There are dozens of endocrine cells in the mucosa of the gastrointestinal tract, and the hormones they secrete are collectively called gastrointestinal hormones. The chemical constituents of gastrointestinal hormones are peptides, which can act as circulating hormones, or act as local secretions in local or secreted into the intestinal cavity. Peptide YY (PYY) is an intestinal hormone, a 36-amino acid peptide that regulates appetite and inhibits pancreatic secretion. Peptide YY (PYY) can be mediated by neuropeptide Y receptors.