Bicarbonate

Examples of Bicarbonate in the following topics:

• The Role of the Kidneys in Acid-Base Balance

  • The kidneys help maintain acid-base balance by excreting hydrogen ions into the urine and reabsorbing bicarbonate from the urine.
  • The kidneys have two very important roles in maintaining the acid-base balance: to reabsorb bicarbonate from urine, and to excrete hydrogen ions into urine.
  • Bicarbonate (HCO3-) does not have a transporter, so its reabsorption involves a series of reactions in the tubule lumen and tubular epithelium.
  • In response to acidosis, tubular cells reabsorb more bicarbonate from the tubular fluid, collecting duct cells secrete more hydrogen and generate more bicarbonate, and ammoniagenesis leads to increased formation of the NH3 buffer.
  • In response to alkalosis, the kidneys may excrete more bicarbonate by decreasing hydrogen ion secretion from the tubular epithelial cells, and lowering rates of glutamine metabolism and ammonium excretion.

• Anion Regulation

  • Anions chloride, bicarbonate, and phosphate have important roles in maintaining balances and neutrality of vital mechanisms in the body.
  • Severe vomiting or diarrhea will also cause a loss of chloride and bicarbonate ions.
  • Bicarbonate is the second most abundant anion in the blood.
  • Bicarbonate is transported in the blood, and once in the lungs, the reactions reverse direction, and CO2 is regenerated from bicarbonate to be exhaled as metabolic waste .
  • In the lungs, CO2 is produced from bicarbonate and removed as metabolic waste through the reverse reaction of the bicarbonate bidirectional equation.

• Chemical Buffer Systems

  • Chemical buffers such as bicarbonate and ammonia help keep blood pH in the narrow range compatible with life.
  • Extracellular buffers include bicarbonate and ammonia, whereas proteins and phosphate act as intracellular buffers.
  • The bicarbonate buffering system is especially key, as carbon dioxide (CO2) can be shifted through carbonic acid (H2CO3) to hydrogen ions and bicarbonate (HCO3-):
  • In response to acidosis, tubular cells reabsorb more bicarbonate from the tubular fluid, collecting duct cells secrete more hydrogen and generate more bicarbonate, and ammoniagenesis leads to increased formation of the NH3 buffer.
  • In responses to alkalosis, the kidneys may excrete more bicarbonate by decreasing hydrogen ion secretion from the tubular epithelial cells, and lowering rates of glutamine metabolism and ammonium excretion.

• Carbon Dioxide Transport

  • The majority (85%) of carbon dioxide travels in the blood stream as bicarbonate ions.
  • The reaction that describes the formation of bicarbonate ions in the blood is:
  • This means that carbon dioxide reacts with water to form carbonic acid, which dissociates in solution to form hydrogen ions and bicarbonate ions.
  • Bicarbonate ions act as a buffer for the pH of blood so that blood pH will be neutral as long as bicarbonate and hydrogen ions are balanced.
  • For carbon dioxide stored in bicarbonate, it undergoes a reaction reversal.

• Alkalosis

  • Compensatory mechanisms for this would include increased dissociation of the carbonic acid buffering intermediate into hydrogen ions, and the related excretion of bicarbonate, both of which lower blood pH.
  • This is the result of decreased hydrogen ion concentration, leading to increased bicarbonate or alternatively a direct result of increased bicarbonate concentrations.
  • A Davenport Diagram, as shown, is a graphical tool developed by Allan Jones Davenport that allows a clinician or investigator to describe blood bicarbonate concentrations and blood pH following a respiratory and/or metabolic acid-base disturbance.

• Chemoreceptor Regulation of Breathing

  • Because most carbon dioxide is converted to carbonic acid (and bicarbonate) in the bloodstream, chemoreceptors are able to use blood pH as a way to measure the carbon dioxide levels of the bloodstream.
  • A person with severe diarrhea loses a lot of bicarbonate in the intestinal tract, which decreases bicarbonate levels in the plasma.
  • As bicarbonate levels decrease while hydrogen ion concentrations stays the same, blood pH will decrease (as bicarbonate is a buffer) and become more acidic.

• Acidosis

  • When metabolic acidosis is severe and can no longer be compensated for adequately by the lungs, neutralizing the acidosis with infusions of bicarbonate may be required.
  • One key to distinguish between respiratory and metabolic acidosis is that in respiratory acidosis, the CO2 is increased while the bicarbonate is either normal (uncompensated) or increased (compensated).
  • Compensation occurs if respiratory acidosis is present, and a chronic phase is entered with partial buffering of the acidosis through renal bicarbonate retention.
  • As metabolic bicarbonate production becomes exhausted, and extraneous bicarbonate infusion can no longer reverse the extreme buildup of carbon dioxide associated with uncompensated respiratory acidosis, mechanical ventilation will usually be applied.

• Pancreatic Juice

  • Pancreatic juice is alkaline in nature due to the high concentration of bicarbonate ions.
  • Pancreatic secretion consists of an aqueous bicarbonate component from the duct cells and enzymatic component from the acinar cells.

• Anatomy of the Digestive System

  • The duodenum contains Brunner's glands which produce bicarbonate, and pancreatic juice which contains bicarbonate to neutralize hydrochloric acid of the stomach.

• Chemical Composition of Bone

  • ., blood pH is low (less than 7.35) due to increased production of hydrogen by the body or the inability of the body to form bicarbonate (HCO3-) in the kidneys.
  • This is the result of decreased hydrogen ion concentration, leading to increased bicarbonate, or alternatively a direct result of increased bicarbonate concentrations.
  • Renal compensation for metabolic alkalosis, less effective than respiratory compensation, consists of increased excretion of HCO3- (bicarbonate), as the filtered load of HCO3- exceeds the ability of the renal tubule to reabsorb it.