fig2

Figure 2. Schematic representation of the relationship between the HPA (hypothalamus-hypophysis-adrenal cortex) axis and the gut microbiota of both mother and child. Traumatic and stressful events during pregnancy lead to a hyper-activation of the hypothalamus with the release of corticotrophin-releasing hormone(CRH) that induces the production of the adrenocorticotrophic hormone (ACTH) secreted by the hypophysis. In addition, ACTH causes the release of cortisol from the adrenal cortex. Cortisol is a glucocorticoid that directly and indirectly changes the composition of the child’s gut microbiota. This hormone is transmitted to the baby via breastfeeding and likewise from the mother’s bloodstream through the placenta barrier. Moreover, cortisol affects the composition of the mother’s gut microbiota, which is then passed on to the child through vertical transmission.