Electrolytes and Body Fluids — MCQs

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?

Q136

What is the normal insensible water loss?

Q137

Which hormone's secretion is primarily stimulated by increased plasma osmolality?

Q138

Normal anion gap is___ mmol/L?

Q139

In which of the following conditions is blood osmolality increased?

Q140

A person working in a hot environment who consumes more water without salt is likely to develop a condition called

Electrolytes and Body Fluids Indian Medical PG Practice Questions and MCQs

Question 131: Good measure of systemic perfusion on ABG is:

A. Bicarbonate
B. Lactate and / or the base deficit (Correct Answer)
C. PCO2
D. pH

Explanation: ***Lactate and / or the base deficit*** - **Lactate** is a direct indicator of **anaerobic metabolism**, which occurs when tissue oxygen supply is insufficient to meet demand, reflecting poor systemic perfusion. - **Base deficit** (or base excess) quantifies the overall metabolic acid-base status and is sensitive to changes in unmeasured anions like lactate, making it a good marker of **tissue hypoperfusion** and metabolic acidosis. *Bicarbonate* - While bicarbonate reflects the body's primary **buffer system**, changes in bicarbonate can be influenced by both respiratory and metabolic processes and thus are not as specific a marker for systemic perfusion as lactate or base deficit. - A low bicarbonate often indicates **metabolic acidosis**, but it doesn't pinpoint the cause as precisely as lactate, which directly reflects anaerobic metabolism. *PCO2* - **PCO2** primarily reflects the **ventilatory status** and respiratory component of acid-base balance. - While extreme changes can indirectly affect perfusion (e.g., hypercapnia leading to vasodilation), it is not a direct or reliable measure of **systemic tissue perfusion**. *pH* - **pH** indicates the overall acid-base balance but is a **composite measure** influenced by both respiratory (PCO2) and metabolic (bicarbonate, lactate) factors. - It does not specifically isolate **perfusion deficits** as clearly as lactate or base deficit, which directly reflect metabolic responses to tissue hypoxia.

Question 132: Which of the following are approximate daily requirements of the common electrolytes in an adult? 1. Sodium 50-90 mM/day 2. Calcium 25-30 mM/day 3. Potassium 90 mM/day 4. Magnesium 15-17 mM/day Select the correct answer using the code given below.

A. 2, 3 and 4
B. 1, 3 and 4 (Correct Answer)
C. 1, 2 and 3
D. 1, 2 and 4

Explanation: ***1, 3 and 4*** - The approximate daily requirements for **sodium** are indeed within the range of **50-90 mM/day** (typical maintenance: 1-2 mEq/kg/day) - **Potassium** is around **90 mM/day** (typical maintenance: 1 mEq/kg/day or ~70 mEq/day) - **Magnesium** is typically **15-17 mM/day** (typical maintenance: 0.2-0.3 mEq/kg/day or ~7-10 mM/day) - These values are essential for maintaining proper physiological functions, including fluid balance, nerve impulse transmission, and muscle contraction *2, 3 and 4* - This option incorrectly includes the daily requirement for **calcium** as **25-30 mM/day**, which is approximately **3-4 times higher** than the typical maintenance requirement - Actual adult calcium requirement is approximately **0.1-0.2 mEq/kg/day** or **3.5-7 mM/day** - While potassium and magnesium values are close to accurate, the calcium value makes this option incorrect *1, 2 and 3* - This option incorrectly states the daily requirement for **calcium** as **25-30 mM/day** - The value of **25-30 mM/day** appears to confuse dietary calcium intake (1000-1200 mg/day ≈ 25-30 mmol) with maintenance electrolyte requirements - Although sodium and potassium requirements are correctly stated, the error in calcium makes this choice incorrect *1, 2 and 4* - This combination is incorrect because it includes the inaccurate daily requirement for **calcium** as **25-30 mM/day** - While sodium and magnesium requirements are generally accurate, the inclusion of the incorrect calcium value (should be ~3.5-7 mM/day) invalidates this option

Question 133: Which one of the following statements regarding Magnesium is NOT true?

A. It is essential for normal metabolism of calcium and potassium
B. Daily requirement of magnesium is estimated to be about 340 mg/day for adults
C. Human adult body contains about 50 g of Magnesium (Correct Answer)
D. It is constituent of bones

Explanation: ***Human adult body contains about 50 g of Magnesium*** - The human adult body contains approximately **21-28 grams** (21000-28000 mg) of magnesium, making 50 grams an overestimation. - While magnesium is an abundant intracellular cation, 50 grams is significantly higher than the average physiological content. *It is essential for normal metabolism of calcium and potassium* - Magnesium plays a crucial role as a **cofactor** in many enzymatic reactions, including those involved in **calcium homeostasis** and **potassium transport** across cell membranes. - Adequate magnesium levels are necessary for the proper functioning of **parathyroid hormone (PTH)**, which regulates calcium and phosphate. *Daily requirement of magnesium is estimated to be about 340 mg/day for adults* - The recommended daily allowance (RDA) for magnesium in adult men is typically around **400-420 mg**, and for adult women, it's roughly **310-320 mg**. - A general estimate of 340 mg/day falls within the typical range of recommended daily intake for adults to maintain optimal health. *It is constituent of bones* - Approximately **50-60% of the body's total magnesium** is stored in the bones, contributing to their structural integrity. - It is present on the surface of **bone crystals** and plays an important role in bone metabolism and bone mineral density.

Question 134: A young patient presents with muscle spasms, numbness in the hands and feet, seizures, and difficulty in breathing due to laryngospasm. His blood work reveals an electrolyte imbalance. What is the most likely cause of these manifestations?

A. Respiratory Alkalosis (Correct Answer)
B. Metabolic Alkalosis
C. Respiratory Acidosis
D. Metabolic Acidosis

Explanation: ***Respiratory Alkalosis*** - **Hyperventilation** (the likely underlying cause) leads to decreased partial pressure of carbon dioxide (**PCO2**), causing an increase in pH and **respiratory alkalosis**. - This **alkalosis** decreases **ionized calcium** levels by increasing calcium binding to albumin, leading to **hypocalcemia**. - **Hypocalcemia** causes increased neuromuscular excitability, resulting in **muscle spasms, numbness** (paresthesias), **seizures**, and **laryngospasm** (difficulty breathing). - This is the classic presentation of **hypocalcemic tetany** secondary to respiratory alkalosis. *Metabolic Alkalosis* - This imbalance is primarily characterized by an increase in **bicarbonate (HCO3-)** concentration, often due to **vomiting** or diuretic use. - While it can also cause alkalosis leading to **hypocalcemia** and similar neurological symptoms, the acute and severe presentation with prominent tetany and laryngospasm is more characteristic of **respiratory alkalosis**. - Metabolic alkalosis typically has a more gradual onset. *Respiratory Acidosis* - Caused by **hypoventilation**, leading to an increase in **PCO2** and a decrease in pH (acidosis). - **Acidosis increases ionized calcium**, so this would not cause hypocalcemic symptoms. - This condition typically manifests as **somnolence, confusion**, or CNS depression, not the neuromuscular excitability seen in this patient. *Metabolic Acidosis* - Characterized by a decrease in **bicarbonate (HCO3-)** and a decrease in pH, often due to conditions like **diabetic ketoacidosis** or **renal failure**. - **Acidosis increases ionized calcium**, making hypocalcemic tetany unlikely. - Symptoms usually include **Kussmaul breathing** (compensatory hyperventilation) and potential cardiac arrhythmias, which do not match this patient's presentation of tetany and laryngospasm.

Question 135: 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 136: What is the normal insensible water loss?

A. 150 mL/hour
B. 50 mL/hour (Correct Answer)
C. 200 mL/hour
D. 100 mL/hour

Explanation: ***50 mL/hour*** - **Insensible water loss** occurs primarily through the **skin** and **respiratory tract** and typically amounts to approximately 1200 mL per day in an adult. - Dividing 1200 mL by 24 hours yields an average of **50 mL/hour**, representing normal physiological fluid loss not readily measurable. *150 mL/hour* - This value represents a significantly **elevated rate** of insensible water loss, which would suggest a patient experiencing **fever**, **tachypnea**, or a **hot environment**. - A sustained loss at this rate would quickly lead to **dehydration** if not compensated for by increased fluid intake. *200 mL/hour* - This is an **extreme rate** of water loss, indicating a severe condition such as **severe burns** affecting a large body surface area, **heat stroke**, or profound **hyperventilation**. - Such a high rate of fluid loss would be a medical emergency requiring aggressive fluid resuscitation. *100 mL/hour* - This rate of insensible water loss is **double the normal physiological rate** and, while not as extreme as 150 or 200 mL/hour, still implies increased metabolic activity or environmental stress. - It could be seen in individuals with moderate fever, increased physical activity, or in warmer ambient temperatures, and could contribute to mild dehydration over time.

Question 137: Which hormone's secretion is primarily stimulated by increased plasma osmolality?

A. EPO
B. PTH
C. ADH (Correct Answer)
D. Aldosterone
E. ANP

Explanation: ***ADH*** - **Antidiuretic hormone (ADH)**, also known as vasopressin, is primarily released in response to an increase in **plasma osmolality**. - Its main function is to promote water reabsorption in the kidneys, thereby decreasing osmolality and concentrating urine. *EPO* - **Erythropoietin (EPO)** is a hormone primarily produced by the kidneys in response to **hypoxia** (low oxygen levels), not increased plasma osmolality. - It stimulates the production of **red blood cells** in the bone marrow. *PTH* - **Parathyroid hormone (PTH)** regulates **calcium** and phosphate levels in the blood, primarily stimulated by low plasma calcium concentrations. - It does not directly respond to changes in plasma osmolality. *Aldosterone* - **Aldosterone** is a mineralocorticoid hormone involved in regulating **blood pressure** and electrolyte balance, particularly sodium and potassium. - Its secretion is primarily stimulated by the **renin-angiotensin-aldosterone system** in response to low blood volume or pressure, and high potassium levels, not plasma osmolality.

Question 138: Normal anion gap is___ mmol/L?

A. 8-16 (Correct Answer)
B. 30-34
C. 20-24
D. 0-4

Explanation: ***8-16*** - The normal range for the **anion gap** is generally considered to be 8-16 mmol/L, reflecting the unmeasured anions in the plasma. - This range can vary slightly between laboratories, but **8-16 mmol/L** is the most commonly accepted range in clinical practice. *30-34* - This range is significantly **higher than normal** and would indicate a **high anion gap metabolic acidosis**, rather than a normal anion gap. - A high anion gap suggests an accumulation of **unmeasured acids** in the body, such as in lactic acidosis or ketoacidosis. *20-24* - This value is also **elevated** compared to the normal range, suggesting a high anion gap. - An anion gap in this range would prompt investigation into causes of **metabolic acidosis** with an increased anion gap. *0-4* - This range is significantly **lower than normal** and could indicate a **low or negative anion gap**, which is a rare finding. - A low anion gap is often associated with conditions like **hypoalbuminemia**, multiple myeloma (due to paraproteins), or severe hypernatremia.

Question 139: 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 140: A person working in a hot environment who consumes more water without salt is likely to develop a condition called

A. Heat cramps (Correct Answer)
B. Heat stroke
C. Heat hyperpyrexia
D. Heat exhaustion

Explanation: ***Heat cramps*** - This condition occurs due to **excessive sweating** in a hot environment, leading to significant **electrolyte (salt) loss**, particularly sodium. - Consuming large amounts of **plain water without electrolyte replacement** further dilutes the remaining electrolytes in the body, exacerbating hyponatremia and increasing the likelihood of painful muscle cramps. *Heat stroke* - **Heat stroke** is a life-threatening condition characterized by a **core body temperature >104°F (40°C)** and central nervous system dysfunction (e.g., altered mental status). - While fluid and electrolyte imbalances can contribute, its defining feature is the severe **thermoregulatory failure** leading to organ damage, which is distinct from simple muscle cramps. *Heat hyperpyrexia* - This term refers to an **extremely high body temperature** (often above 106°F or 41.1°C) but is not a specific diagnosis in the context of heat-related illness. - It is more of a symptom that could be present in severe heatstroke, not a primary condition resulting from excessive plain water intake. *Heat exhaustion* - **Heat exhaustion** presents with symptoms like fatigue, dizziness, nausea, and profuse sweating, but without significant central nervous system dysfunction or extremely high core body temperature. - While it involves fluid and electrolyte loss, the specific scenario of drinking plain water without salt primarily leads to muscle cramps due to electrolyte dilution, rather than the broader symptoms of heat exhaustion.

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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