Regulation of Blood pH in the Human Body

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Regulation of Blood pH in the Human Body

Acid-Base Disorders (medical applications)

Alkalosis (pH > 7.45)

Metabolic Alkalosis

high HCO₃⁻ or low acid

Acidosis (pH < 7.35)

Metabolic Acidosis

low HCO₃⁻ or high acid

Renal System (Kidneys)

The nephron

Key areas

Collecting Duct

traps H⁺ using NH₃ →NH₄⁺ (pee)

Distal tubule

Proximal tubule

metabolizes glutamine → 2 NH₄⁺ + 2 HCO₃⁻

Mechanisms

Secrete H⁺

Reabsorb HCO₃

slower response (hours–days)

excretion of H⁺ and reabsorption of HCO₃⁻

Respiratory System

CO₂ regulation

Le Chatelier’s Principle

CO₂ decreases, equilibrium shifts left → fewer H⁺ → higher pH

CO₂ increases, equilibrium shifts right → more H⁺ → lower pH

↑CO₂ → ↑H₂CO₃ → ↑H⁺ → ↓pH ↓CO₂ → ↓H⁺ → ↑pH

Hyperventilation (↑ breathing rate):

CO₂ eliminated rapidly

Respiratory Alkalosis

Hypoventilation (↓ breathing rate)

CO₂ accumulates

Respiratory Acidosis

Buffer Systems

solutions that can resist pH change upon the addition of an acidic or basic components.

Ammonia Buffer System (Kidneys)

NH3+H+→NH4+

NH₃ freely diffuses, NH₄⁺ is trapped in urine and excreted

Generates new HCO₃⁻ for each H⁺ secreted

Protein Buffers

Hemoglobin in red blood cells

Reduces Hemoglobin's affinity for O₂ (facilitates delivery)

Bohr effect

Binds H⁺ directly

deoxygenated Hemoglobin binds more CO₂ and H⁺

Haldane Effect

Phosphate Buffer System

Urine & Intracellular Fluid

generate new bicarbonate (Le Chatelier’s Principle)

H2PO4−⇌H++HPO42

excrete H⁺ in kidneys via NaH₂PO₄ (acidic salt)

Bicarbonate Buffer System (Main System in Blood)

Act instantly to resist pH changes

CO2+H2O⇌H2CO3 H2CO3⇌H++HCO3

Sources of acid in the body

Other metabolic acids

Dietary intake or drug metabolism

Ketone bodies

fat metabolism, diabetic ketoacidosis

Lactic acid

anaerobic exercise

Cellular Respiration

CO2+H2O↔H2CO3 H2CO3 ↔H+ +HCO3−

carbonic acid dissociating into bicarbonate and hydrogen ions

Normal Blood pH

7.35 – 7.45 (arterial blood)

Ionization of intermediates in biochemical pathways

Oxygen delivery (Bohr effect)

Enzyme activity