Potassium Balance — MCQs

10 questions

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?

Hypokalemia is seen in therapy with

All of the following are features of hyperkalemia on ECG, EXCEPT:

All of the following drugs are known to worsen hyperkalemia except

Hyperkalemia means more than

A patient has hyperaldosteronism. Which lab finding is expected?

Reduced osmolarity ORS does not contain which of the following ion?

Most clinically significant characteristic of Ringer's Lactate is -

Which of the following receptors mediate stretch reflex?

Q10Easy

Which is the most effective buffer system in the blood that is controlled by respiration?

Potassium Balance Indian Medical PG Practice Questions and MCQs

Question 1: 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 2: Hypokalemia is seen in therapy with

A. Diazepam
B. Corticosteroids (Correct Answer)
C. Ibuprofen
D. Digitalis

Explanation: ***Corticosteroids*** - **Corticosteroids** can cause **hypokalemia** due to their mineralocorticoid activity, which promotes renal potassium excretion. - This effect is often dose-dependent and more pronounced with certain corticosteroids like **fludrocortisone** or high doses of prednisolone. *Diazepam* - **Diazepam** is a **benzodiazepine** that acts on GABA receptors in the brain. - It primarily causes central nervous system effects like sedation and anxiolysis, without directly affecting **potassium levels**. *Ibuprofen* - **Ibuprofen** is a **non-steroidal anti-inflammatory drug (NSAID)**. - It can lead to **renal dysfunction** and **fluid retention**, but it does not directly cause **hypokalemia**. *Digitalis* - **Digitalis** (digoxin) is a cardiac glycoside used to treat **heart failure** and **arrhythmias**. - While **hypokalemia** can exacerbate **digitalis toxicity**, digitalis therapy itself does not significantly cause **hypokalemia**; rather, it's a critical electrolyte to monitor.

Question 3: All of the following are features of hyperkalemia on ECG, EXCEPT:

A. Shortened QT interval
B. Peaked T waves
C. Wide QRS complex
D. U waves (Correct Answer)

Explanation: ***U waves*** - **U waves** are typically associated with **hypokalemia**, not hyperkalemia. They are small deflections immediately following the T wave. - Their presence suggests an abnormality in myocardial repolarization due to low potassium levels. *Shortened QT interval* - A **shortened QT interval** is *not* a typical finding in hyperkalemia; hyperkalemia usually causes a **prolonged PR interval** and QRS widening, which can make QT measurement difficult but does not inherently shorten it. - A shortened QT interval is more commonly seen in conditions like **hypercalcemia** or inherited short QT syndrome. *Peaked T waves* - **Peaked T waves** (also known as "tenting" of the T waves) are one of the earliest and most classic ECG signs of hyperkalemia [1]. - This occurs due to abnormally rapid repolarization of the ventricles. *Wide QRS complex* - As hyperkalemia progresses, the **QRS complex widens** due to a slowing of intraventricular conduction [1]. - This widening can eventually lead to a **sine wave pattern** if not treated, indicating severe hyperkalemia and impending cardiac arrest.

Question 4: All of the following drugs are known to worsen hyperkalemia except

A. Furosemide (Correct Answer)
B. ACE inhibitors
C. Amiloride
D. Spironolactone

Explanation: ***Furosemide*** - **Furosemide** is a loop diuretic that acts on the **thick ascending limb of the loop of Henle**, inhibiting the reabsorption of sodium, chloride, and potassium. - This action leads to increased excretion of potassium in the urine, thus **preventing hyperkalemia** and often causing hypokalemia. *ACE inhibitors* - **ACE inhibitors** block the production of angiotensin II, leading to decreased aldosterone secretion. - Reduced aldosterone levels decrease potassium excretion in the renal tubules, which can **worsen hyperkalemia**. *Amiloride* - **Amiloride** is a potassium-sparing diuretic that blocks sodium channels in the collecting duct. - This action reduces potassium secretion, making it a drug that can **worsen hyperkalemia**. *Spironolactone* - **Spironolactone** is an aldosterone antagonist that also acts as a potassium-sparing diuretic. - By blocking aldosterone's effects, it **decreases potassium excretion** in the renal tubules and can therefore worsen hyperkalemia.

Question 5: Hyperkalemia means more than

A. 5.5 mEq/l (Correct Answer)
B. 4.5 mEq/l
C. 10.5 mEq/l
D. 7.5 mEq/l

Explanation: ***5.5 mEq/l*** - **Hyperkalemia** is defined as a serum potassium level greater than **5.5 mEq/L** [1]. - This elevated level can lead to significant cardiac and neurological complications if not promptly addressed. *4.5 mEq/l* - A potassium level of 4.5 mEq/L falls within the normal physiological range for serum potassium, which is typically **3.5 to 5.0 mEq/L** [1]. - Therefore, this value does not indicate hyperkalemia. *10.5 mEq/l* - While 10.5 mEq/L is indeed an elevated potassium level, it represents **severe hyperkalemia**, far exceeding the general threshold for diagnosis. - The definition of hyperkalemia begins at a lower threshold of **5.5 mEq/L** [1]. *7.5 mEq/l* - A potassium level of 7.5 mEq/L indicates **moderate to severe hyperkalemia** and is a critical finding requiring immediate medical intervention [2]. - However, the initial threshold for defining hyperkalemia is **5.5 mEq/L**, making this option too high for the general definition [1].

Question 6: A patient has hyperaldosteronism. Which lab finding is expected?

A. Metabolic acidosis
B. Hyperkalemia
C. Hypokalemia (Correct Answer)
D. Hyponatremia

Explanation: ***Hypokalemia*** - **Aldosterone** increases the excretion of **potassium** in the kidneys, leading to decreased serum potassium levels [1]. - This effect is mediated by aldosterone's action on the principal cells of the collecting duct, promoting potassium secretion into the urine [1]. *Metabolic acidosis* - **Hyperaldosteronism** typically causes **metabolic alkalosis** due to increased hydrogen ion excretion by the kidneys [1]. - Aldosterone promotes the reabsorption of sodium and water, and the excretion of potassium and hydrogen ions, leading to alkalosis [2]. *Hyperkalemia* - **Aldosterone's primary role** is to promote **potassium excretion** in the kidneys [1]. - Therefore, **excessive aldosterone** production would lead to **hypokalemia**, not hyperkalemia. *Hyponatremia* - **Aldosterone** promotes **sodium reabsorption** in the kidneys, which usually leads to normal or even slightly elevated serum sodium levels [1]. - **Hyponatremia** would be an unexpected finding in hyperaldosteronism [3].

Question 7: Reduced osmolarity ORS does not contain which of the following ion?

A. Lactate ion (Correct Answer)
B. Potassium ion
C. Citrate ion
D. Sodium ion

Explanation: ***Lactate ion*** - **Reduced osmolarity ORS** (WHO formulation) does **NOT contain lactate**. - The current WHO-ORS uses **trisodium citrate** as the base provider to correct acidosis. - Some older commercial ORS formulations used lactate, but it has been replaced by citrate in standard formulations due to **better stability, palatability, and effectiveness**. *Potassium ion* - **Potassium ions** (20 mmol/L) are an essential component of reduced osmolarity ORS. - They are crucial for replacing electrolyte losses during diarrhea and maintaining **intracellular fluid balance**. *Citrate ion* - **Citrate** (10 mmol/L) is a key component of reduced osmolarity ORS as the base provider. - It helps correct **metabolic acidosis** associated with diarrhea and improves shelf life and taste. *Sodium ion* - **Sodium ions** (75 mmol/L) are vital in reduced osmolarity ORS. - They facilitate the **sodium-glucose co-transport mechanism** across the intestinal wall, promoting optimal water absorption and rehydration.

Question 8: 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 9: Which of the following receptors mediate stretch reflex?

A. Golgi tendon organ
B. Muscle spindle (Correct Answer)
C. Meissner's corpuscles
D. Merkel's disc

Explanation: ***Muscle spindle*** - Muscle spindles are **stretch-sensitive receptors** located within the muscle belly that detect changes in muscle length and the rate of change in length. - When a muscle is stretched, the muscle spindles are activated, sending signals via **afferent neurons** to the spinal cord, which then initiates a reflex contraction of the same muscle to counteract the stretch—this is the basis of the stretch reflex. *Golgi tendon organ* - **Golgi tendon organs** are located in the tendons and respond to changes in **muscle tension**, not muscle length. Its primary role is to prevent excessive muscle contraction. - When activated by high tension, Golgi tendon organs inhibit the muscle, leading to relaxation (inverse stretch reflex), which is opposite to the stretch reflex. *Meissner's corpuscles* - **Meissner's corpuscles** are **mechanoreceptors** located in the superficial layers of the skin, primarily responsible for detecting **light touch** and **vibrations**. - They are not involved in the regulation of muscle length or tension and therefore do not mediate the stretch reflex. *Merkel's disc* - **Merkel's discs** are **mechanoreceptors** found in the basal layer of the epidermis, specialized for detecting **sustained pressure** and **texture**. - These receptors contribute to fine tactile discrimination but are unrelated to the proprioceptive mechanisms of the stretch reflex.

Question 10: Which is the most effective buffer system in the blood that is controlled by respiration?

A. Bicarbonates (Correct Answer)
B. Hemoglobin
C. Proteins
D. Phosphates

Explanation: **Explanation:** The **Bicarbonate buffer system ($HCO_3^- / CO_2$)** is the most important and effective extracellular buffer in the blood. Its effectiveness stems from being an **"open system."** Unlike other buffers, its components are independently regulated by two major organs: the **lungs** (controlling $CO_2$ via respiration) and the **kidneys** (controlling $HCO_3^-$ excretion and reabsorption). According to the Henderson-Hasselbalch equation, the pH of blood is determined by the ratio of bicarbonate to dissolved $CO_2$. By increasing or decreasing the rate of respiration (ventilation), the body can rapidly adjust $pCO_2$ levels to maintain this ratio, making it the primary respiratory-controlled buffer. **Analysis of Incorrect Options:** * **Hemoglobin (B):** While hemoglobin is a powerful buffer (due to histidine residues) and is the most important buffer **inside erythrocytes**, it is not primarily controlled by respiration; it depends on the oxygenation state (Bohr effect). * **Proteins (C):** Plasma proteins (like albumin) act as buffers in the blood, but their concentration remains relatively static and is not acutely regulated by respiratory changes. * **Phosphates (D):** The phosphate buffer system is crucial **intracellularly** and in the **renal tubules** (where its pKa of 6.8 is close to tubular pH). However, its concentration in the plasma is too low to be the most effective blood buffer. **High-Yield Clinical Pearls for NEET-PG:** * **Normal $HCO_3^- : CO_2$ ratio:** 20:1 (maintains physiological pH of 7.4). * **First line of defense:** Chemical buffers (seconds). * **Second line of defense:** Respiratory system (minutes). * **Third line of defense:** Renal system (hours to days). * **Isohydric Principle:** All buffer systems in the body are in equilibrium with each other; a change in one affects all others.

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