Acid–base physiology

Acid–base physiology is the branch of physiology that deals with the regulation of the acid-base balance in the body, ensuring that the pH of the body's fluids is maintained within a narrow range. This balance is crucial for the proper functioning of metabolic processes and the activity of enzymes, which are sensitive to changes in pH levels. The body employs various mechanisms to maintain this balance, involving the respiratory system, renal system, and buffer systems.

Regulation of Acid-Base Balance

The regulation of the acid-base balance involves three major systems: the buffer system, the respiratory system, and the renal system. Each plays a vital role in maintaining the pH within the physiological range of approximately 7.35 to 7.45.

Buffer Systems

Buffer systems act immediately to prevent drastic changes in pH by neutralizing excess acids or bases. The most important buffer systems in the body include the bicarbonate buffer system, the phosphate buffer system, and the protein buffer system. The bicarbonate buffer system is particularly significant in the extracellular fluid, while the phosphate and protein buffer systems are more active within cells.

Respiratory System

The respiratory system regulates the concentration of carbon dioxide (CO2) in the blood, which plays a significant role in the acid-base balance. An increase in CO2 levels leads to an increase in carbonic acid, lowering the pH, whereas a decrease in CO2 levels raises the pH. The respiratory center in the brainstem adjusts the rate and depth of breathing in response to changes in CO2 levels, thus regulating the pH.

Renal System

The renal system contributes to acid-base balance by excreting or reabsorbing bicarbonate (HCO3-) and hydrogen ions (H+) in the urine. This process is slower than the respiratory compensation but is crucial for the long-term maintenance of acid-base balance. The kidneys can also generate new bicarbonate ions, which are added to the blood, helping to neutralize excess acids.

Disorders of Acid-Base Balance

Disorders of acid-base balance can result from abnormalities in the respiratory or renal systems, leading to acidosis or alkalosis.

Acidosis

Acidosis is a condition characterized by an excess of acid in the body, leading to a decrease in blood pH. It can be classified as either respiratory acidosis, due to inadequate exhalation of CO2, or metabolic acidosis, resulting from excessive production of acids or inadequate excretion of acids by the kidneys.

Alkalosis

Alkalosis is the opposite condition, where there is an excess of base in the body, leading to an increase in blood pH. Respiratory alkalosis occurs due to excessive exhalation of CO2, while metabolic alkalosis can result from excessive loss of acids or an increase in bicarbonate levels.

Clinical Significance

Understanding acid-base physiology is crucial in clinical medicine, as disturbances in the acid-base balance are common in critically ill patients and can significantly impact the outcome. The accurate diagnosis and management of acid-base disorders require a thorough understanding of the underlying physiology and the compensatory mechanisms involved.