Acid-Base Regulation and pH Value in the Blood

Basics of pH Value

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

Cellular Metabolism and Carbon Dioxide

• Normal cellular metabolism constantly produces and expels carbon dioxide
• Carbon dioxide + water = carbonic acid -> dissociates into hydrogen ions and bicarbonate
• Equilibrium: Concentrations influence each other
• Increase in 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
• Decrease in pH value -> 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 returned to the blood (proximal tubule)
• Downstream collecting duct generates new bicarbonate
• Hydrogen ions bind with urine buffers (phosphate, ammonia)
• Ammonia production can react to changes

Additional Factors

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

Pathological Changes and Disorders

Acidosis

• Process causing increased acidity
• Respiratory Acidosis: Insufficient lung function -> CO2 buildup
• Metabolic Acidosis: Excessive production of metabolic acids, decreased acid excretion by kidneys, acid intake or loss of alkali
• Characterized by primary decrease in plasma bicarbonate

Alkalosis

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