Maintenance of pH

Question

Describe how the pH of blood and tissue fluid is maintained in mammals.

Answer 1

Briefly, and without too much attention to minute details of acid-base balance or disorders, and focusing on humans in particular, the lungs expel carbon dioxide which is an acid while the kidneys reabsorb bicarbonate, which is a base. When blood pH lowers, producing acidemia, then the kidneys will respond by reabsorbing more bicarbonate, releasing it back into the blood to raise the pH back to a normal range. The kidneys will also function to secrete acids (such as carbonic acid) from the urine to help raise the pH of blood and tissues. When a person develops an abnormally high pH (alkalemia), the kidneys can secrete more bicarbonate from the body and the lungs can retain CO2 through alterations in breathing. While there are other issues at play, the chemical equation to remember is:

CO2 + H2O <-> H2CO3 <-> HCO3 + H

Depending on the level of detail needed and the course for which this question is posted/education level, then more specific information could always be provided but this is a brief overview. For a complete lecture on acid-base balance I am always happy to help one-on-one!

Answer 2

In mammals, the pH of blood and tissue fluid is maintained through the action of various buffering systems. Buffers are chemical compounds that can react with either an excess of hydrogen ions (H+) or hydroxide ions (OH-) in a solution, effectively neutralizing their effects on pH.

One important buffering system in mammalian blood is the bicarbonate buffer system, which involves the reversible reaction of carbon dioxide (CO2) and water (H2O) to form carbonic acid (H2CO3). The enzyme carbonic anhydrase helps to catalyze this reaction in red blood cells. Carbonic acid then dissociates into bicarbonate ion (HCO3-) and a hydrogen ion (H+), which can be transported and buffered elsewhere in the body.

Proteins and phosphates also act as buffers in mammalian tissues, helping to prevent changes in pH due to excess H+ or OH-. The kidneys also play an important role in regulating blood pH by excreting excess H+ ions or bicarbonate ions in urine as needed.

Overall, these buffering systems work together to maintain a relatively constant pH in mammalian blood and tissues, which is critical for proper cellular function and overall health.