Control of digestive secretion The three main digestive juices are Saliva Gastric juice Pancreatic juice The control of the secretion combines both hormonal and nervous co-ordination

Why control digestive secretion? Waste of energy and nutrients if constantly produced Constant secretion of gastric and pancreatic juice increases risk of self digestion Essential that secretion is timed to be present when food is present in that area of gut

Control of saliva production Entirely nervous control Food in mouth triggers a simple reflex Stimulus (food in the mouth) Nerve impulse to brain Nerve impulse via the vagus nerve to salivary glands response (saliva secreted) A reflex is a quick automatic response to a stimulus

Conditioned reflex Conditioned stimulus (thought/smell of food) Nerve impulse to the brain Nerve impulse via vagus nerve to salivary glands Response (saliva secreted) Remember that the conditioned reflex is learned

Subject to copyright clearance a suitable image showing a cutaway view of a stomach could be inserted here. e.g. one similar to that found at: http://www.bartleby.com/61/imagepages/A4stomac.html

Control of gastric secretion Both nervous and hormonal control Nervous control Stimulus food in the mouth Nerve impulse to brain Motor impulse via vagus nerve to gastric glands Response gastric glands secrete ¼ gastric juice Digestion of protein starts

Hormonal control of gastric secretion Stimulus – partially digested food in the stomach Release of hormone gastrin from the G cells in stomach wall Response - gastric glands secrete ¾ of total gastric juice

Sight/smell/tasted of food Brain nerve impulse Sight/smell/tasted of food Brain Subject to copyright clearance a suitable image showing a cutaway view of a stomach could be inserted here. e.g. one similar to that found at: http://www.bartleby.com/61/imagepages/A4stomac.html nerve impulse Via blood Hormone gastrin released ¼ gastric juice secreted ¾ gastric secretion Partially digested food in stomach

Control of bile and pancreatic juice Stimulus acid food in the stomach Causes the release of 2 hormones Secretin stimulates liver to produce bile and pancreas to produce alkaline fluid Cholecystokinin (CCK) causes the release of bile and the pancreas to secrete enzymes

Secretin stimulates the pancreas to secrete alkaline fluid liver to make bile g b duodenum liver pancreas Cholecystokinin stimulates the Pancreas to produce enzymes Gall bladder to release bile