30.11 : Acid-Base Balance

The human body maintains a narrow pH range regulated through acid-base balance. This balance is crucial as changes in the hydrogen ion concentration can disrupt cell membrane stability, alter protein structures, and change enzyme activities. The normal pH of arterial blood is 7.4, venous blood and interstitial fluid is 7.35, and intracellular fluid averages 7.0.

When the pH of arterial blood rises above 7.45, it results in a condition called alkalosis. Conversely, a drop below 7.35 leads to acidosis. These conditions affect all body systems, particularly the nervous and cardiovascular systems. Severe acidosis can be fatal, causing central nervous system deterioration, weak and irregular cardiac contractions, and a dramatic decrease in blood pressure, potentially leading to circulatory collapse.

Several mechanisms come into play to maintain the pH of body fluids. They include buffer systems and compensations by the respiratory and urinary systems, which work together to keep body pH within narrow limits.

Chemical buffers bind and release hydrogen ions to resist pH fluctuations, ensuring stability. Respiratory compensation involves adjusting breathing rate and depth to control carbon dioxide and carbonic acid concentrations in the blood. Renal regulation, carried out by the kidneys, modulates the secretion and reabsorption rates of hydrogen and bicarbonate ions in response to blood pH changes, contributing to the overall maintenance of the body's acid-base equilibrium.