The physiological acid-base balance refers to the maintenance of a stable pH in the body's fluids and tissues, crucial for cellular functions and enzymatic reactions. The normal pH range for arterial blood is 7.35-7.45.
Regulation Mechanisms
1. Buffer systems:
First line of defense against pH changes.
Consist of a weak acid and its conjugate base or a weak base and its conjugate acid.
Key buffer systems include:
Bicarbonate Buffer System (HCO3-/H2CO3)
Phosphate Buffer System (HPO42-/H2PO4-)
Protein Buffer System (e.g., hemoglobin).
2. Respiratory system:
Regulates acid-base balance by controlling CO2 levels in the blood.
CO2 reacts with water to form carbonic acid (H2CO3), which dissociates into H+ and HCO3-.
Acidosis: Increased breathing expels CO2, reducing H+ concentration and raising pH.
Alkalosis: Decreased breathing retains CO2, increasing H+ concentration and lowering pH.
3. Renal system:
The kidneys contribute to the regulation of the acid-base balance by controlling the excretion of H+ ions and the reabsorption of bicarbonate ions (HCO3-) in the urine.
In response to acidosis, the kidneys increase the excretion of H+ ions and reabsorb more HCO3-, which helps to raise the blood pH.
In response to alkalosis, the kidneys decrease the excretion of H+ ions and reabsorb less HCO3-, which helps to lower the blood pH.
These three mechanisms work together to maintain the physiological acid-base balance and ensure the proper functioning of the body's cells and systems. Disturbances in this balance can lead to acidosis or alkalosis, which can cause various symptoms and complications if not addressed and corrected promptly.
Disorders of Acid-Base Balance
1. Acidosis:
Excess acid or loss of base.
Respiratory Acidosis: Due to CO2 retention.
Metabolic Acidosis: Due to excess non-respiratory acids or bicarbonate loss.
2. Alkalosis:
Excess base or loss of acid.
Respiratory Alkalosis: Due to excessive CO2 excretion.
Metabolic Alkalosis: Due to excessive H+ loss or bicarbonate accumulation.
Compensation Mechanisms
The body compensates for imbalances through:
Respiratory Compensation: For metabolic acidosis, increased ventilation lowers CO2.
Renal Compensation: For respiratory acidosis, increased bicarbonate reabsorption and H+ excretion.
These mechanisms work together to maintain the acid-base balance, ensuring the proper function of the body's systems. Disturbances can lead to acidosis or alkalosis, which require prompt correction to prevent complications.