Electrolytes and Body Fluids — MCQs

Electrolytes and Body Fluids Indian Medical PG Practice Questions and MCQs

Question 181: Maximum storage of magnesium occurs in which part of the body?

A. Adipose tissue
B. Skeletal muscles
C. Blood
D. Bone (Correct Answer)

Explanation: ***Bone*** - Approximately **50-60%** of the body's total magnesium is stored in the **bone**, largely in conjunction with calcium and phosphate. - Bone magnesium serves as a **reservoir**, helping to maintain stable extracellular magnesium concentrations. *Adipose tissue* - Adipose tissue has a relatively **low concentration of magnesium** compared to other tissues. - Its primary function is energy storage, not mineral storage. *Skeletal muscles* - While skeletal muscles contain a significant amount of intracellular magnesium, accounting for about **20% of total body magnesium**, it is not the *maximum* storage site. - Magnesium in muscle is crucial for **muscle contraction** and energy metabolism. *Blood* - Only about **1% of total body magnesium** is found in the blood. - Blood magnesium is tightly regulated, with free ionized magnesium being the **physiologically active form**.

Question 182: How is the volume of interstitial fluid calculated in a 50-year-old individual?

A. Total Body Water (TBW) minus the sum of Plasma Volume and Interstitial Fluid Volume.
B. Intracellular Fluid (ICF) volume minus the sum of Plasma Volume and Interstitial Fluid Volume.
C. Extracellular Fluid (ECF) volume minus Plasma Volume (Correct Answer)
D. Total Body Water (TBW) minus Intracellular Fluid (ICF) volume.

Explanation: ***Correct: Extracellular Fluid (ECF) volume minus Plasma Volume*** - The **extracellular fluid (ECF)** compartment includes both interstitial fluid and plasma - **Interstitial Fluid = ECF - Plasma Volume** - This is the standard formula used to calculate interstitial fluid volume - By subtracting plasma volume from total ECF, we isolate the interstitial fluid component *Incorrect: Total Body Water (TBW) minus the sum of Plasma Volume and Interstitial Fluid Volume* - This calculation is incorrect as it attempts to subtract **interstitial fluid** from a component (TBW) that already includes it - The sum of plasma volume and interstitial fluid volume equals **extracellular fluid (ECF) volume** - This formula (TBW - ECF) would actually yield the **intracellular fluid (ICF) volume**, not interstitial fluid *Incorrect: Intracellular Fluid (ICF) volume minus the sum of Plasma Volume and Interstitial Fluid Volume* - This formula subtracts **extracellular fluid (ECF)** components from the **intracellular fluid (ICF)**, which are separate compartments - This would result in a negative or nonsensical value - ICF and ECF are distinct physiological compartments; neither is a subset of the other *Incorrect: Total Body Water (TBW) minus Intracellular Fluid (ICF) volume* - This calculation correctly determines the **extracellular fluid (ECF) volume** (ECF = TBW - ICF) - However, ECF contains both **interstitial fluid** and **plasma** - This formula does not isolate the interstitial fluid volume alone; it gives total ECF

Question 183: What is the most appropriate method for estimating intracellular fluid volume in a 50-year-old male?

A. Estimating from total body water (Correct Answer)
B. D20 for total body water measurement
C. Dilution method for total body water estimation
D. Evans blue for extracellular fluid measurement

Explanation: ***Estimating from total body water*** - **Intracellular fluid (ICF) cannot be directly measured** because there is no tracer that distributes exclusively in the intracellular compartment. - ICF is **calculated indirectly** using the formula: **ICF = TBW - ECF** - **Total body water (TBW)** is measured using tracers like deuterium oxide (D₂O), tritiated water (T₂O), or antipyrine - **Extracellular fluid (ECF)** is measured using tracers like inulin, mannitol, or radioactive compounds - By measuring both TBW and ECF, ICF can be **estimated** by subtraction - Alternatively, ICF can be approximated as **~40% of body weight** or **~2/3 of TBW**, but direct calculation is more accurate *D20 for total body water measurement* - Deuterium oxide (D₂O) measures **total body water only**, not intracellular fluid specifically - While D₂O is essential for the calculation, measuring TBW alone is insufficient to determine ICF - You would still need to measure ECF separately and subtract it from TBW to get ICF *Dilution method for total body water estimation* - This describes the technique for measuring TBW, not the method for estimating ICF - The dilution principle applies to measuring any fluid compartment, but **ICF requires calculation from multiple measurements**, not a single dilution method *Evans blue for extracellular fluid measurement* - Evans blue binds to plasma albumin and measures **plasma volume only**, not ECF - To measure ECF, tracers like inulin, mannitol, or sucrose are used - Even if ECF is measured, you still need TBW to calculate ICF

Question 184: CSF pressure is increased in all except -

A. Valsalva manoeuvre
B. Crying
C. Forced inspiration (Correct Answer)
D. Coughing

Explanation: ***Forced inspiration*** - During forced inspiration, the **intrathoracic pressure** decreases, which can lead to a slight **reduction** in CSF pressure rather than an increase, by increasing venous return from the head. - This creates a negative pressure gradient that facilitates blood flow from the cranial venous sinuses into the thoracic cavity. *Coughing* - Coughing significantly increases **intrathoracic pressure** and **intra-abdominal pressure**, which in turn impede venous return from the head and increase **intracranial venous pressure**, thereby raising CSF pressure. - This pressure transmission causes a transient but marked surge in CSF pressure. *Valsalva manoeuvre* - The **Valsalva manoeuvre** involves forced expiration against a closed glottis, leading to a significant increase in **intrathoracic** and **intra-abdominal pressures**. - This impedes **venous return** to the heart, causing a rise in **central venous pressure** and subsequently **intracranial venous pressure**, which increases CSF pressure. *Crying* - Crying, particularly vigorous crying, involves sustained **muscle contractions** in the face, neck, and chest, leading to an increase in **intrathoracic pressure** and **venous congestion**. - This rise in venous pressure within the head can cause a temporary increase in **CSF pressure**.

Question 185: What is the significance of the Donnan-Gibbs effect in the distribution of ions between intracellular and extracellular fluids?

A. It explains the unequal distribution of diffusible ions due to non-diffusible charged particles (Correct Answer)
B. It causes higher total ion concentration in intracellular fluid
C. It equalizes ion concentrations across all cellular membranes
D. It primarily determines the activity of the sodium-potassium pump

Explanation: ***Correct: It explains the unequal distribution of diffusible ions due to non-diffusible charged particles*** - This is the **most accurate description** of the Donnan-Gibbs effect, where the presence of **non-permeant charged proteins** inside the cell causes an uneven distribution of permeable ions (like Cl⁻) across the membrane. - The effect strives to maintain **electroneutrality** while also influencing water movement due to **osmotic pressure** exerted by the non-diffusible particles. - The Donnan-Gibbs effect is fundamental in understanding **ion distribution** in biological systems, particularly the role of intracellular proteins. *Incorrect: It equalizes ion concentrations across all cellular membranes* - This statement is incorrect as the **Donnan-Gibbs effect** describes the **unequal distribution** of ions, not equalization, due to the presence of impermeant charged molecules. - The effect leads to an **uneven distribution** of diffusible ions to maintain **electroneutrality** and **osmotic balance**. *Incorrect: It causes higher total ion concentration in intracellular fluid* - The Donnan-Gibbs effect, by itself, doesn't necessarily cause a higher *total* ion concentration intracellularly; rather, it dictates the distribution of *specific* ions, maintaining **osmotic equilibrium**. - While it might increase the concentration of some ions, the overall **osmolarity** inside and outside the cell remains balanced, preventing significant water shifts. *Incorrect: It primarily determines the activity of the sodium-potassium pump* - The **sodium-potassium pump** actively transports ions against their concentration gradients, consuming ATP, and thus it works *against* the passive forces described by the Donnan-Gibbs effect. - While the pump helps set up the concentration gradients that the Donnan equilibrium then acts upon, the pump's activity is driven by **ATP hydrolysis**, not directly determined by the Donnan-Gibbs effect.

Question 186: What activity is known to increase lymph drainage from the lower limbs?

A. Cycling
B. Sleeping
C. Massaging
D. Running (Correct Answer)

Explanation: ***Running*** - The muscle contractions during **running** act as a **muscle pump**, significantly increasing the pressure within the lymphatic vessels. - This increased pressure helps propel lymph fluid upwards against gravity, enhancing **lymphatic drainage** from the lower limbs. - **Running** is the most effective activity among the options due to its high-intensity, weight-bearing muscle contractions. *Massaging* - While massage can locally stimulate superficial lymphatic flow, its effect on deep lymphatic drainage from the entire lower limb during sustained activity is less significant than the muscle pumping from running. - The effectiveness of massage for deep lymph drainage often depends on specific techniques and can be temporary. *Cycling* - **Cycling** involves muscle contractions, but the range of motion and intensity in the lower limbs are generally less dynamic and weight-bearing compared to running. - While it offers some lymphatic benefits, the **muscle pump mechanism** may not be as robust or as effective in promoting overall lymph drainage from the entire lower limb as running. *Sleeping* - During **sleeping**, muscle activity is minimal, and the **muscle pump mechanism** is inactive. - Lymph drainage relies primarily on intrinsic lymphatic vessel contractions and respiratory movements, which are less efficient than active muscle contraction for removing fluid from the lower limbs.

Question 187: Which of the following is seen in fresh water drowning?

A. Hypovolemia
B. Hemoconcentration
C. Hyperkalemia (Correct Answer)
D. Hypernatremia

Explanation: ***Hyperkalemia*** - In **freshwater drowning**, water is hypotonic to blood, leading to rapid absorption into the bloodstream. - This causes **hemolysis** due to osmotic effects on red blood cells, releasing intracellular potassium and resulting in **hyperkalemia**. *Hypovolemia* - **Freshwater drowning** typically causes **hypervolemia** due to the rapid absorption of hypotonic fluid into the circulation. - The influx of water increases plasma volume, diluting blood components rather than decreasing total blood volume. *Hemoconcentration* - **Freshwater drowning** leads to **hemodilution**, not hemoconcentration, as hypotonic fluid is absorbed into the bloodstream. - The increased fluid volume reduces the concentration of blood components, such as red blood cells and plasma proteins. *Hypernatremia* - **Freshwater drowning** causes **hyponatremia** because the absorbed hypotonic water dilutes the extracellular fluid. - This reduces the concentration of sodium ions in the blood, leading to a dilutional hyponatremia.

Question 188: Mannitol infusion causes increase in

A. Osmolarity (Correct Answer)
B. Blood viscosity
C. Intraocular pressure
D. Intracranial pressure

Explanation: ***Osmolarity*** - Mannitol is an **osmotic diuretic** that remains in the extracellular space and pulls water from the intracellular space due to its **osmotic effect**. - This increases the **osmolarity of the blood** and tubular fluid. *Blood viscosity* - Mannitol causes water to shift from the intracellular to the extracellular compartment, leading to **hemodilution**, which would decrease, not increase, blood viscosity initially. - While fluid loss through diuresis could ultimately increase viscosity, the immediate effect of mannitol is an increase in plasma volume. *Intraocular pressure* - Mannitol reduces **intraocular pressure** by drawing fluid from the vitreous humor into the blood. - This effect is clinically useful in treating acute angle-closure glaucoma. *Intracranial pressure* - Mannitol significantly **reduces intracranial pressure** by creating an osmotic gradient that draws water from brain tissue into the cerebral circulation. - This is a primary indication for its use in cerebral edema.

Question 189: Which of the following statements about total body water (TBW) is false?

A. In adults, TBW is 60% of body weight
B. ICF is 2/3rd of TBW
C. Premature newborns have more TBW
D. In newborn TBW is 60% of body weight (Correct Answer)

Explanation: ***In newborn TBW is 60% of body weight*** - This statement is **false** because newborns have a significantly higher percentage of total body water, typically ranging from **75-80%** of their body weight. - The proportion of total body water decreases with age, from birth through adulthood, as **fat mass increases** and **muscle mass proportionally decreases**. *ICF is 2/3rd of TBW* - This statement is **true** in adults. The intracellular fluid (ICF) compartment accounts for approximately **2/3** of the total body water. - The remaining **1/3** of TBW is found in the extracellular fluid (ECF) compartment. *Premature newborns have more TBW* - This statement is **true**. Premature newborns have an even higher percentage of TBW, often reaching **80-85%**, compared to full-term newborns. - This higher proportion is due to their relatively lower fat content and less developed regulatory systems. *In adults, TBW is 60% of body weight* - This statement is **true**. In healthy adult males, total body water typically constitutes about **60%** of their body weight. - In adult females this percentage is slightly lower due to a higher proportion of adipose tissue.

Question 190: What is the effect of infusion of hypotonic saline?

A. Increased ICF only
B. Increased ECF only
C. Increased in both ICF and ECF (Correct Answer)
D. Increased ICF and decreased ECF

Explanation: ***Increased in both ICF and ECF*** - Infusion of **hypotonic saline** introduces water and a small amount of electrolytes, which first expand the **extracellular fluid (ECF)** compartment. - Due to the lower osmolality of the hypotonic solution, water then shifts from the ECF into the **intracellular fluid (ICF)** compartment to maintain osmotic equilibrium, leading to an increase in both. *Increased ICF only* - This option incorrectly suggests that the ECF does not increase, which is contrary to the initial effect of infusing any fluid into the vascular space. - The ECF must first expand before any significant shift into the ICF can occur due to changes in osmolality. *Increased ECF only* - This is incorrect because hypotonic solutions cause a decrease in ECF osmolality, leading to a shift of water into the cells (ICF compartment). - An increase in ECF only would typically be seen with **isotonic fluid** administration, where there is no osmotic gradient to drive water into the cells. *Increased ICF and decreased ECF* - This scenario would imply a net loss of water from the ECF into the ICF exceeding the volume of fluid infused, which is not what happens with hypotonic saline infusion. - A decrease in ECF volume would contradict the fact that fluid has been added to the extracellular space.

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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