|
|
| Cephalic phase |
| |
- accounts for around 30% of the response to a meal
- controlled by the brain
- stimulated by senses - taste,
smell, vision but also by thoughts.
- Vagal impulses releases ACh in main body of the stomach
- apart from directly stimulating secretion of acid it
stimulates histamine release
- histamine stimulates release of gastrin from parietal
G cells
- the three compounds initiate the cascade for production
and release of HCl
|
| Gastric phase |
| |
- accounts for around 60% of the response
involves both neural and humoral reflexes
- initiated by:
|
| |
|
- distension of the stomach
- the presence of polypeptides in the antrum stimulate
G cells to secrete gastrin
|
| |
- low pH at antral mucosa inhibits gastric phase through
the release of somatostatin from endocrine cells
- an important negative feedback regulation of gastric
HCl secretion
|
| Intestinal phase |
| |
- accounts for less than 10%
- principle feedback via hormones from duodenum
- fats in the duodenum cause the release of Cholecystokinin
(CCK) and Gastric Inhibitory Peptide (GIP)
- CCK stimulates chief cells to release pepsinogen
- GIP releases somatostatin- inhibits acid production
- secretin release from the duodenum also causes a release
of stomatostatin
- acid in the duodenum acts by negative feedsback via
intrinsic nerves
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