The bicarbonate ion is an anion with the empirical formula HCO−3.

It drives the acid-base status of the blood.

The bicarbonate ion carries a negative one formal charge and is an amphiprotic species which has both acidic and basic properties.

A bicarbonate salt forms when a positively charged ion attaches to the negatively charged oxygen atoms of the ion, forming an ionic compound.

Many bicarbonates are soluble in water.

CO2 produced as a product of the oxidation of sugars in the mitochondria reacts with water in a reaction catalyzed by carbonic anhydrase to form H2CO3, which is in equilibrium with the cation H+ and anion HCO3−.

It is then transferred to the lung, where the reverse reaction occurs and CO2 gas is released.

The kidneys predominantly regulate bicarbonate concentration and are responsible for maintaining the acid-base balance. 

In the kidney the proximal tubule cells conserve bicarbonate by transporting it from the glomerular filtrate in the lumen of the nephron back into the blood .

Kidneys reabsorb the filtered bicarbonate and also generate new bicarbonate by net acid excretion, which occurs by excretion of both titrable acid and ammonia. 

Bicarbonate (HCO−3) is a vital component of the pH buffering system of the human body helping to maintain acid–base homeostasis.

70%–75% of CO2 in the body is converted into carbonic acid (H2CO3).

Carbonic acid as the central intermediate species forms this buffering system, which is maintained at the volatile equilibrium.

Bicarbonate in conjunction with water, hydrogen ions, and carbon dioxide forms this buffering system.

This buffering system maintained at the volatile equilibrium provides prompt resistance to pH changes in both the acidic and basic directions.

The buffering system is especially important for protecting the central nervous system, where pH changes too far outside of the normal range in either direction could prove disastrous.

Bicarbonate raises the internal pH of the stomach, after highly acidic digestive juices have finished in their digestion of food, and acts to regulate pH in the small intestine.

Bicarbonate is released from the pancreas in response to the hormone secretin to neutralize the acidic chyme entering the duodenum from the stomach.

It is the dominant form of dissolved inorganic carbon in sea water, and in most fresh waters.

The most common salt of the bicarbonate ion is sodium bicarbonate, NaHCO3, which is commonly known as baking soda.

When heated or exposed to an acid such as vinegar, sodium bicarbonate releases carbon dioxide.

It is one of several indicators of the state of acid–base physiology in the body.

It is measured, along with carbon dioxide, chloride, potassium, and sodium, to assess electrolyte levels in an electrolyte panel test.

The standard bicarbonate concentration (SBCe) is the bicarbonate concentration in the blood at a PaCO2 of 40 mmHg.

Chronic low serum bicarbonate concentration, is often a manifestation of kidney function decline,

skeletal muscle breakdown, bone demineralization, and all-cause mortality.

There is a link between serum bicarbonate and all-cause mortality, with an increased risk of death associated with both high and low serum bicarbonate concentration.

Serum bicarbonate concentration level below 22 mEq per liter is associated with malignancy related mortality.

Serum bicarbonate concentration above 26 mEq per liter is associated with cardiovascular mortality.

For each one milliequivalents per liter of higher serum bicarbonate concentration above 26 mEq per liter is associated with an 8% increase in cardiovascular mortality (Al-!ikndi SG).

Both high and low bicarbonate concentrations are associated with increased all-cause mortality in chronic kidney disease.

In patients with the serum bicarbonate concentration less than 22 mEq per liter is associated with a 2.6 fold increase hazard of death and individuals with chronic kidney disease.

The risk of cancer mortality is higher for low serum bicarbonate group and participants younger than 65 years, and the difference with an older group was not statistically significant.

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