Physiology
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Boundless Anatomy and Physiology
Body Fluids and Acid-Base Balance
Acid-Base Balance
Physiology Textbooks Boundless Anatomy and Physiology Body Fluids and Acid-Base Balance Acid-Base Balance
Physiology Textbooks Boundless Anatomy and Physiology Body Fluids and Acid-Base Balance
Physiology Textbooks Boundless Anatomy and Physiology
Physiology Textbooks
Physiology
Concept Version 7
Created by Boundless

The Role of the Kidneys in Acid-Base Balance

The kidneys help maintain acid-base balance by excreting hydrogen ions into the urine and reabsorbing bicarbonate from the urine.

Learning Objective

  • Describe the role of the kidney in acid-base balance


Key Points

    • The kidneys maintain homeostasis through excretion of waste products.
    • Acidosis causes more bicarbonate to be reabsorbed from tubular fluid while collecting ducts secrete more hydrogen to generate more bicarbonate; and more NH3 buffer is formed.
    • Alkalosis causes the kidney to excrete more bicarbonate as there is reduced secretion of hydrogen ions and more ammonium is excreted.

Terms

  • base

    any of a class of generally water-soluble compounds, having bitter taste, that turn red litmus blue, and react with acids to form salts

  • renal

    Pertaining to the kidneys.


Example

    • Urine testing is important because it can detect acid-base imbalances. For instance, uncontrolled diabetes results in highly acidic urine. If the diabetes remains uncontrolled, the kidneys could become over-stressed and malfunction which could lead to coma or death.

Full Text

Within the human body, fluids such as blood must be maintained within the narrow range of 7.35 to 7.45, making it slightly alkaline. Outside the range, pH becomes incompatible with life; proteins are denatured and digested, enzymes lose their ability to function, and the body is unable to sustain itself.

To maintain this narrow range of pH the body has a powerful buffering system. Acid–base imbalances that overcome this system can be compensated in the short term by changing the rate of ventilation.

The kidneys also play an important role in maintaining acid-base homeostasis by regulating the pH of the blood plasma. The kidneys have two very important roles in maintaining the acid-base balance: to reabsorb bicarbonate from urine, and to excrete hydrogen ions into urine. The kidneys are slower to compensate than the lungs, but renal physiology has several powerful mechanisms to control pH by the excretion of excess acid or base. The major homeostatic control point for maintaining a stable balance is renal excretion.

Bicarbonate (HCO3-) does not have a transporter, so its reabsorption involves a series of reactions in the tubule lumen and tubular epithelium. In response to acidosis, tubular cells reabsorb more bicarbonate from the tubular fluid, collecting duct cells secrete more hydrogen and generate more bicarbonate, and ammoniagenesis leads to increased formation of the NH3 buffer. In response to alkalosis, the kidneys may excrete more bicarbonate by decreasing hydrogen ion secretion from the tubular epithelial cells, and lowering rates of glutamine metabolism and ammonium excretion.

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