What's the importance of pH in biological systems?

A pH value is an indication of how acidic or alkaline a substance is. Regulating the acid-base balance or the body pH is vital for maintaining homeostasis in biological systems.  

The ‘H’ in pH represents hydrogen. The pH of a substance indicates the concentration of hydrogen ions present in a particular substance. Acids are proton donors that release hydrogen ions whereas bases are proton acceptors that attract and accept hydrogen ions. 

In human beings, blood is slightly basic with a pH range of 7.35 to 7.45. Even though the body is continuously producing acids, the concentration of free hydrogen ions is maintained at this range with only minor variations. This is because, whenever the pH fluctuates outside of the normal range, the body makes compensatory changes and restores the pH to the optimum range. If the pH deviates even slightly from the optimum range of 7.35 to 7.45, we will start to feel sick.