Buffers are an important part of the biochemical processes of living things because they help keep the pH within organisms' body stable. Most biochemical reactions that are essential for life only take place in a narrow pH range. The presence of buffers ensures that the body's pH remains in this range, despite changes in the surroundings.
Buffers are compounds that are capable of either binding or releasing hydrogen ions depending on the concentration of hydrogen ions in the solution. Since pH is a measure of hydrogen ion concentration, the presence of a buffer keeps the pH of a solution constant within a narrow range. Not all buffers operate in the same range. For example, one buffer may effectively buffer a solution between pH 6 and 6.5, while another may function well between pH 8 and 8.3. Buffers in human blood are able to keep its pH between 7.35 and 7.45, even though acidic and basic compounds are always entering the blood as they are being absorbed by the digestive tract and leaving the blood as they are filtered out by the kidneys or otherwise used by the body's cells.
Three main buffers are present in human bodies: bicarbonate, phosphate and proteins. The bicarbonate buffering system helps prevent acidification of the blood as carbon dioxide is produced through respiration. The phosphate buffering system keeps blood pH constant, and various proteins work as buffers both inside and outside of the body's cells.