Regulation of Body pH and Hydrogen Ions

Hydrogen Ion Regulation and pH

Importance of Hydrogen Ion Regulation

• Hydrogen ion (H^+), often referred to as a proton in physiology, is a crucial homeostatic variable.
• Its concentration must be closely regulated because an imbalance can lead to severe health problems.
• Excessive hydrogen ions can denature proteins, which means altering their three-dimensional shape, hindering their function.

Role of Proteins

• Proteins are vital for various bodily functions:
  • Channels: Regulate the passage of molecules across cell membranes.
  • Receptors: Receive and transmit signals.
  • Enzymes: Catalyze biochemical reactions.
  • Antibodies: Defend against pathogens.
  • Ligands: Signaling molecules.
  • Hemoglobin: Transports oxygen in red blood cells.
• Maintaining proper pH is critical for the optimal functionality of these proteins.

The pH Scale Explained

• The pH scale, ranging from 0 to 14, indicates hydrogen ion concentration.
• A pH of 7 is neutral.
• Values from 0 to 7 are acidic, while those from 7 to 14 are alkaline or basic.
• Lower pH values indicate higher hydrogen ion concentrations and greater acidity. For instance, a pH of 3 is more acidic than a pH of 4 and 10 times more acidic.
• pH is defined mathematically as the negative logarithm of the hydrogen ion concentration: pH = -log[H^+] or pH = log( \frac{1}{[H^+]}).

Bodily pH Values

• Extracellular Fluid (Blood Plasma and Interstitial Fluid):
  • Acceptable range: 7.38 to 7.42 (slightly alkaline).
• Gastric Juices (Stomach):
  • pH range: 1.4 to 3.5 (highly acidic).
  • Acidity deters pathogens and aids protein breakdown during digestion.
• Skin:
  • pH range: 4.7 to 5.7 (acidic), providing a protective barrier against pathogens.
• Urine:
  • pH range: 4.5 to 8.5 (highly variable), depending on the body's needs to eliminate hydrogen ions.

Mechanisms for Homeostatic Regulation of Body pH

Buffers

• Buffers counteract pH changes by binding to free hydrogen ions.
• Free hydrogen ions are problematic because they disrupt biochemistry and denature proteins.
• Examples of buffers:
  • Phosphate ions: Intracellular buffer.
  • Hemoglobin: Intracellular buffer within red blood cells.
  • Bicarbonate: Main extracellular buffer; present in blood plasma at approximately 600,000 times more than hydrogen ions.

Ventilation

• Carbon dioxide (CO2) reacts with water (H2O) to form carbonic acid (H2CO3), which then dissociates into bicarbonate (HCO_3^-) and hydrogen ions (H^+).
• Increased CO_2 levels in the body lead to a decrease in the pH of extracellular fluid.
• Exhalation eliminates CO_2 from the body, helping to increase pH.
• Chemoreceptors (Carotid Bodies):
  • Monitor CO_2 and hydrogen ion levels.
  • Stimulate respiration to exhale excess CO_2 when high levels of hydrogen ions are detected.
  • Extracellular fluid pH below 7 or above 7.7 is incompatible with life.

Renal System

• The kidneys regulate pH by eliminating excess hydrogen ions through urine.