THE CONTROL OF DIGESTIVE SECRETIONS

By NALAN IZZIGIL

PRESENTATION PLAN

The nervous and hormonal systems.Nerves which control the digestive system

(Extrinsic & Intrinsic nerves).Hormones which control the digestive

system (Gastrin, Secretin, CCK-PZ).Differences between nervous & hormonal

control.Simple & conditioned reflexes.

THE CONTROL OF DIGESTIVE SECRETIONS

WHICH TWO SYSTEMS ARE INVOLVED IN THE CONTROL OF DIGESTION?

1) The Nervous system2) The Hormonal system

1) THE NERVES WHICH CONTROL THE DIGESTIVE SYSTEM

a) Extrinsic nervesb) Intrinsic nerves

These two types of nerves do different jobs in the digestive system

a) EXTRINSIC NERVES

DEFINITION: Extrinsic: external/on the outside

Come to the digestive organs from the subconscious part of the brain and the spinal cord.

Chemical transmitters of the hormones acetylcholine and adrenaline.

b) INTRINSIC NERVES

DEFINITION: Intrinsic: internal/on the inside.

b) INTRINSIC NERVES

Act when the walls of the digestive system are stretched by food.

Trigger the release of hormones and of digestive juices.

Make up a very dense network.

2) THE HORMONES WHICH CONTROL THE DIGESTIVE SYSTEM

WHICH ARE THE THREE HORMONES THAT ARE SECRETED WHICH CONTROL DIGESTION?

a) Gastrinb) Secretinc) Cholecystokinenin-pancreozymin (CCK-

PZ)

a) GASTRIN

Stimulated by food expanding the stomach wall. It is the primary regulator of digestion.

Gastrin brings about the secretion of Hydrochloric acid (HCl) and of pepsinogen.

b) SECRETIN

Released when chyme reaches the duodenum.

Stimulates the pancreas to release HCO3- ions.

Stimulates bile production in the liver.

c) CHOLECYSTOKINENIN-PANCREOZYMIN

Released by the presence of fatty foods in the small intestine.

Stimulates bile to be produced.

Increases the amount of digestive enzymes that the pancreas release.

THE HORMONES SECRETED IN THE CONTROL OF DIGESTION

Gastrin, Secretin and Cholecystokinenin-pancreozymin are only secreted when food is present in the digestive system.

Released by the cells in the mucosa of the stomach and the small intestine.

DIFFERENCES BETWEEN NERVOUS & HORMONAL CONTROL

HORMONAL CONTROL NERVOUS CONTROL

RELEASES Hormones/Chemicals Nevous/electrical impulses

CARRIED BY Glands Chemical transmitters

AMOUNT OF TIME NEEDED TO WORK

Long time Quick-acting

HOW LONG THE EFFECTS LAST

Long time Short-lived

RESPONSE Can bring about several responses

Acts specifically

EXAMPLE A single hormone can bring about several different responses

Very specific - some act on single muscle

fibres

ONE OF THE MAIN ROLES OF THE NERVOUS SYSTEM IN DIGESTION IS TO STIMULATE THE RELEASE OF HORMONES.

TYPES OF REFLEX

1) SIMPLE REFLEXESCannot be controlled or learntHappen subconsciouslyControlled by parasympathetic nervous

system

2) CONDITIONED REFLEXESLearnt through association

A SIMPLE REFLEX

Occurs on the inside of the body whilst eating, without the person knowing.

A CONDITIONED REFLEX

REFERENCES

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www1.istockphoto.com/file_thumbview_approve/1