Why Does Blood Become More Acidic When Carbon Dioxide Increases?

Humans breathe in oxygen and breathe out carbon dioxide. This process sounds simple, but the details are actually quite complex. During the process of breathing, humans convert sugar into energy. Carbon dioxide is a waste product of this process. Carbon dioxide is released into the blood, travels to the lungs and is exhaled. Because carbon dioxide is a weak acid, the more carbon dioxide in the blood, the more acidic the blood becomes.

Carbon Dioxide

Carbon dioxide has the chemical formula CO2. This means that for every one molecule of carbon, there are two molecules of oxygen. When dissolved in water, carbon dioxide forms carbonic acid, H2CO3. Carbon acid can lose two hydrogen atoms, or protons. The loss of protons in a solution is what makes that solution acidic.

Carbonate Buffer System

The carbonate buffer system controls the pH levels in blood. PH is a measurement of acidity. The lower the pH, the more acidic a solution is. Carbon dioxide is an essential part of the carbonate buffer system. When carbon dioxide is dissolved in the blood, it creates a buffer composed of bicarbonate ions, HCO3- , carbonic acid, H2CO3, and carbon dioxide, CO2. All three exist in equilibrium with each other. The carbonic acid part of the buffer can neutralize hydroxide ions, which increases the pH of the blood, while the bicarbonate part of the system can neutralize hydrogen ions, which decreases the pH of the blood.

Cellular Respiration

During cellular respiration, humans breathe in oxygen. The body uses this oxygen as part of the process of converting sugar and other molecules into energy. A waste product of this process is carbon dioxide. Carbon dioxide is released into the blood. As the levels of carbon dioxide increase, the equilibrium of the carbonate buffer shifts. More carbonic acid H2CO3 is made, which then increases the acidity of the blood.

Regulation of Blood Acidity

Because the release of carbon dioxide into the blood shifts the carbonate buffer equilibrium, the body needs to remove the excess carbon dioxide in order to regulate the pH level. Therefore, blood carries the carbon dioxide to the lungs where it is exhaled. The speed and depth of breathing regulates the amount of carbon dioxide that is exhaled. Faster, deeper breathing exhales more carbon dioxide.

Acidosis and Alkalosis

The regulation of the pH of the blood is a precise process. When the blood has too much or two little acid, the results are known as acidosis and alkalosis, respectively. Lung or breathing disorders can cause respiratory acidosis and respiratory alkalosis through a disregulation of the amount of carbon dioxide exhaled during respiration. Too little carbon dioxide exhaled will increase the acidity of the blood, whereas too much carbon dioxide exhaled will decrease the acidity of the blood.