Digestion Unit

ACCESSORY ORGANS

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Pancreas

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PancreasGland with both exocrine and endocrine functions6-10 inch in length60-100 gram in weightLocation: retro-peritoneum*, 2nd lumbar vertebral levelExtends in an oblique, transverse positionParts of pancreas: head, neck, body and tail

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Accessory Organs

The pancreasA glandular organ located behind stomachProduces pancreatic juices containing enzymes to digest foodJuices enter duodenum through pancreatic ductEnzymes in juices break down sugars, proteins, and fatsProduces insulin, secreted into bloodstreamRegulates metabolism (or burning) of carbohydrates to convert glucose (blood sugar) into energy

Alkaline fluid introduced with enzymes neutralizes acidic chyme

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Pancreas

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Head of PancreasIncludes uncinate processFlattened structure, 2 3 cm thickAttached to the 2nd and 3rd portions of duodenum on the right

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Neck of Pancreas2.5 cm in lengthAntero-superior surface supports the pylorusSuperior mesenteric vessels emerge from the inferior border

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Pancreas

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Body of PancreasElongated, long structureAnterior surface, separated from stomach by lesser sac

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Tail of PancreasNarrow, short segmentLies at the level of the 12th thoracic vertebraEnds within the splenic hilumMay be injured during splenectomy (fistula)

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Pancreatic DuctMain duct (Wirsung) runs the entire length of pancreasJoins CBD at the ampulla of Vater

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Common bile duct and pancreatic duct lead to duodenal ampulla and papilla

PancreasCompare to Figs 25-22 / 23

Exocrine Pancreas2 major components acinar cells and ductsConstitute 80% to 90% of the pancreatic massAcinar cells secrete the digestive / pancreatoc enzymes

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Exocrine PancreasDuctular system - network of conduits that carry the exocrine secretions into the duodenum

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Exocrine PancreasPancreatic enzymes -> amylase, lipase, and trypsinogen)

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Exocrine Pancreas500 to 800 ml pancreatic fluid secreted per dayAlkaline pH results from secreted bicarbonate which serves to neutralize gastric acid and regulate the pH of the intestineEnzymes digest carbohydrates, proteins, and fats

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Enzymes of the PancreasAmylaseonly digestive enzyme secreted by the pancreas in an active formhydrolyzes starch and glycogen to glucose, maltose, maltotriose, and dextrinsLipasefunction optimally at a pH of 7 to 9emulsify and hydrolyze fat in the presence of bile salts

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Enzymes of PancreasProteasesessential for protein digestionsecreted as proenzymes and require activation for proteolytic activityduodenal enzyme, enterokinase, converts trypsinogen to trypsinTrypsin, in turn, activates chymotrypsin, elastase, carboxypeptidase, and phospholipaseWithin the pancreas, enzyme activation is prevented by an antiproteolytic enzyme secreted by the acinar cells

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Endocrine PancreasAccounts for only 2% of the pancreatic massNests of cells - islets of LangerhansFour major cell typesAlpha (A) cells secrete glucagonBeta (B) cells secrete insulinDelta (D) cells secrete somatostatinF cells secrete pancreatic polypeptide

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InsulinSynthesized in the B cells of the islets of LangerhansMajor stimulantsGlucose, amino acids, glucagon, sulfonylurea compounds, -Sympathetic fibers

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GlucagonSecreted by the A cells of the isletGlucagon elevates blood glucose levels through the stimulation of glycogenolysis and gluconeogenesis

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SomatostatinSecreted by the D cells of the isletInhibits the release of growth hormoneInhibits the release of almost all peptide hormonesInhibits gastric, pancreatic, and biliary secretionUsed to treat both endocrine and exocrine disorders

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LIVER

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ANATOMY OF LIVER

Liver is a large, solid, wedge shaped organ found in the RUQ

It is the largest organ of the body and contributes about 2% of the total body weight.

Weighs 1600gm in male and 1300gm in female

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Liver 4 lobes, located under the diaphragmConnected to the gall bladder via the common hepatic duct

Bile is introduced into the duodenum in the presence of fatty food Produced by cells in the liver

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Circulation of the liverDual Blood SupplyPortal systemHepatic veins drain liver & empty into IVC 1000-1200 ml/min

Hepatic artery400-500 ml/min blood flowOxygenated blood

26 dual blood supplyWhat is the central vein? Center of the lobule

Blood supply

80% of blood supply is derived from portal vein.20% is derived from hepatic artery.Before entering the liver both hepatic artery and portal vein divide into right and left branches.

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Histology of liver

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Liver physiologyLiver performs many different functions which can be summarized as:

1. Synthesis of bile saltsThese are the salts of bile acids.Primary bile acids are cholic and chenodeoxycholic acid.

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2. Synthesis of proteins:

AlbuminBlood coagulation factors I,II,V,VII,IX,X and also fibrinolytic agents.Transport proteins like Ceruloplasmin and Transferrin.Angiotensinogen

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3. Fat metabolism

Oxidation of fatty acids to supply energy for other body functions.Synthesis of large quantities of cholesterol, phospholipids and most lipoproteins.Synthesis of fat from proteins and carbohydrates

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4. Carbohydrate metabolism

Storage of large amounts of glycogen.Conversion of galactose and fructose to glucose.Gluconeogenesis

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5. Vitamin metabolism6. Formation of urea (Ammonia -> urea)7. Responsible for inactivation of many drugs8. Detoxification of many toxic substances.9. Metabolism of ethanol.10. De-activation of various hormones.11. Excretion of bile pigments, cholesterol and some metals.12. Stores iron as ferritin and also vitamins A, D and B12.

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GALLBLADDER

The gallbladderSmall, muscular sac located under liver and attached to it by connective tissueStores and concentrates bile, received from liverWhen bile is needed to emulsify fats in digestive tract, the gallbladder contracts and pushes bile through common bile duct into duodenum

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GallbladderStores and concentrates bileExpels bile into duodenumBile emulsifies fats

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Gallbladder

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Figure 24.22 The Activities of Major Digestive Tract HormonesFigure 24.22

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Figure 24.1

Figure 24.1 The Components of the Digestive System

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Processes of the Digestive System

Figure 14.11

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Aging and the Digestive System

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Age related changes in the digestive system include:Thinner, more fragile epitheliumReduction in epithelial stem cellsWeaker peristaltic contractionsEffects of cumulative damage Increased cancer rates

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The Digestive System in Later LifeMiddle age gallstones and ulcers Old age activity of digestive organs declineFewer digestive juices and enzymes producedAbsorption is less efficientDehydration of fecal mass leads to constipationDiverticulosis and cancer of digestive organs

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end

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