Overview of pH Regulation

  • The biochemical activity of most enzymes are highly sensitive to the surrounding free hydrogen ion concentration. Consequently, even slight changes in the extracellular pH can lead to significant and widespread derangement of cellular functioning. Given the importance of ECF pH to normal physiology, the value of ECF pH is tightly regulated and centers around pH 7.4, ranging from pH 7.37 - 7.42. As discussed below, a variety of physiological mechanisms exist to prevent changes in the ECF pH and operate on different timescales. Here we only briefly introduce these mechanisms whereas their respective sections discuss each in more detail.
pH Regulatory Mechanisms
  • Physiological Buffers: Rapid Correction
    • Physiological Buffers are chemicals found at high concentrations in the extracellular fluid which serve to nearly instantly absorb or release H+ ions in response to changes in the ECF pH. Together, they act as a rapid regulatory system to prevent short-term changes in blood pH. However, use of buffers is ultimately a quick fix as there is not an endless reservoir of these chemicals. Consequently, any additions or removals of free hydrogen ions from the ECF must ultimately be corrected by other physiological mechanisms and levels of physiological buffers must be restored over the long-term.
  • Respiratory Acid-Base Control: Medium-term Correction
    • The lungs can be used to correct medium-term changes in the ECF H+ concentration by modulating the rate at which the volatile acid CO2 is eliminated or colloquially "Breathed off". However, this is not a long-term solution as modulation of the respiratory rate ultimately affects other physiological systems.
  • Renal Acid-Base Control: Long-term Correction
    • Ultimately, the only organ that can definitively excrete excessive H+ when ECF pH is too low, or generate new H+ when ECF pH is too high is the kidney. Therefore, the kidneys are solely responsible for long-term correction of acid-base disturbances.