Body Fluid Compartments and Composition — MCQs
Which of the following is true regarding Na+ (sodium) ions?
Major ions in ECF are:
Major portion of body water lies in:
Interstitial fluid volume can be measured by:
The body fluid compartments of a patient were measured, showing the following ion concentrations: - Sodium (Na): $10 \mathrm{mEq} / \mathrm{L}$ - Potassium (K): $140 \mathrm{mEq} / \mathrm{L}$ - Chloride (Cl): $15 \mathrm{mEq} / \mathrm{L}$ Based on these values, which fluid compartment is being described?
Which of the following is NOT true about body fluids:
Intracellular water constitutes what percentage of total body water?
In which of the following conditions is blood osmolality increased?
A patient with diabetes mellitus for the past 5 years presents with vomiting and abdominal pain. She is non-compliant with medication and appears dehydrated. Investigations revealed a blood sugar value of 500 mg/dl and the presence of ketone bodies. What is the next best step in management of this patient?
A man presents with deep burns covering 60% of his body. What is the immediate concern?
Body Fluid Compartments and Composition Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following is true regarding Na+ (sodium) ions?
- A. Does not help other ions in transport
- B. Responsible for depolarization (Correct Answer)
- C. Responsible for the resting membrane potential
- D. Sodium ion is responsible for Donnan effect
Explanation: ***Responsible for depolarization*** - The rapid influx of **Na+ ions** into the cell through voltage-gated sodium channels is the primary event that causes **depolarization** during an action potential. - This influx makes the inside of the cell more positive, shifting the membrane potential from negative toward positive values. *Sodium ion is responsible for Donnan effect* - The **Donnan effect** describes the unequal distribution of permeable ions across a semi-permeable membrane due to the presence of impermeant charged molecules (e.g., proteins). - **Na+ ions are small, permeable ions** - they do not create the Donnan effect. The effect is caused by large, non-diffusible charged molecules like proteins, not by sodium ions. *Does not help other ions in transport* - The **sodium-potassium pump (Na+/K+-ATPase)** actively transports Na+ out of the cell and K+ into the cell, maintaining their concentration gradients. - These Na+ gradients are crucial for **secondary active transport**, where the energy from Na+ moving down its electrochemical gradient is used to move other ions (e.g., in Na+-glucose cotransport) or molecules against their gradients. *Responsible for the resting membrane potential* - The **resting membrane potential** is primarily established by the differential permeability of the membrane to K+ ions and the activity of the Na+/K+-ATPase. - While Na+ leaking into the cell contributes slightly, the dominant factor is the efflux of **K+ ions** through leak channels, as the membrane is much more permeable to K+ than to Na+ at rest.
Question 2: Major ions in ECF are:
- A. Potassium and phosphate
- B. Sodium and phosphate
- C. Potassium and chloride
- D. Sodium and chloride (Correct Answer)
Explanation: ***Sodium and chloride*** - **Sodium (Na+)** is the primary cation, and **chloride (Cl-)** is the primary anion in the extracellular fluid (ECF). - These ions play crucial roles in maintaining **osmotic pressure**, **fluid balance**, and **nerve impulse transmission**. *Potassium and phosphate* - **Potassium (K+)** is the major intracellular cation, while **phosphate (PO43-)** is a major intracellular anion. - While present in the ECF, their concentrations are significantly lower compared to sodium and chloride. *Sodium and phosphate* - **Sodium** is a major ECF cation, but **phosphate** is predominantly an intracellular anion. - Therefore, phosphate is not considered one of the major extracellular ions. *Potassium and chloride* - **Potassium** is primarily an intracellular ion, not a major ECF cation. - While **chloride** is a major ECF anion, its pairing with potassium does not represent the two major ions in the ECF.
Question 3: Major portion of body water lies in:
- A. Extracellular
- B. Interstitial fluid
- C. Intracellular (Correct Answer)
- D. Plasma
Explanation: ***Intracellular*** - Approximately **two-thirds (60%)** of the total body water is located **inside cells** (intracellular fluid, ICF). - In a 70 kg adult male, out of ~42L total body water, approximately **28L is intracellular**. - This fluid is crucial for maintaining **cell volume**, metabolic processes, and overall cell function. - The ICF contains high concentrations of potassium, magnesium, and phosphate. *Extracellular* - The **extracellular fluid (ECF)** compartment accounts for about **one-third (40%)** of the total body water (~14L in a 70 kg adult). - While vital for nutrient and waste transport, it is a smaller volume compared to the intracellular compartment. - ECF is further divided into interstitial fluid (~75% of ECF) and plasma (~25% of ECF). *Interstitial fluid* - Interstitial fluid is a **component of extracellular fluid**, not a major body water compartment on its own. - It accounts for only about **10-11L** in a typical adult, which is less than the intracellular volume. - It surrounds tissue cells and facilitates exchange between plasma and cells. *Plasma* - Plasma is the **smallest fluid compartment**, representing only about **3-3.5L** (~8% of total body water). - While essential for circulation and transport, it contains far less water than the intracellular compartment. - Plasma is the liquid component of blood, excluding cellular elements.
Question 4: Interstitial fluid volume can be measured by:
- A. Tritium oxide - Sodium thiosulfate
- B. Inulin - Serum albumin labelled with radioactive Iodine (Correct Answer)
- C. Inulin - Radioactive sodium
- D. Aminopyrine - Sucrose
Explanation: ***Inulin - Serum albumin labelled with radioactive Iodine*** - The **interstitial fluid volume** is calculated by subtracting the plasma volume from the extracellular fluid volume. - **Inulin** is used to measure **extracellular fluid volume** because it freely distributes throughout the extracellular space but does not enter cells. - **Serum albumin labeled with radioactive iodine** measures **plasma volume** as it stays primarily within the bloodstream due to its large size. *Tritium oxide - Sodium thiosulfate* - **Tritium oxide** (or D2O) is used to measure **total body water (TBW)**, as it distributes throughout all fluid compartments. - **Sodium thiosulfate** is used to measure **extracellular fluid volume**, similar to inulin. *Inulin - Radioactive sodium* - While **inulin** measures **extracellular fluid volume**, **radioactive sodium** (typically 24Na) also measures extracellular fluid volume but can slightly overestimate it due to slow intracellular penetration. - This combination doesn't directly provide a method for exclusively calculating interstitial fluid by subtraction from plasma volume. *Aminopyrine - Sucrose* - **Aminopyrine** is primarily used to measure the **volume of distribution of specific drugs** or gastric acid secretion, not fluid compartments. - **Sucrose** can be used to measure **extracellular fluid volume** as it does not readily cross cell membranes, similar to inulin, but it's not the primary combination for measuring interstitial fluid from the given options.
Question 5: The body fluid compartments of a patient were measured, showing the following ion concentrations: - Sodium (Na): $10 \mathrm{mEq} / \mathrm{L}$ - Potassium (K): $140 \mathrm{mEq} / \mathrm{L}$ - Chloride (Cl): $15 \mathrm{mEq} / \mathrm{L}$ Based on these values, which fluid compartment is being described?
- A. Plasma
- B. ICF (Correct Answer)
- C. Interstitial fluid
- D. ECF
Explanation: ***ICF*** - The measured ion concentrations, especially **high potassium (140 mEq/L)** and **low sodium (10 mEq/L)**, are characteristic of the **intracellular fluid (ICF)**, where potassium is the primary cation and sodium is kept low by the Na+/K+-ATPase pump. - **Chloride levels (15 mEq/L)** are also significantly lower in the ICF compared to extracellular fluids. *Plasma* - Plasma typically has **high sodium (around 140 mEq/L)** and **low potassium (around 4 mEq/L)**, which contradicts the given measurements. - Chloride levels in plasma are usually much higher, around **100-105 mEq/L**. *Interstitial fluid* - Interstitial fluid has an electrolyte composition very similar to plasma, with **high sodium** and **low potassium**, differing mainly in protein content. - This composition is not consistent with the given measurements. *ECF* - The ECF (extracellular fluid), which includes both plasma and interstitial fluid, is characterized by **high sodium** and **low potassium**. - The given ion concentrations, particularly the very **high potassium** and **low sodium**, are directly opposite to the typical ECF profile.
Question 6: 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 7: 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 8: In which of the following conditions is blood osmolality increased?
- A. SIADH
- B. Psychogenic polydipsia
- C. Diarrhea (Correct Answer)
- D. Cerebral toxoplasmosis
Explanation: ***Diarrhea*** - Diarrhea leads to a significant loss of **water and electrolytes** from the body, primarily from the extracellular fluid compartment. - This imbalance causes **hemoconcentration** and an increase in the concentration of solutes in the blood, thereby raising blood osmolality. *SIADH* - **Syndrome of Inappropriate Antidiuretic Hormone (SIADH)** is characterized by excessive secretion of ADH, leading to **dilutional hyponatremia**. - The excess water retention dilutes the blood, resulting in **decreased serum osmolality**. *Psychogenic polydipsia* - This condition involves excessive water intake due to psychological factors, which causes **dilution of body fluids**. - The increased water volume without a proportional increase in solutes leads to **decreased plasma osmolality**. *Cerebral toxoplasmosis* - **Cerebral toxoplasmosis** is an opportunistic infection of the brain, typically seen in immunocompromised individuals. - It primarily causes neurological symptoms and **does not directly impact blood osmolality** unless complicated by other factors like dehydration or SIADH (which is not a primary effect).
Question 9: A patient with diabetes mellitus for the past 5 years presents with vomiting and abdominal pain. She is non-compliant with medication and appears dehydrated. Investigations revealed a blood sugar value of 500 mg/dl and the presence of ketone bodies. What is the next best step in management of this patient?
- A. Intravenous fluids
- B. Intravenous insulin
- C. Intravenous fluids with regular insulin (Correct Answer)
- D. Intravenous fluids with long-acting insulin
Explanation: Detailed management of diabetic ketoacidosis (DKA) requires both fluid resuscitation and insulin therapy. ***Intravenous fluids with regular insulin*** - The patient presents with classic signs of **diabetic ketoacidosis (DKA)**: hyperglycemia (blood sugar 500 mg/dl), ketone bodies, dehydration, and a history of diabetes non-compliance [1]. - Initial management for DKA involves aggressive **intravenous fluid resuscitation** to correct dehydration and then **intravenous regular insulin** to lower blood glucose and resolve ketosis [2]. *Intravenous fluids with long-acting insulin* - While fluids are essential, **long-acting insulin** is not appropriate for the acute management of DKA because its slow onset of action makes it inefficient for rapidly correcting hyperglycemia and ketosis. - **Regular insulin** is preferred as it has a quicker onset and shorter duration, allowing for more precise titration in an acute setting [2]. *Intravenous fluids* - Although crucial for correcting **dehydration** and improving renal perfusion, fluids alone will not address the underlying **insulin deficiency** and **ketosis** that define DKA. - Without insulin, the body will continue to produce ketones, exacerbating acidosis [3]. *Intravenous insulin* - Giving intravenous insulin without prior or concomitant **fluid resuscitation** can be dangerous, as it can worsen **hypovolemia** and potentially lead to circulatory collapse by shifting glucose and potassium into cells. - It is critical to first restore **circulating volume** before initiating insulin therapy [2].
Question 10: A man presents with deep burns covering 60% of his body. What is the immediate concern?
- A. Risk of infection
- B. Shock (Correct Answer)
- C. Potential for organ failure
- D. Development of sepsis
Explanation: ***Shock*** - Due to extensive body surface area involvement (60%), severe burns lead to massive **fluid loss** and a resultant decrease in circulating volume, immediately leading to **hypovolemic shock**. - This fluid shift from the intravascular to the extravascular space occurs rapidly in the initial hours post-burn, making shock the most immediate life-threatening concern. *Risk of infection* - While a significant concern with large burns, **infection** typically becomes a major issue several hours to days after the initial injury, once the immediate threat of shock has been addressed. - The immediate priority is maintaining hemodynamic stability before focusing directly on infection prevention. *Potential for organ failure* - **Organ failure** is a serious complication that can result from prolonged shock and systemic inflammatory response following severe burns. - However, organ failure is a consequence of unmanaged shock rather than an immediate primary concern itself. *Development of sepsis* - **Sepsis** is a life-threatening organ dysfunction caused by a dysregulated host response to infection. It is a later complication, generally developing days after the burn injury. - Sepsis is often triggered by **burn wound infection** and systemic inflammatory response, which occur after the initial hypovolemic phase.
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