Acid-Base and Electrolyte Balance Practice Questions

Q: Which of the following is NOT caused by hypokalemia?

Tetany. **Explanation:** **1. Why Tetany is the Correct Answer:** Tetany is a state of increased neuromuscular excitability characterized by involuntary muscle spasms. It is classically caused by **hypocalcemia**, **hypomagnesemia**, or **alkalosis**. Hypokalemia, conversely, leads to **hyperpolarization** of the resting membrane potential (making it more negative). This moves the cell further away from the threshold potential, making it *less* excitable. Therefore, hypokalemia typically causes muscle weakness and paralysis, not tetany. **2. Analysis of Incorrect Options:** * **Paralytic Ileus:** Low potassium levels decrease the excitability and motility of smooth muscles in the gastrointestinal tract, leading to intestinal atony and paralytic ileus. * **Hypertension:** Chronic hypokalemia (often associated with high salt intake or primary hyperaldosteronism) can lead to vasoconstriction and increased renal sodium reabsorption, contributing to elevated blood pressure. * **Rhabdomyolysis:** Potassium is a profound vasodilator in skeletal muscle during exercise. In severe hypokalemia, the failure of muscular vasodilation leads to ischemia and subsequent muscle cell breakdown (rhabdomyolysis). **3. Clinical Pearls for NEET-PG:** * **ECG Findings in Hypokalemia:** Flattened T-waves, **prominent U-waves**, ST-segment depression, and prolonged PR interval (High-yield: "U wave is after the T wave"). * **Muscle Effects:** Hypokalemia causes "floppy" muscles (flaccid paralysis), whereas hyperkalemia can cause "peaked T waves" and cardiac arrest in diastole. * **Refractory Hypokalemia:** If hypokalemia does not respond to potassium supplementation, always check **Magnesium** levels; hypomagnesemia must be corrected first.

Q: All of the following cause high anion gap metabolic acidosis except?

Ureterosigmoidostomy. **Explanation:** Metabolic acidosis is classified into two main categories based on the **Anion Gap (AG)**, calculated as $[Na^+] - ([Cl^-] + [HCO_3^-])$. **Why Ureterosigmoidostomy is the correct answer:** Ureterosigmoidostomy causes a **Normal Anion Gap Metabolic Acidosis (NAGMA)**. In this surgical procedure, the ureters are diverted into the sigmoid colon. The colonic mucosa is exposed to urine and actively reabsorbs chloride ions in exchange for bicarbonate ($Cl^-/HCO_3^-$ exchange). The loss of bicarbonate and the retention of chloride lead to **hyperchloremic metabolic acidosis**. Since the decrease in bicarbonate is balanced by an increase in chloride, the anion gap remains within the normal range (8–12 mEq/L). **Why the other options are incorrect:** These options cause **High Anion Gap Metabolic Acidosis (HAGMA)** because they involve the accumulation of unmeasured organic acids: * **Lactic Acidosis:** Accumulation of lactate (e.g., in shock or hypoxia). * **Salicylate Poisoning:** Accumulation of salicylic acid and interference with the Krebs cycle, leading to organic acid buildup. * **Ethylene Glycol Poisoning:** Metabolized into toxic acids like glycolic and oxalic acid. **NEET-PG High-Yield Pearls:** * **Mnemonic for HAGMA:** **MUDPILES** (Methanol, Uremia, DKA, Propylene glycol, Iron/INH, Lactic acidosis, Ethylene glycol, Salicylates). * **Mnemonic for NAGMA:** **USED CARP** (Ureterosigmoidostomy, Small bowel fistula, Extra-alimentation, Diarrhea, Carbonic anhydrase inhibitors, Renal tubular acidosis, Pancreatic fistula). * **Key Distinction:** If the question mentions **Hyperchloremia**, always think of **NAGMA**.

Q: Which of the following are monoprotic acids?

All of the above. **Explanation:** The classification of acids depends on their **basicity**, which is the number of ionizable hydrogen ions ($H^+$) a single molecule of the acid can donate in an aqueous solution. 1. **Why "All of the above" is correct:** A **monoprotic acid** is an acid that can release only one proton per molecule. * **Formic acid ($HCOOH$):** Despite having two hydrogen atoms, only the hydrogen attached to the oxygen in the carboxyl group is ionizable. The hydrogen attached directly to the carbon is non-ionizable. * **Acetic acid ($CH_3COOH$):** Similar to formic acid, only the single hydrogen in the carboxyl group ($-COOH$) dissociates. The three hydrogens in the methyl group ($CH_3$) are covalently bonded to carbon and do not ionize. * **Nitric acid ($HNO_3$):** This is a strong inorganic acid that completely dissociates to release one $H^+$ ion and one $NO_3^-$ ion. 2. **Understanding Polyprotic Acids (The "Incorrect" logic):** If an acid can donate more than one proton, it is polyprotic. Examples include **Diprotic** acids like Sulfuric acid ($H_2SO_4$) or Carbonic acid ($H_2CO_3$), and **Triprotic** acids like Phosphoric acid ($H_3PO_4$). In this question, all options (A, B, and C) strictly meet the criteria for being monoprotic. 3. **Clinical Pearls & High-Yield Facts for NEET-PG:** * **Henderson-Hasselbalch Equation:** Monoprotic weak acids (like acetic acid) are used to demonstrate this equation: $pH = pKa + \log([A^-]/[HA])$. * **Formic Acid Toxicity:** In **Methanol poisoning**, methanol is metabolized to formic acid, leading to a High Anion Gap Metabolic Acidosis (HAGMA) and optic nerve damage. * **Buffer Systems:** The most important physiological buffer, the bicarbonate system, involves **Carbonic acid ($H_2CO_3$)**, which is a **diprotic** acid, though it functions primarily in its first dissociation step in the blood.

Q: Tetany is characterized by which of the following?

Hypertonicity of muscles. **Explanation:** **Tetany** is a clinical manifestation of increased neuromuscular excitability. The correct answer is **Hypertonicity of muscles** because the condition is characterized by involuntary muscle spasms, cramps, and sustained contractions (hypertonia) rather than relaxation. **1. Why Hypertonicity is Correct:** The underlying mechanism is usually **hypocalcemia**. Low extracellular calcium levels decrease the threshold for depolarization of nerve membranes. This leads to increased permeability to sodium ions, causing repetitive spontaneous firing of action potentials. This continuous stimulation results in sustained muscle contraction, clinically presenting as carpopedal spasm, laryngospasm, or generalized seizures. **2. Why Other Options are Incorrect:** * **Hypotonicity of muscles:** This refers to decreased muscle tone (flaccidity), which is the opposite of what occurs in tetany. Hypotonicity is more commonly seen in conditions like lower motor neuron lesions or hypercalcemia. * **Increased serum calcium concentration:** Hypercalcemia actually *decreases* neuromuscular excitability by raising the threshold for depolarization, leading to muscle weakness and lethargy. Tetany is classically associated with **decreased** serum calcium. **High-Yield Clinical Pearls for NEET-PG:** * **Trousseau’s Sign:** Induction of carpal spasm by inflating a BP cuff above systolic pressure for 3 minutes (more sensitive than Chvostek’s). * **Chvostek’s Sign:** Twitching of facial muscles elicited by tapping over the facial nerve. * **Acid-Base Link:** Alkalosis (e.g., hyperventilation) can trigger tetany even with normal total calcium levels because high pH increases calcium binding to albumin, reducing the physiologically active **ionized calcium (Ca²⁺)**. * **Hypomagnesemia:** Often co-exists with hypocalcemia and must be corrected to resolve tetany.

Question 1

Which of the following is NOT caused by hypokalemia?

Accepted Answer

Tetany

Answer

Paralytic ileus

Answer

Hypertension

Answer

Rhabdomyolysis

Question 2

What is the most important buffer system in red blood cells?

Accepted Answer

Carbonic Acid and Sodium Bicarbonate

Answer

Oxygenated Hemoglobin and Sodium Hemoglobinate

Answer

Oxygenated Hemoglobin and Potassium Hemoglobinate

Answer

Carbonic Acid and Potassium Bicarbonate

Question 3

Magnesium is not involved in which of the following processes?

Accepted Answer

Increased neuromuscular excitability

Answer

Cellular oxidation

Answer

Membrane transport

Answer

Glucose tolerance

Question 4

All of the following cause high anion gap metabolic acidosis except?

Accepted Answer

Ureterosigmoidostomy

Answer

Lactic acidosis

Answer

Salicylate poisoning

Answer

Ethylene glycol poisoning

Question 5

Which of the following statements is NOT true regarding the buffering action of hemoglobin?

Accepted Answer

Hemoglobin's buffering action is primarily extracellular, not functional in the plasma.

Answer

Hemoglobin functions as an intracellular buffer.

Answer

Hemoglobin's buffering capacity is significantly attributed to its high histidine content.

Answer

Oxygenated hemoglobin acts as a stronger base compared to deoxygenated hemoglobin.

Question 6

Hypokalemia is associated with which of the following conditions?

Accepted Answer

Organophosphate poisoning

Answer

Alkalosis

Answer

Periodic paralysis

Answer

Type 1 A

Question 7

Which of the following are monoprotic acids?

Accepted Answer

All of the above

Answer

Formic acid

Answer

Acetic acid

Answer

Nitric acid

Question 8

Severe hyperphosphatemia is associated with which of the following?

Accepted Answer

Hypercalcemia

Answer

Hypocalcemia

Answer

Hypokalemia

Answer

Hyperuricemia

Question 9

Hyperchloremic acidosis is seen in:

Accepted Answer

Renal Tubular Acidosis

Answer

Diarrhea

Answer

Diabetic Ketoacidosis

Answer

Dehydration

Question 10

Tetany is characterized by which of the following?

Accepted Answer

Hypertonicity of muscles

Answer

Hypotonicity of muscles

Answer

Increased serum calcium concentration

Answer

None of the above

Acid-Base and Electrolyte Balance — MCQs

Acid-Base and Electrolyte Balance — MCQs

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