胃腸肝膽消化系統(tǒng)

1、1,VII GI SECRETIONS,2,Exocrine of the GI tract,CompositionFunctionDigest foodDilute the food into iso-osmotic fluidProvide a favorable pH for the digestive enzymesProvide mucus for lubrication and protection of th

2、e alimentary tractRegulation,Saliva 1.5 l/dpH 6.8-7.0,Ingest 2 l/d water,Gastric secretion 2 l/d, pH 1.5-3,Bile 0.5 l/d pH 7.8-8.0,Pancreatic juice 1.5 ml/d pH 8.0-8.4,Intestinal secretion 1.5 l/d pH 7.8-8.0,Small int

3、estine absorbs 8.5 l/d,Colon absorbs 0.4-1 l/d,0.1 l/d water excreted,,3,VII.1 Salivary secretion,4,Salivary gland,5,Secretion,Saliva: water, ions, mucus, enzymes,Acinar Cells: 腺泡細(xì)胞,6,Functions of Salivary Secretion,1. M

4、oisten food2. Begin chemical digestion (amylase, 淀粉酶)3. Adjust appetite4. Bacteriostatic action （抑菌作用) (bacteriolysin, 溶菌素),7,Control of salivary secretion,Secretion rate depends entirely on neural control both paras

5、ympathetic (Ach, M receptor) (water secretion)and sympathetic (NA, β receptor) (enzyme)lead to increased secretion,FearSleepTired Dehydration,,Nausea,SecretionVasodilationCell contractionMetabolism,,,PNS(IP3),SNS

6、(cAMP),8,VII.2 Gastric secretion,9,Temporary store of ingested materialDissolve food particles and initiate digestive processControl delivery of contents to small intestineSterilize ingested materialProduce intrinsic

7、 factor (Vitamin B12 absorption),Functions of Stomach,10,,,Oesophagus,,Lower Oesophageal,Sphincter,,,,,Fundus,,Body,,,Antrum,,,Duodenum,,Pylorus,Functional Anatomy of Stomach,Fundus,Body,Antrum,Storage,StorageMucusHCl

8、PepsinogenIntrinsic factor,Mixing/GrindingGastrin,11,Gastric gland cells,1. Oxyntic gland (泌酸腺） Parietal cell Chief cell Mucous neck cell2. Pyloric gland Mucus cell3. Cardiac gland Mucus cell4.

9、 Endocrine cells (G, D, ECL)ECL:enterochromaffin-like cell (腸嗜鉻樣細(xì)胞）,12,Composition and function of gastric secretions,1. HClconverts pepsinogen to pepsin for chemical digestion provides optimal pH environment for peps

10、indestroys some bacteriastimulates the small intestinal mucosa to release secretin and CCKpromotes the absorption of Ca2+ and Fe2+ in small intestine,,13,Composition and function of gastric secretions,2. Pepsinogen (p

11、recursor of pepsin) digestion of proteins 3. Mucus forms a protective barrier: Mucus-bicarbonate barrier4. Intrinsic factor combines with vitamin B12 to make it absorbable,,14,,HCl secretion,光面管泡,微管,15,,HC

12、l secretion,16,HCl secretion,17,,Cells,Inactive precursor of pepsin which initiates protein digestionIs not necessary for complete digestion of dietray protein – pancretic enzymes are sufficientActive only when the pH

13、 < 3.5,18,,Physical/chemical barrier to attack by gastric juiceStimulated by:AchMechanical StimChemicals (ethanol)If breached e.g. hypersecretion of acid - ulceration,19,,Gastric Mucus-Bicarbonate Barrier,20,Gast

14、ric Mucus-bicarbonate barrier,The insoluble mucus and bicarbonate construct a barrier prevent hydrogen ions from diffusing to the mucosal layerprotect the stomach mucosa from injury by hydrochloric acid and pepsin,21,I

15、ntrinsic Factor,The only gastric secretion that is essential for healthSecreted from parietal cells in humans, chief cells in other speciesForms a complex with vitamin B12 in the gutResistant to digestion and enables

16、absorption of vitamin B12Lack of intrinsic factor causes Vit B12 deficiency (pernicious anaemia),22,VII.3 Regulation of Secretion,23,Control of Gastric Acid Secretion,Neurocrine(vagus/local reflexes)Endocrine (gastri

17、n)Paracrine (histamine),24,Endocrine gland cells of gastric pits,,,,,Stimulates acid secretion,Inhibits acid secretion gastrin and pepsin release pancreatic exocrine secretions,Stimulates acid secretion,25,stimula

18、tory signals of Gastric Secretions,Autonomic nerves Release Ach, stimulates smooth muscle contraction Chief , Parietal , ELC and G cells secretion,Gastrin Stimulates Chief , Parietal , ELC cells secretion,Histamin S

19、timulates Parietal cells secretin,Protein products such as peptides, A.A’s Stimulates G-cells,Acids Stimulate D cells,26,,Endogenous substances regulating gastric secretion,協(xié)同作用,27,,GASTRIN,,,,K,H,~,HISTAMINE,,ACETYLCH

20、OLINE,,28,Gastric secretion during digesting food,29,Mechanisms Stimulating Gastric Acid Secretion in Cephasic Phase,Cephalic Phase,GRP,30,,Cephalic PhaseUnconditioned and conditioned reflex Only occurs when we want f

21、ooddepression dampens this reflexAccount for 10% - 15% total volume of secretionLarge amount of HCl and pepsinogen, high digestive ability,31,Gastric Phase,Distensionof stomach(arrival of food),Peptidesin lumen,Gas

22、trin/ACh,32,Intestinal PhaseAccount for about 5% of secretionPrimarily hormonal – denervated stomach will be stimulated to secrete acid by protein in duodenumHormone still unknownVery small number of G-cells in duode

23、num also release gastrin,33,Regulation of Gastric Secretions occurs via 3 phases,34,Regulation of gastric secretion,,,,,Secretion of Ach or other transmittersby nerve endings,D,,Mechanical stimulationEntero-oxyntin,Fa

24、tty acids,Hyperosmotic solution,HCl,Gastric gland,35,Mechanisms Inhibiting Gastric Acid Secretion,Cephalic Phase,Gastric Phase,Intestinal Phase,Acid induodenum,Fat induodenum,36,VIII. Secretion of the pancreas,37,Secre

25、tion of the pancreas,Endocrine - insulin & glucagonExocrine - enzymes and bicarbonateessential for digestionalmost under separate hormonal control,38,,Gall bladder,,Sphincter of Oddi,,39,Exocrine Pancreas,Respon

26、sible for digestive function of pancreas,FunctionSecretion of bicarbonate by duct cellsSecretion of digestive enzymes by acinar cells,40,Zymogens (酶原）,Acinar cells contain digestive enzymes stored as inactive zymogen g

27、ranulesPrevents autodigestion of pancreasEnterokinase (bound to brush border of duodenal enterocytes) converts trypsinogen to trypsin Trypsin converts all other zymogens to active forms,41,Cleave peptide bondsHydroly

28、ze DNA/RNACollagen digestionPhospholipidsto fatty acidsTriglycerides to fatty acids+ glycerolStarch to maltose + glucose,Categories of Pancreatic Enzymes,ProteasesNucleasesElastasesPhospholipasesLipases

29、Amylase,42,Activation of pancreatic proteases,43,,H2O,Bicarbonate secretion,Lumen,Blood,44,,Bicarbonate function,Function 1. Neutralize gastric acid emptied into the duodenum 2. Provide a favorable alkaline en

30、vironment for optimal activity of pancreatic enzymes,45,Control of Pancreatic Function,Bicarbonate secretion stimulated by secretinSecretin released in response to acid in duodenum,Zymogen secretion stimulated by cholec

31、ystokinin (CCK)CCK released in response to fat/amino acids in duodenumunder neural control (vagal/local reflexes) - triggered by arrival of organic nutrients in duodenum,46,Control of pancreatic secretion,- secretion

32、in 3 phasesCephalic phase - only 10-15% of total secretion Activation of vagal efferent stimulates enzyme release Gastric phase - only present in some speciesNOT SIGNIFICANT IN HUMANS Intestinal phase - majorit

33、y of secretionCombination of hormones CCK and secretin and neuronal reflex Results in maximal enzyme and bicarbonate release,47,Control of pancreatic secretion,,Key hormones in stimulation of secretion:Cholecystokin

34、in (CCK) Secretin Inhibiting factors: SS, PP, glucagon,48,,Cholecystokinin,,,,,,,,,,,,,,,,I cells,Peptides Amino acids, Fatty Acid H+,Enzymes,,,,,,Fat,stomach,pancreas,duodenum,CCK release peptide,,5-HT,,,49,,Secretin

35、,,,,,,,,,,,,,,,,,,,,,,,,,,,H+,S cells,Fat,Peptides,50,Control of Pancreatic Function,51,,,,,,,,,,,,,,,,Peptides Amino acidsFat, H+,,,,,,,,,,,,,,,Intestinal phase of secretion,,52,IX Biliary secretion,,53,Structure/Func

36、tion of Liver,Liver lobule,,Portal triad,,Bilecanaliculus,Hepaticartery,Hepaticportal vein,,,Centralvein,54,55,Secretion and storage of bile,Constituents of bile Liver GallbladderWater98%92%Bi

37、le salts1%6%Bilirubin(膽紅素）0.04%0.3%Cholesterol（膽固醇）0.1%0.3-0.9%Fatty acids0.12%0.3-1.2%Lecithin（卵磷脂）0.04%0.3%Na, K, Ca, Cl, HCO3,56,Emulsification of fatsIncreased absorption of lipids int

38、o enterocytes (include vitamin A, D, E, K)Increased synthesis and secretion of bileCholesterol excretion (only route)Excretion of breakdown products of haemoglobin (bilirubin，膽紅素),Functions of bile,,57,(a)A molecular

39、 model of a bile salt, with the cholesterol-derived “core” in yellow.,(b)A space-filling model of a bile salt. The non-polar surface helps emulsify fats, The polar surface promotes water solubility.,Bile Salt,58,Bile

40、salts and phospholipids aidOnly component useful in digestive processes. convert large fat globules into smaller pieces polar surfaces inhibit re-aggregation.,emulsification,,59,Emulsified fat globules are small enou

41、gh lipase enzymes gain access degrade triglycerides to monoglycerides and fatty acidsMonoglycerides and fatty acids enter the absorptive cells by simple diffusion aggregate to form loosely held micelleswhich read

42、ily break down.,60,Regulation of bile secretion and empty of gallbladder,1. Nervous regulation: Vagus-vagus reflex2. Humoral regulation: CCK , Gastrin, Secretin, SS3. Bile salt: Enteroheptic circulation (Def.),61,,,,,

43、,,Sphincter of Oddi(closed),,,In fasting stateBile stored in gall bladder& concentrated,,,Liver,62,,,,,,,,FAT,Digestion- fat in duodenum stimulates CCK release from I cells,CCK,63,,,,,,Liver - secretion,Gallbladd

44、er-storage & concentration,Duodenum-digestion & emulsification,Ileum - absorption of bile acids,The enterohepatic circulation,,Portal vein,Common bile duct,64,Up to 95% of the cholesterol-based bile salts are “re

45、cycled” by reabsorption along the intestine. Inhibition of reabsorption results in synthesis of new bile acids and lowering of cholesterol levels.Increasing dietary fiber could trap a greater percentage of the bile i

46、n the fibrous feces.,65,Regulation of Bile Release,Acidic, fatty chyme causes the duodenum to release:Cholecystokinin (CCK) and secretin into the bloodstreamBile salts and secretin transported in blood stimulate the li

47、ver to produce bileVagal stimulation causes weak contractions of the gallbladderCholecystokinin causes:The gallbladder to contractThe sphincter of Oddi to relax,66,X Small Intestine secretion,,67,Composition and func

48、tion,Digestive enzymes not secreted from small intestine - from pancreas or found on enterocytesexcept enterokinase secreted from duodenal mucosa Mucus/alkali secretions - mucosal protection Aqueo

49、us secretions,Function Lubricate and protect intestinal surface (Ig A) Dilute digestive products Digest specific food substances (enzymes in enterocytes: peptidase, sucrase, etc ),68,Regulation of sm