Bicarbonate, scientifically known as HCO₃⁻, is a negatively charged ion that circulates throughout the human body. Bicarbonate is considered a base, which is a substance that can accept hydrogen ions.
Understanding Bicarbonate’s Role
Bicarbonate functions as a component of the bicarbonate buffer system, which is a primary mechanism for maintaining the body’s acid-base balance. A buffer system resists changes in pH when acids or bases are added. The bicarbonate buffer system involves a dynamic relationship between bicarbonate ions (HCO₃⁻), carbonic acid (H₂CO₃), and carbon dioxide (CO₂).
Carbon dioxide, a byproduct of cellular processes, dissolves in the blood and reacts with water to form carbonic acid. This reaction is facilitated by an enzyme called carbonic anhydrase, which rapidly converts carbon dioxide and water into carbonic acid. Carbonic acid is a weak acid that readily dissociates into bicarbonate ions and hydrogen ions (H⁺).
When hydrogen ions are abundant, bicarbonate acts as a weak base, combining with these excess hydrogen ions to form carbonic acid. Conversely, if hydrogen ion levels decrease, carbonic acid can dissociate to release more hydrogen ions and bicarbonate, helping to restore balance.
The Body’s pH Balancing Act
The human body maintains a tightly controlled pH range in the blood, typically between 7.35 and 7.45, which is slightly alkaline. This specific pH is necessary for various bodily functions, including the proper activity of enzymes and metabolic processes.
When acidic substances enter the bloodstream, bicarbonate ions “sponge up” the excess hydrogen ions, forming carbonic acid. This prevents a sharp drop in pH. The carbonic acid then converts into carbon dioxide and water, with the carbon dioxide being exhaled through the lungs. This process removes the acidic component from the body.
Conversely, if the blood becomes too alkaline due to a decrease in hydrogen ions, carbonic acid within the buffer system can dissociate, releasing hydrogen ions and bicarbonate. This release of hydrogen ions helps to lower the pH back towards the normal range.
How Bicarbonate Levels are Controlled
The body employs mechanisms involving both the lungs and kidneys to regulate bicarbonate levels and, by extension, blood pH. The respiratory system plays a role by controlling the amount of carbon dioxide in the blood. When blood pH decreases, the respiratory rate can increase, leading to more carbon dioxide being exhaled. This reduction in carbon dioxide shifts the bicarbonate buffer equilibrium, raising blood pH.
The kidneys also contribute to maintaining bicarbonate levels by reabsorbing bicarbonate ions from the filtered fluid back into the blood and excreting hydrogen ions into the urine. If the blood pH is too high (alkaline), the kidneys can excrete more bicarbonate into the urine and reabsorb fewer hydrogen ions. If the blood pH is too low (acidic), the kidneys can reabsorb more bicarbonate and excrete additional hydrogen ions. This renal regulation process is slower than respiratory adjustments, taking hours to days to fully impact acid-base balance.
When Bicarbonate Levels Go Awry
Disruptions to bicarbonate levels can lead to acid-base imbalances. When bicarbonate levels fall too low, or the body produces too much acid, a condition called acidosis can occur. This can result from various factors, including kidney disease where the kidneys cannot adequately remove acids, or uncontrolled diabetes. Symptoms of acidosis may include fatigue, confusion, and an increased breathing rate.
Conversely, if bicarbonate levels become too high, or there is a loss of acid, alkalosis can develop. This can happen due to prolonged vomiting, which leads to a loss of stomach acid, or certain kidney diseases. Symptoms of alkalosis might include dizziness, muscle twitching, or tingling sensations. Severe or prolonged imbalances can impair organ function and require medical intervention.