Gastric acid secretion is stimulated by all except
There are following phases of gastric acid secretion: -

1. The cephalic phase:- Just as salivary secretion may start before food enters the mouth, gastric secretion is also indicated before food enters the stomach. Sight, smell or even thought of food stimulate gastric acid secretion. It is by the parasympathetic system through vagus.
This phase accounts for 20% of acid secretion.
2. The gastric phase:- This phase of acid secretion comes into play when food makes contact with the gastric mucosa.
Acid secretion in this phase is brought about two factors
(i) Hormonal simulation due to gastrin release and
(ii) Stretch of stomach wall due to gastric distension which activates a vague-vagal reflex as well as a local intragastric reflex.
This phase accounts for 72-80% of acid secretion.
3. The internal phase:- Once the food enters upper portion of small intestine (i.e., duodenum) it causes small amounts of gastric juice secretion because of gastrin released from duodenal mucosa.
While the internal phase plays only a minor role in the simulation of gastric secretion, the presence of food in the intenstine plays a major role in its inhibition. With the entry of food into the duodenum, gastric secretion starts slowing down.
The presence of acid, fats, and products of protein digestion; and increased osmolarity in the duodenum inhibit gastric secretion by
(i) Hormonal mechanism : These mentioned stimuli cause the release of several internal hormones like secretin, cholecystokinin (CCK), vasoactive internal peptide (VIP), gastric inhibitory polypeptide (GIP) and somatostatin.
These local hormones inhibit the gastric secretion as well as gastric motility',
(ii) The neural mechanism (enterogastric reflex): The above-mentioned stimuli inhibit gastric secretion and mobility by intrinsic
neural reflex.
Gastricdistension
Gastrin
Smell of food
Somatostan