This video describes how the kidney uses type A and type B intercalated cells in the collecting duct to regulate blood pH in the normal range of 7.35-7.45. Type A cells are more active when the blood becomes acidic and type B cells are more active when the blood becomes basic. These cells are able to either secrete or reabsorb hydrogen and bicarbonate ions depending on the pH of the blood, to act as a negative feedback mechanism to help maintain homeostasis.