An Easy Approach to Understanding Acid-Base Balance in a Blood Buffer System

Understanding acid-base disorders using weak-acid concepts learned in general chemistry class is challenging for pre-nursing and pre-professional biology students enrolled in anatomy/physiology and biochemistry classes. We utilized a graphic seesaw model of carbonic acid-bicarbonate equilibrium using the Henderson-Hasselbalch (H-H) equation of a weak acid. We then used real-world clinical case studies for students to identify acid-base disorders and the appropriate compensatory responses of the lungs and kidneys. Students developed a working knowledge of how the bicarbonate blood buffer system maintains a physiological pH of 7.4 using a “seesaw” with metabolic [$HCO3−$] on one side, and respiratory PCO₂ on the other at a ratio of 20:1 in the H-H equation. When the dysfunction of either the kidneys or lungs causes the seesaw to tip, homeostasis pH is disrupted, causing an acid-base disorder classified as metabolic or respiratory acidosis or alkalosis. The functioning organ can “level the seesaw” by compensating for the dysfunction of the opposite organ to regain homeostasis. Unlike traditional ways of explaining acid-base disorders, this graphic seesaw method is a simple and easy way to achieve understanding.