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## II. Regulatory Substances in the Gastrointestinal Tract (Figure 6.2) ### *A. GI hormones (Table 6.1)* - are released from endocrine cells in the GI mucosa into the portal circulation, enter the general circulation, and have physiologic actions on target cells. - Four substances meet the require...

## II. Regulatory Substances in the Gastrointestinal Tract (Figure 6.2) ### *A. GI hormones (Table 6.1)* - are released from endocrine cells in the GI mucosa into the portal circulation, enter the general circulation, and have physiologic actions on target cells. - Four substances meet the requirements to be considered “official” GI hormones; others are considered “candidate” hormones. The four official GI hormones are gastrin, cholecystokinin (CCK), secretin, and glucose-dependent insulinotropic peptide (GIP). ### 1. Gastrin - Contains 17 amino acids ("little gastrin"). - Little gastrin is the form secreted in response to a meal. - All of the biologic activity of gastrin resides in the four C-terminal amino acids. - “Big gastrin” contains 34 amino acids, although it is not a dimer of little gastrin.