The human body is built to naturally maintain a healthy balance of acidity and alkalinity. The lungs and kidneys play a key role in this process. Your blood needs the right balance of acidic and basic (alkaline) compounds to function properly. The kidneys and lungs work to maintain the proper acid-base balance.
The blood's acid-base balance is precisely controlled because even a minor deviation from the normal range can severely affect many organs. The body uses different mechanisms to control the blood's acid-base balance. These mechanisms involve the lungs, kidneys and chemical buffer systems.
When the levels of acid in your blood are too high, it’s called acidosis. When your blood is too alkaline, it is called alkalosis. Respiratory acidosis and alkalosis are due to a problem with the lungs. Metabolic acidosis and alkalosis are due to a problem with the kidneys. Each of these conditions is normally caused by an underlying disease or disorder and treatment depends on the cause.
The lungs control blood pH through the release of carbon dioxide. Carbon dioxide is mildly acidic, and a waste product of the processing (metabolism) of oxygen and nutrients (which all cells need) and is constantly produced by cells. It then passes from the cells into the blood. The blood carries carbon dioxide into the lungs, where it is exhaled.
The kidneys are able to affect blood pH by excreting excess acids or bases. The kidneys have some ability to alter the amount of acid or base that is excreted, but because the kidneys make these adjustments more slowly than the lungs do, this compensation generally takes several days.
Chemical Buffer Systems
Another mechanism for controlling blood pH involves the use of chemical buffer systems, which guard against sudden shifts in acidity and alkalinity. The pH buffer systems are combinations of the body's own naturally occurring weak acids and weak bases. These weak acids and bases exist in pairs that are in balance under normal pH conditions. The pH buffer systems work chemically to minimize changes in the pH of a solution by adjusting the proportion of acid and base.
The most important pH buffer system in the blood involves carbonic acid (a weak acid formed from the carbon dioxide dissolved in the blood) and bicarbonate ions (the corresponding weak base).
Compensating for Imbalances
To regain acid-base balance, the lungs may respond to a metabolic disorder, and the kidneys may respond to a respiratory disorder. If pH remains abnormal, the respiratory or metabolic response is called partial compensation. If the pH returns to normal, the response is called complete compensation. The respiratory or renal system will never overcompensate. A compensatory mechanism won’t make an acidotic patient alkalotic or an alkalotic patient acidotic.