Module 2 Part II

Define an acid and a base according to the Brønsted-Lowry definition.

Acid = proton donor; Base = proton acceptor.

What is the main difference between a strong and a weak acid?

Strong acids completely dissociate in water; weak acids only partially dissociate

Give two examples of strong acids.

Hydrochloric acid (HCl), Nitric acid (HNO₃), Sulfuric acid (H₂SO₄)

Give two examples of strong bases.

NaOH, KOH, Ca(OH)₂.

What is pH, and how is it calculated?

pH = –log[H⁺]; a measure of hydrogen ion concentration.

State the normal blood pH range.

7.35 – 7.45.

What is the Henderson-Hasselbalch equation?

pH = pKa + log([A⁻]/[HA]).

What is the pKa of the bicarbonate buffer system?

The pKa of the bicarbonate buffer system is approximately 6.1, which reflects the acid dissociation constant of carbonic acid.

Name the three major buffer systems in the body.

Bicarbonate, protein, phosphate.

Which buffer system is the most important in extracellular fluid (ECF)?

Bicarbonate buffer system.

Which protein acts as a major buffer in blood?

Hemoglobin.

Why can’t the bicarbonate buffer system correct respiratory acidosis?

: Because it cannot buffer changes in CO₂ directly.

Where is phosphate buffering most important?

Intracellular fluid, kidneys, and urine.

Define acidemia and alkalemia.

Acidemia = blood pH < 7.35; Alkalemia = blood pH > 7.45.

What are the primary disturbances in respiratory acidosis?

↑ pCO₂, ↓ pH, with renal compensation via ↑ HCO₃⁻

List two causes of respiratory alkalosis.

Anxiety/panic, pain, drug-induced hyperventilation.

What happens to HCO₃⁻ and pCO₂ in metabolic acidosis?

HCO₃⁻ decreases, pCO₂ decreases (respiratory compensation)

List two causes of metabolic alkalosis.

Bicarbonate ingestion, iatrogenic infusion.

What is base excess and its normal range?

Amount of acid needed to restore 1 L blood to pH 7.4 at pCO₂ 40 mmHg; normal –3 to +3 mmol/L.

What is the anion gap formula and normal range?

Anion gap = [Na⁺] – ([HCO₃⁻] + [Cl⁻]); normal 12 ± 2.

Which two conditions produce the largest anion gaps?

Diabetic ketoacidosis and lactic acidosis.

Describe the bicarbonate buffer system, its mechanism, and its physiological importance.

• Bicarbonate (HCO₃⁻) has pKa 6.1, present in large amounts, and is an “open” system regulated by lungs (CO₂ elimination) and kidneys (HCO₃⁻ reabsorption).

• Reaction: H⁺ + HCO₃⁻ ↔ H₂CO₃ ↔ H₂O + CO₂.

• ↑ H⁺ → drives reaction to CO₂ (exhaled); ↑ HCO₃⁻ → buffers excess acid.

• Most important ECF buffer; maintains blood pH within 7.35–7.45

Explain the compensatory mechanisms in respiratory and metabolic acid-base disorders.

• Respiratory acidosis (↑ pCO₂): renal ↑ HCO₃⁻ reabsorption.

• Respiratory alkalosis (↓ pCO₂): renal ↓ HCO₃⁻ reabsorption.

• Metabolic acidosis (↓ HCO₃⁻): respiratory hyperventilation → ↓ pCO₂.

• Metabolic alkalosis (↑ HCO₃⁻): hypoventilation → ↑ pCO₂.

• Compensation maintains pH but rarely returns it fully to normal

Discuss the role of the kidneys in acid-base balance.

• Kidneys excrete H⁺ and reabsorb/regenerate HCO₃⁻.

• H⁺ secreted in proximal tubule via Na⁺/H⁺ antiport.

• Urinary buffers (phosphate, ammonia) trap H⁺ (H₂PO₄⁻, NH₄⁺).

• HCO₃⁻ reabsorbed via carbonic anhydrase reaction: H⁺ + HCO₃⁻ → H₂CO₃ → CO₂ + H₂O → diffuses into tubule cell, reforms HCO₃⁻, enters blood.

• Prevents acidosis by maintaining plasma [HCO₃⁻]

Define and explain the diagnostic use of the anion gap in metabolic acidosis.

• Anion gap = [Na⁺] – ([Cl⁻] + [HCO₃⁻]).

• Normal = 12 ± 2.

• Used to distinguish causes of metabolic acidosis:

  • ↑ Anion gap = accumulation of unmeasured anions (lactate, ketones, toxins, renal failure).

  • Normal anion gap (hyperchloremic acidosis) = HCO₃⁻ loss replaced by Cl⁻ (diarrhea, renal tubular acidosis).