Acid-Base Balance

Acid-Base Balance

Blood pH is maintained between 7.35–7.45 (normal = 7.40). This narrow range is critical for enzyme function, oxygen delivery (Bohr effect), and cellular electrolyte balance.

Buffer Systems

  • Bicarbonate (pKa 6.1): Primary extracellular buffer. CO₂ (regulated by lungs) + HCO₃⁻ (regulated by kidneys). Henderson-Hasselbalch: pH = 6.1 + log([HCO₃⁻]/[H₂CO₃]). Normal: [HCO₃⁻] = 24 mEq/L, pCO₂ = 40 mmHg.
  • Phosphate (pKa 6.8): Important intracellular and urinary buffer.
  • Proteins: Histidine residues (pKa ~6). Hemoglobin is major blood buffer — accepts H+ when O₂ is released (Bohr effect).
  • Ammonia: Renal ammoniagenesis — NH₃ + H+ → NH₄+ excreted in urine (↑in acidosis).

Primary Acid-Base Disorders

  • Metabolic Acidosis (↓pH, ↓HCO₃⁻): - High AG: MUDPILES (Methanol, Uremia, DKA, Propylene glycol, Isoniazid/Iron, Lactic acidosis, Ethylene glycol, Salicylates) - Normal AG: GI HCO₃⁻ loss (diarrhea), Renal Tubular Acidosis (RTA), NH₄Cl ingestion - Compensation: Hyperventilation (↓pCO₂) — Kussmaul breathing
  • Metabolic Alkalosis (↑pH, ↑HCO₃⁻): - Causes: Vomiting (↑HCl loss), diuretics (↑K+ loss), hyperaldosteronism, antacid overuse - Compensation: Hypoventilation (↑pCO₂)
  • Respiratory Acidosis (↓pH, ↑pCO₂): - Hypoventilation: COPD, sedation, neuromuscular disease, OSA - Compensation: ↑HCO₃⁻ retention (kidneys — slow, days)
  • Respiratory Alkalosis (↑pH, ↓pCO₂): - Hyperventilation: Anxiety, altitude, ↑progesterone (pregnancy), aspirin early, liver failure - Compensation: ↓HCO₃⁻ (kidneys)

Anion Gap (AG)

AG = Na+ − (Cl− + HCO₃⁻). Normal = 8–12 mEq/L (unmeasured anions: albumin, phosphate, sulfate). Elevated AG = unmeasured acids present (lactate, ketone bodies, organic acids). Hypoalbuminemia lowers AG (correct: add 2.5 for each 1 g/dL albumin below normal).

Renal Handling of Acid

  • Proximal tubule: 85% of filtered HCO₃⁻ reabsorbed; NH₄+ secretion
  • Collecting duct: Intercalated cells secrete H+ (via H+-ATPase and H+/K+-ATPase) → titratable acid + NH₄+
  • Aldosterone: ↑H+ secretion and Na+ reabsorption → alkalosis
  • Type I RTA: Distal H+ secretion defect → cannot acidify urine (urine pH >5.5), hyperchloremic MAC, nephrocalcinosis
  • Type II RTA: Proximal HCO₃⁻ reabsorption defect → HCO₃⁻ wasting, Fanconi syndrome
  • Type IV RTA: Hypoaldosteronism (diabetic nephropathy most common) → hyperkalemic MAC

Oxygen-Hemoglobin Dissociation Curve

Shifted RIGHT (↓O₂ affinity, ↑O₂ release) by: ↑Temperature, ↑CO₂, ↑H+ (↓pH = Bohr effect), ↑2,3-BPG (RBC product of glycolysis; ↑in chronic hypoxia). Shifted LEFT (↑O₂ affinity) by: ↓Temp, ↓CO₂, ↓H+, ↓2,3-BPG, CO poisoning, HbF (fetal Hb, lacks β-chains).

Quiz - Exam Preparation Strategy

When studying Quiz for your final board exams, it is critical to focus on the core concepts and fundamental formulas. Relying strictly on NCERT textbook solutions and practicing previous year questions (PYQs) is the proven methodology for scoring high marks. Avoid rote memorization and instead focus on the logical application of the theories presented in this chapter.

⚠️ Common Mistakes to Avoid

❓ Frequently Asked Questions

How can I quickly memorize the concepts of Quiz?

The most effective way is to create short, handwritten revision notes and continuously test your knowledge using our interactive Mock Tests. Spaced repetition and active recall are much better than passive reading.

What type of questions are most commonly asked from Quiz?

Board exams tend to favor conceptual application questions and direct formula-based derivations from the NCERT syllabus. Ensure you have solved every single exercise in the official textbook.

Is reading the NCERT book enough for this chapter?

Yes, the NCERT textbook is the absolute gold standard for board exams. However, to improve your speed and accuracy during the actual exam, you must supplement your reading by solving timed mock tests and objective questions.