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Unstirred water layer in canine jejunum
The American Journal of Physiology
|April 1, 1982
Summary
Researchers estimated the unstirred water layer thickness in canine jejunum using [14C]inulin. Findings reveal significant water absorption and a substantial unstirred layer barrier affecting nutrient uptake.
Area of Science:
- Gastroenterology
- Physiology
- Biophysics
Background:
- The unstirred water layer adjacent to the intestinal epithelium influences nutrient absorption.
- Quantifying this layer is crucial for understanding intestinal transport mechanisms.
Purpose of the Study:
- To estimate the thickness of the unstirred water layer in the canine jejunum in vivo.
- To investigate the role of diffusion and solvent drag in the transport of substances into the intervillus space (IVS).
Main Methods:
- In vivo lavage of canine jejunum with [14C]inulin.
- Measurement of inulin concentrations in the IVS at different levels and over time.
- Kinetic analysis of inulin's entrance into the IVS to infer water absorption and layer thickness.
Main Results:
- Inulin concentrations in the IVS increased slowly, suggesting minimal convective mixing.
- IVS inulin concentrations were significantly higher than lavage fluid after 1-2 hours, indicating water absorption.
- Water absorption was localized to the uppermost IVS level.
- A small secretory stream from crypts was necessary to explain observations.
Conclusions:
- The unstirred water layer in the canine jejunum is substantial, ranging from 500-1,000 micrometers at villus tips.
- An additional barrier of up to 800 micrometers exists for absorption at villus lateral surfaces.
- Both diffusion and solvent drag contribute to substance entry into the IVS, with water absorption primarily at the villus tips.
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