Recycling of K⁺, Acid-Base Equivalents, and Fluid between Gut and Hemolymph in Lepidopteran Larvae

Abstract

These studies show that the ileum and possibly the rectum of larval lepidopterans are important sites of recovery of base equivalents secreted by the midgut. A model for recycling of fluid and solutes between gut lumen and hemolymph is presented. In this model K⁺, bicarbonate, and fluid return from posterior to anterior parts of the animal both in the form of hemolymph and as Malpighian tubule fluid flowing in tubular loops closely apposed to the hemolymphal surface of the midgut. This arrangement appears adapted to maximize the eficiency of excretion of uric acid and other weak acids, while recycling K⁺ and bicarbonate.