Acid-Base Balance in the Human Body

Acid-base balance in the human body refers to the mechanisms the body uses to maintain the pH of blood and other fluids within a narrow, healthy range. The normal pH of human blood is slightly alkaline, around 7.35 to 7.45. The body must carefully regulate this pH to ensure proper functioning of enzymes, cells, and metabolic processes.

Key Components of Acid-Base Balance:

1. Acids: Substances that release hydrogen ions (H⁺) when dissolved in water. Common acids in the body include carbonic acid (H₂CO₃), formed from carbon dioxide (CO₂) and water.
2. Bases: Substances that can accept hydrogen ions (H⁺) or release hydroxide ions (OH⁻). Bicarbonate (HCO₃⁻) is the most important base in the body, acting as a buffer to neutralize excess acids.
3. Buffers: These are substances that stabilize pH by either accepting or donating H⁺ ions. The bicarbonate buffer system is one of the most important in maintaining blood pH.

Mechanisms that Maintain Acid-Base Balance:

1. Buffer Systems

• Bicarbonate buffer system: Carbonic acid (H₂CO₃) and bicarbonate (HCO₃⁻) work together to regulate pH. When H⁺ levels rise, bicarbonate neutralizes excess H⁺, and when H⁺ is low, carbonic acid releases H⁺.
  Reaction: CO₂ + H₂O ↔ H₂CO₃ ↔ H⁺ + HCO₃⁻
• Protein buffers: Proteins, such as hemoglobin, can also buffer changes in pH by binding to excess H⁺ ions.
• Phosphate buffer system: Primarily active in the kidneys and intracellular fluids, where phosphate ions help buffer excess H⁺.

2. Respiratory System

• The lungs regulate the amount of carbon dioxide (CO₂) in the blood, which is a major component of carbonic acid (H₂CO₃).
• CO₂ exhalation: When CO₂ levels rise, blood becomes more acidic. The body compensates by increasing the breathing rate to expel more CO₂, thereby reducing acidity.
• Respiratory acidosis: Occurs when there is impaired CO₂ excretion (e.g., in chronic lung diseases), leading to excess H₂CO₃ and a drop in pH.
• Respiratory alkalosis: Happens when too much CO₂ is expelled (e.g., during hyperventilation), causing pH to rise.

3. Renal System (Kidneys)

• The kidneys help regulate acid-base balance by excreting excess H⁺ ions into the urine and reabsorbing bicarbonate (HCO₃⁻) into the bloodstream.
• The kidneys can also generate new bicarbonate ions to buffer excess acids.
• Renal compensation is slower than respiratory compensation but is crucial for long-term pH balance.
• Metabolic acidosis: Occurs when there is an accumulation of acid (e.g., lactic acid from exercise or ketoacidosis from diabetes) or loss of bicarbonate (e.g., in diarrhea), resulting in low pH.
• Metabolic alkalosis: Results from an excess of bicarbonate (e.g., due to excessive vomiting or ingestion of antacids), leading to a higher pH.

Disorders of Acid-Base Balance:

1. Acidosis

Blood pH falls below 7.35.

• Respiratory Acidosis: Caused by inadequate CO₂ elimination (e.g., due to lung diseases like COPD).
• Metabolic Acidosis: Results from excessive acid production (e.g., lactic acidosis, ketoacidosis) or bicarbonate loss (e.g., diarrhea).

2. Alkalosis

Blood pH rises above 7.45.

• Respiratory Alkalosis: Caused by excessive CO₂ elimination (e.g., due to hyperventilation or high altitudes).
• Metabolic Alkalosis: Occurs due to an excess of bicarbonate or loss of acids (e.g., prolonged vomiting or excessive use of diuretics).

Compensation Mechanisms:

• Respiratory Compensation: The lungs can adjust CO₂ levels to quickly balance pH changes caused by metabolic disturbances (e.g., breathing faster to compensate for metabolic acidosis).
• Renal Compensation: The kidneys adjust bicarbonate and H⁺ excretion to balance pH changes caused by respiratory disturbances (e.g., excreting more H⁺ in response to respiratory acidosis).

Importance of Acid-Base Balance:

Enzymes and biochemical processes in the body are highly sensitive to pH changes. Even small deviations from the normal pH range can lead to significant dysfunction in cellular activities, nerve function, and cardiovascular stability. Maintaining acid-base balance is critical for homeostasis, ensuring that the body's internal environment remains stable despite external changes.

In summary, the body uses a combination of buffer systems, respiratory regulation, and renal control to maintain acid-base balance and ensure the proper functioning of cells and organs.