Acid-Base Balance Practice Questions

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

Bicarbonates. **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.

Q: Which of the following can cause metabolic alkalosis?

Addison's disease. **Explanation:** **Correct Answer: B. Addison’s Disease** In Addison’s disease (primary adrenocortical insufficiency), there is a deficiency of **aldosterone**. Aldosterone normally acts on the distal tubules to reabsorb Na⁺ and secrete H⁺ and K⁺. Its absence leads to decreased H⁺ secretion, resulting in **Metabolic Acidosis** (specifically Normal Anion Gap Metabolic Acidosis). *Note: There appears to be a discrepancy in the provided key. Addison’s disease causes acidosis, while the other options (A and C) are classic causes of alkalosis. In the context of standard physiology:* * **Option A (Furosemide):** Causes **Metabolic Alkalosis**. Loop diuretics inhibit the Na-K-2Cl cotransporter, increasing distal delivery of Na⁺, which promotes H⁺ and K⁺ secretion (Contraction alkalosis). * **Option C (Hypokalemia):** Causes **Metabolic Alkalosis**. When extracellular K⁺ is low, K⁺ shifts out of cells in exchange for H⁺ shifting into cells, raising extracellular pH. It also promotes "paradoxical aciduria." * **Option D (Hyponatremia):** This is an electrolyte imbalance, not a primary cause of acid-base disturbance, though it often co-exists with various states. **High-Yield NEET-PG Pearls:** 1. **Conn’s Syndrome (Hyperaldosteronism):** The opposite of Addison’s; it causes **Metabolic Alkalosis** and Hypokalemia. 2. **Vomiting/NG Suction:** The most common clinical cause of metabolic alkalosis due to loss of HCl. 3. **Saline Responsive vs. Resistant:** Alkalosis due to diuretics or vomiting is "Saline Responsive" (Urinary Cl⁻ 20 mEq/L).

Q: Metabolic alkalosis is seen in all the following conditions except?

Methanol poisoning. **Explanation:** The correct answer is **Methanol poisoning** because it causes **High Anion Gap Metabolic Acidosis (HAGMA)**, not alkalosis. 1. **Methanol Poisoning (Correct Answer):** Methanol is metabolized by alcohol dehydrogenase into **formic acid**. The accumulation of formate ions and the associated increase in hydrogen ion concentration lead to a severe metabolic acidosis. This is often associated with an increased "osmolal gap." 2. **Why the other options are incorrect (Causes of Metabolic Alkalosis):** * **Vomiting:** Gastric juice is rich in HCl. Loss of stomach acid leads to a relative increase in bicarbonate levels (H+ loss). Additionally, volume depletion activates the Renin-Angiotensin-Aldosterone System (RAAS), further promoting bicarbonate reabsorption. * **Cushing’s Disease:** Excess cortisol has mineralocorticoid activity. This leads to increased secretion of H+ and K+ in the distal renal tubules, resulting in **hypokalemic metabolic alkalosis**. * **Diuretic Therapy:** Loop and Thiazide diuretics cause the loss of Na+, Cl-, and water. This leads to "contraction alkalosis" and increased distal delivery of sodium, which stimulates H+ secretion. **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic for HAGMA:** "MUDPILES" (Methanol, Uremia, DKA, Paraldehyde, Iron/INH, Lactic acidosis, Ethylene glycol, Salicylates). * **Conn’s Syndrome & Cushing’s:** Both are classic endocrine causes of metabolic alkalosis due to mineralocorticoid excess. * **Bartter’s and Gitelman’s Syndromes:** These are important genetic causes of metabolic alkalosis that mimic diuretic use (Loop and Thiazide-like effects, respectively).

Q: What is the normal urinary anion gap?

Zero. **Explanation:** The **Urinary Anion Gap (UAG)** is a clinical tool used to indirectly estimate the concentration of ammonium ($NH_4^+$) in the urine, which is difficult to measure directly. It is calculated using the formula: **UAG = $[Na^+] + [K^+] - [Cl^-]$** 1. **Why "Zero" is the correct answer:** In a healthy individual with normal renal function and acid-base balance, the sum of measured cations ($Na^+$ and $K^+$) is approximately equal to the measured anion ($Cl^-$). Therefore, the normal UAG is typically **zero or slightly positive** (ranging from 0 to +20 mEq/L). This reflects a baseline state where the kidneys are not required to excrete excess acid. 2. **Why other options are incorrect:** * **Negative:** A negative UAG (e.g., -20 to -50 mEq/L) occurs when there is an increase in unmeasured cations, primarily $NH_4^+$. This is the expected physiological response in **diarrhea** (Hyperchloremic Metabolic Acidosis with intact renal acidification). * **Positive:** While a "normal" gap can be slightly positive, a significantly positive UAG in the presence of metabolic acidosis indicates a failure of the kidneys to excrete $NH_4^+$. This is characteristic of **Distal Renal Tubular Acidosis (Type 1 RTA)**. * **Cannot be determined:** UAG is easily determined using a spot urine sample for electrolytes. **NEET-PG High-Yield Pearls:** * **Mnemonic for Negative UAG:** **"NeGUTive"** – A negative UAG points toward a **GUT** (gastrointestinal) cause of acidosis, like diarrhea. * **Positive UAG in Acidosis:** Suggests **RTA** (Renal cause). * The UAG is only valid for diagnosing **Normal Anion Gap Metabolic Acidosis (NAGMA)**. It is not used for High Anion Gap Metabolic Acidosis (HAGMA).

Question 1

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

Accepted Answer

Bicarbonates

Answer

Hemoglobin

Answer

Proteins

Answer

Phosphates

Question 2

Metabolic alkalosis is seen in:

Accepted Answer

Primary mineralocorticoid excess

Answer

Deficiency of mineralocorticoid

Answer

Decreased acid excretion

Answer

Decreased base excretion

Question 3

Which of the following can cause metabolic alkalosis?

Accepted Answer

Addison's disease

Answer

Furosemide

Answer

Hypokalemia

Answer

Hyponatremia

Question 4

Metabolic alkalosis is seen in all the following conditions except?

Accepted Answer

Methanol poisoning

Answer

Cushing's disease

Answer

Vomiting

Answer

Diuretic therapy

Question 5

What is the normal urinary anion gap?

Accepted Answer

Zero

Answer

Positive

Answer

Negative

Answer

Cannot be determined

Acid-Base Balance — MCQs

Acid-Base Balance — MCQs

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