Electrolytes and Body Fluids Practice Questions

Q: Major cation in ECF

Na+. ***Na+*** - **Sodium (Na+)** is the primary cation found in the **extracellular fluid (ECF)**, playing a crucial role in maintaining **osmotic pressure**, fluid balance, and **nerve and muscle function**. - Its concentration in the ECF is significantly higher than in the intracellular fluid (ICF), a gradient maintained by the **Na+/K+ ATPase pump**. *Ca2+* - **Calcium (Ca2+)** is an important cation, but its concentration in the ECF is considerably lower than sodium's. - While essential for **bone health**, muscle contraction, and **neurotransmitter release**, it does not represent the major cation of the ECF. *K+* - **Potassium (K+)** is the major cation of the **intracellular fluid (ICF)**, not the ECF. - Its primary role is in maintaining **resting membrane potential** and cellular excitability. *Mg2+* - **Magnesium (Mg2+)** is an important cation involved in many enzymatic reactions and **neuromuscular function**, but its concentration in the ECF is much lower than that of sodium. - It is predominantly found within cells and bone.

Q: In intracellular fluid, which of the following has least concentration?

Calcium. ***Calcium*** - The concentration of **free ionized calcium** in the intracellular fluid is kept extremely low (around 0.1 µM) compared to extracellular fluid. - This low intracellular concentration is crucial for its role as a **second messenger** in many cellular processes and is maintained by active transport mechanisms. *Potassium* - **Potassium** is the most abundant intracellular cation, with high concentrations actively maintained inside cells. - It plays a vital role in maintaining **cell volume**, **nerve impulse transmission**, and **muscle contraction**. *Magnesium* - **Magnesium** is also found in relatively high concentrations within the intracellular fluid, second only to potassium among cations. - It is crucial for **enzyme activity**, **ATP metabolism**, and **DNA/RNA synthesis**. *Protein* - **Proteins** are highly concentrated within the intracellular fluid, constituting a large portion of the cell's mass and volume. - They serve diverse functions, including **enzymatic catalysis**, **structural support**, and **transport**, contributing significantly to intracellular osmotic pressure.

Q: Which of the following is the most abundant extracellular ion?

Sodium. ***Sodium*** - **Sodium** is the most abundant extracellular ion with a concentration of approximately **140 mEq/L** in the extracellular fluid - It is the primary **extracellular cation** and plays a crucial role in regulating **extracellular fluid volume**, **osmotic pressure**, and **blood pressure** - Essential for **nerve impulse transmission** and **muscle contraction** *Chloride* - **Chloride** is the most abundant extracellular **anion** with a concentration of approximately **103 mEq/L** - While it is the predominant anion, its absolute concentration is lower than sodium - Important for maintaining **acid-base balance** and **osmotic pressure** *Potassium* - **Potassium** is primarily an **intracellular cation** with extracellular concentration of only **4-5 mEq/L** - Although critical for **nerve and muscle function**, it is not abundant in the extracellular space *Calcium* - **Calcium** has a much lower extracellular concentration of approximately **2.5 mEq/L** (or 5 mg/dL) - Important for **bone formation**, **muscle contraction**, and **blood clotting**, but not the most abundant extracellular ion

Q: 5 g mannitol was injected intravenously. 40% of mannitol is excreted. After equilibrium, plasma concentration of mannitol is 30 mg%. Calculate extracellular fluid volume.

10 L. ***10 L*** - The amount of mannitol retained in the body is 5 g - (40% of 5 g) = 5 g - 2 g = **3 g**. - Extracellular fluid volume (ECFV) is calculated by dividing the retained amount of substance by its plasma concentration: ECFV = 3000 mg / 30 mg/dL = **100 dL = 10 L**. *18 L* - This value would result if a different amount of retained mannitol or plasma concentration were used, not aligning with the given problem's parameters. - It implies either a miscalculation of the retained substance or an incorrect conversion during the volume calculation. *14 L* - This answer would imply a different calculation of the retained mannitol, potentially not accounting for the exact percentage excreted. - It is not consistent with the given dose, excretion percentage, and final plasma concentration. *24 L* - This volume is significantly larger than what would be expected, suggesting a substantial overestimation of the retained substance or an underestimation of the plasma concentration. - Such a large volume for extracellular fluid is physiologically improbable given the parameters.

Q: The concentration of sodium ion in extracellular fluid is ___.

140 mmol/L. ***140 mmol/L*** - This value represents the typical and **normal concentration of sodium ions** ([Na+]) in the **extracellular fluid** (ECF). - Sodium is the **primary cation** determining ECF osmolality and volume. *10 mmol/L* - This concentration is significantly **too low** for extracellular fluid sodium and would indicate severe **hyponatremia**, incompatible with normal physiological function. - Such low levels are more characteristic of **intracellular fluid sodium** concentrations, which are actively maintained at low levels by the Na+/K+-ATPase pump. *25 mmol/L* - This value is also considerably **lower than the normal range** for extracellular sodium, suggesting severe hyponatremia. - It does not reflect the physiological concentration required for maintaining crucial bodily functions like nerve impulse transmission and fluid balance. *100 mmol/L* - While closer to the normal range than 10 or 25 mmol/L, this value is still below the typical physiological concentration of sodium in the ECF. - It would indicate **moderate hyponatremia**, which can have significant clinical consequences.

Q: Organs involved in calcium homeostasis are all except

Lungs. ***Lungs*** - The **lungs** are primarily involved in gas exchange (oxygen and carbon dioxide) and do not play a direct role in the regulation of **calcium homeostasis**. - While other organs contribute to calcium balance through absorption, excretion, or hormone production, the lungs' physiological functions are unrelated to calcium metabolism. *Intestines* - The **intestines**, particularly the small intestine, are crucial for the **absorption of dietary calcium** under the influence of **active vitamin D**. - Without proper intestinal absorption, calcium levels in the body cannot be maintained. *Skin* - The **skin** is essential for the endogenous synthesis of **vitamin D3 (cholecalciferol)** when exposed to ultraviolet B (UVB) radiation. - This **vitamin D3** is then metabolized into active forms that regulate calcium and phosphate levels. *Kidneys* - The **kidneys** play a vital role in calcium homeostasis by **reabsorbing calcium** from the filtrate and excreting excess calcium. - They also hydroxylate calcidiol to form the active hormone **calcitriol** (1,25-dihydroxyvitamin D), which significantly influences calcium levels.

Q: Sodium content of one liter of isotonic saline is:-

154 mEq. ***154 mEq*** - Isotonic saline, also known as **0.9% sodium chloride**, contains 0.9 grams of NaCl per 100 mL, or 9 grams per liter. - To convert grams to mEq, we use the formula: mEq = (weight in mg / molecular weight) * valence. Given that **molecular weight of NaCl is approximately 58.5 g/mol** and its valence is 1, a liter contains (9000 mg / 58.5) * 1 = **153.8 mEq**, which is rounded to 154 mEq. *140 mEq* - This value is close to the normal **physiological range of serum sodium** but does not represent the precise sodium content of isotonic saline. - Using 140 mEq/L would indicate a slightly **hypotonic solution** compared to standard 0.9% saline. *70 mEq* - This value signifies a significantly **hypotonic solution**, which would not be considered isotonic in a clinical context. - Infusing a solution with 70 mEq sodium per liter would lead to **dilutional hyponatremia** and fluid shifts into the intracellular space. *40 mEq* - This is an extremely **hypotonic solution**, far from the sodium concentration of isotonic saline. - A solution with only 40 mEq of sodium per liter would cause severe **fluid and electrolyte disturbances**, including rapid intracellular fluid shifts.

Q: Interstitial fluid volume can be measured by:

Inulin - Serum albumin labelled with radioactive Iodine. ***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.

Q: The effect seen due to decreased serum calcium concentration is

Excitability of muscle. ***Excitability of the muscle*** - A decrease in serum calcium concentration (**hypocalcemia**) reduces the threshold potential for sodium channels, making nerve and muscle cells **more excitable**. - This increased excitability can lead to symptoms like **tetany**, muscle spasms, and even convulsions. *Depression of Nervous system* - This is typically seen with **hypercalcemia** (increased serum calcium), where elevated calcium levels stabilize nerve membranes, making them less excitable. - **Hypocalcemia**, conversely, leads to neuronal hyperexcitability, not depression. *Increase the renal absorption* - Renal calcium reabsorption is primarily regulated by **parathyroid hormone (PTH)**. Low serum calcium stimulates PTH release, which *increases* renal calcium reabsorption to restore calcium levels. - This is a *physiological response* to hypocalcemia, not an *effect* of hypocalcemia on neural or muscular function. *Relaxation of muscle* - Muscle relaxation requires ATP and the re-sequestration of calcium into the sarcoplasmic reticulum, and is not a direct consequence of low extracellular calcium. - Instead, **hypocalcemia** causes increased muscle **contraction** and spasms due to enhanced neuromuscular excitability.

Q: 5 percent dextrose is

Hypotonic. **Hypotonic** - 5% dextrose in water (D5W) is initially **isotonic in the bag**, but once administered intravenously, the **dextrose is rapidly metabolized** by the body's cells. - This leaves behind free water, which acts as a hypotonic solution, causing water to shift from the extracellular space into the cells. *Hypertonic* - A hypertonic solution has a **higher concentration of solutes** than the body's fluids, causing water to move out of the cells. - D5W's effect after metabolism is the opposite, leading to a hypotonic state. *Isotonic* - An isotonic solution has a solute concentration similar to that of the body's fluids, causing no net water movement into or out of cells. - While D5W is isotonic in the bag, its physiological effect after glucose metabolism is **not isotonic**. *Normotonic* - Normotonic is another term for isotonic, meaning it has a normal or equivalent tonicity compared to body fluids. - As explained, D5W acts as a **hypotonic solution** in the body once the dextrose is utilized.

Question 1

Major cation in ECF

Accepted Answer

Na+

Answer

Ca2+

Answer

K+

Answer

Mg2+

Question 2

In intracellular fluid, which of the following has least concentration?

Accepted Answer

Calcium

Answer

Potassium

Answer

Magnesium

Answer

Protein

Question 3

Which of the following is the most abundant extracellular ion?

Accepted Answer

Sodium

Answer

Potassium

Answer

Calcium

Answer

Chloride

Question 4

5 g mannitol was injected intravenously. 40% of mannitol is excreted. After equilibrium, plasma concentration of mannitol is 30 mg%. Calculate extracellular fluid volume.

Accepted Answer

10 L

Answer

18 L

Answer

14 L

Answer

24 L

Question 5

The concentration of sodium ion in extracellular fluid is ___.

Accepted Answer

140 mmol/L

Answer

10 mmol/L

Answer

25 mmol/L

Answer

100 mmol/L

Question 6

Organs involved in calcium homeostasis are all except

Accepted Answer

Lungs

Answer

Intestines

Answer

Skin

Answer

Kidneys

Question 7

Sodium content of one liter of isotonic saline is:-

Accepted Answer

154 mEq

Answer

140 mEq

Answer

70 mEq

Answer

40 mEq

Question 8

Interstitial fluid volume can be measured by:

Accepted Answer

Inulin - Serum albumin labelled with radioactive Iodine

Answer

Tritium oxide - Sodium thiosulfate

Answer

Inulin - Radioactive sodium

Answer

Aminopyrine - Sucrose

Question 9

The effect seen due to decreased serum calcium concentration is

Accepted Answer

Excitability of muscle

Answer

Depression of nervous system

Answer

Increased renal absorption

Answer

Relaxation of muscle

Question 10

5 percent dextrose is

Accepted Answer

Hypotonic

Answer

Hypertonic

Answer

Isotonic

Answer

Normotonic

Electrolytes and Body Fluids — MCQs

Electrolytes and Body Fluids — MCQs

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