Electrolytes and Body Fluids — MCQs

Electrolytes and Body Fluids Indian Medical PG Practice Questions and MCQs

Question 211: Which of the following best describes the principal ionic composition of extracellular fluid in the human body?

A. Potassium and phosphate
B. Sodium and chloride (Correct Answer)
C. Calcium and bicarbonate
D. Intracellular and extracellular ion compositions differ significantly, with potassium predominant intracellularly and sodium predominant extracellularly.
E. Magnesium and sulfate

Explanation: ***Sodium and chloride*** **Sodium (Na+)** is the most abundant cation in extracellular fluid (ECF) with a normal range of **135-145 mEq/L**, accounting for approximately **90% of ECF cations**. It is the primary determinant of **ECF osmolality** and plays a crucial role in: - Maintaining fluid balance and blood pressure - Nerve impulse transmission - Muscle contraction **Chloride (Cl-)** is the most abundant anion in ECF with a normal range of **95-105 mEq/L**, comprising about **70% of ECF anions**. Together with sodium, chloride maintains: - Electrical neutrality - Acid-base balance - Proper fluid distribution between compartments *Potassium and phosphate* - **Potassium (K+)** is the principal **intracellular** cation (140 mEq/L inside cells vs only 3.5-5 mEq/L in ECF) - **Phosphate (PO4^3-)** is also predominantly intracellular, with ECF levels around 3-4 mg/dL *Calcium and bicarbonate* - While both are present in ECF, they are not the **principal** ions - **Calcium** (total 8.5-10.5 mg/dL) is important but in much lower concentration than Na+ and Cl- - **Bicarbonate** (22-28 mEq/L) is the second most abundant ECF anion but less than chloride *Magnesium and sulfate* - **Magnesium** (1.5-2.5 mEq/L) is primarily intracellular and present in very low ECF concentrations - **Sulfate** is a minor anion in ECF with concentrations around 1 mEq/L

Question 212: What is the primary mechanism by which corticosteroids affect calcium levels in the body?

A. Decreased absorption from gut (Correct Answer)
B. Increased excretion from kidney
C. No significant effect
D. Decreased plasma calcium level

Explanation: ***Decreased absorption from gut*** - This is the **primary mechanism** by which corticosteroids affect calcium homeostasis - Corticosteroids directly **antagonize vitamin D action** in the intestinal mucosa, reducing calcium absorption - They decrease the expression of **calcium-binding proteins** (calbindins) in the gut - This impaired intestinal absorption is the **predominant mechanism** contributing to corticosteroid-induced hypocalcemia and osteoporosis *Increased excretion from kidney* - While corticosteroids do increase renal calcium excretion by decreasing tubular reabsorption, this is a **secondary mechanism** - The renal effects are less significant than the intestinal absorption defect - This contributes to but is not the primary mechanism of calcium loss *No significant effect* - This is completely incorrect - Corticosteroids have **profound effects on calcium homeostasis**, leading to hypocalcemia and increased risk of osteoporosis - These effects are a major clinical concern in long-term corticosteroid therapy *Decreased plasma calcium level* - This describes the **result** of corticosteroid action, not the mechanism - The question asks for the mechanism by which corticosteroids *affect* calcium levels - Decreased plasma calcium is the consequence of reduced intestinal absorption and increased renal excretion

Question 213: At what age is the extracellular fluid equal to the intracellular fluid?

A. 2 months
B. 3 months
C. 1 year (Correct Answer)
D. 14 days

Explanation: ***1 year*** - At **birth**, the **extracellular fluid (ECF)** is significantly larger than the **intracellular fluid (ICF)**, approximately **45-50% versus 30-35%** of total body weight. - During the **first year of life**, ECF volume **decreases** while ICF volume **increases** until they reach **equilibrium at approximately 1 year of age**, with each constituting about **30-35%** of total body weight. - This represents a critical developmental transition in body fluid compartment maturation. *2 months* - At two months of age, the **ECF** volume is still considerably **larger** than the ICF volume. - The transition towards equal fluid compartments is incomplete at this early stage. *3 months* - At three months, the **ECF** volume remains **higher** than the ICF volume. - The process of fluid compartment redistribution is ongoing but has not yet reached equilibrium. *14 days* - In the **neonatal period** (14 days), the **ECF** volume is at its **highest** relative to the ICF volume. - The infant's body contains a disproportionately large amount of ECF compared to ICF at this stage.

Question 214: Which extracellular fluid is characterized by high potassium and low sodium levels?

A. Synovial fluid
B. CSF
C. Perilymph
D. Endolymph (inner ear fluid) (Correct Answer)

Explanation: ***Endolymph (inner ear fluid)*** - **Endolymph** is unique among extracellular fluids, featuring a very **high potassium concentration** and a **low sodium concentration**, resembling intracellular fluid. - This ionic composition is crucial for the function of hair cells in the **cochlea** and **vestibular system**, enabling sound transduction and balance. *Synovial fluid* - **Synovial fluid** generally has electrolyte concentrations similar to **plasma**, with higher sodium and lower potassium. - Its primary role is **lubrication** and nutrition of articular cartilage, not electrochemical signaling based on potassium gradients. *Perilymph* - **Perilymph** is found in the **scala vestibuli** and **scala tympani** of the cochlea, surrounding the endolymphatic duct. - Its ionic composition is similar to **extracellular fluid** (plasma), characterized by **high sodium** and **low potassium**. *CSF* - **Cerebrospinal fluid (CSF)** has electrolyte concentrations that are generally similar to **plasma**, though slightly different due to the **blood-brain barrier**. - It maintains **homeostasis** of the brain and spinal cord, with **high sodium** and **low potassium** relative to the intracellular environment.

Question 215: Prolonged immobilization leads to?

A. Hypercalcemia due to increased bone resorption (Correct Answer)
B. Hypocalcemia due to altered calcium metabolism
C. Hypokalemia
D. Hyperkalemia

Explanation: ***Hypercalcemia due to increased bone resorption*** - Prolonged **immobilization** reduces mechanical stress on bones, leading to decreased osteoblast activity and increased **osteoclast activity**. - This imbalance results in a net increase in **bone resorption**, releasing calcium into the bloodstream and causing **hypercalcemia**. - This is a well-established complication of prolonged bed rest and is clinically significant in bedridden patients. *Hypocalcemia due to altered calcium metabolism* - **Hypocalcemia** is typically associated with conditions like **hypoparathyroidism**, vitamin D deficiency, or malabsorption. - Immobilization primarily affects **bone turnover** in a way that *increases* serum calcium, rather than decreasing it. - The reduced mechanical loading leads to bone loss, not calcium retention in bones. *Hypokalemia* - **Hypokalemia** (low potassium) is usually caused by conditions like **diuretic use**, gastrointestinal losses, or certain endocrine disorders. - While immobilization can have various systemic effects, it does not directly lead to **hypokalemia**. - Potassium metabolism is distinct from the bone resorption process triggered by immobilization. *Hyperkalemia* - **Hyperkalemia** (high potassium) is often linked to **renal failure**, certain medications (e.g., ACE inhibitors, potassium-sparing diuretics), or massive tissue breakdown. - Immobilization does not typically cause **hyperkalemia** through any direct mechanism. - The primary electrolyte disturbance in immobilization is related to calcium, not potassium.

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

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Fluid Shifts Between Compartments

Practice Questions

Edema Formation Mechanisms

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Dehydration Physiology

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Disorders of Electrolyte Balance

Practice Questions

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