A Balancing Act: How the Body Maintains Blood pH

The normal pH of blood lies between 7.35 to 7.45 which is right around the neutral mark of 7. Generally anything over 7 is termed basic, while anything under is acidic. With respect to blood pH, anything under 7.35 is termed acidosis and anything over 7.45 is termed alkalosis. pH in the blood can change for a wide variety of different reasons, including breathing changes, exercise, and health complications. For example, during strenuous exercise, lactic acid accumulates in the body, which per the name is acidic, and leads to a drop in pH in the body. This places blood pH in conditions of acidosis for a short time until the body is able to adapt to the lactic acid and revert back to its normal pH. Much of this process is performed by the lungs and kidneys, regulating blood pH through breathing and excreting unneeded compounds (namely carbon dioxide) (Shaw & Gregory, 2022).

So How Does Blood pH Stay Stable?

Prolonged changes to blood pH can be deadly, so the mechanisms that regulate this system and keep blood pH in the small window of 7.35-7.45 are crucial to life. This is largely done through the bicarbonate buffer system. Before diving into what the bicarbonate buffer actually does, it is important to define how a general buffer system works. A buffer is a chemical system that can absorb excess hydrogen and hydroxide ions preventing extreme changes in pH. From a chemistry standpoint, pH decreases when extra hydrogen ions (H+) are added to a solution while pH increases when hydroxide (OH-) ions are added to a solution.

The bicarbonate buffer system works through the use of carbonic acid (H2CO3) and bicarbonate ions (HCO3-). These two components exist in the body preventing any fast or extreme changes to blood pH. Carbonic acid will act as a weak acid and neutralize bases while bicarbonate ions do the opposite for acids. The central reaction of this system involves carbon dioxide (CO2) and water (H2O), which reversibly combine to form the carbonic acid (Biology Insights, 2025). Carbonic acid then can dissociate into a hydrogen ion (H+) and a bicarbonate ion (HCO3-). When the body experiences an increase in acidity the bicarbonate ions come into action with bicarbonate ions (HCO3-) combining with excess hydrogen ions (H+) to form carbonic acid (H2CO3). This reaction gets rid of free hydrogen ions, reducing the acidity of the solution. The newly formed carbonic acid then rapidly dissociates into carbon dioxide and water which can be breathed out in the lungs or urinated away by the kidneys. A similar, yet different, process plays out when excess base is present in the body, however the key information is understanding the bicarbonate buffer system and the importance of carbon dioxide and water within that process. 

What Happens When the System Becomes Overwhelmed?

Even though an established system is in place, it can still become overwhelmed from time to time. When the body’s pH deviates significantly from the narrow normal range, serious medical conditions can develop. Additionally, several medical conditions can yield acidosis and alkalosis conditions. These medical complications can be broken down into metabolic acidosis, metabolic alkalosis, respiratory acidosis, and respiratory alkalosis.

Metabolic acidosis is characterized by an increase in acidity resulting either from an increase in acid production, a loss of bicarbonate, or reduced kidney function in excreting excess acids. This condition is commonly caused by unmanaged diabetes, kidney disease, and severe diarrhea. Symptoms can include accelerated heartbeat, fatigue, increased confusion, and more. Metabolic alkalosis is characterized by an excess of bicarbonate ions yielding too high of a blood pH. Common causes can include excessive vomiting, the use of diuretics (a class of medications that increase urination), and other medical conditions. Symptoms can include muscle cramps, confusion, etc. that is often the result from the lack of water and salts in the body that are needed for function.

Respiratory acidosis is characterized by an increase in acidity due to the inability of the lungs to remove enough carbon dioxide from the body. This can be caused by a variety of respiratory issues, both acute and chronic, including pneumonia, asthma attacks, chronic obstructive pulmonary disease, and more. Additionally, this can be the result of neuromuscular disorders and obstructions blocking the airway. Symptoms can include anxiety, increased confusion, headaches, shortness of breath, muscle twitching, and coma. Respiratory alkalosis is the opposite and the result of too much carbon dioxide being released from the body. This is typically the result of hyperventilation (taking too many breaths too quickly). This can be caused by an anxiety attack, fever or other sickness, and other respiratory conditions making it difficult to breath and requiring increased breaths to get the air one needs. Symptoms generally include dizziness, chest tightness, confusion, muscle cramps, and more. All of these different conditions can yield blood pH outside of the normal range and have long-lasting complications for ones health.

Sources:

Biology Insights. (2025, August 20). How Does the Bicarbonate Buffer System Work? Biology Insights. https://biologyinsights.com/how-does-the-bicarbonate-buffer-system-work/#google_vignette

Shaw, I., & Gregory, K. (2022). Acid–base balance: a review of normal physiology. BJA Education, 22(10), 396–401. https://doi.org/10.1016/j.bjae.2022.06.003

Assessed and Endorsed by the MedReport Medical Review Board