Electrolytes Water Digestive enzymes Regulated by Neuroendocrince system SALIVARY GLANDS Three pairs of major salivary glands Parotid submaxillary mandibular amp sublingual Numerous small glands ID: 1032632
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1. SECRETIONS OF GITActive Secretion of ElectrolytesWaterDigestive enzymesRegulated by Neuro-endocrince system
2. SALIVARY GLANDSThree pairs of major salivary glandsParotid, submaxillary (mandibular) & sublingualNumerous small glands – buccal glands Classification of salivary glandsBased on the type secretionSerous – thin watery saliva enzymes may be / not present Mucus –Mucin (glycoprotein)No enzymesMixed type
3. Salivary glandsParotid in most mammals is Serous typeSubmaxillary Serous in rodentsMixed in man & ungulatesSublingual Mucous inrodentsMixed in horse, ox, pig, cat & dogCells lining salivary duct influence the composition of salivaPAROTIDSUBLINGUAL
4. COMPOSITION OF SALIVAMixed saliva obtained from mouthColor less opalscent, liquidContains electrolytes & proteinsIn some animals a CHO splitting enzyme –a-amylasePtyalin in man and Pige absent in carnivores and rutsDesquamted cells & Lymphocytes (salivary corpuscles) presentComposition changes with rateEx: sodium and chloride increase with rate
5. FUNCTIONS OF SALIVALubricates mouthMastication & deglutitionimportant in herbivoresHelps bolus formation due to presence of mucinDetection of taste of water soluble substancesProtection of mouth by keeping it moistDilution of harmful substances due to presence of waterInitiation of CHO digestion if a-amylase is present Bacteriostatic activityThiocyanate, lysozyme, antibodiesThermoregulation in cat and dog by providing water for evaporationIn ruminants providesLarge volume of fluid needed for fermentation in rumenBuffers acids produced in the rumen
6. REGULATION OF SALIVARY SECRETIONSpontaneous secretionRespond to neural and hormonal stimuliNeural regulation is more important in most speciesBoth Sympathetic and parasympathetic innervation presentSS and PSS act synergistically to increase secretionSalivary secretory centre is present in medullaBecomes a conditioned reflex easily
7. GASTRIC SECRETIONMucus secreting cells line the entire stomachTwo types of tubular glands present Oxyntic Glands secrete hydrochloric acidPepsinogenIntrinsic factorMucusPyloric Glands Mainly mucusSome pepsinogenGastrinOxyntic &Pyloric glands are both tubularHave similar cell types and structureDepending on the predominance of cell types and location classified into two types
8. GASTRIC GLAND parietal cells secrete isotonic acid with pH 0.8 Inactive Pepsinogen activated by gastric acid & pepsin pH range: 1.8-3.5 Gastric lipase: tributyraseDigests butter fatBut not significant quantitativelyNo action on other fats Gastric amylase minor role in digestion of starch Ggelatinase: liquification of proteoglucans in meat intrinsic factor:absorption of vit.B12
9. SYNTHESIS OF HYDROCHLORIC ACID IN STOMACHECFLUMEN OF CANLICULIPARIETAL CELLCO2CO2H20+ 0H-H+SATk+HCO3-HCO3-H+Cl-Cl-Cl-PATHClNa+PATk+Na+k+Na+PATk+Na+k+k+
10. PYLORIC GLANDSMain secretions: Mucus and GastrinMucusLubricates movement of ingesta into small intestineNeutralizes gastric acidProtects stomach wall from corroding effects
11. REGULATION OF GASTRIC SECRETIONThree PhasesCephalic PhaseGastric PhaseIntestinal PhaseNeural and chemical regulation
12. CEPHALIC PHASEOccurs when food is being eatenStimulated by sight, smell, taste or even thought of foodBut before food enters stomachQuickly becomes a conditioned reflexGreater the appetite greater is cephalic phaseAccounts for 20% of total gastric secretion
13. GASTRIC PHASEStarts when the food enters stomachInduced byVagovagal reflexesLocal enteric reflexesGastrinContinues for several hours till food remains in stomachAccounts for 70% of gastric secretion
14. INTESTINAL PHASEInitiated when food enters duodenumProbably due to small amounts of gastrin secretd by duodenal mucosa
15. Neural and Chemical Regulation of Gastric secretionFour important regulatorsAcetylcholine, Gastrin, Histamine & pH of gastric juiceAcetylcholineParasympathetic neuro-transmitterExcites all secretory cells in gastric glandsInduces pepsinogen, hydrochloric acid, Gastrin and mucusHistamine & Gastrin stimulate acid secretionRate of acid secretion is ∞ amount of histamineHistamine is secreted by chromaffin (ECL) cellsECL cells are located next to parietal cells Acetyl choline & Gastrin stimulate ECL cellsWhen the pH of gastric juice falls below 3.0stimulation of gastric secretion by Gastrin is blockedEither by blocking Gastrin secreting cellsOr nervous reflexes or BOTH
16. Vagus NerveAcetylcholineECL cellsHistamineParietal cellsHydrochloric acidG-cellsGastrinD-cellsSomatostatinChief cellsPepsinogenpH of gastric contents <3.0
17. REGULATION OF PEPSINOGEN SECRETIONTwo types of signals induce pepsinogen secretionStimulation of peptic cells by acetyl cholineSecretion of acid by parietal cellsRate of pepsinogen secretion ∞ gastric acid secreted
18. DIGESTION IN THE SMALL INTESTINEChymeAdmixture of partially digested food with Gastric and salivary secretionsThat leaves stomachFor further digestion in small intestineDigestion in the small intestine is helped by bile and pancreatic secretions
19. PANCREATIC SECRETIONSPancreas is made up ofExocrine and Endocrine cellsExocrine portion is made up of acinar cellsAcinar cells secrete digestive enzymesDuctules and ducts from acini secrete large volumes of sodium bicarbonate solution
20. Duct cellsacinar cells
21. COMPOSITION OF PANCREATIC JUICEClear alkaline secretionConsits ofAquesous phase high bicarbonate & less chlorideNeutralizes chyme partiallyMaintains a pH suitable for pancreatic enzymesOrganic phase Enzymes to digest all types of nutrientsProteins, fats & carbohydrates
22. PROTEOLYTIC ENZYMES IN PANCREATIC JUICEImportant proteolytic enzymesTrypsinChymotrypsinCarboxy peptidaseElastases and nucleases are present in small quantityAction of Trypsin and chymotrypsinSplit whole and partially digested proteins intoPeptides of various sizesBut not into amino acidsAction of Carboxy peptidaseSplits peptides into individual amino acids
23. SECRETION AND ACTIVATION OF PANCREATIC PROTEOLYTIC ENZYMESSecreted in inactive formTrypsinogenChymotrypsinogenProcarboxy peptidaseActivated only after secretion into duodenumEnterokinase (Enteropeptidase)an enzyme secreted by intestinal mucosa on stimulation by chyme activates trypsinogenAlso autocatylytic activation by trypsinTrypsin also activates chymotrypsinogen and procarboxy peptidase
24. WHY PANCREATIC PROTEOLYTIC ENZYMES ARE SECRETED IN INACTIVE FORM?In active form they can digest the Pancreas Activated only after secretion into intestineTrypsin inhibitor from acinar cellsInhibits activation of trypsinogenAlso inhibits activation of other enzymes As trypsin could activate other enzymes
25. TrypsinogenTrypsinTrypsin Inhibitor
26. PANCREATIC AMYLASEMost important in carbohydrate digestion Hydrolyzes starches, Glycogen and most other carbohydrates into disacharides and a few trisacharidesBut cannot digest cellulose
27. PANCREATIC LIPASESHydrolyze neutral fat intoFatty acidsMonoglyceridesCholesterol esterase hydrolyzes cholesterolPhospholipase splits fatty acids from phospholipids
28. SECRETION OF BICARBONATE BY PANCREASEpithelial cells of ducts & ductulesLeading from acinar cellsSecrete bicarbonate and waterOn strong stimulation of PancreasBicarbonate secretion could increase by 5 times
29. HCO3-CO2 CO2 + H2OH2CO3H+SATH+Na++Na++PATHCO3-Na++SECRETION OF BICARBONATE IONS IN PANCREATIC JUICEBloodLumenPancreatic duct cellCl-Cl-
30. SPECIAL FEATURES OF PANCREATIC SECRETIONIN DIFFERENT SPECIESEquinesRate of pancreatic secretion is highest in equinesAt rest produces large volumes of electrolytes & water10-12L/100Kg body wt./24hEven under maximal stimulation enzyme secretion is smallBovinesCow: 3-5L/100Kg body wt./24hCat & DogNo resting flowAfter feeding 2-3ml/min
31. PHASES IN PANCREATIC SECRETIONThree phasesSame as in gastric juice secretion Cephalic phase Sight, smell, taste or even thought of food stimulatesaccounts for 20% of pancreatic secretionMostly enzymes and little fluid secretionTherefore not immediately released into intestineGastric PhaseOccurs when food enters stomachEnzyme secretion continuesAccounts for another 5-10%Intestinal PhaseOccurs when chyme enters intestineCopious fluid secretion occurs in this phaseMainly due to secretinCCK continues to induce enzyme secretion
32. REGULATION OF PANCREATIC SECRETIONThree basic stimuli cause secretionAcetyl cholineVagal endingsEnteric nerve endingsCholecystokinin (CCKP/ CCK)Secretin
33. Ach & CCKEnzymesSecretinFluid & electrolytesEnzymes stored in acinar cells till fluid is secreted by duct cells Synergism among the three stimuli
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35. SIGNIFICANCE OF SECRETINSecretion of Secretin begins when duodenal pH falls below 4.5Maximum release occurs if pH < 3.0Results in secretion of bicarbonate into intestineBicarbonate neutralizes the acidThus bicarbonate ions buffer the intestinal pHWithin a range 7.0-7.8 where pancreatic enzymes function optimally.
36. LIVER AND BILE SECRETIONLargest gland in the bodyMost absorbed products reach liver firstVia the portal circulationMajor functions of liver includeSecretion of bileMetabolism of nutrientsDetoxificationStorage of vitamins esp. A, D, & B12Storage of IronDestruction of RBCSynthesis of plasma proteins including coagulation factors
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38. SECRETION OF BILEBile secretion occurs in two stagesHepatocytes secrete initital portion of bileRich in bile acids (salts), cholesterol, & other organic constitutentsBile duct cells secrete the second portionRich in sodium, bicarbonate & waterBile is secreted continuously by liverMost of it is stored in gall bladderMany animal do not have a gall bladderHorse, deer, giraffe, camel, elephant, pigeonGall bladder may not be essential for normal digestion In animals without gall bladder, bile is thin & wateryGall bladder when present concentrates bile
39. COMPOSITION AND FUNCTIONS OF BILEGreenish /greenish-yellow alkaline secretionContains bile salts Bile pigment - bilirubinCholesterolLecithinElectrolytesPlays important role in fat digestionDue to presence of bile saltsBut not enzymesServes as an excretory vehicleFor end products of heaemoglobin destruction –bilirubincholesterol
40. BILE ACIDS (SALTS)Primary bile acids areCholic acidDeoxycholic acidChenodeoxycholic acidLithocholic acidDerived from cholesterol except for deoxycholic acidConjugated with Taurine / glycineForm taurocholic / Glycocholic acidsSalts of these acids – mainly sodium salts-secreted in bile
41. FUNCTIONS OF BILE SALTSTwo important functions in the intestineEmulsifying / detergent actionDecreases surface tension of fatAllows agitation of fats in intestineBreaks fat globules into minute sizeHelp absorptionFatty acids, monoglycerides, cholesterol & other lipidsBy forming minute complexes with lipds – micellesMicelles are soluble in CM because of charge on bile saltsLipids are ferried as micelles to mucosa for absorptionWithout bile salts upto 40% ingested fat is lost in feces
42. RECYCLING OF BILE SALTSCalled “Entero-hepatic circulation”Occurs 6 times/dayEHC = 95% of bile secretion
43. BILE PIGMENTSBrekadown products of hemoglobinBilirubin is a brownish yellow pigment present in bile of all speciesBilirubin is readily oxidized to biliverdinBiliveridin imparts green color to bile of herbivoresBile pigments are excretion productsConverted to urobilinogens and excreted in fecesUrobilinogens urobilinsUrobilins give the color to fecesLight
44. REGULATION OF BILE SECRETIONUnder Hormonal, chemical and Neural controlVagal stimulation increases bile secretionBut complete denervation of liver does not abolish bile secretionSecretin and substances inducing secretin stimulate bile secretionSo bile and pancreatic secretions run parallelSecretin stimulates secretion of second portion of bile rich in water and electrolytesCCK, Vagus & ENS cause contractions of gall bladderResults in relaxation of sphincter of OddiAnd emptying of stored bile into duodenumBile salts are important choleretics
45. SECRETIONS OF THE SMALL INTESTINEBrunner’s glandsCrypts of LieberkuhnEnterocytes on villi
46. Brunner’s GlandsCompound mucous glandsLarge in numberSecrete alkaline mucousRich in bicarbonateProtects duodenal wall from acidic chymeIn response toTactile stimuliVagal stimulationSecretinSympathetic stimulation inhibits Brunner’s glands
47. Crypts of LieberkuhnLocated over the entire SI surfaceLie in between villiIntestinal surface coverd byGoblet cellsSecrete mucusLubricates and protects intestinal surfaceEnterocytesActively Secrete chloride & bicarbonateFollowed passively by sodium and waterThis water is reabsorbed on villiEnterocytes also havePeptidasesSucrase, maltase, isomaltase and lactaseSmall amounts of lipases
48. REGULATION OF SMALL INTESTINAL SECRETIONLocal enteric nerve refelexes are the most important regulatorsInitiated by tactile or other irritating stimuliIncreases ENS activity associated with GI movementsThus most of the secretion occurs in response to presence of chymeRate of secretion amount of chymeCCK & secretin also increase secretion ∞
49. SECRETIONS IN THE LARGE INTESTINENo villiCrypts of lieberkuhn are presentConsist exclusively of mucus secreting cells Tactile stimulation and ENS reflexes regulate rate of mucus secretionStimulation of PSS causes copious mucus secretionMucus binds together the fecal matterProtects intestinal wall from bacterial activity and acids produced by bacteriaNon mucus secreting cells secrete bicarbonate in moderate amountIntense irritation (infection, poisoning) cause secretion of water and electrolytes in addition to mucusThis causes excessive motility leading to diarrheaDiarrhea protects by washing away the irritantNo enzymes in epithelial cells