Lecture on Kidney Regulation of Acid-Base Balance

Introduction

• Focus on how kidneys regulate acid-base balance.
• Mention of the bicarbonate buffer equation.

Metabolism and CO2 Production

• Cells produce ATP by metabolizing proteins, fats, and carbohydrates.
• Metabolism leaves behind carbon dioxide (CO2) as a byproduct.
• CO2 combines with water in the blood to form carbonic acid (H2CO3).
• Carbonic acid dissociates into hydrogen and bicarbonate ions.

Respiratory Regulation of pH

• Lungs regulate CO2 levels, affecting blood acidity.
• High CO2 leads to more hydrogen ions (more acidic blood).
• Low CO2 (e.g., hyperventilation) leads to fewer hydrogen ions (more alkaline blood).

Role of Kidneys

• Kidneys regulate bicarbonate levels in the blood.
• Three key functions:
  1. Reabsorb bicarbonate.
  2. Excrete hydrogen ions.
  3. Generate new bicarbonate.
• Kidney regulation is longer-term (hours to days).

Kidney Structure and Function

• Kidneys contain cortex and medulla; blood enters through renal artery.
• Nephrons are the functional units for filtration.
• Blood filters through nephron tubules; most substances reabsorbed.
• 180 L of blood filtered per day; 1.8 L excreted as urine.

Reabsorption of Bicarbonate

• Occurs mainly in the proximal convoluted tubule.
• Bicarbonate is reabsorbed via conversion to carbon dioxide and water.
• Sodium-potassium pump plays a role in reabsorption.
• For every bicarbonate reabsorbed, a hydrogen ion is excreted as water.

Handling Excess Bicarbonate and Hydrogen Ions

• Excess bicarbonate is excreted to prevent alkalosis.
• If excess hydrogen ions exist, a new buffer (phosphate buffer) is used.
• New bicarbonate is generated when hydrogen ions are buffered.

Generation of New Bicarbonate

• Phosphate buffer system allows excretion of hydrogen ions.
• Glutamine metabolism produces bicarbonate and ammonium ions.
• Ammonia binds with hydrogen to form ammonium, which is excreted.

Conclusion

• Kidneys manage pH by reabsorbing bicarbonate, excreting hydrogen ions, and generating new bicarbonate.
• This process is vital for maintaining acid-base balance.