Electrolytes and Body Fluids Practice Questions

Q: Which of the following hormones stimulates the uptake of potassium into cells?

Insulin. **Explanation:** The regulation of plasma potassium ($K^+$) is critical for maintaining resting membrane potential. **Insulin** is one of the most potent physiological stimulators of cellular potassium uptake. **1. Why Insulin is Correct:** Insulin stimulates the **$Na^+$-$K^+$ ATPase pump** located in the cell membranes of skeletal muscle, liver, and adipose tissue. By increasing the activity of this pump, insulin promotes the influx of $K^+$ from the extracellular fluid (ECF) into the intracellular fluid (ICF). This occurs independently of its role in glucose transport, although both processes often happen simultaneously. **2. Why Other Options are Incorrect:** * **Glucagon:** Generally has the opposite effect of insulin; it can cause a shift of $K^+$ out of cells (hyperkalemia), particularly in the liver, though its clinical effect is less pronounced than insulin's. * **TSH & FSH:** These are anterior pituitary hormones involved in thyroid regulation and reproductive functions, respectively. They do not have a direct, significant role in acute potassium homeostasis. **3. Clinical Pearls for NEET-PG:** * **Management of Hyperkalemia:** Because insulin shifts $K^+$ into cells, a combination of **Insulin and Dextrose** (to prevent hypoglycemia) is a standard emergency treatment for severe hyperkalemia. * **Other Factors Increasing $K^+$ Uptake:** Besides insulin, **$\beta_2$-adrenergic agonists** (e.g., Salbutamol) and **Aldosterone** also stimulate the $Na^+$-$K^+$ ATPase pump to lower plasma $K^+$. * **Acid-Base Link:** Alkalosis promotes $K^+$ uptake into cells (hypokalemia), while Acidosis causes $K^+$ to shift out of cells (hyperkalemia).

Q: Dye studies were completed on a healthy man of average build to determine the distribution of water in his body. Which range is most likely to represent the percentage of his lean body mass that is intracellular water?

40% to 50%. ### Explanation **Concept Overview:** Total Body Water (TBW) accounts for approximately **60% of the total body weight** in a healthy adult male. This water is distributed into two primary compartments: 1. **Intracellular Fluid (ICF):** Comprises 2/3 (approx. 40%) of total body weight. 2. **Extracellular Fluid (ECF):** Comprises 1/3 (approx. 20%) of total body weight. **Why Option C is Correct:** The question asks for the percentage of **lean body mass** that is **intracellular water**. Since ICF makes up roughly 40% of the total body weight, the range **40% to 50%** is the most accurate representation. In a standard 70 kg man, ICF is about 28 liters (40% of 70). **Analysis of Incorrect Options:** * **Option A (5% to 6%):** This represents the **Plasma volume**, which is a sub-compartment of the ECF (approx. 1/4th of ECF). * **Option B (18% to 20%):** This represents the **Extracellular Fluid (ECF)** volume, not the intracellular volume. * **Option D (60% to 70%):** This represents the **Total Body Water (TBW)** percentage, not the specific intracellular fraction. **High-Yield NEET-PG Pearls:** * **The 60-40-20 Rule:** TBW is 60%, ICF is 40%, and ECF is 20% of body weight. * **Dye Dilution Method (Indicator Dilution Principle):** * **TBW** is measured using Tritiated water ($^3H_2O$), Deuterium oxide ($D_2O$), or Aminopyrine. * **ECF** is measured using Inulin (Gold Standard), Mannitol, or Thiosulfate. * **Plasma Volume** is measured using Evans Blue (T-1824) or Radio-iodinated Albumin ($^{131}I$-Albumin). * **ICF** cannot be measured directly; it is calculated as **TBW – ECF**. * **Variation:** TBW is lower in females and the elderly due to a higher percentage of adipose tissue (fat is hydrophobic). In infants, TBW is highest (approx. 75%).

Q: What is the approximate sucrose space in the body?

14 L. **Explanation:** The correct answer is **14 L** because sucrose is used as a marker to measure the **Extracellular Fluid (ECF) volume**. In a standard 70 kg adult, Total Body Water (TBW) is approximately 60% of body weight (42 L). This is divided into: 1. **Intracellular Fluid (ICF):** 2/3 of TBW (~28 L). 2. **Extracellular Fluid (ECF):** 1/3 of TBW (~14 L). Sucrose, along with substances like inulin and mannitol, is a large saccharide that can freely cross capillary walls but cannot cross the cell membrane. Therefore, it distributes evenly throughout the interstitial fluid and plasma but remains excluded from the cells, making its volume of distribution equal to the ECF. **Analysis of Incorrect Options:** * **A (9 L):** This value does not correspond to a major fluid compartment. However, the interstitial fluid (a sub-component of ECF) is approximately 11 L. * **C (28 L):** This represents the **Intracellular Fluid (ICF)** volume. Markers like potassium or magnesium are found here, but ICF cannot be measured directly by dilution. * **D (40-42 L):** This represents the **Total Body Water (TBW)**. Markers for TBW must be able to cross all membranes (e.g., Tritiated water, Deuterium oxide, or Antipyrine). **High-Yield Clinical Pearls for NEET-PG:** * **Plasma Volume Markers:** Evans Blue dye or Radio-iodinated Serum Albumin (RISA). * **ECF Markers:** Inulin (Gold Standard), Sucrose, Mannitol, and Sodium thiosulfate. * **Formula:** Volume = Amount of substance injected / Concentration in plasma. * **Rule of Threes:** Remember the 60-40-20 rule (60% TBW, 40% ICF, 20% ECF of total body weight).

Q: Which of the following is a true statement regarding extracellular fluid (ECF) and intracellular fluid (ICF)?

ECF has high sodium and low potassium concentration.. **Explanation:** The distribution of electrolytes between fluid compartments is maintained by the **Na+-K+ ATPase pump**, which actively pumps 3 Na+ ions out of the cell and 2 K+ ions into the cell. This creates a distinct chemical gradient: the **Extracellular Fluid (ECF)** is characterized by high concentrations of **Sodium (Na+)**, Chloride (Cl-), and Bicarbonate (HCO3-), while the **Intracellular Fluid (ICF)** is rich in **Potassium (K+)**, Magnesium (Mg2+), and organic phosphates. **Analysis of Options:** * **Option D (Correct):** As per the physiological gradient, ECF sodium is high (~142 mEq/L) and potassium is low (~4 mEq/L). * **Option A:** Incorrect. Potassium is the primary **intracellular** cation (~140 mEq/L). * **Option B:** Incorrect. In a standard 70kg adult, Total Body Water (TBW) is 60% of body weight. Of this, **ICF makes up 2/3 (40%)** and **ECF makes up 1/3 (20%)**. Thus, ICF volume is actually twice that of ECF. * **Option C:** Incorrect. Organic anions (like proteins and organic phosphates) are found in much higher concentrations inside the cell (ICF) compared to the ECF. **High-Yield NEET-PG Pearls:** 1. **Indicator Dilution Method:** Used to measure compartments. * **TBW:** Tritiated water (D2O). * **ECF:** Inulin, Mannitol, or Sucrose. * **Plasma:** Evans Blue dye or Radio-iodinated albumin. 2. **ICF Volume** cannot be measured directly; it is calculated as **TBW minus ECF**. 3. **Interstitial Fluid (ISF)** is calculated as **ECF minus Plasma volume**.

Q: Intracellular and interstitial body fluids have similar:

Total osmotic pressure. **Explanation:** **1. Why Total Osmotic Pressure is Correct:** The cell membrane is highly permeable to water but selectively permeable to solutes. According to the principle of **osmotic equilibrium**, water moves freely between the intracellular fluid (ICF) and the interstitial fluid (ISF) until the concentration of osmotically active particles is equal on both sides. Therefore, the **total osmotic pressure** (approximately 280–300 mOsm/L) is essentially the same in all fluid compartments. If a difference in osmolarity occurs, water shifts rapidly to restore equality. **2. Why Other Options are Incorrect:** * **Colloid Osmotic Pressure (COP):** This is exerted by proteins (mainly albumin). The ICF has a high protein concentration, whereas the ISF has very low protein levels. Thus, COP is significantly higher in the ICF. * **Chloride Ion Concentrations:** Chloride is the primary extracellular anion. Its concentration is high in the ISF (~108 mEq/L) but very low in the ICF (~4–10 mEq/L). * **Potassium Ion Concentrations:** Potassium is the major intracellular cation. Its concentration is high in the ICF (~140 mEq/L) and low in the ISF (~4 mEq/L), maintained by the Na⁺-K⁺ ATPase pump. **High-Yield NEET-PG Pearls:** * **Major Cations:** ICF = Potassium ($K^+$); ECF = Sodium ($Na^+$). * **Major Anions:** ICF = Phosphates and Proteins; ECF = Chloride ($Cl^-$) and Bicarbonate ($HCO_3^-$). * **Gibbs-Donnan Effect:** Explains why plasma has a slightly higher osmotic pressure than interstitial fluid due to non-diffusible plasma proteins. * **Osmolarity vs. Osmolality:** In clinical practice, these are used interchangeably, but osmolality (mOsm/kg) is more accurate as it is independent of temperature.

Q: The use of 5% dextrose as an intravenous resuscitation fluid can lead to which of the following?

Reduce serum osmolality and cause brain edema. **Explanation:** The correct answer is **D. Reduce serum osmolality and cause brain edema.** **Why it is correct:** 5% Dextrose (D5W) is technically isotonic in the bag, but once infused, the glucose is rapidly metabolized by cells. This leaves behind "free water," making the solution functionally **hypotonic**. This free water reduces the serum osmolality, creating an osmotic gradient that shifts water from the intravascular space into the intracellular space. In the brain, this leads to cellular swelling and **cerebral edema**, which can dangerously increase intracranial pressure (ICP). Therefore, D5W is strictly contraindicated as a resuscitation fluid, especially in trauma or head injury patients. **Why the other options are wrong:** * **A & B:** While glucose is the primary fuel for the brain, D5W does not improve perfusion. In fact, by causing cerebral edema, it increases ICP, which *decreases* cerebral perfusion pressure (CPP = MAP - ICP). Furthermore, hyperglycemia during acute brain injury can exacerbate neuronal damage via lactic acidosis. * **C:** This is contradictory. Reducing ICP would require a hypertonic solution (like Mannitol or 3% Saline) to draw water *out* of the brain. D5W does the opposite—it increases ICP by causing edema. **High-Yield Clinical Pearls for NEET-PG:** * **Fluid of Choice for Resuscitation:** Isotonic crystalloids (Ringer’s Lactate or Normal Saline) are preferred as they stay in the extracellular compartment. * **The "Free Water" Rule:** 1 liter of D5W provides roughly 1000ml of free water, whereas 1 liter of Normal Saline provides 0ml. * **Indication for D5W:** It is primarily used to treat hypernatremia (to replace a free water deficit) or to provide calories in a non-stressed patient, but never for volume expansion.

Q: What is the normal serum potassium level?

Below 3.5 mEq/L. **Explanation:** Potassium ($K^+$) is the primary intracellular cation, with approximately 98% of the body's potassium located inside cells. The normal serum potassium range is typically **3.5 to 5.0 mEq/L**. **Why Option A is correct:** In the context of the question asking for the threshold of "normal" levels, **3.5 mEq/L** represents the lower limit of the physiological range. Therefore, a value falling **below 3.5 mEq/L** is clinically defined as **hypokalemia**. Maintaining this narrow range is critical for the resting membrane potential of excitable tissues, particularly the myocardium. **Analysis of Incorrect Options:** * **Option B (4.5 mEq/L):** This is the midpoint of the normal range. Values below 4.5 but above 3.5 are considered normal, not pathological. * **Option C (5.6 mEq/L):** This value exceeds the upper limit (5.0–5.5 mEq/L) and indicates **hyperkalemia**. * **Option D (6.5 mEq/L):** This represents **severe hyperkalemia**, a medical emergency associated with a high risk of cardiac arrest (sine wave pattern on ECG). **High-Yield Clinical Pearls for NEET-PG:** 1. **ECG Changes in Hypokalemia ( 5.5):** **Tall peaked T-waves**, prolonged PR interval, and widening of the QRS complex. 3. **Insulin and Alkalosis:** Both shift potassium from the extracellular fluid (ECF) into the cells, potentially causing hypokalemia. 4. **Aldosterone:** The primary hormone regulating potassium excretion via the principal cells of the distal convoluted tubule and collecting duct.

Question 1

Chronic hypokalemia leads to the development of which of the following?

Accepted Answer

Metabolic alkalosis

Answer

Metabolic acidosis

Answer

Brugada pattern in ECG

Answer

Vasopressin-resistant diabetes insipidus

Question 2

Which of the following hormones stimulates the uptake of potassium into cells?

Accepted Answer

Insulin

Answer

Glucagon

Answer

Thyroid-stimulating hormone (TSH)

Answer

Follicle-stimulating hormone (FSH)

Question 3

Which of the following statements regarding ions in extracellular and intracellular compartments is NOT true?

Accepted Answer

Bicarbonate (HCO3-) is mainly present in intracellular fluid.

Answer

Chloride (Cl-) is the main anion in interstitial fluid.

Answer

Sodium (Na+) is the main cation in plasma.

Answer

Magnesium (Mg2+) is the second major cation present in intracellular fluid after Potassium (K+).

Question 4

The "sickle cell syndrome" is characterized by what electrolyte imbalance?

Accepted Answer

Hyponatremia

Answer

Hypernatremia

Answer

Hypokalemia

Answer

Hyperkalemia

Question 5

Dye studies were completed on a healthy man of average build to determine the distribution of water in his body. Which range is most likely to represent the percentage of his lean body mass that is intracellular water?

Accepted Answer

40% to 50%

Answer

5% to 6%

Answer

18% to 20%

Answer

60% to 70%

Question 6

What is the approximate sucrose space in the body?

Accepted Answer

14 L

Answer

9 L

Answer

28 L

Answer

40 L

Question 7

Which of the following is a true statement regarding extracellular fluid (ECF) and intracellular fluid (ICF)?

Accepted Answer

ECF has high sodium and low potassium concentration.

Answer

ECF is rich in potassium (K+).

Answer

ECF volume is twice that of the ICF.

Answer

ECF is rich in organic anions.

Question 8

Intracellular and interstitial body fluids have similar:

Accepted Answer

Total osmotic pressure

Answer

Colloid osmotic pressure

Answer

Chloride ion concentrations

Answer

Potassium ion concentrations

Question 9

The use of 5% dextrose as an intravenous resuscitation fluid can lead to which of the following?

Accepted Answer

Reduce serum osmolality and cause brain edema

Answer

Improve cerebral perfusion

Answer

Provide glucose substrate for cerebral metabolism

Answer

Reduce intracranial pressure and cause cerebral edema

Question 10

What is the normal serum potassium level?

Accepted Answer

Below 3.5 mEq/L

Answer

Below 4.5 mEq/L

Answer

Below 5.6 mEq/L

Answer

Below 6.5 mEq/L

Electrolytes and Body Fluids — MCQs

Electrolytes and Body Fluids — MCQs

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