Acid-Base Regulation and Blood pH

Basics of pH Value

• pH Value: Indicator of acidity
• Blood pH Value: Narrow range between 7.35 and 7.45
• Slight changes can impair protein stability and biochemical processes

Cell Metabolism and Carbon Dioxide

• Normal cell metabolism constantly produces and excretes carbon dioxide
• Carbon dioxide + water = carbonic acid -> dissociates into hydrogen ions and bicarbonate
• Equilibrium: concentrations influence each other
• Increasing the concentration of one component shifts the equation

Importance of Equilibrium

• Key to understanding acid-base regulation
• Continued carbon dioxide production shifts equilibrium to the right -> more hydrogen ions
• More hydrogen ions -> lower pH value (higher acidity)
• Normal metabolism makes blood more acidic

Mechanisms for pH Regulation

Respiratory System (fast)

• Removal of carbon dioxide through exhalation
• pH value decrease -> deeper, faster breathing
• More carbon dioxide is exhaled -> acidity decreases -> pH value normalizes

Renal System (slow)

• Excretion of hydrogen ions, reabsorption of bicarbonate
• Regulation takes days
• Almost all bicarbonate is reabsorbed into the blood (proximal tubule)
• Downstream collecting duct produces new bicarbonate
• Hydrogen ions combine with urinary buffers (phosphate, ammonia)
• Ammonia production can respond to changes

Additional Factors

• Blood pH value controls acid excretion
• Potassium, chloride concentrations, hormones play important roles

Pathological Changes and Disorders

Acidosis

• Process that causes increased acidity
• Respiratory acidosis: Inadequate lung function -> CO2 accumulation
• Metabolic acidosis: Excessive production of metabolic acids, reduced acid excretion by kidneys, acid intake or alkali loss
• Characterized by a primary decrease in plasma bicarbonate

Alkalosis

• Process that causes increased alkalinity
• Respiratory alkalosis: Increased ventilation -> excessive exhalation of CO2
• Metabolic alkalosis: Excessive acid loss (kidneys/gastrointestinal tract), bicarbonate retention, alkali intake
• Characterized by a primary increase in plasma bicarbonate