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.

• Salts that Produce Basic Solutions

  • An example of a basic salt is sodium bicarbonate, NaHCO3.
  • The bicarbonate ion is the conjugate base of carbonic acid, a weak acid.
  • Because it is capable of deprotonating water and yielding a basic solution, sodium bicarbonate is a basic salt.
  • Because the bicarbonate ion is the conjugate base of carbonic acid, a weak acid, sodium bicarbonate will yield a basic solution in water.

• 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.

• Overview of the Acid-Base Properties of Salt

  • Some salts, such as ammonium bicarbonate (NH4HCO3), contain cations and anions that can both undergo hydrolysis.
  • However, as we have already discussed, the ammonium ion acts as a weak acid in solution, while the bicarbonate ion acts as a weak base.
  • Because both ions can hydrolyze, will a solution of ammonium bicarbonate be acidic or basic?
  • In this case, the value of Kb for bicarbonate is greater than the value of Ka for ammonium.
  • Therefore, bicarbonate is a slightly more alkaline than ammonium is acidic, and a solution of ammonium bicarbonate in pure water will be slightly basic (pH > 7.0).

• Transport of Carbon Dioxide in the Blood

  • Dissolution, hemoglobin binding, and the bicarbonate buffer system are ways in which carbon dioxide is transported throughout the body.
  • Third, the majority of carbon dioxide molecules (85 percent) are carried as part of the bicarbonate buffer system.
  • When the blood reaches the lungs, the bicarbonate ion is transported back into the red blood cell in exchange for the chloride ion.
  • The H+ ion dissociates from the hemoglobin and binds to the bicarbonate ion.
  • The presence of this bicarbonate buffer system also allows for people to travel and live at high altitudes.

• 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.

• Carbon Oxides and Carbonates

  • In aqueous solutions, carbonate, bicarbonate (HCO3-), carbon dioxide, and carbonic acid exist together in equilibrium.
  • In strongly basic conditions, the carbonate ion predominates, while in weakly basic conditions, the bicarbonate ion predominates.
  • Sodium carbonate is basic when dissolved in water (meaning it results in a basic solution upon dissolution), and sodium bicarbonate is weakly basic.
  • That's because it reacts with water to produce H2CO3, a small amount of which will dissociate into H+ and a bicarbonate ion.
  • Although the carbonate salts of most metals are insoluble in water, this is not true of the bicarbonate salts.