Key Principles of Acids and Bases:

Acids and bases are defined by their ability to donate or accept hydrogen ions

• Acids are chemical substances that can donate/release, hydrogen ions in water.
• Bases, aka, alkalines, are chemical substances that can accept hydrogen ions.

pH

• pH is a measure of the concentration of hydrogen ions in solution
• pH scale displays the concentration of hydrogen ions from 0 – 14.
  • An acidic solution has a pH less than 7; it has a high concentration of hydrogen ions.
  • A neutral solution has a pH of 7
  • A basic solution has a pH of greater than 7; it has a lower concentration of hydrogen ions.
• Calculation of pH:
  • Negative logarithmic function.

pH values for human bodily fluids:

• Gastric juice, which is secreted by organs of the digestive system, has a pH value around 2; its acidity aids in food digestion.
• Saliva is slightly acidic, but much closer to neutral than are the gastric juices.
• For comparison, pure water has a neutral pH, 7.
• Arterial blood has a pH of approximately 7.4

Homeostasis

Biological organisms are constantly adding acids to their bodily fluids during metabolism, but our blood is slightly basic.

• Intra- and extra-cellular buffers operate to maintain homeostasis.
  • Buffers minimize changes of pH in solutions; they reversibly donate or accept hydrogen ions.
• Example: Bicarbonate buffer system:
  When hydrogen ions are added to the extracellular fluid, they combine with bicarbonate to produce carbonic acid, which is a weaker acid.
  • If the extracellular fluid becomes too basic, the reaction can be reversed:
    Carbonic acid can dissociate to form hydrogen ions and bicarbonate; when pH increases (becomes more alkaline), carbonic acid dissociates to form bicarbonate, which is a base, and hydrogen ions.

Clinical Consequences

• If the body cannot maintain homeostasis due to pathology, disturbances in bodily fluid pH inhibit enzymatic reactions.
  -Thus, failure to regulate pH causes a range of clinical symptoms associated with acidosis (too high blood acid content) or alkalosis (too low blood acid content); elsewhere, we discuss how the kidneys and lungs work to maintain homeostatic pH levels.