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Physiology of the Gastrointestinal System II: Digestion and Absorption01:22

Physiology of the Gastrointestinal System II: Digestion and Absorption

The gastrointestinal (GI) tract, extending from the mouth to the anus, plays a pivotal role in the digestion and absorption of nutrients. This process involves both mechanical and chemical actions facilitated by various enzymes.
Digestion begins in the mouth, where food undergoes mechanical breakdown by chewing and combines with saliva. Salivary amylase, an enzyme in saliva, starts the breakdown of starches into maltose. The food then travels down the esophagus to the stomach.
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Digestive physiology: a view from molecules to ecosystem.

William H Karasov1

  • 1Department of Forest and Wildlife Ecology, University of Wisconsin, Madison, Wisconsin 53706, USA. wkarasov@wisc.edu

American Journal of Physiology. Regulatory, Integrative and Comparative Physiology
|June 10, 2011
PubMed
Summary

Bird digestive physiology offers insights into ecology, toxicology, and conservation. Flexible digestion in species like house sparrows aids survival, while passive absorption influences toxin sensitivity and contaminant bioaccumulation.

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Area of Science:

  • Comparative physiology
  • Avian ecology
  • Ecological toxicology

Background:

  • Digestive physiology is crucial for ecological applications, including species management and conservation.
  • Dietary adaptations reveal trade-offs influencing ecological niche partitioning.
  • Some avian species exhibit remarkable digestive flexibility, adapting to varied food sources.

Purpose of the Study:

  • To illustrate the applied and integrative perspective of digestive physiology using avian case studies.
  • To explore the link between digestive features, diet, and ecological niche.
  • To examine the implications of digestive flexibility and absorption mechanisms for ecological toxicology and conservation.

Main Methods:

  • Analysis of digestive features and diet in various avian species.
  • Investigation of intestinal maltase activity and mRNA expression in house sparrow nestlings.
  • Assessment of paracellular absorption mechanisms and their role in toxin and contaminant uptake.

Main Results:

  • Digestive specializations influence ecological niche partitioning, but some birds show significant digestive flexibility.
  • House sparrows (Passer domesticus) exhibit reversible changes in intestinal maltase activity with dietary shifts.
  • Passive paracellular absorption, common in birds, affects sensitivity to certain toxins and facilitates contaminant bioaccumulation, as seen in common loon (Gavia immer) chicks with methyl mercury.

Conclusions:

  • Avian digestive physiology provides valuable insights into ecological processes, including niche partitioning and adaptation.
  • Understanding absorption mechanisms is critical for assessing wildlife exposure to environmental contaminants and setting regulatory standards.
  • Digestive flexibility and absorption pathways have significant implications for species conservation and ecological risk assessment.