There are three phases of gastric secretion i.e.
cephalic,gastric and intestinal phases. The
secretion is controlled by both nerves and hormones. All the 3
phases can occur simultaneously. They can inhibit or exhibit the
gastric activity
Cephalic phase -
- It takes place before the food enters the stomach.
- The smell,taste,sight or thought of food acts for impulsing
secretion of gastric juice. This happens due to activation of
Parasympathetic nervous system via vagus nerve
- this phase prepares the stomach for digestion
- the gastric cells secrete histamine in this phase and histamine
takes responsibility of inducing acid production in the
stomach.
- depression and loss of appetite can suppress the phase
Gastric phase -
- It is the period when the food is swallowed.
- This is activated by the swallowed food and semidigested
protein.
- This can happen by 2 ways i.e by stretching the stomach
stimulation(via vagus nerve) or by activating acetylcholine by
Enteric nervous system.
- Line of events is protein break downs to peptide and amino
acids which stimulates the G cells to secrete gastrin. Gastrin in
turn secretes histamine.
Intestinal phase -
- It is the period when partially digested food arrives the
duodenum.
- The mucosal cells then release intestional gastrin,which
exhibits secretion.
Function of gastrointestinal reflex-
Gastrointestinal reflex is one the reflexes of gastrointestinal
tract.Following are the functions of GI reflex-
- Helps in digestive movement and chemical changes.
- It releases acid in duodenum and suppresses the release of
digestive proteins.
- helps in movement of food/digested material in small
intestine.
- stimulates the urge to defecate.