Bicarbonate

Bicarbonate is the HCO₃⁻ ion, formed when carbonic acid loses a proton. It transports much of the carbon dioxide in blood and buffers changes in acidity.

Carbonic anhydrase: An enzyme that rapidly interconverts carbon dioxide and water with carbonic acid and protons. It accelerates bicarbonate formation in tissues and carbon dioxide release in the lungs.
Blood gas test: A laboratory test measuring blood pH, oxygen, carbon dioxide, and related acid–base values. Its calculated bicarbonate value helps distinguish respiratory from metabolic disturbances.
Acid–base reaction: A chemical reaction involving transfer of a proton between an acid and a base. Bicarbonate acts as a base when accepting a proton and as an acid when donating one.
Respiration: The cellular process that extracts energy from molecules, commonly using oxygen and producing carbon dioxide. Its carbon dioxide output enters the reactions that generate bicarbonate in tissues.
Carbonic acid: The weak acid H₂CO₃, formed when dissolved carbon dioxide reacts with water. It is the short-lived acid that dissociates to produce bicarbonate and a proton.
Metabolic acidosis: An acid–base disorder in which a primary reduction in bicarbonate lowers blood pH. Bicarbonate depletion is the defining biochemical feature of this disorder.
pH: A logarithmic measure of hydrogen-ion activity in a solution. Bicarbonate buffering limits changes in this measure when acid or base is added.
Hemoglobin: The iron-containing protein in red blood cells that binds and transports oxygen. Hemoglobin buffers protons produced alongside bicarbonate and supports carbon dioxide carriage.
Henderson–Hasselbalch equation: An equation relating a buffer’s pH to its acid-to-base ratio and dissociation constant. It quantifies how bicarbonate concentration and dissolved carbon dioxide determine blood pH.
Respiratory acidosis: An acid–base disorder caused by carbon dioxide retention that lowers blood pH. Kidneys raise bicarbonate over time to partly compensate for retained carbon dioxide.

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