From the Guidelines
Bicarbonate production in the body occurs primarily through the conversion of carbon dioxide into bicarbonate ions, a process catalyzed by carbonic anhydrase in red blood cells and regulated by the kidneys. The mechanism involves carbon dioxide combining with water to form carbonic acid, which then dissociates into hydrogen ions and bicarbonate ions 1. This process is crucial for maintaining the body's acid-base balance.
Key Mechanisms of Bicarbonate Production
- The kidneys play a significant role in bicarbonate production and regulation through the excretion of hydrogen ions and reabsorption of filtered bicarbonate.
- The pancreas contributes by secreting bicarbonate-rich fluid into the small intestine to neutralize stomach acid.
- The liver is also involved in bicarbonate production during protein metabolism.
Importance of Bicarbonate Levels
Maintaining normal blood bicarbonate levels, ranging from 22-28 mEq/L, is essential for preventing acid-base disorders such as acidosis or alkalosis 1. Disruptions in bicarbonate production can lead to these disorders, which may require medical intervention. For individuals with chronic kidney disease (CKD) and serum bicarbonate concentrations <22 mmol/l, treatment with oral bicarbonate supplementation is suggested to maintain serum bicarbonate within the normal range, unless contraindicated 1.
Clinical Implications
Correction of metabolic acidosis by maintaining serum bicarbonate at or above 22 mmol/L is a goal in the management of individuals undergoing dialysis, as it can lead to increased serum albumin, decreased protein degradation rates, and improved overall health outcomes 1.
From the Research
Mechanism of Bicarbonate Production
The mechanism of bicarbonate production in the body involves several processes and systems.
- Bicarbonate is primarily generated by the kidney through the carbonic acid/bicarbonate (H2CO3/HCO3-) couple, which is the most predominant extracellular buffer to keep plasma pH within a physiological range 2.
- The kidney plays a crucial role in maintaining acid-base balance by generating bicarbonate and capturing any bicarbonate filtered by the kidney 3.
- Carbonic anhydrase is an enzyme that catalyzes the hydration-dehydration reaction of CO2 and is abundantly distributed in renal tissue, functioning to prevent the rapid development of limiting pH gradients in the proximal tubule 4.
- The proximal tubule is responsible for at least 80% of whole kidney bicarbonate transport, which is mediated by proton secretion 4.
- Bicarbonate transport beyond the proximal tubule occurs in the loop of Henle and the medullary collecting tubule, and can be transported passively as a result of favorable outwardly directed bicarbonate concentration gradients 4.
Regulation of Bicarbonate Production
The regulation of bicarbonate production involves various hormones, including:
- Aldosterone, angiotensin II, and endothelin, which can affect acid-base balance and contribute to an adaptive increase in renal acid excretion and bicarbonate generation 3.
- Other hormones such as PTH, glucocorticoids, insulin, thyroid hormone, and growth hormone can also impact acid-base balance 3.
- The endocrine system plays a significant role in regulating acid-base balance, and alterations in hormone levels can contribute to the progression of chronic kidney disease (CKD) 3.
Clinical Significance of Bicarbonate Production
Bicarbonate production is essential for maintaining acid-base balance, and alterations in bicarbonate levels can have significant clinical implications, including:
- Metabolic acidosis, which can occur in CKD and is associated with muscle wasting, bone disease, hypoalbuminemia, inflammation, and increased mortality 5.
- The administration of base may decrease muscle wasting, improve bone disease, and slow the progression of CKD, but the target serum bicarbonate concentration is unclear 5.
- Impaired bicarbonate transport can lead to various diseases, including immune disorders, kidney diseases, and systemic acidosis 6.