Electrolytes and Body Fluids — MCQs

Electrolytes and Body Fluids Indian Medical PG Practice Questions and MCQs

Question 121: Extracellular fluid includes all except?

A. Interstitial fluid
B. Mesenchymal fluid
C. Blood plasma
D. Intracellular fluid (Correct Answer)

Explanation: ### Explanation **Core Concept:** Total Body Water (TBW) is divided into two primary compartments: **Intracellular Fluid (ICF)** and **Extracellular Fluid (ECF)**. The ECF is defined as all body fluid located outside the cells. It is further subdivided into interstitial fluid, plasma, and transcellular fluids. **Why Option D is Correct:** **Intracellular Fluid (ICF)** constitutes approximately 2/3 (40% of body weight) of the TBW. By definition, it is the fluid contained *within* the cell membrane. Therefore, it is the opposite of extracellular fluid and cannot be a part of it. **Why Other Options are Incorrect:** * **A. Interstitial fluid:** This is the fluid that bathes the cells and lies outside the vascular system. It accounts for about 3/4 of the ECF. * **B. Mesenchymal fluid:** This refers to fluid in dense connective tissues (bone, cartilage, and tendons). It is a sub-component of the ECF. * **C. Blood plasma:** This is the non-cellular, liquid component of blood. It accounts for about 1/4 of the ECF. **High-Yield Facts for NEET-PG:** 1. **Transcellular Fluid:** A specialized sub-compartment of ECF (1–2 liters) including CSF, intraocular fluid, synovial fluid, and pleural/peritoneal fluids. 2. **The 60-40-20 Rule:** TBW is 60% of body weight; ICF is 40%; ECF is 20%. 3. **Marker Substances:** * **TBW:** Deuterium oxide ($D_2O$), Tritiated water, Antipyrine. * **ECF:** Inulin (Gold Standard), Mannitol, Sucrose, Thiosulfate. * **Plasma Volume:** Evans Blue dye (T-1824), Radio-iodinated Albumin ($RISA$). 4. **ICF Volume Calculation:** It cannot be measured directly; it is calculated as **TBW – ECF**.

Question 122: What are the major symptoms of hypernatremia?

A. Cardiac
B. Neurologic (Correct Answer)
C. Respiratory
D. Musculoskeletal

Explanation: **Explanation:** The correct answer is **Neurologic**. Hypernatremia is defined as a serum sodium concentration >145 mEq/L. It fundamentally represents a state of **hyperosmolality**. Because sodium is the primary extracellular solute, an increase in its concentration creates an osmotic gradient that pulls water out of the intracellular compartment into the extracellular space. In the brain, this results in **cellular dehydration and neuronal shrinkage**. As the brain cells shrink, mechanical traction on cerebral vessels can lead to intracranial hemorrhages. Clinically, this manifests as altered mental status, irritability, lethargy, seizures, and in severe cases, coma. **Why other options are incorrect:** * **Cardiac:** While severe electrolyte imbalances like hyperkalemia or hypokalemia primarily affect cardiac conduction, hypernatremia’s effect on the heart is minimal compared to its profound impact on the CNS. * **Respiratory:** Respiratory symptoms are rarely primary features of hypernatremia, though they may occur secondary to severe neurological depression (e.g., hypoventilation in coma). * **Musculoskeletal:** While muscle weakness or twitches can occur, they are non-specific and secondary to the neurological dysfunction. **High-Yield Clinical Pearls for NEET-PG:** * **The "Brain-Shrinkage" Rule:** Hypernatremia causes brain shrinkage (risk of hemorrhage); Rapid correction of chronic hypernatremia causes **Cerebral Edema** (due to accumulated idiogenic osmoles). * **Correction Rate:** To avoid cerebral edema, the serum sodium should not be lowered by more than **10–12 mEq/L in 24 hours**. * **Common Cause:** The most common cause in clinical practice is a deficit in free water intake, often seen in elderly patients with impaired thirst mechanisms or patients with Diabetes Insipidus.

Question 123: What is true about hyperkalemia?

A. Causes cardiac arrest in systole
B. Insulin and glucose are administered
C. Serum potassium is greater than 5.2 mmol/L (Correct Answer)
D. ECG changes correlate with serum potassium levels

Explanation: ### Explanation **Correct Option: C (Serum potassium is greater than 5.2 mmol/L)** Hyperkalemia is clinically defined as a serum potassium concentration exceeding the upper limit of the normal range (typically **3.5 to 5.2 mmol/L** or 5.5 mmol/L depending on the laboratory). Potassium is the primary intracellular cation; even minor elevations in the extracellular fluid can significantly alter the resting membrane potential of excitable tissues, particularly the myocardium. **Analysis of Incorrect Options:** * **A. Causes cardiac arrest in systole:** Severe hyperkalemia causes the heart to stop in **diastole**. High extracellular potassium prevents repolarization, leaving the cardiac myocytes in a refractory state. (Note: Calcium causes arrest in systole). * **B. Insulin and glucose are administered:** While this is a standard treatment, the question asks what is "true about hyperkalemia" as a condition. In the context of NEET-PG, if a definition (Option C) is provided alongside a management step, the definition is the more fundamental "truth." Furthermore, insulin/glucose is used to *treat* it, not a characteristic *of* it. * **D. ECG changes correlate with serum potassium levels:** This is a common misconception. While there is a general progression (Tall T waves → PR prolongation → Loss of P wave → Wide QRS → Sine wave), the **correlation is poor**. A patient may have severe hyperkalemia with a normal ECG or sudden V-fib without prior classic changes. **Clinical Pearls for NEET-PG:** * **Earliest ECG change:** Tall, peaked, "tented" T-waves. * **Treatment Priority:** If ECG changes are present, the first step is **Calcium Gluconate** (stabilizes the cardiac membrane) but it does *not* lower potassium levels. * **Potassium Shifters:** Insulin + Dextrose, Beta-2 agonists (Salbutamol), and Sodium Bicarbonate move $K^+$ into cells. * **Pseudohyperkalemia:** Often caused by hemolysis during blood draw or marked leukocytosis/thrombocytosis.

Question 124: Edema occurs when plasma protein level falls below which value?

A. 8 g/dL
B. 2 g/dL
C. 5 g/dL (Correct Answer)
D. 10 g/dL

Explanation: **Explanation:** The formation of edema is governed by **Starling’s Forces**, which regulate fluid exchange between capillaries and the interstitium. The two primary forces are capillary hydrostatic pressure (pushing fluid out) and **plasma colloid osmotic pressure (COP)** (pulling fluid in). **Plasma proteins**, specifically albumin, are the primary determinants of COP. Normal total plasma protein levels range from **6.4 to 8.3 g/dL**. When these levels drop significantly (hypoproteinemia), the COP decreases, allowing fluid to leak into the interstitial space, resulting in edema. Clinically, edema typically manifests when: 1. **Total plasma protein** levels fall below **5 g/dL**. 2. **Albumin** levels fall below **2.5 g/dL**. **Analysis of Options:** * **Option A (8 g/dL):** This is within the normal physiological range; no edema occurs. * **Option B (2 g/dL):** While edema is definitely present at this level, it is a severe state. The threshold for the *onset* of edema is higher (5 g/dL). * **Option C (5 g/dL):** **Correct.** This is the critical threshold where the oncotic pressure can no longer counteract hydrostatic pressure. * **Option D (10 g/dL):** This represents hyperproteinemia (e.g., in Multiple Myeloma), which would actually increase COP and prevent edema. **High-Yield NEET-PG Pearls:** * **Albumin** contributes to about 75–80% of the total plasma COP because of its high concentration and low molecular weight. * Common causes of hypoproteinemic edema include **Nephrotic syndrome** (protein loss), **Cirrhosis** (decreased synthesis), and **Kwashiorkor** (malnutrition). * **Myxedema** (Hypothyroidism) is a "non-pitting" edema caused by the accumulation of mucopolysaccharides, not a drop in plasma proteins.

Question 125: Hyperkalemia can occur in all of the following conditions, except?

A. Insulin deficiency
B. Metabolic acidosis
C. Acute renal failure
D. Cushing's syndrome (Correct Answer)

Explanation: **Explanation:** **Cushing’s syndrome** is characterized by an excess of glucocorticoids (cortisol). At high levels, cortisol exerts a **mineralocorticoid effect**, acting like aldosterone on the principal cells of the renal collecting ducts. This leads to increased sodium reabsorption and enhanced **potassium secretion** into the urine, resulting in **hypokalemia**, not hyperkalemia. **Analysis of Incorrect Options:** * **Insulin deficiency:** Insulin normally stimulates the Na+/K+-ATPase pump, shifting potassium into cells. In conditions like Type 1 Diabetes or DKA, the lack of insulin causes potassium to remain in the extracellular fluid, leading to hyperkalemia. * **Metabolic acidosis:** In states of high H+ concentration, cells buffer the excess acid by taking in H+ ions in exchange for K+ ions (via the H+/K+ exchange mechanism). This shift of potassium from the intracellular to the extracellular compartment causes hyperkalemia. * **Acute renal failure (ARF):** The kidneys are the primary route for potassium excretion. In ARF, a decreased Glomerular Filtration Rate (GFR) and tubular dysfunction lead to the retention of potassium, making it a classic cause of life-threatening hyperkalemia. **High-Yield Clinical Pearls for NEET-PG:** * **Aldosterone's Rule:** High aldosterone (or cortisol) = Low Potassium (Hypokalemia). Low aldosterone (Addison’s disease) = High Potassium (Hyperkalemia). * **ECG in Hyperkalemia:** Look for tall "tented" T-waves, widened QRS complexes, and loss of P-waves. * **Beta-2 Agonists:** Like insulin, salbutamol shifts K+ into cells and is used in the emergency management of hyperkalemia.

Question 126: What percentage of body weight does total body water constitute?

A. 80%
B. 60% (Correct Answer)
C. 33%
D. 25%

Explanation: **Explanation:** Total Body Water (TBW) is a fundamental concept in physiology, representing the sum of water in all fluid compartments. In a healthy, young adult male (the standard physiological model), water constitutes approximately **60% of the total body weight**. This percentage is slightly lower in females (approx. 50%) due to a higher proportion of subcutaneous adipose tissue, which contains very little water. **Breakdown of Options:** * **60% (Correct):** This is the standard physiological value. It follows the **"60-40-20 rule"**: 60% of body weight is TBW, 40% is Intracellular Fluid (ICF), and 20% is Extracellular Fluid (ECF). * **80% (Incorrect):** This value is characteristic of **neonates**. Newborns have a much higher water content (75–80%), which decreases rapidly during the first year of life. * **33% (Incorrect):** This value roughly corresponds to the fraction of TBW that is Extracellular Fluid (1/3 of TBW = 20% of body weight). * **25% (Incorrect):** This does not represent a standard body fluid compartment percentage. **NEET-PG High-Yield Pearls:** 1. **Tissue Variation:** Lean muscle tissue has high water content (approx. 75%), whereas adipose tissue (fat) is hydrophobic and contains only about 10% water. Therefore, obese individuals have a lower percentage of TBW compared to lean individuals. 2. **Aging:** TBW decreases with age as muscle mass declines and fat percentage increases. 3. **Calculation:** For a 70 kg man, TBW is approximately 42 Liters (70 x 0.6). 4. **ECF Sub-divisions:** The 20% ECF is further divided into Interstitial Fluid (15%) and Plasma (5%).

Question 127: Osmolality of plasma is mainly contributed by?

A. Glucose
B. Sodium (Correct Answer)
C. Urea
D. Uric acid

Explanation: **Explanation:** The osmolality of plasma is a measure of the concentration of solutes per kilogram of solvent. In the extracellular fluid (ECF), **Sodium (Na⁺)** is the most abundant cation and, along with its associated anions (primarily chloride and bicarbonate), accounts for approximately **90-95% of the total osmotic pressure** of plasma. The formula for calculated plasma osmolality is: **Calculated Osmolality = 2[Na⁺] + [Glucose]/18 + [BUN]/2.8** **Why the other options are incorrect:** * **Glucose:** While glucose is an active osmole, its contribution is relatively small in healthy individuals (approx. 5-6 mOsm/L) because its concentration is much lower than sodium. It only becomes a major contributor in pathological states like Diabetes Mellitus. * **Urea:** Urea is a "permeable" or "ineffective" osmole because it freely crosses cell membranes. While it contributes to total osmolality, it does not create an osmotic gradient across the cell membrane (tonicity). * **Uric Acid:** Present in very minute quantities in the plasma, its contribution to total plasma osmolality is negligible. **High-Yield Clinical Pearls for NEET-PG:** * **Normal Plasma Osmolality:** 280–295 mOsm/kg. * **Osmolar Gap:** The difference between measured and calculated osmolality. A gap >10 mOsm/kg suggests the presence of unmeasured osmoles (e.g., Ethanol, Methanol, Ethylene glycol). * **Major Intracellular Osmole:** Potassium (K⁺) is the primary determinant of intracellular fluid (ICF) osmolality. * **Plasma Oncotic Pressure:** While sodium determines osmolality, **Albumin** is the primary contributor to oncotic (colloid osmotic) pressure, which keeps fluid inside the capillaries.

Question 128: Dehydration is more severe in infants compared to adults. What is the PRIMARY reason for this increased susceptibility?

A. Total body water in infants is more than in adults (Correct Answer)
B. Intracellular fluid (ICF) is more than extracellular fluid (ECF)
C. Extracellular fluid (ECF) is more than intracellular fluid (ICF)
D. Extracellular fluid equals intracellular fluid

Explanation: ***Total body water in infants is more than in adults*** - Newborn infants have a significantly higher percentage of **Total Body Water (TBW)**, approximately **75-80%** of their body weight, compared to adults (~60%). - This large volume of water, combined with their greater **surface area-to-volume ratio** and higher **metabolic rate**, necessitates rapid fluid turnover, dramatically increasing their risk of severe dehydration. - This is the **primary physiological reason** why infants are more vulnerable to dehydration compared to adults. *Intracellular fluid (ICF) is more than extracellular fluid (ECF)* - This fluid distribution pattern is characteristic of **adults and older children**, not infants. - In young infants, the **ECF** compartment is actually greater than or nearly equal to the **ICF** compartment. - This represents the adult fluid distribution pattern, not the infant pattern. *Extracellular fluid (ECF) is more than intracellular fluid (ICF)* - While this statement is **anatomically true** for newborns (who have a disproportionately large ECF volume), it does not explain the **primary mechanism** of increased dehydration risk. - The ECF:ICF ratio changes with age, but the overall higher **total body water percentage** is the fundamental reason for severe dehydration susceptibility. - This is a characteristic of infant fluid distribution but not the main answer to why dehydration is more severe. *Extracellular fluid equals intracellular fluid* - In normal physiological states, the volume of the **ECF** compartment rarely equals the volume of the **ICF** compartment at any age. - In infants, ECF typically exceeds ICF; in adults, ICF exceeds ECF. - This statement is not accurate for either infants or adults.

Question 129: Which of the following is the principal constituent of serum osmolality?

A. Potassium
B. Sodium (Correct Answer)
C. Bicarbonate
D. Hydrogen ions

Explanation: ***Sodium*** - **Sodium** is the most abundant cation in the extracellular fluid (ECF) and serum, typically present at concentrations of 135-145 mEq/L. - It is the primary determinant of **serum osmolality**, accounting for approximately 90% of the total measured osmoles, along with its accompanying anions. *Potassium* - **Potassium** is the major intracellular cation; its concentration in the serum (ECF) is very low (3.5–5.0 mEq/L). - Due to its low serum concentration, it contributes minimally and is not considered a significant factor in determining overall **serum osmolality**. *Bicarbonate* - Bicarbonate is an anion that contributes to the charge balance, but its plasma concentration (around 22–26 mEq/L) is substantially lower than that of **sodium**. - While included in the calculation of total solutes, it is not the **principal constituent** determining osmolality. *Hydrogen ions* - The concentration of **hydrogen ions** is extremely low (measured in nanomoles per liter, reflecting the pH). - Although crucial for **acid-base homeostasis**, their negligible concentration precludes any meaningful contribution to total **serum osmolality**.

Question 130: In a child with suspected tetany, the following test is performed. Identify the sign?

A. Chvostek sign
B. Allen sign
C. Trousseau sign (Correct Answer)
D. Turner sign

Explanation: ***Trousseau sign*** - The image depicts a blood pressure cuff inflated on the arm, leading to **carpopedal spasm** in the hand, which is characteristic of the **Trousseau sign**. - This sign is indicative of **latent tetany** and is often seen in conditions causing **hypocalcemia**. *Chvostek sign* - The Chvostek sign involves a **facial muscle twitch** elicited by tapping the facial nerve anterior to the ear. - This sign is also associated with hypocalcemia but differs clinically from the presentation in the image. *Allen sign* - The Allen test (not "sign") is performed to assess the **patency of the ulnar and radial arteries** before arterial puncture or cannulation. - It involves digitally compressing both arteries and observing the return of color to the hand after releasing one artery, which is unrelated to the image. *Turner sign* - The Turner sign refers to **flank ecchymosis** (bruising) and is a physical finding associated with **hemorrhagic pancreatitis**. - This sign indicates retroperitoneal bleeding, which is not represented by the image or related to tetany.

Practice by Chapter

Body Fluid Compartments and Composition

Practice Questions

Osmolality and Tonicity

Practice Questions

Sodium and Water Balance

Practice Questions

Potassium Homeostasis

Practice Questions

Calcium and Phosphate Regulation

Practice Questions

Magnesium Metabolism

Practice Questions

Fluid Shifts Between Compartments

Practice Questions

Edema Formation Mechanisms

Practice Questions

Dehydration Physiology

Practice Questions

Disorders of Electrolyte Balance

Practice Questions

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