Transcript THE CONTROL OF DIGESTIVE SECRETIONS

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
Mouth
Stomach
Hormonal
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
Nervous Control
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
HCO3- 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
HORMONAL
NERVOUS
RELEASES
Hormones /Chemicals
Chemical transmitters
/ electrical impulses
CARRIED BY
blood
Nerves
AMOUNT OF TIME
NEEDED TO WORK
Long time
Quick-acting
HOW LONG THE
EFFECTS LAST
Long time
Short-lived
RESPONSE
General
(several responses)
Very specific
EXAMPLE
CCKPZ stimulates gall
bladder and pancreas
Peristalsis
ONE OF THE MAIN ROLES OF THE NERVOUS SYSTEM IN DIGESTION
IS TO STIMULATE THE RELEASE OF HORMONES.