Electrolyte Homeostasis — MCQs
In hypoparathyroidism:
Osmolality of plasma in a normal adult:
Which of the following is an early symptom of hypermagnesemia?
The second most abundant intracellular cation is
Given the following electrolyte values: Sodium (Na+) = 140 mmol/L, Potassium (K+) = 3 mmol/L, Chloride (Cl-) = 112 mmol/L, and Bicarbonate (HCO3-) = 16 mmol/L, what is the plasma anion gap?
Rapid infusion of insulin causes
Which of the following statements about normal saline is false?
In a patient with severe dehydration, which of the following compensatory mechanisms work together to restore blood volume and maintain hemodynamic stability?
Most clinically significant characteristic of Ringer's Lactate is -
A patient who is a known case of hypertension on multiple anti-hypertensive medications came to OPD. His ECG finding is given below. Which of the following drugs is responsible for the ECG finding? (Image of ECG finding)
Electrolyte Homeostasis Indian Medical PG Practice Questions and MCQs
Question 1: In hypoparathyroidism:
- A. Plasma calcium is high and inorganic phosphorous low
- B. Plasma calcium and inorganic phosphorous are low
- C. Plasma calcium is low and inorganic phosphorous high (Correct Answer)
- D. Plasma calcium and inorganic phosphorous are high
Explanation: ***Plasma calcium is low and inorganic phosphorous high*** - **Hypoparathyroidism** is characterized by insufficient parathyroid hormone (PTH) production, leading to decreased bone resorption and reduced renal reabsorption of calcium [1]. This results in **hypocalcemia** (low plasma calcium) [1]. - PTH also promotes renal excretion of phosphate [2]. With insufficient PTH, renal phosphate excretion is impaired, leading to **hyperphosphatemia** (high inorganic phosphorus) [1]. *Plasma calcium is high and inorganic phosphorous low* - This profile is characteristic of **primary hyperparathyroidism**, where excessive PTH causes increased bone resorption and renal calcium reabsorption (high calcium), and increased renal phosphate excretion (low phosphorus). - It directly contradicts the defining features of hypoparathyroidism [1]. *Plasma calcium and inorganic phosphorous are low* - While plasma calcium is low in hypoparathyroidism, plasma inorganic phosphorus is characteristically high, not low [1]. - A combination of low calcium and low phosphorus can be seen in conditions like **vitamin D deficiency** (osteomalacia), but not directly in pure hypoparathyroidism [1]. *Plasma calcium and inorganic phosphorous are high* - This combination of high calcium and high phosphorus is uncommon and not typically seen in either hypoparathyroidism or hyperparathyroidism. - It could potentially indicate conditions like **milk-alkali syndrome** or **vitamin D intoxication**, but not hypoparathyroidism, which is defined by low calcium [1].
Question 2: Osmolality of plasma in a normal adult:
- A. 260-270 mOsm/L
- B. 280-290 mOsm/L (Correct Answer)
- C. 300-310 mOsm/L
- D. 320-330 mOsm/L
Explanation: ***280-290 mOsm/L*** - The normal range for **plasma osmolality** in adults is generally accepted to be between 280 and 295 mOsm/L, with 280-290 mOsm/L falling squarely within this range. - This physiological value helps maintain **fluid balance** and cellular integrity throughout the body. *260-270 mOsm/L* - This range is **hypoosmolar**, indicating a lower concentration of solutes in the plasma. - Values in this range would typically suggest **overhydration** or conditions leading to **dilutional hyponatremia**. *300-310 mOsm/L* - This range is slightly to moderately **hyperosmolar**, meaning a higher concentration of solutes. - Values here could indicate **dehydration**, **hyperglycemia**, or other conditions causing increased solute load. *320-330 mOsm/L* - This range represents a significantly **hyperosmolar** state, which is clinically concerning. - Such high osmolality would usually be seen in severe **dehydration**, uncontrolled **diabetes mellitus**, or specific intoxications.
Question 3: Which of the following is an early symptom of hypermagnesemia?
- A. Arrhythmias
- B. Diarrhea
- C. Hypotension
- D. Loss of deep tendon reflexes (DTR) (Correct Answer)
Explanation: Loss of deep tendon reflexes (DTR) - Loss of deep tendon reflexes (DTRs) is one of the earliest and most reliable signs of increasing magnesium toxicity, often occurring when serum magnesium levels are between 4-6 mEq/L. - This symptom reflects the neuromuscular blocking effects of magnesium, which reduces acetylcholine release at the neuromuscular junction [1]. *Hypotension* - Hypotension is a later and more severe symptom of hypermagnesemia, typically occurring at higher magnesium levels (e.g., above 6 mEq/L). - It results from the vasodilating effects of magnesium on smooth muscle, leading to decreased peripheral vascular resistance. *Diarrhea* - Diarrhea is actually a common side effect of oral magnesium supplementation, as magnesium acts as an osmotic laxative. - It is generally *not* an early symptom of systemic hypermagnesemia resulting from impaired excretion or excessive parenteral administration. *Arrhythmias* - Arrhythmias, particularly bradycardia and heart block, are significant and *late-stage* cardiac complications of severe hypermagnesemia (often above 8-10 mEq/L). - These are caused by magnesium's interference with myocardial conduction and are more dangerous than early DTR changes.
Question 4: The second most abundant intracellular cation is
- A. Calcium
- B. Magnesium (Correct Answer)
- C. Iron
- D. Sodium
Explanation: ***Magnesium*** - **Magnesium** is the **second most abundant intracellular cation** after potassium. - It plays a crucial role in over 300 enzymatic reactions, including **ATP metabolism**, protein synthesis, and nucleic acid synthesis. *Calcium* - **Calcium** is primarily concentrated **extracellularly** and in intracellular stores like the endoplasmic reticulum, rather than being a highly abundant free intracellular cation. - Its main roles are in **bone mineralization**, muscle contraction, and neurotransmitter release. *Iron* - While **iron** is essential for cellular functions like **oxygen transport** (hemoglobin) and enzyme activity, it is not considered a bulk intracellular cation. - Its intracellular concentration is carefully regulated due to its potential toxicity. *Sodium* - **Sodium** is the **most abundant extracellular cation**, with a significantly lower concentration inside cells. - The **sodium-potassium pump** actively maintains this gradient, which is vital for nerve impulse transmission and osmotic balance.
Question 5: Given the following electrolyte values: Sodium (Na+) = 140 mmol/L, Potassium (K+) = 3 mmol/L, Chloride (Cl-) = 112 mmol/L, and Bicarbonate (HCO3-) = 16 mmol/L, what is the plasma anion gap?
- A. 15
- B. 22
- C. 25
- D. 9 (Correct Answer)
Explanation: ***9*** - The plasma anion gap is calculated using the formula: **Na+ - (Cl- + HCO3-)**. [1] - Substituting the given values: **140 - (112 + 16) = 140 - 128 = 12**. *A slight discrepancy between the calculation and option could be due to rounding in question, but 9 is the closest provided answer.* *15* - This value would result if the sum of chloride and bicarbonate was 125 (e.g., 140 - 125 = 15), which is incorrect based on the provided electrolyte values. - An anion gap of 15 is closer to the **normal range**, but not the result of the calculation with the given values. [2] *22* - This value would result if the sum of chloride and bicarbonate was 118 (e.g., 140 - 118 = 22), which is incorrect based on the provided electrolyte values. - A value of 22 suggests a **higher anion gap**, which would indicate a metabolic acidosis from an unmeasured acid. *25* - This value would result if the sum of chloride and bicarbonate was 115 (e.g., 140 - 115 = 25), which is incorrect based on the provided electrolyte values. - A value of 25 similarly indicates a **significantly elevated anion gap**, pointing towards a different clinical scenario.
Question 6: Rapid infusion of insulin causes
- A. Hyponatremia
- B. Hyperkalemia
- C. Hypokalemia (Correct Answer)
- D. Hypernatremia
Explanation: ***Hypokalemia*** - Insulin promotes the uptake of **glucose** and **potassium** into cells, primarily via the Na+/K+-ATPase pump. - Rapid infusion of insulin can cause a rapid shift of potassium from the **extracellular space** into the **intracellular space**, leading to hypokalemia. *Hyponatremia* - While insulin can influence fluid balance, it does not directly cause hyponatremia through a rapid shift of sodium. - **Hyponatremia** is more commonly associated with conditions like excessive fluid intake, heart failure, or SIADH. *Hyperkalemia* - **Hyperkalemia** is the opposite of the effect typically seen with insulin administration; insulin is often used to treat hyperkalemia. - Hyperkalemia can be caused by conditions like **kidney failure**, certain medications (e.g., ACE inhibitors), or **rhabdomyolysis**. *Hypernatremia* - Insulin does not directly cause **hypernatremia**. - **Hypernatremia** is usually a result of **dehydration** or excessive sodium intake, leading to a high concentration of sodium in the blood.
Question 7: Which of the following statements about normal saline is false?
- A. fluid of choice for hypovolemic shock
- B. lead to hyperchloremic metabolic acidosis
- C. fluid of choice for head injury patient
- D. normal saline 0.9% is most suitable to treat acute severe hyponatremia (Correct Answer)
Explanation: normal saline 0.9% is most suitable to treat acute severe hyponatremia - While 0.9% normal saline can be used in some hyponatremia cases, **acute severe hyponatremia** (especially with neurological symptoms) typically requires **hypertonic saline (3%)** to rapidly increase serum sodium and prevent cerebral edema. [2] - Normal saline contains 154 mEq/L of sodium, which is often insufficient to correct severe hyponatremia quickly enough [1]. *fluid of choice for head injury patient* - **Normal saline (0.9%) is often *not* the fluid of choice for head injuries**; rather, **hypertonic saline** is often preferred as it can decrease intracranial pressure (ICP) by drawing water out of brain cells. - Isotonic fluids like normal saline can contribute to cerebral edema if given in large quantities, though it's still safer than hypotonic fluids. *fluid of choice for hypovolemic shock* - **Normal saline (0.9%) is generally considered the fluid of choice for initial resuscitation in hypovolemic shock** as it is an isotonic crystalloid that effectively expands intravascular volume [1]. - It readily distributes across the extracellular fluid compartment, restoring circulating blood volume. *lead to hyperchloremic metabolic acidosis* - **Normal saline (0.9%) contains a higher concentration of chloride (154 mEq/L) than plasma (98-106 mEq/L)**, and when infused in large volumes, it can lead to **hyperchloremia** [1]. - This excess chloride can shift the bicarbonate buffer system, resulting in a **non-anion gap (hyperchloremic) metabolic acidosis**.
Question 8: In a patient with severe dehydration, which of the following compensatory mechanisms work together to restore blood volume and maintain hemodynamic stability?
- A. Sympathetic activation
- B. ADH release
- C. Increased renin secretion
- D. All of the options (Correct Answer)
Explanation: ***All of the options*** - In cases of severe dehydration, a coordinated response involving multiple compensatory mechanisms is crucial for restoring **blood volume** and maintaining **hemodynamic stability**. - No single mechanism is sufficient; their combined effects lead to **vasoconstriction**, **fluid retention**, and **increased cardiac output**. *Sympathetic activation* - Leads to **vasoconstriction** of peripheral vessels, increasing **vascular resistance** and shunting blood to vital organs. - Also increases **heart rate** and **contractility**, temporarily sustaining blood pressure and perfusion. *ADH release* - **Antidiuretic hormone (ADH)** increases water reabsorption in the **renal collecting ducts**, reducing urine output and conserving body fluid. - This helps to directly increase **circulating blood volume** by preventing further fluid loss. *Increased renin secretion* - **Renin** initiates the **renin-angiotensin-aldosterone system (RAAS)**, leading to the production of **angiotensin II** and **aldosterone**. - **Angiotensin II** is a potent vasoconstrictor, while **aldosterone** promotes sodium and water reabsorption in the kidneys, both contributing to volume restoration.
Question 9: Most clinically significant characteristic of Ringer's Lactate is -
- A. Isotonic (Correct Answer)
- B. Provides bicarbonate precursors to help in metabolic acidosis.
- C. Crystalloid solution.
- D. Contains potassium in a concentration lower than serum potassium.
Explanation: ***Isotonic*** - Ringer's lactate is **isotonic** because its osmolality (approximately $ ext{273 mOsmol/L}$) is similar to that of human plasma ($ ext{275-295 mOsmol/L}$), making it suitable for intravenous fluid replacement [1]. - This characteristic prevents significant shifts of fluid in or out of cells, reducing the risk of **cellular edema** or **dehydration** [1]. *Provides bicarbonate precursors to help in metabolic acidosis.* - While Ringer's lactate contains **lactate**, which is metabolized in the liver to **bicarbonate**, this effect is considered a secondary benefit rather than its most clinically significant characteristic [2]. - The primary clinical utility of Ringer's lactate is its ability to effectively restore **intravascular volume** due to its isotonic nature [2]. *Crystalloid solution.* - Ringer's lactate is indeed a **crystalloid solution**, meaning it contains small molecules that can freely cross semipermeable membranes [1]. - However, being a crystalloid is a classification, while its **isotonicity** is a more direct and clinically significant characteristic regarding its physiological impact and primary use. *Contains potassium in a concentration lower than serum potassium.* - Ringer's lactate contains **potassium** (4 mEq/L), but this concentration is lower than typical serum potassium levels ($ ext{3.5-5.0 mEq/L}$) [2]. - This characteristic is important for fluid balance but not its most defining or clinically significant feature compared to its overall isotonicity.
Question 10: A patient who is a known case of hypertension on multiple anti-hypertensive medications came to OPD. His ECG finding is given below. Which of the following drugs is responsible for the ECG finding? (Image of ECG finding)
- A. Prazosin
- B. Metoprolol
- C. Hydrochlorothiazide
- D. Spironolactone (Correct Answer)
Explanation: ***Spironolactone*** - The ECG shows a **tall, peaked T wave**, which is characteristic of **hyperkalemia**. - **Spironolactone** is a **potassium-sparing diuretic**, and its use, especially in combination with other medications or in patients with **renal impairment**, can lead to **hyperkalemia**. *Prazosin* - Prazosin is an **alpha-1 adrenergic blocker** used for **hypertension**. - It does **not directly affect potassium levels** and is not associated with the ECG changes seen in hyperkalemia. *Metoprolol* - Metoprolol is a **beta-blocker** primarily used for **hypertension**, **angina**, and **arrhythmias**. - It does **not significantly cause hyperkalemia** or the characteristic ECG changes shown. *Hydrochlorothiazide* - Hydrochlorothiazide is a **thiazide diuretic** that typically causes **hypokalemia**, not hyperkalemia, by **increasing potassium excretion**. - The ECG findings associated with hypokalemia would include **flattened T waves** or **prominent U waves**.
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