Table 3.

Main locations and functions of different components of the endocannabinoid system (ECS) within the gastrointestinal (GI) tract.

RECEPTORS
COMPONENT	LOCATION	FUNCTION
CB1 (binds AEA, 2-AG)	ENS: cholinergic neurons Mucosa: epithelial and plasma cells Vascular smooth muscle cells Lamina propria: macrophages and plasma cells	Reduces GI motility and secretion Modulates immune function
CB2 (binds AEA, 2-AG)	ENS (under inflammatory conditions) Mucosa: epithelial cells, macrophages > plasma cells Lamina propria: macrophages and plasma cells	Reduces GI motility and secretion Modulates immune function
TRPV1 (binds AEA > OEA)	Extrinsic afferent fibers, running through the muscle layers Immune cells adjacent to blood vessels.	Visceral hypersensitivity signaling Increase in intestinal contractility (under inflammatory conditions)
PPAR-α (binds AEA, 2-AG, OEA, PEA, others)	Enterocytes of the small intestine ENS Vagal afferent fibers Enteric glial cells
GPR55 (binds PEA)	Epithelial cells and ENS of the small intestine
GPR119 (binds OEA, PEA > AEA)	Villi: enteroendocrine L cells	Regulates the release of GLP-1
METABOLIC ENZYMES
COMPONENT	LOCATION	FUNCTION
FAAH	Cells of the myenteric plexus in stomach and intestine	Degrades AEA, PEA, OEA
MAGL	Nerve cells and fibers in the muscle layers and mucosa of duodenum, ileum and colon	Degrades 2-AG Activity decreases from proximal to distal locations
LIGANDS
COMPONENT	LOCATION	FUNCTION
AEA	Higher levels in colon than in ileum	Increased levels in IBD, celiac disease, diverticulitis, CRC
2-AG	Higher levels in ileum than in colon	Increased levels in CRC

See abbreviations at the end of the chapter.