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Last update: August 5, 2015

Carbon Dioxide is Inversely Related to pH in the Human Body
Posted: August 5th, 2015
Carbon dioxide
carbon dioxide

Carbon dioxide is an infamous molecule in the news today. Usually it is associated with carbon emissions and known for being the leading greenhouse gas, a villainous molecule that is a byproduct of carbon emissions from fossil fuel based transportation or from burning coal at power plants. Carbon dioxide is known to be the primary greenhouse gas and the other greenhouse gases that pollute the air are sometimes referred to as "carbon dioxide equivalents" such as methane, nitrous oxide, hydrofluorocarbons, sulfur hexafluoride, and perflurocarbons. So it may be surprising to learn that carbon dioxide is a naturally occuring gas in the human body that is removed through exhalation.

Carbonic acid molecule
carbonic acid

What are the most common elements in the human body?
The 4 most common elements in the human body are hydrogen, carbon, oxygen and nitrogen. Three of those elements are the same as in carbonic acid, carbon dioxide, water, and bicarbonate all of which are part of the composition of the human body.

What is carbonic acid made of?
Carbonic acid is made from water and carbon dioxide. This chemical reaction is reversible and carbonic acid can decompose to form carbon dioxide and water. The breakdown of carbonic acid occurs automatically in the body or it is speeded up by the enzyme carbonic anhydrase. Carbonic acid is one of the most important acids in chemistry as discussed in The 5 Important Acids to Know- Chm-3. The following equation shows the decomposition of carbonic acid to form carbon dioxide and water:

Carbonic acid molecule Reversible reaction arrows symbol Water molecular formula
Carbon dioxide molecule
carbonic acid
  carbon dioxide

If you look for carbonic acid in a college level human anatomy and physiology textbook, you might find information about this compound in the chapters about the metabolic system, the respiratory system, the circulatory system and the urinary system.

“Carbonic acid is an important acid in body fluids. At the lungs, carbonic acid breaks down into carbon dioxide and water; the carbon dioxide diffuses into the alveoli."

Essentials of Anatomy and Physiology p. 624

What are Alveoli? Alveoli are the cells at the end of the respiratory tree of the lungs. They are the site of gas exchange in the blood, the place where the circulatory system (heart and blood) transitions to the respiratory system (lungs). Carbon dioxide travels from the blood to the alveoli to the lungs and then is it removed from the body during exhalation.

Pulmonary Circuit

The fact that carbon dioxide must be constantly removed from the human body, should be a sign that it is not wise to fill up our breathing air with this molecule. Carbon dioxide is naturally occurring in the atmosphere in very small levels, however due to carbon emissions from anthropomorphic sources like transportation and burning of coal or natural gas, the levels of carbon dioxide are known to be rising.

Carbon Dioxide and pH Levels
As written in a college level physiology textbook, carbon dioxide is the most important molecule in the human body for regulating pH levels in body tissues.

What is a pH level? The scientific abbreviation pH means parts Hydrogen and the amount of hydrogen molecules in a solution is the essential indicator of its acidity or alkalinity. Parts Hydrogen (pH) are measured on a scale from 1 to 14. 7 is neutral, below 7 is acidic, and above 7 is alkaline. Water is a 7 on the scale of pH meaning it is neither acidic nor alkaline. Human blood is between 7.35 and 7.45 pH. If a person’s blood is below 7.35 pH they might suffer from a condition called acidosis. If their blood has a pH above 7.45 they might suffer from a condition called alkalosis. A low pH (below 7) indicates an acidic solution and a high pH (above 7) indicates an alkaline or basic solution.

The first person to recognize the essential nature of acids and bases was Svante Arrhenius. On the basis of his experiments with electrolytes, Arrhenius postulated that acids produce hydrogen ions in aqueous solution, whereas bases produce hydroxide ions.”

Introductory Chemistry: a Foundation p. 457

The equation below shows how carbonic acids break down to release Hydrogen ions and a negative ion (anion).

Carbonic acid

According to a college physiology textbook, carbon dioxide levels in the human body are inversely related to pH. The higher the pH- the Hydrogen ions in the blood- the lower the carbon dioxide levels, and the less acidic the body. The lower the pH- the higher the carbon dioxide levels, and the more acidic the body.

“Because most of the carbon dioxide in solution is converted to carbonic acid, and most of the carbonic acid disassociates, the partial pressure of carbon dioxide and pH are inversely related. When carbon dioxide concentrations rise, additional hydrogen ions and bicarbonate ions released and pH goes down. (Recall that the greater the concentration of hydrogen ions, the lower the pH value.) The carbon dioxide is the most important factor affecting pH in body tissues.”

Essentials of Anatomy and Physiology p. 624

Hypothesis about Elevated Carbon Dioxide Levels in Enivornment on Humans
The most common elements in the human body are also some of the most common elements in the atmosphere such as oxygen and nitrogen.

Atmospheric gases
The lower circle represents the percent composition of the trace gases in the above circle. wikipedia

By volume, dry air contains 78.09% nitrogen, 20.95% oxygen,0.93% argon, 0.039% carbon dioxide, and small amounts of other gases. Air also contains a variable amount of water vapor, on average around 1% at sea level, and 0.4% over the entire atmosphere.

Atmosphere of the Earth - Wikipedia

What will living in elevated carbon dioxide levels do to humans? Considering that carbon dioxide is inversely related to pH levels in body tissue, it seems reasonable to think that higher carbon dioxide levels in the air may cause the human population to suffer from a drop in pH levels in their body tissue leading to health problems associated with higher acid levels in the body.

by Andrea Boggs










Martini & Bartholomew (2010) Essentials to Anatomy and Physiology. 5e. Pearson.

Zumdahl, Steven S. (2004) Introductory Chemistry: a Foundation. 5e. Houghton Mifflin Company.

Atmosphere of the Earth - Wikipedia

Acidosis - Wikipedia

Alkalosis - Wikipedia




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