STARCK, J.M.: Morphological Flexibility of the Intestine of Snakes

The small intestine of snakes responds to feeding by rapid upregulation of organ size. After absorption of nutrients the small intestine size is down regulated to fasting size. The mechanisms of the morphological flexibility of the small intestine are compared in Burmese pythons (Python molurus bivittatus) which are infrequent feeding ‘sit and wait’ foraging snakes, and red sided garter snakes (Thamnophis sirtalis parietalis) which are actively hunting and frequently feeding snakes. Ultrasonography, light microscopy, transmission electron microscopy, and flow cytometry were used to study the mechanisms of small intestine size response to feeding. Independent of the feeding strategies, both species showed the same responsiveness of the small intestine to feeding and the small intestine had the same histological architecture. The mucosal epithelium a was a transitional (pseudostratified) epithelium that allowed for size changes without production of new tissue. Driving force of the size increase were a fluid pressure pump (lymph and blood pressure) and incorporation of lipid droplets into the enterocytes. No cell proliferation was associated with upregulation of organ size. Instead, cell proliferation, i.e., production of new tissue was observed during down regulation of organ size. A possible explanation is that cells that deteriorated during absorption of nutrients were replaced when digestion and absorption ended. Based on preliminary comparative evidence it is suggested that the described histological properties of the small intestine are an ancestral feature of snakes, and, possibly, of other non-avian sauropsids (supported by German Research Council STA 345/5-1).