Cephalic (neural) and peripheral (gastric and intestinal) endocrine and paracrine regulation of gastric acid secretion. G, G cell; P, parietal cell; D, D cell; M cell, mucus cell; ENS, enteric nervous system; GRP, gastrin-releasing peptide; GRPR, GRP receptor; SMS, somatostatin; VIP, vasoactive intestinal polypeptide; M, muscarinic receptor; M₃, muscarinic receptor type 3; SST2, somatostatin type 2 receptor; CCKA and CCKB, cholecystokinin type A and B receptors; Y₁, PYY type 1 receptor; PYY, peptide YY; H2, histamine type 2 receptor; Gal1, galanin type 1 receptor. Green lines indicate stimulation; red lines indicate inhibition.