Figure 9.

Intestine/brain axis in stressful environmental conditions: stress activates the hypothalamic–pituitary–adrenal axis (HPA axis), leading to the hypothalamus secretion of the corticotropin releasing hormone (CRH) and, subsequently, the secretion of the adrenocorticotropic hormone (ACTH) from the pituitary gland. This, in turn, leads to the secretion of cortisol by the adrenal glands. Cortisol acts in the CNS communication pathways, hormonal and neural, which, interacting, influence the activities of the cells: intestinal effector, smooth muscle, epithelial, enterochromaffin, interstitial Cajal’s cells, enteric neurons, and immune cells. Thus, stress conditions cause the variation in microbiome, immune function, mucus, intestinal motility, and permeability [1,5,203]. Credits: Original figure by I.A. Charitos.