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# Long description

A schematic illustration shows the gut-brain axis. The illustration shows the lower back region of the brain is connected via the vagus nerve and blood vessels (circulation) to different regions of the small intestine and large intestine. A magnified view of the large intestine shows a layer of intestinal epithelial cells with microvilli surrounding the intestinal lumen. The intestinal lumen contains numerous types of intestinal microbiota which produce metabolites that are then sensed by the intestinal cells. This relays a signal via the vagus nerve to the brain. The immune cells also pass from the intestinal lumen through the epithelial cells into the blood circulation. The metabolites of the microbiota can also be detected by the immune cells, which can directly stimulate the brain, or indirectly stimulate the brain via the vagus nerve.