Bicarbonate is alkaline, and a vital component of the pH buffering system of the human body (maintaining acid-base homeostasis). 70 to 75 percent of CO2 in the body is converted into carbonic acid (H2CO3), which can quickly turn into bicarbonate (HCO3−).
With carbonic acid as the central intermediate species, bicarbonate – in conjunction with water, hydrogen ions, and carbon dioxide – forms this buffering system, which is maintained at the volatile equilibrium required to provide prompt resistance to drastic pH changes in both the acidic and basic directions. This is especially important for protecting tissues of the central nervous system, where pH changes too far outside of the normal range in either direction could prove disastrous.
Bicarbonate also acts to regulate pH in the small intestine. It is released from the pancreas in response to the hormone secretin to neutralize the acidic chyme entering the duodenum from the stomach.
The most common salt of the bicarbonate ion is sodium bicarbonate, NaHCO3, which is used as baking powder. When exposed to an acid such as acetic acid (vinegar), sodium bicarbonate releases carbon dioxide. This is used as a leavening agent in baking.
The flow of bicarbonate ions from rocks weathered by the carbonic acid in rainwater is an important part of the carbon cycle.
Bicarbonate also serves in the digestive system. It raises the internal pH of the stomach, after highly acidic digestive juices have finished in their digestion of food. Ammonium bicarbonate is used in digestive biscuit manufacture.
Cells in the blood conserve energy and nutrients by converting a waste product of aerobic respiration into a powerful buffer that stabilizes blood pH.
During aerobic respiration, cells of the human body use oxygen and chemical fuel to power functions required for life. The key waste product of this process is carbon dioxide (CO2), and its efficient removal is crucial. In physiological systems, a strategy has evolved for the transport and removal of this molecule, while simultaneously using it to regulate blood acid-base balance.
When CO2 is created in the mitochondrial "powerhouses" of aerobic cells, it immediately diffuses across cell membranes into capillaries. There, it is picked up by red blood cells (RBCs) beginning a journey through the blood to the lungs, ending in excretion through the ventilation process. In RBCs, about 75% of this CO2 is reversibly converted to a molecule called bicarbonate, using the enzyme carbonic anhydrase. This bicarbonate is then excreted out of the RBC where it dissolves in the watery liquid of blood. Upon reaching the lungs, the bicarbonate re-inters the RBC and is converted back to CO2 using the same enzyme. The molecule again diffuses out, and into the lung alveoli where it is expelled in the breath.
Bicarbonate is a small molecule with the formula HCO3- and a molecular weight of 61.01. The body uses this compound as a buffer to help regulate blood pH. Buffers are substances that absorb the impact of an acid or base to maintain a neutral solution. Generally, acids donate hydrogen protons in a solution while bases accept them so pH refers to the concentration of these protons donated. In practice, pH is used to describe the acidity or alkalinity of a substance, enlisting a rating of 0 to 14. Water is considered neutral, and has a pH of 7. Acidic substances have a pH less than 7 while alkaline ones (bases) have a pH greater than 7.
Regulation and Influences in Human Blood
Elevated concentrations of acid (acidosis) or base (alkalosis) have negative effects on the structure and function of biological systems. Regulatory strategies in organisms attempt to keep things as neutral as possible. In Humans, blood pH ranges between 7.35 and 7.45. Above or below this, the body's systems fail, and death ensues. Diet, toxins, exercise, and disease may impair or modify this regulation. Plant-based diets tend to induce a slightly alkaline blood and urine while those high in animal and processed foods are more acidic.
Organisms are continually exposed to hazards of acids and bases through diet, physiological conditions, and the environment. Utilizing CO2 as a buffer is an ingenious strategy since this molecule is already available in mass quantities as a waste product that must be removed. In the process of removal, it is put to work in a crucial role.
In general, the severity of these effects are related to the amount of bicarbonate used. These undesirable effects include:
hypernatraemia
hyperosmolality
volume overload
rebound or 'overshoot' alkalosis
hypokalaemia
impaired oxygen unloading due to left shift of the oxyhaemoglobin dissociation curve
acceleration of lactate production by removal of acidotic inhibition of glycolysis
CSF acidosis
hypercapnia