Fluid and Electrolytes

pH Definition

Measure of hydrogen ion (H⁺) concentration in a solution

pH Scale Range

0–14

Acid vs Neutral vs Base

→ Acid: pH < 7
→ Neutral: pH = 7
→ Base: pH > 7

pH Scale Property

Each unit = 10× change in acidity/basicity

Acid Definition

Substance with excess H⁺ ions

Base definition

Substance with excess OH⁻ ions (accepts H⁺)

Buffer Definition

Solution that resists pH changes when acid/base is added

Electrolyte Definition

Compound that dissociates into ions in water and conducts electricity

Cations vs Anions

→ Cations: positive (Na⁺, K⁺, Ca²⁺)
→ Anions: negative (Cl⁻, PO₄³⁻, OH⁻)

Strong Electrolytes

→ Fully dissociate → conduct electricity well

Non-electrolytes

→ Do NOT form ions → do NOT conduct electricity

4 Main Functions of Electrolytes

→ Enzyme cofactors
→ Fluid balance (osmosis)
→ Acid–base balance (pH)
→ Nerve & muscle activity (electrical signals)

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3 Fluid Compartments

→ Intracellular fluid (ICF)
→ Interstitial fluid
→ Plasma

Major Cation in Extracellular fluid

→ Sodium (Na⁺)

Major Anion in ECF

→ Chloride (Cl⁻)

Sodium Role in Extracellular Fluid (ECF)

→ Nerve impulses, muscle contraction, fluid balance

Major Cation in ICF

→ Potassium (K⁺)

Sources of Acid in Body

→ CO₂ → carbonic acid
→ Metabolism (proteins, fats, glucose)
→ Uric acid
→ Gastric HCl

Sources of Bases

→ Bile
→ Pancreatic secretions
→ Alkaline drugs

3 Mechanisms of pH Control (Critical exam section)

1. Buffer System
   → Works Immediately (seconds)

2. Respiratory System
   → Controls CO₂
   → Works in minutes

3. Renal (Kidney) System
   → Controls H⁺ and HCO₃⁻
   → Works hours–days

Main Buffer System

Carbonic acid–bicarbonate system

Carbonic acid Core equation

CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻

Other Buffer Systems

→ Phosphate buffer
→ Protein buffer (e.g., hemoglobin)

If Blood Becomes Acidic (↓ pH), Respiratory regulation

→ Increase breathing
→ Remove CO₂
→ ↓ H⁺

If Blood Becomes Alkaline (↑ pH), Respiratory regulation

→ Decrease breathing
→ Retain CO₂
→ ↑ H⁺

Renal regulation in acidosis

→ Kidneys excrete H⁺
→ Reabsorb HCO₃⁻

In Alkalosis

→ Kidneys excrete HCO₃⁻
→ Retain H⁺

Normal Blood pH

7.35 – 7.45

Acidosis

pH < 7.35

Respiratory Acidosis Cause

CO₂ retention (lung problems)

Metabolic Acidosis Cause

Excess acids or loss of bicarbonate

Alkalosis

pH > 7.45

Respiratory Alkalosis Cause

Hyperventilation (↓ CO₂)

Metabolic Alkalosis Cause

Loss of acid (vomiting) or excess base

ROME Rule

Respiratory = Opposite

Metabolic = EqualI