GASTRIC SECRETION OCCURS IN THREE PHASES:::
1. NERVOUS PHASE OR CEPHALIC PHASE
2. GASTRIC PHASE AND
3. INTESTINAL PHASE
In nervous phase the secretion occurs due to stimulation of the vagus nerve while in gastric and intestinal phase chemical substances such as histamine gastrin etc acts as stimuli in gastric phase further secretion of gastric juice takes palce after the entry of food into the stomach due to stimulation and activation of gastrin hormone after half an hour the gastric phase is the strongest and the longest of all the phase being hormonal it is independent of nervous control when food enters the duodenum further secretion of gastric juice is stopped this is known as intestinal phase the secretion of gastric juice is inhibited by enterogastrin hormone which is secreted by the duodenum and passes into the blood and acts on the stomach secretin cholesystokinin and gastric inhibiting peptide (GIP) are hormones secreted by the intestine they all inhibit the gastric acid secretion
funcations of gastric juice::
1.The enzyme pepsin with hydrochloric acid digests proteins into peptone and proteoses
2. Renin acts on milk protein caseinogen and converts it into casein which is then digested by pepsin
3.Hydrochloric acid carries out hydrolysis of the food stuff and also acts as an antiseptic
4.Gastric juice excretes toxins heavy metals and certain drugs like opium
Normal gastric juice also contains blood forming factor known as intrinsic factor of castle s This factor is necessary for absorption of vitamin B12 (Cyanocobalamine ) which is new recognised as the extrinsic food factor vitamin B12 is stored in the liver and reaches the bone marrow to stimulate new blood formation
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