Acid base homeostasis

Acid-Base Homeostasis

Acid-base homeostasis refers to the physiological processes that maintain the hydrogen ion concentration ([H+]) in the body fluids within a narrow range, ensuring optimal cellular function. The human body is highly sensitive to changes in pH, and even slight deviations can lead to significant physiological disturbances. The normal arterial blood pH is tightly regulated between 7.35 and 7.45.

Mechanisms of Acid-Base Balance

The body employs several mechanisms to maintain acid-base balance:

Buffer Systems

Buffer systems are the first line of defense against pH changes. They act quickly to neutralize excess acids or bases. The major buffer systems in the body include:

• Bicarbonate Buffer System: The most important extracellular buffer, consisting of carbonic acid (H2CO3) and bicarbonate ions (HCO3-). It is regulated by the lungs and kidneys.
• Phosphate Buffer System: Operates in the intracellular fluid and renal tubular fluid.
• Protein Buffer System: Proteins, including hemoglobin, act as buffers by binding to hydrogen ions.

Respiratory Regulation

The respiratory system regulates pH by controlling the levels of carbon dioxide (CO2) in the blood. CO2 is a byproduct of metabolism and can combine with water to form carbonic acid. The lungs can increase or decrease the rate and depth of breathing to expel or retain CO2, thus influencing blood pH.

Renal Regulation

The kidneys maintain acid-base balance by excreting hydrogen ions and reabsorbing bicarbonate from urine. This process is slower than respiratory regulation but is crucial for long-term pH balance. The kidneys can also generate new bicarbonate ions to replenish the buffer system.

Disorders of Acid-Base Balance

Acid-base disorders are classified based on the primary disturbance and the compensatory response:

Acidosis

• Respiratory Acidosis: Caused by hypoventilation leading to CO2 retention. Common causes include chronic obstructive pulmonary disease (COPD) and respiratory depression.
• Metabolic Acidosis: Results from an increase in acid production or a loss of bicarbonate. Causes include diabetic ketoacidosis, lactic acidosis, and renal failure.

Alkalosis

• Respiratory Alkalosis: Caused by hyperventilation leading to excessive CO2 loss. It can occur in anxiety, fever, or high altitude.
• Metabolic Alkalosis: Results from excessive loss of hydrogen ions or gain of bicarbonate. Causes include vomiting, diuretic use, and antacid overuse.

Diagnosis and Management

Diagnosis of acid-base disorders involves:

• Arterial Blood Gas (ABG) Analysis: Measures pH, partial pressure of CO2 (PaCO2), and bicarbonate (HCO3-) levels.
• Anion Gap Calculation: Helps differentiate between types of metabolic acidosis.

Management strategies depend on the underlying cause and may include:

• Correcting the underlying disorder
• Administering intravenous bicarbonate for severe acidosis
• Adjusting ventilation settings in respiratory disorders

Also see

• Buffer solution
• Respiratory system
• Renal physiology
• Metabolic acidosis
• Metabolic alkalosis