Rationale: Serum osmolality is primarily determined by sodium concentration
(along with glucose and BUN). The formula is: 2(Na+) + Glucose/18 + BUN/2.8.
Sodium is the major extracellular osmole, and changes in sodium are the primary
drivers of osmotic shifts.*
6. The normal range for serum osmolality is:
• A) 240–260 mOsm/kg
• B) 275–295 mOsm/kg
• C) 300–320 mOsm/kg
• D) 350–375 mOsm/kg
Correct Answer: B
*Rationale: Normal serum osmolality is 275–295 mOsm/kg. Values < 275 indicate
hypo-osmolality (usually due to low sodium), and values > 295 indicate
hyperosmolality (usually due to hypernatremia or hyperglycemia).*
7. The term "third spacing" refers to:
• A) Fluid loss through sweating
• B) Fluid accumulation in a body cavity (e.g., pleural space, peritoneal cavity)
that is not easily exchanged with the ECF
• C) Fluid in the intracellular space
• D) Fluid in the vascular space
, Correct Answer: B
Rationale: Third spacing is the accumulation of fluid in a "non-functional" space
such as the pleural cavity (pleural effusion), peritoneal cavity (ascites), or
interstitial space in burns. This fluid is trapped and does not readily exchange with
the circulating blood volume.
8. The primary hormone that regulates sodium and water balance is:
• A) Aldosterone
• B) Antidiuretic hormone (ADH)
• C) Atrial natriuretic peptide (ANP)
• D) Both A and B (aldosterone regulates sodium, ADH regulates water)
Correct Answer: D
Rationale: Aldosterone (from the adrenal cortex) promotes sodium reabsorption
and potassium excretion in the kidneys. ADH (from the posterior pituitary)
promotes water reabsorption in the collecting ducts. Both work together to
maintain fluid and electrolyte balance.
9. Atrial natriuretic peptide (ANP) is released in response to:
• A) Hypovolemia
• B) Atrial stretch (increased blood volume/pressure)
• C) Hyperkalemia
• D) Decreased blood pressure
Correct Answer: B
Rationale: ANP is released from cardiac atrial cells in response to atrial stretch
(increased blood volume or pressure). It promotes sodium and water excretion
(natriuresis and diuresis), reducing blood volume and pressure. It counteracts the
effects of the renin-angiotensin-aldosterone system.
ACTUAL QUESTIONS AND ANSWERS|GRADED A+
SECTION 1: FLUID COMPARTMENTS & OSMOLALITY
1. Total body water (TBW) constitutes approximately what percentage of body
weight in an average adult male?
• A) 40%
• B) 50%
• C) 60%
• D) 70%
Correct Answer: C
Rationale: Total body water accounts for approximately 60% of body weight in
adult males (50–55% in females due to higher body fat). It is divided into
intracellular fluid (ICF, ~40% of body weight) and extracellular fluid (ECF, ~20% of
body weight).
2. The intracellular fluid (ICF) compartment contains approximately what
percentage of total body water?
• A) 20%
• B) 33%
• C) 67%
• D) 80%
Correct Answer: C
*Rationale: The ICF contains approximately two-thirds (67%) of total body water.
,The ECF contains the remaining one-third. The ICF is the larger of the two
compartments and is where most cellular metabolic activity occurs.*
3. The primary cation in the intracellular fluid is:
• A) Sodium (Na+)
• B) Potassium (K+)
• C) Calcium (Ca2+)
• D) Magnesium (Mg2+)
Correct Answer: B
*Rationale: Potassium is the primary intracellular cation (approx. 140 mEq/L).
Sodium is the primary extracellular cation. The Na+/K+ ATPase pump maintains
this gradient by actively pumping Na+ out of cells and K+ into cells.*
4. The primary cation in the extracellular fluid is:
• A) Potassium (K+)
• B) Sodium (Na+)
• C) Magnesium (Mg2+)
• D) Calcium (Ca2+)
Correct Answer: B
*Rationale: Sodium is the dominant cation in the ECF (approx. 135–145 mEq/L). It
is the primary determinant of serum osmolality and plays a critical role in fluid
balance, nerve impulse transmission, and muscle contraction.*
5. Serum osmolality is primarily determined by which electrolyte?
• A) Potassium
, • B) Chloride
• C) Sodium
• D) Bicarbonate
Correct Answer: C
*Rationale: Serum osmolality is primarily determined by sodium concentration
(along with glucose and BUN). The formula is: 2(Na+) + Glucose/18 + BUN/2.8.
Sodium is the major extracellular osmole, and changes in sodium are the primary
drivers of osmotic shifts.*
6. The normal range for serum osmolality is:
• A) 240–260 mOsm/kg
• B) 275–295 mOsm/kg
• C) 300–320 mOsm/kg
• D) 350–375 mOsm/kg
Correct Answer: B
*Rationale: Normal serum osmolality is 275–295 mOsm/kg. Values < 275 indicate
hypo-osmolality (usually due to low sodium), and values > 295 indicate
hyperosmolality (usually due to hypernatremia or hyperglycemia).*
7. The term "third spacing" refers to:
• A) Fluid loss through sweating
• B) Fluid accumulation in a body cavity (e.g., pleural space, peritoneal cavity)
that is not easily exchanged with the ECF
• C) Fluid in the intracellular space
• D) Fluid in the vascular space
, Correct Answer: B
Rationale: Third spacing is the accumulation of fluid in a "non-functional" space
such as the pleural cavity (pleural effusion), peritoneal cavity (ascites), or
interstitial space in burns. This fluid is trapped and does not readily exchange with
the circulating blood volume.
8. The primary hormone that regulates sodium and water balance is:
• A) Aldosterone
• B) Antidiuretic hormone (ADH)
• C) Atrial natriuretic peptide (ANP)
• D) Both A and B (aldosterone regulates sodium, ADH regulates water)
Correct Answer: D
Rationale: Aldosterone (from the adrenal cortex) promotes sodium reabsorption
and potassium excretion in the kidneys. ADH (from the posterior pituitary)
promotes water reabsorption in the collecting ducts. Both work together to
maintain fluid and electrolyte balance.
9. Atrial natriuretic peptide (ANP) is released in response to:
• A) Hypovolemia
• B) Atrial stretch (increased blood volume/pressure)
• C) Hyperkalemia
• D) Decreased blood pressure
Correct Answer: B
Rationale: ANP is released from cardiac atrial cells in response to atrial stretch
(increased blood volume or pressure). It promotes sodium and water excretion
(natriuresis and diuresis), reducing blood volume and pressure. It counteracts the
effects of the renin-angiotensin-aldosterone system.
