ABSTRACT
The human body is colonized from the birth by a large number of microorganisms. This will constitute a real "functional microbial organ" that is fundamental for homeostasis and therefore for health in humans. Those microorganisms. The microbial populations that colonize humans creating a specific ecosystem they have been collectively referred to as "human microbiota" or "human normal microflora". The microbiota play an important pathophysiological role in the various locations of the human body. This article focuses on one of the most important, that is the enteric microbiota. The composition (quantitative and qualitative) of microbes is analyzed in relation to age and environment during the course of human life. It also highlights eubiosis and dysbiosis as key terms for its role in health and disease. Finally, it analyzes its bi-directional relationship with the microbiota of the lungs, skin and that of the brain, and consequently for the whole central and peripheral nervous system for the maintenance of health in the human body.