Acid Base Balance

What is pH?

  • pH Definition: A scale used to specify the acidity or alkalinity of an aqueous solution.

  • Neutral pH: 7.0, where H⁺ and OH⁻ concentrations are equal.

  • Acidic Solution: pH less than 7.0, indicating higher H⁺ concentration.

  • Basic (Alkaline) Solution: pH greater than 7.0, indicating higher OH⁻ concentration.

Normal pH Range in Blood

  • Arterial Blood pH: Approximately 7.45.

  • Venous Blood pH: Slightly lower at about 7.35.

  • Overall Normal Range: Typically, between 7.35 to 7.45.

Mechanisms Controlling pH

Buffer Mechanisms

  • Chemical Buffers: Substances that neutralize small amounts of added acid or base, thus preventing sharp pH changes. Example includes bicarbonate buffers in blood.

  • Buffer Salts: These weaken strong acids or bases when they enter the bloodstream.

Physiological Mechanisms

Respiratory Mechanism

  • Role of CO₂: Respiration helps to remove CO₂, a component of carbonic acid (H₂CO₃), from blood.

  • Breathing Rate Adjustment: Control centers in the brainstem regulate breathing to maintain pH balance. Increased respiration expels more CO₂, thus reducing acidity, while decreased respiration retains CO₂, increasing acidity.

Urinary Mechanism

  • Kidney Function: The kidneys are effective regulators of blood pH. They excrete or retain acids and bases, adjusting the pH over hours to days.

pH Imbalances

Acidosis

  • Respiratory Acidosis: Results from conditions that cause CO₂ retention, such as hypoventilation.

  • Metabolic Acidosis: Due to a bicarbonate (NaHCO₃) deficit, often from conditions like chronic diarrhea or renal failure.

Alkalosis

  • Respiratory Alkalosis: Occurs from excessive CO₂ loss, often due to hyperventilation.

  • Metabolic Alkalosis: Results from an excess of bicarbonate, commonly due to severe vomiting or overuse of diuretics.

Related Disturbances

  • Metabolic Acidosis Compensation: The body may adjust by increasing breathing to expel more CO₂.

  • Uncompensated vs. Compensated States: In an uncompensated state, the ratio of bicarbonate to carbonic acid is disturbed. In compensated metabolic acidosis, although the levels of bicarbonate and carbonic acid change, their ratio remains constant at 20:1.