Electrolytes and Body Fluids — MCQs

Electrolytes and Body Fluids Indian Medical PG Practice Questions and MCQs

Question 201: Insensible water loss per day is ?

A. 100 ml
B. 1000 ml (Correct Answer)
C. 700 ml
D. 300 ml

Explanation: ***1000 ml*** - **Insensible water loss** occurs through the skin (evaporation) and respiratory tract (exhalation) without conscious perception. - The typical daily insensible water loss in an adult is approximately **800-1000 ml/day**. - **Breakdown**: Skin evaporation (~400-500 ml) + Respiratory tract (~300-400 ml) = **~900-1000 ml total**. - **1000 ml** is the standard value cited in major physiology textbooks (Guyton & Hall, Ganong) and is the most commonly accepted answer for NEET PG examinations. *100 ml* - This value is significantly **lower** than the actual insensible water loss, which occurs continuously throughout the day. - Such a low volume would imply negligible evaporation and respiratory loss, which is not physiologically accurate. *300 ml* - While greater than 100 ml, 300 ml is still **far below** the typical range for daily insensible water loss. - This amount represents only about one-third of the actual insensible losses from the skin and respiratory system combined. *700 ml* - Although this value is sometimes mentioned in literature, it is at the **lower end** of the physiological range. - The more widely accepted standard value for insensible water loss in a healthy adult under normal conditions is **900-1000 ml/day**. - 700 ml would underestimate the normal daily insensible losses.

Question 202: What electrolyte imbalance is commonly associated with laxative abuse?

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

Explanation: ***Hypokalemia*** - Chronic laxative abuse, particularly with stimulant laxatives, can lead to significant **potassium loss** through increased fecal excretion and altered colonic fluid and electrolyte transport. - **Hypokalemia** can manifest with symptoms like muscle weakness, cramps, fatigue, and even cardiac arrhythmias. *Hypomagnesemia* - While laxative abuse can occasionally contribute to **magnesium depletion**, it is not as consistently or significantly associated as potassium loss. - Primarily, **hypomagnesemia** is related to malabsorption syndromes, chronic alcoholism, or certain medications. *Hyponatremia* - **Hyponatremia** is not typically a direct consequence of laxative abuse; rather, it can be associated with excessive fluid intake in an attempt to alleviate constipation or with certain diuretic use. - Laxative abuse primarily causes loss of water and electrolytes from the gut, not a primary dilution of plasma sodium. *Hyperkalemia* - **Hyperkalemia** (high potassium) is the opposite of what occurs with laxative abuse, which causes potassium loss. - It is more commonly associated with kidney failure, certain medications (e.g., ACE inhibitors, potassium-sparing diuretics), or acidosis.

Question 203: Intracellular water constitutes what percentage of total body water?

A. 25%
B. 80%
C. 40%
D. 60% (Correct Answer)

Explanation: ***60%*** - **Intracellular fluid (ICF)** makes up approximately **two-thirds (67%)** of the total body water. - Among the given options, **60% is the closest approximation** to the actual value. - ICF refers to the fluid contained within cells, crucial for mediating cellular reactions and maintaining cell volume. - ICF comprises about **40% of total body weight** (67% of 60% TBW). *40%* - This represents the approximate percentage of **total body weight** that is intracellular water, not the percentage of total body water. - As a proportion of total body water, ICF is much higher (approximately 67%). *25%* - This value is significantly lower than the actual proportion of intracellular water. - No major fluid compartment accounts for 25% of total body water. *80%* - This percentage is much higher than the actual proportion of intracellular water. - An 80% proportion would be physiologically inconsistent with normal fluid distribution between ICF and ECF compartments.

Question 204: Among the following gastrointestinal compartments, maximum K+ concentration is seen in which one?

A. Saliva
B. Colon (Correct Answer)
C. Small intestine
D. Stomach

Explanation: ***Colon*** - The **colon** exhibits the highest potassium (K+) concentration among gastrointestinal compartments, with levels reaching **75-90 mEq/L** in the distal colon. - This high concentration is due to active **K+ secretion**, which is regulated by aldosterone and increases with high dietary K+ intake. - The colonic epithelium actively secretes K+ to maintain systemic electrolyte balance. *Saliva* - **Saliva** has a K+ concentration of approximately **20-30 mEq/L**, which is lower than colonic fluid. - While relatively high compared to plasma (3.5-5 mEq/L), it is still significantly less than the colon. - Its primary functions are lubrication, initial digestion, and buffering. *Small intestine* - The **small intestine** has a relatively low K+ concentration of approximately **5-10 mEq/L**. - It is primarily involved in **K+ absorption**, particularly in the jejunum and ileum. - Net K+ movement is towards absorption rather than secretion. *Stomach* - The **stomach** has a K+ concentration of approximately **10-15 mEq/L**, similar to plasma levels. - Its main function is secretion of **hydrochloric acid (HCl)** for digestion. - K+ handling is not a primary gastric function.

Question 205: What is the typical amount of insensible water loss per day?

A. 600 ml
B. 100 ml
C. 800 ml (Correct Answer)
D. 1000 ml

Explanation: ***800 ml*** - The typical amount of **insensible water loss** per day in an adult is approximately **800-1000 ml**, with **800 ml** being a commonly cited average value. - This loss occurs primarily through the **skin** (~500-600 ml via evaporation) and **respiratory tract** (~300-400 ml via exhaled moist air). - Insensible losses occur **without conscious awareness** and are not visible like sweat or urine. *100 ml* - This amount is **far too low** for daily insensible water loss. - Even in cool, resting conditions, insensible losses are several times higher than this value. - This would not account for the continuous evaporation from skin and respiratory surfaces. *600 ml* - This is **below the typical range** for total daily insensible water loss. - While skin alone may contribute ~500-600 ml, this doesn't account for **respiratory losses** (~300-400 ml). - Total insensible loss is the sum of both skin and respiratory components. *1000 ml* - This represents the **upper end of the normal range** for insensible water loss. - While physiologically accurate in many contexts, **800 ml** is more commonly cited as the **typical average** in standard physiology references. - Actual losses vary with temperature, humidity, activity level, and metabolic rate.

Question 206: All of the following are present in sweat, except which of the following?

A. Calcium
B. Uric acid (Correct Answer)
C. Urea
D. Lactic acid

Explanation: ***Uric acid*** - **Uric acid** is the **best answer** because it is present in sweat in only **trace/negligible amounts** (approximately 20-30 μmol/L), significantly lower than other waste products. - While technically present, its concentration is so minimal that it is often considered clinically insignificant in sweat composition. - The primary excretory routes for uric acid are the **kidneys (urine)** and, to a lesser extent, the gastrointestinal tract. - Among the given options, uric acid has the **lowest concentration** in sweat. *Calcium* - **Calcium** is present in sweat in measurable concentrations (0.2-1.0 mmol/L). - Significant calcium loss can occur through sweating, especially during prolonged physical activity. *Lactic acid* - **Lactate** is present in substantial amounts in sweat (5-25 mmol/L). - Concentration increases significantly during **intense physical activity** due to anaerobic metabolism. - Important for pH buffering and thermoregulation. *Urea* - **Urea** is abundantly present in sweat (5-25 mmol/L). - One of the major waste products in sweat, contributing to its characteristic odor. - Provides an important alternative excretory route, especially relevant in patients with renal impairment.

Question 207: Which ion is considered the chief intracellular ion in the human body?

A. K+ (Correct Answer)
B. Na+
C. Ca2+
D. Mg2+

Explanation: ***K+*** - **Potassium (K+)** is the most abundant cation **within cells**, playing a critical role in cellular function, particularly in nerve impulse transmission and muscle contraction. - Its high intracellular concentration is maintained by the **Na+/K+ ATPase pump**, which actively transports K+ into the cell. *Na+* - **Sodium (Na+)** is the primary cation of the **extracellular fluid**, rather than the intracellular fluid. - It is crucial for maintaining **osmotic pressure**, fluid balance, and electrical potentials across cell membranes. *Ca2+* - **Calcium (Ca2+)** is important for bone formation, muscle contraction, and neurotransmitter release, but its concentration is typically **low within the cytoplasm** of cells. - Most intracellular calcium is stored in organelles like the **endoplasmic reticulum** or mitochondria. *Mg2+* - **Magnesium (Mg2+)** is an important intracellular ion and a cofactor for many enzymes, but it is **not the chief (most abundant)** intracellular ion. - Its concentration is substantially lower than that of potassium within the cell.

Question 208: What percentage of body weight is total body water (TBW) in a one-year-old child?

A. 70% (Correct Answer)
B. 90%
C. 80%
D. 50%

Explanation: ***70%*** - In a one-year-old child, **total body water (TBW)** constitutes approximately **70%** of their body weight. - This represents a decrease from the **75-80%** seen in newborns but remains significantly higher than the **60%** seen in adult males. - This high TBW percentage is crucial for understanding **fluid balance**, **medication dosing**, and **dehydration risk** in pediatric patients. *90%* - This percentage is **too high** for a one-year-old child. - Values around 90% are seen in **extremely premature infants** or the **fetus**. - TBW decreases progressively with age and development. *80%* - This value is typically associated with **full-term newborns** and **young infants (0-3 months)**. - By one year of age, the TBW percentage has declined significantly from the newborn level. *50%* - This percentage represents the TBW found in **adult females**, which is the lowest among all age groups. - A one-year-old child has a much higher proportion of body water compared to adults due to higher metabolic rate and greater extracellular fluid volume.

Question 209: Maximum concentration of plasma calcium exists as

A. Complexed to phosphate
B. Complexed to citrate
C. Bound to plasma albumin
D. Ionized form (Correct Answer)

Explanation: ***Ionized form*** - Approximately **50% of plasma calcium** exists as **free, ionized calcium (Ca2+)**, which is the biologically active form regulating various physiological processes. - This form is not bound to proteins or complexed with organic anions, allowing it to easily interact with target cells and receptors. *Complexed to phosphate* - Only a **small percentage (around 5-10%)** of plasma calcium is complexed with anions like phosphate, citrate, and bicarbonate. - Phosphate complexation is less significant than protein binding or the ionized form in terms of overall plasma calcium concentration. *Complexed to citrate* - **Citrate** also forms complexes with calcium, but like phosphate, this accounts for a minor fraction of total plasma calcium. - While important in specific contexts (e.g., blood storage due to anticoagulant effect), it is not the dominant form in vivo. *Bound to plasma albumin* - Roughly **40-45% of plasma calcium** is bound to plasma proteins, primarily **albumin**. - While a significant fraction, it is still less than the ionized form, which is the functional component that is tightly regulated.

Question 210: QT shortening is associated with which electrolyte imbalance?

A. Hypercalcemia (Correct Answer)
B. Hypokalemia
C. Hypocalcemia
D. Hyperkalemia

Explanation: ***Hypercalcemia*** - **Elevated calcium levels** lead to a shortened **plateau phase of the cardiac action potential**, which manifests as a **shortened QT interval** on an ECG. - This imbalance increases the risk of ventricular arrhythmias, although profound shortening can lead to **QRS widening** with further increase in calcium. *Hypokalemia* - **Low potassium** levels typically cause **QT prolongation**, usually due to prominent U waves and T wave flattening. - It does not cause QT shortening; instead, it is associated with an **increased risk of Torsades de Pointes**. *Hypocalcemia* - **Low calcium** levels cause **QT prolongation** by lengthening the **plateau phase of the cardiac action potential**, increasing the duration of ventricular repolarization. - ECG findings include prolonged ST segment and can increase the risk of arrhythmias, including Torsades de Pointes. *Hyperkalemia* - **High potassium** levels primarily cause **peaked T waves**, a **widened QRS complex**, and a **prolonged PR interval**, potentially leading to asystole or ventricular fibrillation. - It does not cause QT shortening; instead, severe hyperkalemia can lead to **loss of P waves** and a **sine wave pattern**.

Practice by Chapter

Body Fluid Compartments and Composition

Practice Questions

Osmolality and Tonicity

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Sodium and Water Balance

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Potassium Homeostasis

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Calcium and Phosphate Regulation

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Magnesium Metabolism

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Fluid Shifts Between Compartments

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Edema Formation Mechanisms

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Dehydration Physiology

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Disorders of Electrolyte Balance

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