THE CONTROL OF DIGESTIVE SECRETIONS By NALAN IZZIGIL ADAPTED BY M.HOPKINS

Digestive Secretions: Saliva Gastric Pancreatic Intestinal Bile Mucus

THE CONTROL OF DIGESTIVE SECRETIONS Why do we need to control the release of digestive juices? Two systems work together to coordinate digestion : The Nervous system The Endocrine system

Two systems working together Nervous Hormonal Mouth Stomach Small Intestine

Nervous Control Extrinsic Nerves (outside) via CNS Automatic Nervous System Parasympathetic (Acetylcholine) Sympathetic (Adrenaline) Muscle action in intestines / stomach Trigger release of digestive secretions and enzymes

Intrinsic Nerves Own nervous system (not via CNS) Messages travel within digestive tract Act when walls are stretched by food. Trigger the release of hormones and digestive secretions.

Simple Neural Reflexes Cannot be controlled or learnt Triggered by presence of food e.g. 1.Food on taste buds stimulates: Secretion of saliva Secretion of gastric juice 2. Food in the stomach stimulates: Release of HCL in stomach Peristalsis of small intestine

Conditioned Neural Reflexes Learnt through association Unrelated stimulus produces a response originally associated with appropriate stimulus Sight / smell of food stimulates: Secretion of saliva Secretion of gastric juice In anticipation of food Pavlov’s dogs

A CONDITIONED REFLEX

Hormonal control Released by mucosa of stomach and small intestine Released when food present Gastrin Cholecystokinin Pancreozymin (CCK-PZ) Secretin

Gastrin Food stretches stomach wall Gastrin is secreted by stomach mucosa Gastrin stimulates HCl and pepsinogen secretion

Secretin Released when acid chyme reaches the duodenum. Stimulates the pancreas to release HCO 3 - ions. Stimulates bile production in the liver.

Cholecystokinin Pancreozymin (CCK-PZ) Released by the presence of fatty foods in the small intestine. Stimulates bile release from gall bladder Increases release of pancreatic digestive enzymes

Nervous and hormonal comparison HORMONALNERVOUS RELEASESHormones /ChemicalsChemical transmitters / electrical impulses CARRIED BYbloodNerves AMOUNT OF TIME NEEDED TO WORK Long timeQuick-acting HOW LONG THE EFFECTS LAST Long timeShort-lived RESPONSEGeneral (several responses) Very specific EXAMPLECCKPZ stimulates gall bladder and pancreas Peristalsis ONE OF THE MAIN ROLES OF THE NERVOUS SYSTEM IN DIGESTION IS TO STIMULATE THE RELEASE OF HORMONES.