| Foregut | Midgut | Hindgut | |
| Localization | Stomach, duodenum, bronchus, thymus | Jejunum, ileum, appendix, ascending colon | Transverse, descending, and sigmoid colon, rectum, genitourinary |
| Secretory products | 5-hydroxytryptophan, histamine, multiple polypeptides | Serotonin prostaglandins, polypeptides | Variable |
| Carcinoid syndrome | Rare, and atypical when it happens | Classic | Rare |
