How does each of the three phases of gastric secretion promote and facilitate gastric control?

Phases of Gastric Secretion
Similarly to Salivary secretion, gastric secretion can be divided into three phases:
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