Buffer systems

1. What Acid–Base Balance Actually Means

• Your body must keep blood pH tightly between 7.35–7.45.

• Even small shifts affect enzyme function, protein shape, oxygen binding, and cell metabolism.

• pH is controlled by three systems: chemical buffers, respiratory regulation, and renal regulation.

🧪 2. Chemical Buffer Systems (Immediate Response — Seconds)

Buffers resist sudden pH changes by binding or releasing H⁺.

Major Buffers

• Bicarbonate buffer system

  • Most important in extracellular fluid

  • Equation:CO2+H2O⇌H2CO3⇌H++HCO3−

    • If pH drops → H⁺ binds to bicarbonate

    • If pH rises → carbonic acid releases H⁺

    • Phosphate buffer system

      • Works mainly in ICF and kidneys

      • Uses H₂PO₄⁻ / HPO₄²⁻ pair

    • Protein buffer system

      • Most abundant buffer (especially inside cells)

      • Hemoglobin is a major player in RBCs

    🌬 3. Respiratory Regulation (Minutes)

    The lungs adjust pH by controlling CO₂, which acts like an acid.

    If blood becomes acidic (↓ pH)

    • Respiratory rate increases

    • More CO₂ is exhaled → carbonic acid drops → pH rises

    If blood becomes alkaline (↑ pH)

    • Respiratory rate decreases

    • CO₂ accumulates → carbonic acid rises → pH drops

    This is fast but not long‑term.

    🩺 4. Renal Regulation (Hours–Days)

    The kidneys are the most powerful acid–base regulators.

    Kidneys control pH by:

    • Secreting H⁺ into urine

    • Reabsorbing HCO₃⁻

    • Generating new bicarbonate

    • Adjusting ammonia production (NH₃ binds H⁺ → NH₄⁺)

Renal compensation is slow but precise and long‑lasting.

⚠ 5. Acid–Base Imbalances (Exam‑Heavy)

Acidosis (pH < 7.35)

• Respiratory acidosis: CO₂ retention (hypoventilation, COPD)

• Metabolic acidosis: loss of bicarbonate or excess acid (diarrhea, DKA, renal failure)

Alkalosis (pH > 7.45)

• Respiratory alkalosis: excessive CO₂ loss (hyperventilation, anxiety)

• Metabolic alkalosis: excess bicarbonate or loss of acid (vomiting, diuretics)

6. Compensation Patterns (How the body corrects)

• Respiratory problems → kidneys compensate

• Metabolic problems → lungs compensate

• Compensation may be partial or complete

1. Core Concept: What Determines pH?

Blood pH is controlled by the balance between:

• Acids (H⁺ donors)

• Bases (H⁺ acceptors)

• Buffers (resist pH change)

• Respiratory system (controls CO₂ → carbonic acid)

• Renal system (controls H⁺ and HCO₃⁻)

Exam tip:
pH is ultimately determined by the ratio of HCO₃⁻ (metabolic) to CO₂ (respiratory).

. Buffer Systems — Additional Details

Bicarbonate Buffer System

• Most important in ECF

• Controlled by lungs + kidneys

• Works best when both systems are functioning

• Key exam point:

  • Bicarbonate buffer is the only buffer system that is actively regulated by two organs.

Phosphate Buffer System

• Strongest in ICF and urine

• Important for renal tubular fluid, where phosphate concentration is high

• Helps kidneys excrete H⁺ as H₂PO₄⁻

Protein Buffer System

• Most abundant buffer overall

• Works in both ICF and plasma

• Hemoglobin is a major buffer in RBCs

• Important detail:

  • Hemoglobin binds H⁺ when it releases O₂ (Bohr effect)

🌬 3. Respiratory Regulation — Additional Exam Points

CO₂ = Acid

• CO₂ + H₂O → H₂CO₃ → H⁺ + HCO₃⁻

• More CO₂ = more acid

• Less CO₂ = less acid

Respiratory compensation speed

• Begins within 1–3 minutes

• Cannot fully correct severe metabolic issues

Patterns to memorize

• Acidosis → hyperventilation

• Alkalosis → hypoventilation

High‑yield clinical examples

• Panic attack → respiratory alkalosis

• COPD → chronic respiratory acidosis

• High altitude → respiratory alkalosis (low CO₂ due to hyperventilation)

4. Renal Regulation — Additional Details

Kidneys regulate pH by:

• Secreting H⁺

• Reabsorbing HCO₃⁻

• Generating new HCO₃⁻

• Producing ammonia (NH₃) to bind H⁺ → NH₄⁺

Why kidneys are essential

• Only system that can eliminate nonvolatile acids:

  • Lactic acid

  • Ketones

  • Phosphoric acid

  • Sulfuric acid

Exam trap:

Renal compensation takes hours to days, but it is the only system capable of fully restoring pH.

⚠ 5. Acid–Base Disorders — Additional Exam‑Level Details

Respiratory Acidosis

• CO₂ retention

• Causes:

  • COPD

  • Hypoventilation

  • Chest trauma

  • Opioid overdose

• Compensation:

  • Kidneys retain HCO₃⁻

  • Kidneys secrete more H⁺

• Respiratory Alkalosis

  • CO₂ loss

  • Causes:

    • Hyperventilation

    • Pain

    • Anxiety

    • High altitude

  • Compensation:

    • Kidneys excrete HCO₃⁻

  Metabolic Acidosis

  • Loss of HCO₃⁻ or gain of acid

  • Causes:

    • DKA

    • Diarrhea

    • Renal failure

    • Lactic acidosis

  • Compensation:

    • Hyperventilation (Kussmaul breathing)

  Metabolic Alkalosis

  • Loss of acid or excess HCO₃⁻

  • Causes:

    • Vomiting

    • Diuretics

    • Antacid overuse

  • Compensation:

    • Hypoventilation

  🧭 6. Compensation — Additional Details

  Uncompensated

  • pH abnormal

  • Only one value (CO₂ or HCO₃⁻) abnormal

  Partially compensated

  • pH abnormal

  • Both CO₂ and HCO₃⁻ abnormal

  Fully compensated

  • pH normal

  • CO₂ and HCO₃⁻ abnormal

  • Exam trick:

    • If pH is normal but CO₂ and HCO₃⁻ are off → fully compensated.

  📊 7. Henderson–Hasselbalch Concept (BIO 139 loves this)

Even if they don’t give the formula, they test the idea:

pH depends on the ratio of:

• HCO₃⁻ (base)

• CO₂ (acid)

If the ratio increases → pH increases
If the ratio decreases → pH decreases

🧠 8. Additional Clinical Patterns (High‑Yield)

DKA

• Metabolic acidosis

• Compensation: deep, rapid breathing

Vomiting

• Metabolic alkalosis

• Compensation: slow breathing

Diarrhea

• Metabolic acidosis (loss of bicarbonate)

Renal failure

• Metabolic acidosis (cannot excrete acids)

Anxiety

• Respiratory alkalosis

COPD

• Chronic respiratory acidosis

• Kidneys retain HCO₃⁻ over time