| Recall Cue | Notes |
|---|---|
| Gastrin — source? | G-cells of pyloric stomach |
| Gastrin — trigger? | Food entering stomach, especially proteins |
| Gastrin — action? | Stimulates HCl secretion from parietal cells + pepsinogen from chief cells |
| Secretin — source? | S-cells of duodenal mucosa |
| Secretin — trigger? | Acidic chyme entering duodenum (pH <4.5) |
| Secretin — action? | Stimulates pancreatic bicarbonate secretion to neutralize acid; inhibits gastric acid secretion |
| CCK — source? | I-cells of duodenal mucosa |
| CCK — trigger? | Fats AND amino acids entering duodenum |
| CCK — action? | Stimulates gallbladder contraction (bile release) AND pancreatic enzyme secretion |
| GIP — source? | K-cells of duodenal mucosa |
| GIP — trigger? | Fats AND glucose entering duodenum |
| GIP — action? | Inhibits gastric acid secretion; stimulates insulin release (incretin effect) |
| Key distinction: secretin vs CCK? | Secretin → BICARBONATE (no bile); CCK → ENZYMES + BILE (no bicarbonate) |
| Negative feedback? | Low stomach pH inhibits G-cells → less gastrin → less HCl (self-limiting acid production) |
Bottom Summary: Four GI hormones form an elegant coordination network. Gastrin starts gastric digestion ("on switch"). When processed food (acid, fats, amino acids) reaches the duodenum, three hormones fine-tune the response: Secretin neutralizes the acid, CCK calls for bile and enzymes, and GIP taps the brakes on gastric output while preparing the body for incoming glucose (insulin release). The hormone → source cell → trigger → action chain must be memorized precisely for NEET.