Renal physiology: acid–base balance

Tight control of acid–base balance is fundamental to many core physiological processes. $pH$ affects the transmembrane movement of charged ions and the conformation of proteins and consequently, acidosis and alkalosis can cause multi-system adverse effects in the human body.

The most clinically relevant concepts to understanding human acid–base physiology are the Bronsted–Lowry theory, $pH$, ${pK}_a$ (which has a significant influence on local anaesthetic pharmacokinetics) and the Henderson–Hasselbalch equation. The human body has evolved multiple endogenous buffer systems to maintain exquisite control of intra-cellular and extracellular $pH$, including proteins, haemoglobin, phosphate and the bicarbonate system.

Bicarbonate is one of the most important buffer systems and is involved in both respiratory and renal control of acid–base balance through a series of reactions mediated by carbonic anhydrase. The renal system is an important medium to long term regulator of acid base balance through its ability to excrete hydrogen ions and retain bicarbonate. Systemic metabolic derangements and exogenous drugs can disrupt the renal acid–base system and will be discussed in this article.