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Introduction to the digestive tract

The digestive tract consists of the mouth, esophagus, stomach and the small and large intestines.

The small intestine is actually the longest part of the intestines. According to the latest estimates the average length in adults is in the range of 10 ft (3 m).1 The main function of the small intestine is to absorb nutrients. To improve this function hair-like projections called villi and micro-villi increases the surface area of the small intestine to approx. 320 sq. ft, or 30 m2.1
The large intestine, or colon, is shorter (approx. 5 ft, or 1.5 m), but with a larger diameter.1 Important functions carried out by the colon include water retention and bacterial fermentation of undigested nutrients that reach this region.
The intestinal epithelium is a single layer of cells that forms the lining between the body and the contents of the intestines. The intestinal epithelial cells are responsible for nutrient absorption and at the same time keeping noxious molecules as well as intestinal bacteria from entering the body.
On top of the epithelial cells is a constantly renewed layer of mucus that helps keeping intestinal bacteria at a distance from the epithelium.2, 3
Below the layer of epithelial cells is connective tissue, the lamina propria. Associated with the lamina propria is a massive collection of immune cells.4 As much as 70% of all immune cells in the body are located in this region.5
Different probiotics work in different ways in different parts of the gastrointestinal tract.

The article is provided for informational purposes regarding probiotics and is not meant to suggest that any substance referenced in the article is intended to diagnose, cure, mitigate, treat, or prevent any disease.

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Microbiome dysbiosis

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Surviving the stomach

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Mucus layer

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Immune system

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Intestinal barrier

References Open Close

  1. Helander HF, Fändriks L.Surface area of the digestive tract - revisited. Scand J Gastroenterol. 2014;49(6):681–9. (Pubmed)
  2. Johansson MEV.Fast renewal of the distal colonic mucus layers by the surface goblet cells as measured by in vivo labeling of mucin glycoproteins. PLoS One. 2012;7(7): e41009. (Pubmed)
  3. Wells JM, et al.Homeostasis of the gut barrier and potential biomarkers. Am J Physiol Gastrointest Liver Physiol. 2017;312: G171–G193. (Pubmed)
  4. Shi N, et al.Interaction between the gut microbiome and mucosal immune system. Mil Med Res. 2017;4(1):1–7.(Pubmed)
  5. Vighi G, et al.Allergy and the gastrointestinal system. Clin Exp Immunol. 2008;153(SUPPL. 1):3–6. (Pubmed)