Electrolytes and Body Fluids — MCQs

Electrolytes and Body Fluids Indian Medical PG Practice Questions and MCQs

Question 171: All of the following are true about potassium, except

A. Mostly concentrated inside the cells
B. Leaves the cell in the presence of insulin (Correct Answer)
C. Plasma concentration increases at time of metabolic acidosis
D. Ingestion of acetazolamide results in potassium loss

Explanation: ***Leaves the cell in the presence of insulin*** - Insulin promotes the uptake of **potassium into cells**, primarily by stimulating the Na+/K+-ATPase pump. - Therefore, insulin actually causes potassium to enter the cell, not leave it, which helps to **lower extracellular potassium levels**. *Mostly concentrated inside the cells* - **Potassium (K+)** is the primary intracellular cation, with concentrations approximately 30 times higher inside cells than outside. - This high intracellular concentration is crucial for maintaining **resting membrane potential** and cellular functions. *Plasma concentration increases at time of metabolic acidosis* - In **metabolic acidosis**, hydrogen ions (H+) shift into cells in exchange for potassium ions, which move out of cells into the extracellular fluid. - This H+/K+ exchange mechanism leads to an **increase in plasma potassium concentration**. *Ingestion of acetazolamide results in potassium loss* - **Acetazolamide** is a carbonic anhydrase inhibitor that acts on the proximal tubule of the kidney. - It inhibits bicarbonate reabsorption, leading to increased delivery of sodium and water to the collecting duct, which promotes **potassium secretion and loss**.

Question 172: Which of the following is NOT true about body fluids:

A. Synovial fluid is transcellular fluid (Correct Answer)
B. ECF volume of 70 kg adult man would be approximately 14 L
C. The total body fluid per unit body weight is more in infants as compared to adults
D. Intracellular fluid is 40% of total body weight

Explanation: ***Synovial fluid is transcellular fluid*** - This statement is **NOT true** according to most standard classifications. - **Synovial fluid** is classified as a component of **interstitial fluid**, not transcellular fluid. - **Transcellular fluid** refers to specialized fluids formed by active transport across epithelial membranes and includes cerebrospinal fluid (CSF), pleural fluid, peritoneal fluid, pericardial fluid, and digestive secretions. - Synovial fluid, while specialized, is formed by ultrafiltration of plasma and secretion by synoviocytes, and is considered part of the interstitial compartment. *ECF volume of 70 kg adult man would be approximately 14 L* - This statement is **TRUE**. - **Extracellular fluid (ECF)** constitutes approximately **20% of total body weight** in adult males. - For a **70 kg man**: 20% × 70 kg = **14 kg ≈ 14 L** of ECF. *The total body fluid per unit body weight is more in infants as compared to adults* - This statement is **TRUE**. - **Infants** have approximately **75-80% total body water (TBW)** compared to adults with **50-60% TBW**. - This is due to higher metabolic rate, less fat tissue, and different body composition in infants. *Intracellular fluid is 40% of total body weight* - This statement is **TRUE**. - **Intracellular fluid (ICF)** represents approximately **two-thirds of total body water**, which equals about **40% of total body weight** in adults. - ICF is the largest fluid compartment in the body.

Question 173: Which of the following is not a general compartment of body fluid?

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

Explanation: ***Peritoneal*** - The **peritoneal fluid** is a component of the **extracellular fluid**, but it is not considered one of the *general* body fluid compartments in the typical physiological classification. - General compartments refer to the broad categories of **intracellular** and **extracellular fluid**, with extracellular being further divided into **interstitial fluid** and **blood plasma**. *Blood plasma* - **Blood plasma** is a major component of the **extracellular fluid** compartment, specifically the **intravascular fluid** that circulates within blood vessels. - It is crucial for **transporting nutrients**, waste products, hormones, and blood cells throughout the body. *Interstitial* - **Interstitial fluid** is a part of the **extracellular fluid**, located in the spaces between cells. - It acts as an **interface** between blood plasma and intracellular fluid, facilitating the exchange of substances. *Intracellular* - **Intracellular fluid (ICF)** is the fluid found *inside* cells and constitutes about two-thirds of the total body water. - It is a primary compartment, essential for **cellular metabolism** and maintaining cell volume.

Question 174: Interstitial fluid volume can be determined by:

A. Radioactive iodine and radiolabelled water
B. Radioactive sodium and radioactive water
C. Radioactive sodium and radioactive labelled albumin (Correct Answer)
D. Radioactive water and radiolabelled albumin

Explanation: ***Radioactive sodium and radioactive labelled albumin*** - **Interstitial fluid volume** (ISF) is the difference between **extracellular fluid** (ECF) and **plasma volume**. - **Radioactive sodium** can be used to estimate ECF, and **radioactive labelled albumin** can be used to estimate plasma volume. *Radioactive iodine and radiolabelled water* - **Radioactive iodine** (often as iodide) is used for **extracellular fluid** (ECF) measurement, not directly for ISF alone. - **Radiolabelled water** (e.g., tritiated water) is used to measure **total body water** (TBW), which includes intracellular and extracellular components. *Radioactive sodium and radioactive water* - **Radioactive sodium** is used to measure **extracellular fluid** (ECF) due to its limited entry into cells. - **Radioactive water** (e.g., tritiated water) measures **total body water** (TBW), not specifically interstitial fluid. *Radioactive water and radiolabelled albumin* - **Radioactive water** measures **total body water** (TBW), which encompasses all fluid compartments. - **Radiolabelled albumin** measures **plasma volume** because albumin remains within the vascular space.

Question 175: Osmolality of plasma in a normal adult:

A. 260-270 mOsm/L
B. 280-290 mOsm/L (Correct Answer)
C. 300-310 mOsm/L
D. 320-330 mOsm/L

Explanation: ***280-290 mOsm/L*** - The normal range for **plasma osmolality** in adults is generally accepted to be between 280 and 295 mOsm/L, with 280-290 mOsm/L falling squarely within this range. - This physiological value helps maintain **fluid balance** and cellular integrity throughout the body. *260-270 mOsm/L* - This range is **hypoosmolar**, indicating a lower concentration of solutes in the plasma. - Values in this range would typically suggest **overhydration** or conditions leading to **dilutional hyponatremia**. *300-310 mOsm/L* - This range is slightly to moderately **hyperosmolar**, meaning a higher concentration of solutes. - Values here could indicate **dehydration**, **hyperglycemia**, or other conditions causing increased solute load. *320-330 mOsm/L* - This range represents a significantly **hyperosmolar** state, which is clinically concerning. - Such high osmolality would usually be seen in severe **dehydration**, uncontrolled **diabetes mellitus**, or specific intoxications.

Question 176: In an adult man weighing 70 kg, the Total body water volume will be about -

A. 42L (Correct Answer)
B. 12L
C. 25L
D. 15L

Explanation: ***42L*** - Total body water (TBW) in an adult male is approximately **60% of body weight**. - For a 70 kg man, this calculates to 0.60 * 70 kg = **42 L**. *12L* - This volume is significantly **lower** than the typical total body water volume for an adult man. - 12L would represent around 17% of body weight, which is not physiologically accurate for total body water. *25L* - This value is more representative of the **intracellular fluid (ICF)** volume, which is about 40% of body weight. - It does not account for the total body water, which includes both intracellular and extracellular fluid. *15L* - This volume is generally closer to the **extracellular fluid (ECF)** volume, which is about 20% of body weight. - It significantly underestimates the total body water content of an adult male.

Question 177: A patient with severe dehydration exhibits decreased skin turgor and sunken eyes. What is the primary mechanism responsible for these symptoms?

A. Hypertonic fluid loss
B. Isotonic fluid loss (Correct Answer)
C. Hypotonic fluid gain
D. Hypertonic fluid gain

Explanation: ***Isotonic fluid loss*** - **Severe dehydration** with decreased skin turgor and sunken eyes indicates **significant extracellular fluid (ECF) volume depletion**. - **Isotonic fluid loss** occurs when water and electrolytes are lost in proportional amounts (e.g., from **diarrhea, vomiting, hemorrhage, or burns**). - Loss of ECF leads to **decreased interstitial fluid volume**, causing **decreased skin turgor** (loss of tissue elasticity) and **sunken eyes** (reduced periorbital fluid). - These are classic **physical examination findings** of volume depletion affecting the extracellular compartment. *Hypertonic fluid loss* - Occurs when **water loss exceeds electrolyte loss** (e.g., diabetes insipidus, excessive sweating). - Initially affects the **intracellular compartment** more than ECF, with relatively preserved blood volume. - Primary symptoms include **intense thirst, altered mental status, and hypernatremia**, rather than the prominent ECF depletion signs described. *Hypotonic fluid gain* - Results from **excessive water intake** or hypotonic IV fluids causing **hyponatremia**. - Leads to **cellular swelling**, presenting with confusion, seizures, and cerebral edema. - Would not cause dehydration signs like decreased skin turgor. *Hypertonic fluid gain* - Uncommon scenario involving gain of **hypertonic fluid** (high solute concentration). - Would increase plasma osmolarity and potentially cause **cellular dehydration** with thirst. - Does not cause the **ECF volume depletion** signs seen in this patient.

Question 178: A patient presents with confusion and muscle cramps after running a marathon. His serum sodium level is 125 mEq/L. Which physiological process is primarily responsible for his condition?

A. Increased sodium absorption
B. Increased water retention (Correct Answer)
C. Decreased potassium levels
D. Increased renal excretion of sodium

Explanation: ***Increased water retention*** - The patient's symptoms (confusion, muscle cramps) and a **serum sodium level of 125 mEq/L** indicate **hyponatremia**, most likely **exercise-associated hyponatremia (EAH)**. - In EAH, excessive fluid intake (often hypotonic fluids) during prolonged exercise, coupled with antidiuretic hormone (ADH) release, leads to **dilution of plasma sodium** due to increased water retention. *Increased sodium absorption* - This option would typically lead to **hypernatremia** (high sodium levels), not the **hyponatremia** observed in the patient. - Sodium absorption in the GI tract or kidneys does not directly explain a low serum sodium level in this context. *Decreased potassium levels* - While **hypokalemia** (low potassium) can cause muscle cramps and weakness, it does not directly lead to the **hyponatremia** described. - The primary issue here is the low sodium concentration in the blood, not potassium. *Increased renal excretion of sodium* - While **renal sodium loss** can contribute to hyponatremia due to volume depletion, this patient's presentation after a marathon, especially with confusion and cramps, suggests **dilutional hyponatremia** from water retention. - In EAH, kidneys often retain water rather than actively excrete a significant amount of sodium to cause such a drastic drop.

Question 179: A 55-year-old patient with hypertension is found to have hypernatremia. What is the likely effect on his body fluid compartments?

A. ICF volume increase
B. ECF volume decrease
C. ICF volume decrease (Correct Answer)
D. ECF volume unchanged

Explanation: ***ICF volume decrease*** - **Hypernatremia** increases the **osmolality** of the extracellular fluid (ECF). - Water will move from the intracellular fluid (ICF), where osmolality is lower, to the ECF to re-establish **osmotic equilibrium**, leading to a decrease in ICF volume. *ICF volume increase* - An increase in ICF volume would generally occur with **hyponatremia**, where ECF osmolality is lower than ICF, causing water to move into cells. - This option is incorrect because hypernatremia would draw water out of the cells. *ECF volume decrease* - While fluid shifts occur, hypernatremia usually results in an **increased ECF osmolality**, which can lead to a shift of water from the ICF to the ECF, and thus, the ECF volume may *increase* or remain similar, not decrease, unless there's a significant overall fluid deficit. - **ECF volume decrease** is more commonly associated with conditions like dehydration where both water and sodium are lost. *ECF volume unchanged* - It is unlikely for ECF volume to remain completely unchanged in hypernatremia; the **osmotic shift** of water from the ICF into the ECF directly impacts ECF volume. - The ECF volume tends to **increase** due to the fluid shift from cells, unless accompanied by significant overall body water loss.

Question 180: A patient with severe burns covering 40% of his body surface area presents with hypotension and tachycardia. Which of the following is the most likely cause of his symptoms?

A. Increased systemic vascular resistance
B. Increased plasma protein levels
C. Increased capillary permeability (Correct Answer)
D. Increased cardiac output

Explanation: ***Increased capillary permeability*** - Severe burns cause extensive damage to the **endothelial cells** of capillaries, leading to a significant increase in their **permeability**. - This increased permeability allows **plasma proteins** and fluid to leak out of the intravascular space into the interstitial space, resulting in **hypovolemia**, hypotension, and tachycardia. *Increased systemic vascular resistance* - While initial sympathetic response to shock can cause some vasoconstriction, severe burn shock leads to profound **fluid loss** and **reduced cardiac output**, which would typically lead to a **decrease** in effective systemic vascular resistance due to inadequate vascular filling, not an increase as the primary cause of hypotension. - Increased SVR would generally cause hypertension, not hypotension, unless coupled with severe pump failure, which isn't the primary mechanism in early burn shock. *Increased plasma protein levels* - In severe burns, plasma proteins leak out of the capillaries, leading to a **decrease** in plasma protein levels, especially albumin. - This reduction in plasma oncotic pressure further exacerbates fluid shifts out of the intravascular space. *Increased cardiac output* - Severe burn injury leads to significant **fluid loss** and a large decrease in **preload**, which consequently causes a **decrease** in cardiac output despite compensatory tachycardia. - An increased cardiac output would typically raise blood pressure, not lead to hypotension.

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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