Regulation of Blood pH: Learn about the kidneys' role in maintaining acid-base balance through bicarbonate reabsorption and hydrogen ion secretion. The kidneys play a crucial role in maintaining the body's acid-base balance, also known as pH balance. The balance between acidic and alkaline substances in the body's fluids is essential for normal physiological processes. The kidneys regulate blood pH by reabsorbing bicarbonate ions (HCO3-) and secreting hydrogen ions (H+) into the urine. Here's how the kidneys help maintain acid-base balance: 1. Bicarbonate Reabsorption:  Bicarbonate Ions (HCO3-): Bicarbonate is a buffer in the blood that helps regulate pH. When it reacts with hydrogen ions, it forms carbonic acid (H2CO3), which can be converted back into HCO3- and H+.  Proximal Convoluted Tubule (PCT): The majority of bicarbonate reabsorption occurs in the PCT. Hydrogen ions are actively secreted into the tubular lumen, and bicarbonate ions are reabsorbed into the bloodstream in exchange. This process helps prevent the loss of bicarbonate from the body. 2. Hydrogen Ion Secretion:  Renal Tubules: Hydrogen ions are actively secreted into the renal tubules, particularly in the distal convoluted tubule (DCT) and collecting ducts.  Role of Ammonia: Ammonia (NH3) is produced by the deamination of amino acids in the liver. In the kidneys, ammonia combines with hydrogen ions to form ammonium ions (NH4+), which can be excreted in the urine. This helps eliminate excess hydrogen ions and maintain blood pH. 3. Acid-Base Regulation:  Acidosis: In cases of acidosis (low blood pH), the kidneys respond by increasing hydrogen ion secretion and bicarbonate reabsorption. This helps remove excess hydrogen ions from the blood and increase the buffering capacity.  Alkalosis: In cases of alkalosis (high blood pH), the kidneys reduce bicarbonate reabsorption and hydrogen ion secretion, allowing more bicarbonate to be eliminated in the urine. 4. Regulation of Respiratory Acid-Base Balance:  Respiratory Compensation: The lungs and kidneys work together to regulate acid-base balance. When there's a primary respiratory disturbance (e.g., hypoventilation leading to increased carbon dioxide), the kidneys compensate by retaining bicarbonate ions. Similarly, if there's a primary metabolic disturbance (e.g., increased production of acids), the lungs can compensate by altering ventilation to adjust carbon dioxide levels. In summary, the kidneys play a crucial role in maintaining blood pH within a narrow range by reabsorbing bicarbonate ions and secreting hydrogen ions. These processes help prevent the accumulation of excess acids or bases in the body, contributing to overall acid-base balance and ensuring proper physiological function.