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THE CONTROL OF DIGESTIVE SECRETIONS By NALAN IZZIGIL
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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.
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THE CONTROL OF DIGESTIVE SECRETIONS WHICH TWO SYSTEMS ARE INVOLVED IN THE CONTROL OF DIGESTION? 1) The Nervous system 2) The Hormonal system
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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
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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.
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b) INTRINSIC NERVES DEFINITION: Intrinsic: internal/on the inside.
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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.
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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)
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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.
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b) SECRETIN Released when chyme reaches the duodenum. Stimulates the pancreas to release HCO 3 - ions. Stimulates bile production in the liver.
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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.
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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.
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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.
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TYPES OF REFLEX 1) SIMPLE REFLEXES Cannot be controlled or learnt Happen subconsciously Controlled by parasympathetic nervous system 2) CONDITIONED REFLEXES Learnt through association
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A SIMPLE REFLEX Occurs on the inside of the body whilst eating, without the person knowing.
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A CONDITIONED REFLEX
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REFERENCES www.tow.com/.../thumbs/2003-07- 12_1939-01.jpg www1.istockphoto.com/file_thumbview_ap prove/1
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