Electrolytes and Body Fluids Practice Questions

Q: Which of the following is a cause of hyperkalemia?

Exercise. **Explanation:** **Correct Answer: A. Exercise** Hyperkalemia occurs during exercise due to the repeated depolarization of skeletal muscle cells. During an action potential, potassium ($K^+$) exits the cell. In vigorous exercise, the rate of $K^+$ efflux exceeds the capacity of the $Na^+/K^+$-ATPase pump to re-uptake it, leading to a transient increase in extracellular potassium. Additionally, exercise-induced minor cell trauma and local acidosis can further shift $K^+$ out of the cells. **Analysis of Incorrect Options:** * **B. Alkalosis:** In alkalotic states, hydrogen ions ($H^+$) move out of cells to compensate for the high pH. To maintain electroneutrality, $K^+$ moves **into** the cells, resulting in **hypokalemia**. * **C. Insulin injection:** Insulin stimulates the $Na^+/K^+$-ATPase pump in skeletal muscle and liver cells, driving $K^+$ **into** the intracellular compartment. This is why insulin (with glucose) is a standard treatment for acute hyperkalemia. * **D. Decreased serum osmolarity:** Hypertonicity (increased osmolarity) causes water to leave cells via osmosis. This "solvent drag" and the resulting increase in intracellular $K^+$ concentration (which favors diffusion out of the cell) cause hyperkalemia. Conversely, **decreased** osmolarity tends to keep $K^+$ inside the cell. **High-Yield Clinical Pearls for NEET-PG:** * **"ASID" (Acidosis, Sugar/Insulin deficiency, Isotonicity/Hyperosmolarity, Digoxin/Drugs):** Common causes of $K^+$ shifting out of cells. * **Beta-blockers** can cause hyperkalemia, while **Beta-agonists** (like Salbutamol) cause hypokalemia by stimulating the $Na^+/K^+$ pump. * **Pseudohyperkalemia:** Always consider hemolysis during blood collection or extreme leukocytosis/thrombocytosis as a cause of falsely elevated $K^+$ levels.

Q: Cerebrospinal fluid, fluid in the eye, and synovial fluid are examples of which type of fluid?

Transcellular fluid. **Explanation:** The correct answer is **A. Transcellular fluid.** **Why Transcellular Fluid is Correct:** Transcellular fluid is a specialized sub-compartment of the **Extracellular Fluid (ECF)**. It is defined as fluid that is separated from the blood plasma by both a capillary endothelial layer and a layer of **epithelial cells**. These fluids are formed by the active transport activities of cells. Examples include: * **Cerebrospinal fluid (CSF):** Formed by the choroid plexus. * **Intraocular fluid:** Aqueous humor in the eye. * **Synovial fluid:** Found in joint cavities. * **Serous fluids:** Pleural, pericardial, and peritoneal fluids. * **Digestive secretions.** **Why Other Options are Incorrect:** * **B. Extracellular fluid:** While transcellular fluid is technically a part of the ECF, "Transcellular fluid" is the **most specific** and accurate classification for these localized fluids. In NEET-PG, always choose the most specific anatomical/physiological category. * **C. Intracellular fluid (ICF):** This refers to the fluid contained within the cell membranes (approx. 2/3 of total body water). The fluids mentioned in the question exist outside of cells. **NEET-PG High-Yield Pearls:** 1. **Volume:** Transcellular fluid typically accounts for only **1–2%** of total body water (approx. 1–2 Liters). 2. **Composition:** Unlike interstitial fluid, transcellular fluid composition differs significantly from plasma due to the selective barrier of epithelial cells. 3. **Total Body Water (TBW) Rule:** 60-40-20 Rule (60% TBW, 40% ICF, 20% ECF). 4. **Marker for ECF:** Inulin, Mannitol, or Sucrose are used to measure ECF volume.

Q: Hypo-osmotic dehydration is seen in which of the following conditions?

Adrenocortical insufficiency. **Explanation:** To solve questions on body fluid compartments, it is essential to analyze the net change in both **solute (Sodium)** and **solvent (Water)**. **1. Why Adrenocortical Insufficiency is correct:** In conditions like Addison’s disease, there is a deficiency of **Aldosterone**. Aldosterone normally functions to reabsorb Sodium ($Na^+$) and excrete Potassium ($K^+$). Its absence leads to "pathological salt wasting." Since more solute (NaCl) is lost relative to water, the ECF becomes **hypo-osmotic**. To maintain osmotic equilibrium, water shifts from the ECF into the ICF, causing cells to swell. This results in **decreased ECF volume** (dehydration) with **low osmolarity**. **2. Analysis of Incorrect Options:** * **Decreased water intake:** This leads to **Hyper-osmotic dehydration**. Pure water loss increases ECF osmolarity, drawing water out of cells. * **Chronic Renal Failure:** This typically presents with **Isosmotic fluid retention** or complex electrolyte imbalances, but not classic hypo-osmotic dehydration. * **SIADH:** This causes **Hypo-osmotic overhydration** (Hyponatremia). Excessive ADH leads to water retention, increasing ECF volume and diluting osmolarity. It is not a dehydration state. **3. NEET-PG High-Yield Pearls:** * **Isosmotic Dehydration:** Seen in diarrhea, vomiting, or hemorrhage (loss of fluid equal to plasma tonicity). * **Hyper-osmotic Dehydration:** Seen in Diabetes Insipidus, excessive sweating, or simple water deprivation. * **The "Shift" Rule:** Water always moves from a compartment of lower osmolarity to higher osmolarity. In hypo-osmotic dehydration, the ICF volume actually *increases* despite overall body fluid loss.

Q: Each body fluid compartment has different electrolyte concentrations. Which of the following is the most abundant extracellular anion?

Chloride. **Explanation:** The composition of body fluid compartments is a fundamental concept in physiology. The extracellular fluid (ECF) and intracellular fluid (ICF) maintain distinct ionic gradients through the action of selective membrane permeability and active transport pumps (like the Na⁺-K⁺ ATPase). **Why Chloride is Correct:** Chloride (Cl⁻) is the **most abundant extracellular anion**, with a normal plasma concentration of approximately **100–108 mEq/L**. It plays a crucial role in maintaining osmotic pressure and acid-base balance. In the ECF, the high concentration of positive sodium ions is primarily balanced by chloride ions to maintain electrical neutrality. **Analysis of Incorrect Options:** * **B. Bicarbonate (HCO₃⁻):** While it is a major extracellular anion involved in buffering, its concentration is significantly lower (approx. **24–28 mEq/L**) compared to chloride. * **C. Sodium (Na⁺):** Sodium is the most abundant extracellular **cation** (approx. 142 mEq/L), not an anion. * **D. Potassium (K⁺):** Potassium is the most abundant **intracellular cation** (approx. 140 mEq/L). Its extracellular concentration is very low (3.5–5.0 mEq/L). **High-Yield Clinical Pearls for NEET-PG:** * **Most abundant intracellular anion:** Phosphate (followed by proteins). * **Gibbs-Donnan Effect:** Plasma has a slightly higher protein concentration than interstitial fluid; since proteins are negatively charged, plasma chloride levels are slightly lower than interstitial chloride levels to maintain equilibrium. * **Anion Gap:** Calculated as $[Na^+] - ([Cl^-] + [HCO_3^-])$. It represents unmeasured anions (like albumin and phosphates) in the ECF. * **Chloride Shift (Hamburger Phenomenon):** The movement of Cl⁻ into RBCs in exchange for HCO₃⁻ to maintain electrical neutrality during CO₂ transport.

Q: Calculate the plasma osmolality given serum Na+ is 130 mEq/L, glucose is 180 mg/dL, BUN is 56 mg/dL, K+ is 5 mEq/L, and Cl- is 117 mEq/L.

290 mOsm/kg. **Explanation:** The plasma osmolality is calculated using the standard clinical formula, which accounts for the primary solutes contributing to osmotic pressure in the extracellular fluid: **Formula:** $\text{Plasma Osmolality} = 2 \times [\text{Na}^+] + \frac{\text{Glucose}}{18} + \frac{\text{BUN}}{2.8}$ **Calculation:** 1. **Sodium component:** $2 \times 130 = 260$ (Sodium is doubled to account for associated anions like $Cl^-$ and $HCO_3^-$). 2. **Glucose component:** $180 / 18 = 10$ 3. **BUN component:** $56 / 2.8 = 20$ 4. **Total:** $260 + 10 + 20 = \mathbf{290\text{ mOsm/kg}}$ **Why other options are incorrect:** * **Option A (260):** Only accounts for Sodium and its anions, ignoring glucose and urea. * **Option B (270):** Likely misses the BUN contribution or uses an incorrect divisor. * **Option C (280):** Incorrectly calculates the contribution of glucose or urea. * **Note on $K^+$ and $Cl^-$:** These are not added separately in the standard formula. $Cl^-$ is accounted for by doubling the $Na^+$, and $K^+$ is an intracellular cation with negligible impact on plasma osmolality calculations. **High-Yield Clinical Pearls for NEET-PG:** * **Normal Range:** 275–295 mOsm/kg. * **Osmolar Gap:** The difference between measured osmolality (via freezing point depression) and calculated osmolality. A gap **>10 mOsm/L** suggests the presence of unmeasured osmotically active substances (e.g., Ethanol, Methanol, Ethylene glycol). * **Effective Osmolality (Tonicity):** Calculated as $2 \times [Na^+] + \text{Glucose}/18$. Urea is excluded because it is an "ineffective osmole" that freely crosses cell membranes and does not cause water shifts.

Q: Which of the following ions is present in the greatest amount to determine the volume of extracellular fluid?

Na+. **Explanation:** The volume of the **Extracellular Fluid (ECF)** is primarily determined by the total amount of osmotically active solutes it contains. **Sodium (Na+)** is the correct answer because it is the most abundant cation in the ECF (normal range: 135–145 mEq/L). According to the principle of osmosis, "water follows salt." Since sodium and its associated anions (primarily chloride and bicarbonate) account for over 90% of ECF osmolarity, the total body sodium content is the main determinant of ECF volume. **Analysis of Incorrect Options:** * **B. K+ (Potassium):** This is the primary **intracellular** cation. While it determines intracellular fluid (ICF) volume, its ECF concentration is very low (3.5–5.0 mEq/L), making its contribution to ECF volume negligible. * **C. Cl- (Chloride):** Although chloride is the most abundant anion in the ECF, its movement is usually passive and secondary to sodium to maintain electroneutrality. Sodium is considered the primary "driver." * **D. Ca2+ (Calcium):** Calcium is present in very small concentrations in the ECF (8.5–10.5 mg/dL) and functions mainly in cell signaling, bone mineralization, and coagulation rather than volume regulation. **High-Yield Clinical Pearls for NEET-PG:** * **Gibbs-Donnan Effect:** Explains why plasma has a slightly higher protein concentration and different electrolyte distribution than interstitial fluid. * **Osmolarity vs. Tonicity:** Sodium is an "effective osmole" because it does not easily cross cell membranes, thus exerting an osmotic pressure that keeps water in the ECF. * **Clinical Correlation:** Disorders of sodium *concentration* (Hyponatremia/Hypernatremia) usually reflect issues with **water balance**, whereas disorders of total sodium *content* reflect issues with **ECF volume** (Edema or Dehydration).

Question 1

Which of the following is a cause of hyperkalemia?

Accepted Answer

Exercise

Answer

Alkalosis

Answer

Insulin injection

Answer

Decreased serum osmolarity

Question 2

A muscular man weighing 70 kg has a hematocrit of 45%. What would be his plasma volume?

Accepted Answer

2720 ml

Answer

2310 ml

Answer

2695 ml

Answer

2890 ml

Question 3

Cerebrospinal fluid, fluid in the eye, and synovial fluid are examples of which type of fluid?

Accepted Answer

Transcellular fluid

Answer

Extracellular fluid

Answer

Intracellular fluid

Answer

None of the above

Question 4

Hypo-osmotic dehydration is seen in which of the following conditions?

Accepted Answer

Adrenocortical insufficiency

Answer

Decreased water intake

Answer

Chronic renal failure

Answer

Syndrome of inappropriate antidiuretic hormone secretion (SIADH)

Question 5

Each body fluid compartment has different electrolyte concentrations. Which of the following is the most abundant extracellular anion?

Accepted Answer

Chloride

Answer

Bicarbonate

Answer

Sodium

Answer

Potassium

Question 6

Calculate the plasma osmolality given serum Na+ is 130 mEq/L, glucose is 180 mg/dL, BUN is 56 mg/dL, K+ is 5 mEq/L, and Cl- is 117 mEq/L.

Accepted Answer

290 mOsm/kg

Answer

260 mOsm/kg

Answer

270 mOsm/kg

Answer

280 mOsm/kg

Question 7

Which of the following ions is present in the greatest amount to determine the volume of extracellular fluid?

Accepted Answer

Na+

Answer

K+

Answer

Cl-

Answer

Ca2+

Question 8

Hyponatremia results in?

Accepted Answer

Increased secretion of aldosterone

Answer

Increased excretion of potassium

Answer

Increased secretion of ADH

Answer

All of the above

Question 9

Neurological manifestations of water intoxication are all of the following except?

Accepted Answer

Increased risk of intracerebral hemorrhage

Answer

Headache

Answer

Confusion

Answer

Convulsions

Question 10

Hyperosmolar coma is caused by all of the following except?

Accepted Answer

Increased concentration of plasma proteins

Answer

Hyperglycemia

Answer

Uremia

Answer

Increase in plasma sodium concentration

Electrolytes and Body Fluids — MCQs

Electrolytes and Body Fluids — MCQs

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