Starting from the lumen of the gastrointestinal tract, the layers of the gut are mucosa (consists of enterocytes, lamina propria and muscularis mucosae), submucosa (sm), muscularis (consists of two muscle layers, inner circular muscle [cm], and outer longitudinal muscle [lm]) and serosa. The functions of the gut are regulated by two nervous systems, intrinsic which is also referred to as the enteric nervous system and consists of two plexuses: submucosal plexus (sp) resides under the sm, and myenteric plexus (mp) resides between the cm and lm, and extrinsic which consists of the vagus nerve (1) and the splanchnic nerve (2). Each of these nerves consists of two components (denoted by the dotted circles around them); afferent and efferent. The vagal afferents (straight line in 1, with cell bodies in the nodose ganglia (ng)) consists of three afferents: intravillus arbors (iva=i), interganglionic laminar endings (igle=ii) and intramuscular arrays (ima=iii), and the spinal afferents (dotted straight line in 2, with cell bodies in the dorsal root ganglia along the thoraco-lumbar area of the spinal cord), communicate the signals generated by the intestinal contents or regulatory peptides (e.g. Stretch, movement, temperature, acidity or chemical content) with the dorsal vagal complex (dvc) in the central nervous system. The orders of the brain to the gut are carried by the vagal parasympathetic efferents (dotted straight line in 1, with cell bodies in the dorsal motor nucleus of the vagus) and the sympathetic efferents (solid straight line in 2, with cell presynaptic cell bodies in the thoraco-lumbar area of the spinal cord and postsynaptic cell bodies in the celiaco-mesenteric ganglia or cmg). A=artery, v=vein, l=lacteal or lymphatic vessel.
