How to Understand Metabolic Alkalosis

This article is an overview about the medical syndrome of metabolic alkalosis.

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→ Know what is metabolic alkalosis. Metabolic alkalosis is one of the disorders which affects acid and base balance in the blood and the extracellular space. This disorder is manifested by increased amount of base in the blood and a decreased amount of acid with concomitant increase in blood pH. It can have several causes that will be mentioned in this article.

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→ Learn what are acids and bases. Acids and bases are concepts that when applied to the body means protonic acid and inorganic bases such as the bicarbonate base and phosphate base. There are different types of acids and bases which are called Lewis acids and Lewis bases. Lewis acids are available in the chemistry laboratory but are not found in the body.

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→ Lewis bases can be found in the body such as an electron pair on nitrogen of amino acids. Most bases in the body are weak in nature such as the bicarbonate base and phosphate base. Acids and bases abound in the body and are subject to many chemical reactions that can alter the basicity and acidity of the blood.

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→ Fortunately, these changes in acidity and basicity are well controlled by well defined buffers in the body which usually are effective within a given range of pH. There are several buffers in the body. Some of them function mainly outside the cell and others function only inside the cell.

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→ Know what is a buffer. The most important buffer inside the cell is the base phosphate in addition to proteins that are present inside the cell which can function also as a base due to the charged amino acids on its structure. These two types of bases usually buffer acids that enter the cell by way of the specialized ion pump H+/K+ pump or by diffusion. This pump exchanges hydrogen ions for potassium ions.

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→ Acids usually enter the cell and are buffered there by either the phosphate ion of the proteins. Especially important is the protein hemoglobin which is an important buffer in the body.

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→ Learn the most important ions in the extracellular space. The main extracellular base is the bicarbonate ion which is along with carbonic acid is under the regulation of the carbonic anhydrase enzyme which produces water and CO2 from carbonic acid. Bicarbonate ions are the most important extracellular buffer in the body. Also ammonia is another base which can trap acids. Ammonia is a Lewis base which is toxic to the body in high concentration. It is obtained as a metabolic product of the deamination process of amino acids in the liver.

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→ Know how metabolic alkalosis occurs. Metabolic alkalosis is the opposite syndrome to metabolic acidosis. It can be caused for example due to vomiting from the stomach. Usually, the stomach secretes large amount of gastric juice which functions to digest food that is present in the stomach. This acid is secreted by the parietal cells of the stomach.

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→ This acid can sometimes cause peptic ulcer to the stomach mucosa due to its corrosive nature. Vomiting of the gastric content leaves behind basic content in the duodenum and the small intestine which is obtained by the basic secretions from the gallbladder and the pancreas which contain the bicarbonate ion.

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→ This basic environment is then absorbed to the blood circulation causing alkalosis of the blood.

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→ Also ingestion of large amount of base such as bicarbonate ions in order to treat an existing metabolic acidosis can by itself induce a state of metabolic alkalosis if the base is taken in large quantity. Large amount of the base bicarbonate has not only an effect on the basicity of the blood but also can affect the blood pressure inside the arteries. Bicarbonate ions contain the counter ion sodium in addition to the bicarbonate ion which is a known potent factor in elevating blood pressure by conserving water in the kidney.