Title: The small intestine microbiota, nutritional modulation and relevance for health - ScienceDirect
Headings: The small intestine microbiota, nutritional modulation and relevance for health
Current Opinion in Biotechnology
The small intestine microbiota, nutritional modulation and relevance for health
Highlights
Graphical abstract
http://dx.doi.org/10.1016/j.copbio.2014.09.005
Introduction
Sampling of the small intestine
The human small intestinal microbiota
Microbiota-driven SI immune development in health and disease
Microbiota impacts on SI metabolism and gut-brain signaling
Targeting the SI ecosystem to improve consumer health
References and recommended reading
References

Content: In contrast, limited information is available for the human small intestine (SI) microbiota characterized by its relatively low-density (102 –10 7 cells/g), which is largely due to the rapid luminal flow and secretion of bactericidal substances (e.g. bile acids) in this part of the intestinal tract [ 3 ]. The SI is responsible for approximately 90% of the overall energy absorption from the diet [ 4] facilitated by the large surface area of its mucosa. Adequate absorptive capacity depends on maintenance of mucosal integrity that is constantly challenged by its exposure to the luminal milieu, including the microbiota. Mechanisms that contribute to this mucosal integrity, include the production of antimicrobial peptides (AMPs), a physical mucin barrier, and mucosal antibodies. Especially the terminal ileum is associated with the largest mass of lymphoid tissue in the human body, that is, the gut-associated lymphoid tissue (GALT) and Peyer's patches [ 5 ], which are essential for maintenance of a microbiota-accommodating immune homeostasis via dedicated luminal antigen-sampling (see also Box 1 ). Box 1
The small versus large intestine, morphometry and function
Along the length of the human small intestine three regions are recognized, that is, duodenum, jejunum and ileum, while the large intestine encompasses the cecum, the ascending-colon, transversing-colon and descending-colon, the rectum and the anal canal. The terminal ileum region is connected to the large intestine and excessive retrograde flow from the large intestine content into the small intestine is prevented by the ileocecal valve. The mucosa in the intestinal tract is composed of the lumen-exposed monolayer of epithelium that overlays the lamina propria (a layer of connective tissue) and the muscularis mucosae (a thin layer of smooth muscle). The small intestinal villi protrude into the intestinal lumen from proliferative crypts, ensuring the large surface area of the lumen-exposed small intestine mucosa that supports the main function of the small intestine, that is, the absorption of digested food. The immune system of the gut is largely organized in the gut-associated lymphoid tissue (GALT) that plays a major role in the development and maintenance of the immune system.