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 system 2) The Hormonal system

1) THE NERVES WHICH CONTROL THE DIGESTIVE SYSTEM a) Extrinsic nerves b) 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) Gastrin b) Secretin c) 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 HCO 3 - 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 CONTROLNERVOUS CONTROL RELEASESHormones/ChemicalsNevous/electrical impulses CARRIED BYGlandsChemical transmitters AMOUNT OF TIME NEEDED TO WORK Long timeQuick-acting HOW LONG THE EFFECTS LAST Long timeShort-lived RESPONSECan bring about several responses Acts specifically EXAMPLEA 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 REFLEXES Cannot be controlled or learnt Happen subconsciously Controlled by parasympathetic nervous system 2) CONDITIONED REFLEXES Learnt through association

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

A CONDITIONED REFLEX

REFERENCES 12_ jpg www1.istockphoto.com/file_thumbview_ap prove/1