Invertebrate gut diverticula are nutrient absorptive organs

Abstract

Physiological mechanisms of gastrointestinal absorption and secretion of organic and inorganic solutes among invertebrates remain severely underinvestigated. In this review we briefly discuss some of the physical and biological forces affecting solute transfer across epithelial cells and membranes of vertebrate and invertebrate guts. Next, we present some features of the described processes for sugar and amino acid transport in the tubular portion of gastrointestinal tracts of three major invertebrate groups: echinoderms, molluscs, and arthropods. A detailed discussion follows of recent nutrient transport studies using purified epithelial brush-border membrane vesicles of two invertebrate gut diverticula, the crustacean hepatopancreas and the starfish pyloric cecum. Lastly, transepithelial nutrient and ion transport studies of crustacean hepatopancreatic epithelial cell monolayers, grown in primary culture and mounted in flux chambers, are used to demonstrate the nature of absorption and secretion of solutes by this organ and to show the general applicability of these methods to structurally complex invertebrate organs.