Shaping up: how vertebrates adjust their digestive system to changing environmental conditions

Abstract

The vertebrate gastrointestinal tract is a flexible system that can individually be modified to account for changes in amount and quality of food as well as changes in internal demands. In this paper, I summarise some recent findings and ideas about processes on the level of tissues and cells that allow vertebrates to adjust their intestines to fluctuating conditions. In mammals and birds intestinal flexibility is based on a balance of cell proliferation and cell loss. Maintenance as well as up- and down-regulation of the mucosa involves bio-production or dystrophy of tissue. Both are assumed to be energetically expensive. In contrast, up- and down-regulation of the mucosal epithelium of ectotherm sauropsids is based on configuration changes of the pseudostratified mucosal epithelium. Up-regulation of the mucosa size does not involve cell proliferation, thus it is presumably an energetically cheap process. A comparison of mammals, birds, and ectotherm sauropsids (mainly snakes) allows the development of some new ideas about the historical path of the evolution of gastrointestinal flexibility. Snakes seem to share with other basal tetrapods a phylogenetically plesiomorphic pattern. Birds and mammals have independently evolved new mechanisms that sustain flexibility at a high metabolic level.

Patterns of blood flow during the postprandial response in ball pythons, Python regius

“…The histological samples necessarily had to be taken from a different group of individual snakes. The configuration changes observed in the tissue and the loading of cells with lipid droplets followed the pattern described earlier for Burmese pythons (Starck and Beese, 2001), garter snakes (Starck and Beese, 2002) and other ectotherm sauropsids (Starck, 2003(Starck, , 2005. Thus, it is safe to say that the ball pythons in the experiment performed a postprandial response that did not differ from that seen in other snake species.…”

“…The upregulation of the gastrointestinal system is fast and a threefold increase of total organ size can be observed within 24-48·h after feeding. Python species have been intensively studied over recent years as an ectotherm model system and there has been significant progress in understanding the energy allocation during SDA and the structural and functional upregulation of the gastrointestinal system (Secor et al, 1994;Secor and Diamond, 1995, 1997, 2000Overgaard et al, 1999Overgaard et al, , 2002Thompson and Withers, 1999;Bedford and Christian, 2001;Beese, 2001, 2002;Secor, 2003;Starck et al, 2004;Wang et al, 2003Wang et al, , 2005Andrade et al, 2005;Starck, 1999Starck, , 2003Starck, , 2005McCue et al, in press). The threefold increase in size of the small intestine is associated with a configuration change of the mucosal epithelium, which changes from a pseudostratified epithelium into a single layered, high prismatic epithelium within 24-48·h after feeding Beese, 2001, 2002;Starck, 2003Starck, , 2005.…”

Desarrollo del Aparato Digestivo

“…La mayor parte de los vertebrados tienen un tubo digestivo formado por un esófago, un estómago, intestinos y una cloaca. Por muy distintos que parezcan ser, todos comparten un diseño similar subyacente (Starck, 2003).…”

“…La mayor parte de los vertebrados tienen un tubo digestivo formado por un esófago, un estómago, intestinos y una cloaca. Por muy distintos que parezcan ser, todos comparten un diseño similar subyacente (Starck, 2003).El desarrollo del aparato digestivo se rige por un patrón conservado a lo largo de las especies (McLin et al, 2009). En términos muy generales sigue la secuencia de eventos que van desde la gastrulación, formación del intestino primitivo desde el endodermo y aposición de parte de la hoja esplácnica del mesodermo lateral (Gilbert, 2005) Debido al plegamiento del embrión durante el perío-do somítico, la parte dorsal del saco vitelino queda incluida dentro de éste y constituye el intestino primitivo, un tubo endodérmico que consta de tres partes intestino anterior, intestino medio e intestino posterior (Fig.1a) La mayor parte del epitelio de revestimiento y de las glándulas del tubo digestivo se originan en el endodermo del intestino primitivo (Wells & Melton, 1999).…”

Physiological and morphological responses to feeding in broad-nosed caiman (Caiman latirostris)

“…Although only little information is available yet, these histological patterns that have been observed during the postprandial response of ectotherm sauropsids and anurans differ from those processes that drive the organ size changes in birds and mammals, observed after diet shifts or during fasting. In birds and mammals, the size changes of the small intestine are primarily based on cell proliferation during size increase, and epithelial cell loss during decreasing size (Konarzewski and Starck, 2000;Dunel-Erb et al, 2001;Starck, 2003;Habold et al, 2004;Karasov et al, 2004;Starck, 2005). Enterocytes may also experience some degree of hypertrophy when changing from fasting to fed condition in mammals.…”