Electrolytes and Body Fluids — MCQs

Electrolytes and Body Fluids Indian Medical PG Practice Questions and MCQs

Question 71: What is the approximate rate of lymph flow in the human body?

A. 10 ml/hr
B. 20 ml/hr
C. 50 ml/hr
D. 120 ml/hr (Correct Answer)

Explanation: **Explanation:** The correct answer is **120 ml/hr**. **1. Understanding the Concept:** Lymph is formed from interstitial fluid that enters the lymphatic capillaries. In a resting human, the total thoracic duct lymph flow is approximately **100 ml per hour**, and an additional **20 ml per hour** flows into the circulation through other channels (like the right lymphatic duct). This brings the total estimated lymph flow to approximately **120 ml/hr**, which equates to roughly **2 to 3 liters per day**. This mechanism is crucial for returning filtered plasma proteins and excess fluid back to the venous circulation to maintain fluid homeostasis. **2. Analysis of Incorrect Options:** * **A (10 ml/hr) & B (20 ml/hr):** These values are far too low. At this rate, the body would fail to return the 2-3 liters of fluid filtered out of the capillaries daily, leading to massive systemic edema. * **C (50 ml/hr):** While higher, this still only accounts for about 1.2 liters per day, which is significantly less than the physiological average required to maintain oncotic and hydrostatic balance. **3. NEET-PG High-Yield Pearls:** * **Factors increasing lymph flow:** Increased capillary hydrostatic pressure, decreased plasma colloid osmotic pressure, increased interstitial fluid protein concentration, and increased capillary permeability. * **The "Lymphatic Pump":** Lymph flow is facilitated by the intrinsic contraction of smooth muscle in the lymphatic vessel walls (distension triggers contraction) and extrinsic compression (skeletal muscle pump). * **Protein Transport:** The lymphatic system is the **only** route by which high-molecular-weight proteins can be returned to the blood from interstitial spaces. * **Fat Absorption:** Remember that long-chain fatty acids are absorbed via lacteals (lymphatics of the small intestine) as chyle.

Question 72: The percentage of body water is greater in which group?

A. Males than in females (Correct Answer)
B. Children than in adults
C. Obese than in lean individuals
D. Old than in young individuals

Explanation: **Explanation:** Total Body Water (TBW) is inversely proportional to body fat content. Adipose tissue is hydrophobic and contains very little water (approx. 10%), whereas lean muscle mass is hydrophilic and contains significant water (approx. 75%). Therefore, individuals with higher muscle mass and lower fat percentages have a higher percentage of TBW. **Why Option A is Correct:** Adult males typically have a higher proportion of lean muscle mass and lower subcutaneous fat compared to adult females (due to the effects of testosterone vs. estrogen). Consequently, TBW is approximately **60%** of body weight in males and **50%** in females. **Analysis of Incorrect Options:** * **B. Children than in adults:** This is actually a factually correct statement (Infants have ~75% TBW). However, in the context of standard NEET-PG MCQ patterns, when comparing gender vs. age, the physiological baseline for "greater" usually refers to the male/female dichotomy unless "Infants" is specifically specified. *Note: If this were a "Multiple Correct" scenario, B would also be true.* * **C. Obese than in lean:** Incorrect. Obese individuals have more adipose tissue (fat), which displaces water, leading to a lower percentage of TBW compared to lean individuals. * **D. Old than in young:** Incorrect. As age increases, muscle mass decreases (sarcopenia) and fat percentage typically increases, leading to a progressive decline in TBW. **Clinical Pearls for NEET-PG:** * **Highest TBW:** Premature infants (~80%) > Term neonates (~70-75%). * **Standard TBW:** 60% (0.6 × body weight). * **Fluid Compartments:** TBW is divided into Intracellular Fluid (ICF = 2/3 or 40% of body weight) and Extracellular Fluid (ECF = 1/3 or 20% of body weight). * **Rule of Thumb:** Fat is "dry," muscle is "wet." Any condition increasing fat decreases the percentage of body water.

Question 73: Transcellular fluids are present in which of the following locations?

A. Body cavities (Correct Answer)
B. Plasma
C. Interstitial space
D. Intranuclear space

Explanation: **Explanation:** Total Body Water (TBW) is divided into two main compartments: Intracellular Fluid (ICF, 2/3rd) and Extracellular Fluid (ECF, 1/3rd). **Transcellular fluid** is a specialized sub-compartment of the ECF. **Why the correct answer is right:** Transcellular fluids are defined as fluids separated from the main ECF by a layer of epithelium. They are found within **body cavities** and epithelial-lined spaces. Examples include cerebrospinal fluid (CSF), intraocular fluid, synovial fluid, pleural fluid, pericardial fluid, peritoneal fluid, and digestive secretions. Although small in volume (approx. 1–2 liters), they play vital physiological roles. **Why the incorrect options are wrong:** * **Plasma:** This is the fluid component of the blood and is a major sub-compartment of the ECF, but it is not transcellular. * **Interstitial space:** This is the fluid bathing the cells (excluding plasma). It is the largest component of the ECF but is distinct from the transcellular compartment. * **Intranuclear space:** This refers to the fluid inside the nucleus, which is part of the Intracellular Fluid (ICF) compartment. **High-Yield Facts for NEET-PG:** * **Volume:** Transcellular fluid accounts for approximately **1–3%** of TBW. * **Composition:** Unlike plasma or interstitial fluid, its composition is highly variable and specialized (e.g., CSF is low in protein). * **Clinical Pearl:** In certain pathological states (e.g., ascites or pleural effusion), transcellular fluid volume can increase significantly, a phenomenon often referred to as "third-spacing."

Question 74: What is the maximum cation concentration in the extracellular fluid (ECF)?

A. K+
B. Ca+2
C. Cl-
D. Na+ (Correct Answer)

Explanation: **Explanation:** The distribution of electrolytes across the cell membrane is governed by the activity of the **Na+-K+ ATPase pump**, which actively pumps sodium out of the cell and potassium into the cell. This creates a distinct chemical gradient between the intracellular fluid (ICF) and the extracellular fluid (ECF). **Why Na+ is the correct answer:** Sodium (Na+) is the **predominant cation** of the ECF. Its normal concentration ranges from **135–145 mEq/L**. Because it is the most abundant solute in the ECF, it is the primary determinant of plasma osmolality and ECF volume. **Analysis of Incorrect Options:** * **K+ (Potassium):** This is the primary **intracellular** cation. Its ECF concentration is very low (3.5–5.0 mEq/L). High ECF potassium (hyperkalemia) is a medical emergency due to its effects on cardiac excitability. * **Ca+2 (Calcium):** While vital for coagulation and muscle contraction, its ECF concentration is tightly regulated at low levels (approx. 8.5–10.5 mg/dL or 2.2–2.6 mmol/L). * **Cl- (Chloride):** This is the most abundant **anion** (not cation) in the ECF, with a concentration of approximately 98–106 mEq/L. **High-Yield Clinical Pearls for NEET-PG:** * **Gibbs-Donnan Effect:** Explains why the concentration of cations is slightly higher in plasma than in interstitial fluid (due to negatively charged plasma proteins). * **Anion Gap:** Calculated using the major ECF ions: $[Na^+] - ([Cl^-] + [HCO_3^-])$. Normal range is 8–12 mEq/L. * **Major ICF Anion:** Phosphate and proteins (not Chloride). * **Osmolality Formula:** $2[Na^+] + \text{Glucose}/18 + \text{BUN}/2.8$. Since Na+ is the major cation, it is doubled to account for accompanying anions.

Question 75: All of the following are found in higher concentrations in CSF compared to plasma, EXCEPT:

A. Mg++
B. Cl-
C. HCO3-
D. Glucose (Correct Answer)

Explanation: The Cerebrospinal Fluid (CSF) is an ultrafiltrate of plasma formed primarily by the choroid plexus. While it is similar to plasma, it is not identical; its composition is strictly regulated by the blood-CSF barrier to maintain an optimal environment for neuronal function. ### **Explanation of the Correct Answer** **D. Glucose:** Glucose levels in the CSF are significantly **lower** than in plasma. In a healthy individual, the CSF glucose concentration is approximately **60-70%** of the simultaneous plasma glucose level (roughly 45–80 mg/dL). This gradient exists because glucose is transported into the CSF via facilitated diffusion (GLUT-1), and the brain actively consumes glucose for metabolism. ### **Analysis of Incorrect Options** * **A. Mg++:** Magnesium concentration is **higher** in the CSF than in plasma. This is essential for regulating NMDA receptor activity and neuronal excitability. * **B. Cl-:** Chloride is the primary anion in the CSF and is maintained at a **higher** concentration (approx. 115–125 mEq/L) compared to plasma (approx. 100 mEq/L) to maintain electrical neutrality. * **C. HCO3-:** While some texts suggest it is similar, physiologically, the CSF is slightly more acidic than plasma (pH ~7.33), and in most physiological states, the concentration of **H+** is higher and **pCO2** is higher in CSF. However, compared to glucose, which is significantly lower, electrolytes like Cl- and Mg++ are classic examples of substances that are higher in CSF. ### **High-Yield Clinical Pearls for NEET-PG** * **Higher in CSF:** Na+, Cl-, Mg++, H+. * **Lower in CSF:** Glucose, Protein (significantly lower), K+, Ca++, Cholesterol, and Urea. * **Clinical Correlation:** A decrease in CSF glucose (**Hypoglycorrhachia**) is a hallmark of **Bacterial Meningitis**, as bacteria and infiltrating white blood cells consume the available glucose. In contrast, viral meningitis typically presents with normal CSF glucose levels.

Question 76: What is the approximate percentage of body water in the human body?

A. 70%
B. 60% (Correct Answer)
C. 50%
D. 40%

Explanation: **Explanation:** The correct answer is **60%**. In a healthy, young adult male (the standard reference), Total Body Water (TBW) constitutes approximately 60% of the total body weight. This is a fundamental physiological constant used to calculate fluid distribution and deficit. **Why 60% is correct:** The "Rule of 60-40-20" is the gold standard for medical exams: * **60%** of body weight is Total Body Water. * **40%** is Intracellular Fluid (ICF). * **20%** is Extracellular Fluid (ECF), which is further divided into Interstitial fluid (15%) and Plasma (5%). **Why other options are incorrect:** * **70%:** This value is seen in infants. Newborns have a higher water content (approx. 75%) due to lower fat stores, which decreases with age. * **50%:** This is the approximate TBW for adult females. Women generally have a higher percentage of subcutaneous adipose tissue; since fat is hydrophobic and contains little water, the overall TBW percentage is lower. * **40%:** This represents the Intracellular Fluid (ICF) compartment, not the total body water. **High-Yield Clinical Pearls for NEET-PG:** 1. **Fat vs. Water:** TBW is inversely proportional to body fat. Therefore, obese individuals have a lower percentage of body water compared to lean individuals. 2. **Aging:** TBW decreases with age as muscle mass (which is water-rich) decreases and fat increases. 3. **Calculation Tip:** To calculate TBW in kilograms (where 1L = 1kg), use the formula: $0.6 \times \text{Body Weight (kg)}$. 4. **Indicator Dilution Method:** Remember that **Tritium** or **Deuterium oxide ($D_2O$)** are used to measure TBW experimentally.

Question 77: What is the reason for increased interstitial fluid?

A. Increase in hydrostatic pressure, increase in oncotic pressure
B. Decrease in hydrostatic pressure, decrease in oncotic pressure
C. Increase in hydrostatic pressure, decrease in oncotic pressure (Correct Answer)
D. Decrease in hydrostatic pressure, increase in oncotic pressure

Explanation: ### Explanation The movement of fluid between the vascular compartment and the interstitium is governed by **Starling’s Forces**. The net filtration pressure is determined by the balance between hydrostatic pressure (which pushes fluid out) and oncotic pressure (which pulls fluid in). **1. Why Option C is Correct:** Increased interstitial fluid (Edema) occurs when the forces favoring filtration exceed the forces favoring reabsorption. * **Increased Capillary Hydrostatic Pressure ($P_c$):** Acts as a "pushing force." When this increases (e.g., in heart failure or venous obstruction), more fluid is forced out of the capillaries into the interstitium. * **Decreased Plasma Oncotic Pressure ($\pi_p$):** Primarily maintained by albumin, this acts as a "pulling force" to keep fluid inside the vessel. A decrease (e.g., in nephrotic syndrome or liver failure) reduces the reabsorptive capacity, leading to fluid accumulation in the tissues. **2. Why Other Options are Incorrect:** * **Option A:** While increased hydrostatic pressure promotes edema, increased oncotic pressure would counteract this by pulling fluid back into the vessel. * **Option B:** Decreased hydrostatic pressure would reduce fluid exit, and decreased oncotic pressure would reduce fluid return; these opposing forces do not inherently guarantee increased interstitial fluid. * **Option D:** This combination (low push, high pull) actually promotes fluid retention within the vascular space and is the opposite of the mechanism for edema. **High-Yield NEET-PG Pearls:** * **Starling Equation:** $Net\ Fluid\ Movement = K_f [(P_c - P_i) - \sigma(\pi_p - \pi_i)]$ * **Common Causes of Edema:** * **$\uparrow$ Hydrostatic Pressure:** Congestive Heart Failure (CHF), Deep Vein Thrombosis (DVT). * **$\downarrow$ Oncotic Pressure:** Kwashiorkor (malnutrition), Cirrhosis (decreased synthesis), Nephrotic Syndrome (increased loss). * **$\uparrow$ Capillary Permeability:** Inflammation, burns, or toxins (increases $K_f$). * **Lymphatic Obstruction:** Lymphedema (e.g., Filariasis or post-mastectomy).

Question 78: Which of the following electrolyte imbalances are seen in a patient with chronic vomiting?

A. Hyponatremia
B. Hypochloremia
C. Hypokalemia
D. All of the above (Correct Answer)

Explanation: Chronic vomiting leads to a complex metabolic state known as **Metabolic Alkalosis with Paradoxical Aciduria**. The development of the electrolyte imbalances mentioned in the options occurs through both direct loss and compensatory mechanisms: 1. **Hypochloremia:** Gastric juice is rich in Hydrochloric acid (HCl). Persistent vomiting leads to the direct loss of chloride ions, making this the primary electrolyte abnormality. 2. **Hyponatremia:** Sodium is lost directly in the vomitus. Furthermore, the resulting volume depletion triggers the release of **ADH (Antidiuretic Hormone)**, which causes water retention, further diluting serum sodium levels. 3. **Hypokalemia:** This occurs via three mechanisms: * Direct loss in gastric juice (minor). * **Secondary Hyperaldosteronism:** Volume depletion activates the RAAS pathway. Aldosterone acts on the distal tubule to reabsorb Na+ and water at the expense of secreting K+ into the urine. * **Bicarbonaturia:** To compensate for alkalosis, the kidney excretes excess HCO3-. Since HCO3- is negatively charged, it "drags" positively charged K+ with it to maintain electrical neutrality. **Why "All of the above" is correct:** Chronic vomiting creates a cycle of volume depletion and acid loss that forces the kidneys to sacrifice sodium, chloride, and potassium to maintain hemodynamic stability and pH balance. **High-Yield Clinical Pearls for NEET-PG:** * **Paradoxical Aciduria:** Despite systemic alkalosis, the urine is acidic because the kidney prioritizes Na+ reabsorption (due to low volume) in exchange for H+ ions when K+ stores are depleted. * **Treatment of Choice:** Isotonic Saline (0.9% NaCl) with Potassium supplementation. Saline corrects the volume deficit and provides chloride, which is essential to stop the renal bicarbonate wasting.

Question 79: Rapid infusion of insulin causes which of the following?

A. Hyperkalemia
B. Hypokalemia (Correct Answer)
C. Hypernatremia
D. Hyponatremia

Explanation: **Explanation:** **Mechanism of Action (Why B is correct):** Insulin is a potent stimulator of the **Na⁺-K⁺ ATPase pump** located on the cell membranes of skeletal muscle and liver cells. When insulin levels rise rapidly, it increases the activity and number of these pumps, leading to an active influx of potassium (K⁺) from the extracellular fluid (ECF) into the intracellular fluid (ICF). This shift results in a rapid decrease in plasma potassium levels, causing **hypokalemia**. **Analysis of Incorrect Options:** * **A. Hyperkalemia:** This is the opposite effect. Hyperkalemia is typically seen in insulin deficiency (e.g., Diabetic Ketoacidosis) because potassium shifts out of the cells. * **C & D. Hypernatremia/Hyponatremia:** While insulin does have some minor effects on renal sodium handling (promoting reabsorption), its primary and most immediate clinical effect during rapid infusion is on potassium distribution. It does not significantly alter serum sodium concentration acutely. **Clinical Pearls for NEET-PG:** 1. **Management of Hyperkalemia:** Because insulin shifts K⁺ into cells, a combination of **Insulin + Dextrose** (to prevent hypoglycemia) is a standard emergency treatment for severe hyperkalemia. 2. **DKA Management:** In Diabetic Ketoacidosis, patients often have high serum K⁺ but low total body K⁺. When treating with insulin, clinicians must monitor K⁺ levels closely, as insulin will drive K⁺ into cells and can precipitate life-threatening hypokalemia. 3. **Other factors shifting K⁺ into cells:** Alkalosis, Beta-2 agonists (e.g., Salbutamol), and Aldosterone.

Question 80: In a 70-Kg adult, what is the approximate volume of intracellular fluid?

A. 5 L
B. 12 L
C. 14 L
D. 28 L (Correct Answer)

Explanation: **Explanation:** The distribution of body fluids follows the **"60-40-20 Rule,"** where Total Body Water (TBW) constitutes approximately 60% of the total body weight. For a standard 70-kg adult: * **Total Body Water (TBW):** 60% of 70 kg = **42 L** * **Intracellular Fluid (ICF):** 2/3 of TBW (or 40% of body weight) = **28 L** * **Extracellular Fluid (ECF):** 1/3 of TBW (or 20% of body weight) = **14 L** **Analysis of Options:** * **Option D (28 L) is Correct:** As calculated above, the ICF makes up the largest compartment of body water, residing within the cell membranes. * **Option C (14 L) is Incorrect:** This represents the **Extracellular Fluid (ECF)** volume (1/3 of TBW). * **Option B (12 L) is Incorrect:** This represents the **Interstitial Fluid** volume (which is 3/4 of the ECF; 0.75 × 14 L ≈ 10.5–12 L). * **Option A (5 L) is Incorrect:** This represents the approximate **Total Blood Volume**. The plasma component alone is only about 3–3.5 L (1/4 of ECF). **High-Yield Clinical Pearls for NEET-PG:** 1. **Indicator Dilution Method:** Remember the substances used to measure compartments: * **TBW:** Tritiated water ($H_3O$), Deuterium oxide ($D_2O$), or Antipyrine. * **ECF:** Inulin (Gold Standard), Mannitol, or Sucrose. * **Plasma Volume:** Evans Blue dye or Radio-iodinated albumin ($I^{131}$-albumin). 2. **ICF Volume Calculation:** ICF cannot be measured directly. It is calculated as: **TBW – ECF**. 3. **Gender/Age Variations:** TBW is lower in females and the elderly due to a higher percentage of adipose tissue (fat is hydrophobic). Conversely, infants have the highest TBW percentage (~75%).

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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