Understanding:
• Nervous and hormonal mechanisms control the secretion of digestive juices
• The volume and content of gastric secretions are controlled by nervous and hormonal mechanisms
The secretion of digestive juices is controlled by both nervous and hormonal mechanisms
- These mechanisms control both the volume of secretions produced and the specific content (e.g. enzymes, acids, etc.)
Nervous Mechanism:
- The sight and smell of food triggers an immediate response by which gastric juice is secreted by the stomach pre-ingestion
- When food enters the stomach it causes distension, which is detected by stretch receptors in the stomach lining
- Signals are sent to the brain, which triggers the release of digestive hormones to achieve sustained gastric stimulation
Hormonal Mechanism:
- Gastrin is secreted into the bloodstream from the gastric pits of the stomach and stimulates the release of stomach acids
- If stomach pH drops too low (becomes too acidic), gastrin secretion is inhibited by gut hormones (secretin and somatostatin)
- When digested food (chyme) passes into the small intestine, the duodenum also releases digestive hormones:
- Secretin and cholecystokinin (CCK) stimulate the pancreas and liver to release digestive juices
- Pancreatic juices contain bicarbonate ions which neutralise stomach acids, while the liver produces bile to emulsify fats
Control of Gastric Secretions
