Acids, Bases, & Buffers Lab Notes

Acids, Bases, & Buffers

• Lab for BIO 169 Anatomy and Physiology II.

Definitions

• Hydrogen Ions (H+): Very reactive.

• pH: Concentration of H+ in a solution. Scale numbers are inversely related to [H+].

• Acids: Solutes that act as a Proton Donor in solution.

• Base: Solutes that act as a Proton Acceptor in solution (donate –OH-).

• Buffers: Substances that Neutralize acids and bases.

pH Scale

• Inverse relationship with H+ concentration.

• More H+ ions mean lower pH, less H+ ions mean higher pH.

• Pure water is neutral – pH 7.0.

• [H^+] = 0.0000001 mol/L

Indicators

• Organic substance that changes color at a specific pH.

Buffers

• Neutralize either strong acid or strong base by removing or adding H+.

• Weak acid or weak base.

• Sodium bicarbonate (NaHCO_3) is very important in humans.

  • Eg. Antacids - Basic compounds that neutralize acid like Alka-Seltzer, Tums, Rolaids, etc.

• Physiological health is dependent on a narrow pH range (7.35 - 7.45).

• Digestion and metabolism are sources of H+ in the body.

• Buffer systems (4) act to neutralize H+ in the body.

Phosphate Buffer System

• Primary role in regulating intracellular and urine pH.

• In acidic conditions: H^+ + HPO4^{2-} ighthleftharpoons H2PO_4^- (dihydrogen phosphate)

  • This neutralizes excess acidity by binding H+ ions and removing them from the body fluids.

• In alkaline conditions: H2PO4^- ighthleftharpoons H^+ + HPO_4^{2-}

  • This neutralizes excess base by releasing free H+ into body fluids.

Protein Buffer System

• Amino Acid Buffers and Plasma Proteins Buffers

• Amino acids can accept or donate H+.

• In acidic conditions, the amino group binds H+ ions: NH2 + H^+ ighthleftharpoons -NH3^+

• In alkaline conditions, the carboxyl groups of amino acids release H+ ions: -COOH
  ighthleftharpoons -COO^- + H^+

Ammonia Buffer System

• Glutamine is an amino acid that is metabolized in the kidney and generates NH_3.

• This can lead to H+ excretion.

Hemoglobin Buffer System

• Regulates pH in response to fluctuating PCO_2 in plasma

• Hb binds the H+

• CO2 + H2O \rightarrow H2CO3 \rightarrow H^+ + HCO_3^-

Carbonic Acid-Bicarbonate Buffer System

• Regulates pH in response to metabolic acids in ECF.

• Carbonic Anhydrase catalyzes this reaction

  • Present in RBC, Parietal Cells, Pancreatic and Renal Cells

pH Scale & Alkalosis and Acidosis

• Normal pH range of arterial blood: 7.35 - 7.45

• Acidosis: pH < 7.35

• Alkalosis: pH > 7.45

• Survival range: 6.8 - 8.0

pH Balance

• Maintained by collaboration of:

  • Buffer Systems

  • Respiratory System

  • Renal System

Compensation

• Lungs:

  • Hypoventilation: Increase of pCO_2, Fall in plasma pH, Respiratory acidosis

  • Hyperventilation: Decrease of pCO_2, Increase in plasma pH, Respiratory compensation

• Kidneys:

  • Reabsorption of HCO_3: Increase in plasma pH, Metabolic compensation

  • Secretion of H^+: Increase in plasma pH, Metabolic compensation

  • Renal failure: Loss of HCO_3, Retention of H^+, Fall in plasma pH, Metabolic acidosis