Figure 5.

Implications of endocrine output of the gut microbiota in health and disease. The hormonal output of the gut microbiota is vital for host health and well-being. In addition to the local impact in the GI tract and ENS, it is also critical for control of host metabolism and the normal development of the immune system. Through as yet unknown mechanisms, the gut microbiota also seems to be able to regulate glucocorticoid production in the HPA axis. Similarly, through controlling the availability of the serotonin precursor tryptophan, the gut microbiota can potentially influence brain and behavior. Metabolites produced by the gut microbiota from choline can also affect the cardiovascular system.