Movement and coordination of the GI tract

Question 1

The cephalic phase

Answer 1

Stomach responds to sight, smell taste or thought of food
Acid and gastric secretion via parietal and G cells
Neural activation through nerve fibres from the medulla stimulate the parasympathetic nervous system of the stomach

Question 2

The gastric phase

Answer 2

Neural and hormonal activation stimulates gastric activity by stretching the stomach and gastric contents and stimulating mechanoreceptors in the stomach
Stretch activates a parasympathetic reflex to the medulla oblongata which stimulates G cells (endocrine) and ECL cells (paracrine) via vagus nerve secretions
Gastrin and histamine enter circulation and stimulate further secretion

Question 3

Intestinal phase

Answer 3

Neural and hormonal activation
Duodenum responds to arriving chyme and moderates gastric activity through hormones and nervous reflexes
Low pH inhibits parasympathetic nerves which decreases gastric secretions
Secretin and cholecystokinin produced by the duodenum both decreases gastric secretion
Both promotes the production of pancreatic juice and bile
CKK slows gastric emptying by contracting the pyloric sphincter