Chemical and Bicarbonate Buffers

Chemical Buffers

• Three major chemical buffers exist: phosphate, protein, and bicarbonate buffers.
• Phosphate buffer primarily functions inside cells and at the renal tubules.
• Protein buffer is abundant inside cells.
• Bicarbonate buffer is considered the most clinically important buffer.

Bicarbonate Buffer System

• Buffers resist changes in pH, where pH indicates the concentration of hydrogen ions; high levels mean acidity, low levels mean alkalinity.
• Carbonic acid (H2CO3), when split, releases hydrogen ions (H+) and bicarbonate ions (HCO3-).
• The process is reversible.
• Carbon dioxide (CO2) produced by the body as a byproduct of metabolism mixes with water (H2O) to form carbonic acid.
• Increased carbon dioxide levels in the blood lead to more carbonic acid, raising hydrogen ion levels and increasing acidity.
• Lungs can remove excess carbon dioxide.

Metabolism and Carbon Dioxide Production

• Body creates carbon dioxide as a byproduct of metabolism.
• Proteins, fats, and carbohydrates are made of carbons, hydrogens, and oxygens and are turned into ATP energy.
• To make ATP, the body rearranges glucose molecules (C6H12O6) in the mitochondria by plucking off hydrogens.
• Hydrogens are given to carrier molecules (NADH, FADH2), which hand off hydrogen ions and electrons to the electron transport chain to produce ATP.
• Carbons and oxygens that are left after hydrogens are taken off form carbon dioxide, which must be removed from the body.

Hydrogen Ions Production

• Increased carbon dioxide in the blood means more carbonic acid and more hydrogen ions, leading to increased acidity.
• Lactic acid, produced during exercise, can also produce hydrogen ions independently of carbon dioxide.
• Accumulated hydrogen ions bond with bicarbonate, forming carbonic acid, then carbon dioxide and water, leading to increased ventilation.

Detection of Changes in Hydrogen Ion and Carbon Dioxide Levels

• Peripheral chemoreceptors, located in the aortic bodies (aortic arch) and carotid bodies (splitting of common carotid arteries), detect hydrogen ions and carbon dioxide.
• Peripheral chemoreceptors trigger neurons that travel to the respiratory zone in the brain stem, signaling to increase ventilation.
• Increased ventilation reduces carbon dioxide levels, which in turn reduces hydrogen ion levels.
• Central chemoreceptors in the brain stem can also be directly stimulated by hydrogen ions and carbon dioxide.

Respiratory Control

• The respiratory system controls the amount of hydrogen ions by managing carbon dioxide levels through breathing.
• Holding breath increases carbon dioxide and hydrogen ion levels, leading to acidity.
• Hyperventilating reduces carbon dioxide and hydrogen ion levels, leading to alkalinity.
• Respiratory control is a short-term mechanism for managing blood pH.

Respiratory Acidosis and Alkalosis

• Respiratory alkalosis occurs when hyperventilation causes excessive reduction of carbon dioxide, leading to lower levels of carbonic acid and hydrogen ions, making the blood too alkaline.
• Respiratory acidosis occurs when the lungs cannot effectively remove carbon dioxide, leading to increased carbon dioxide and hydrogen ion levels, making the blood too acidic.
• Conditions affecting lungs, muscles controlling lungs, bones surrounding lungs, or neurons controlling muscles can cause respiratory acidosis.
• Examples include chronic obstructive pulmonary disease (COPD), rib breakages, and polio.

Renal System

• The renal system regulates the bicarbonate side of the equation in acid-base balance.
• The renal system can increase bicarbonate levels to bind hydrogen ions or pee out excess hydrogen ions.
• Renal control is a long-term control mechanism, taking hours to days to take effect.