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 the alimentary tractRegulation,Saliva 1.5 l/dpH 6.8-7.0,Ingest 2 l/d water,Gastric secret
2、ion 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 intestine 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 C
3、ells: 腺泡细胞,6,Functions of Salivary Secretion,1. Moisten 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 parasympathetic (Ach, M receptor) (water
4、 secretion)and sympathetic (NA, receptor) (enzyme)lead to increased secretion,FearSleepTired Dehydration,Nausea,SecretionVasodilationCell contractionMetabolism,PNS(IP3),SNS (cAMP),8,VII.2 Gastric secretion,9,Temporary store of ingested materialDissolve food particles and initiate digestive processCo
5、ntrol delivery of contents to small intestineSterilize ingested materialProduce intrinsic 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,StorageMucusHClPepsino
6、genIntrinsic 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. Endocrine cells (G, D, ECL)ECL:enterochromaffin-like cell (肠嗜铬样细胞）,12,Composition and function of gastric secreti
7、ons,1. HClconverts pepsinogen to pepsin for chemical digestion provides optimal pH environment for pepsindestroys 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 secretio
8、ns,2. Pepsinogen (precursor 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,HCl secretion,16,HCl secretion,17,Cells,Inactive precursor of pepsin which initia
9、tes protein digestionIs not necessary for complete digestion of dietray protein pancretic enzymes are sufficientActive only when the pH 3.5,18,Physical/chemical barrier to attack by gastric juiceStimulated by:AchMechanical StimChemicals (ethanol)If breached e.g. hypersecretion of acid - ulceration,1
10、9,Gastric Mucus-Bicarbonate Barrier,20,Gastric 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,Intrinsic Factor,The only gastric secret
11、ion 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 absorption of vitamin B12Lack of intrinsic factor causes Vit B12 deficiency (pernicious anaemia),22,VII.3 Regulation of Se
12、cretion,23,Control of Gastric Acid Secretion,Neurocrine(vagus/local reflexes)Endocrine (gastrin)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,stim
13、ulatory 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 Stimulates Parietal cells secretin,Protein products such as peptides, A.As Stimulat
14、es G-cells,Acids Stimulate D cells,26,Endogenous substances regulating gastric secretion,协同作用,27,GASTRIN,K,H,HISTAMINE,ACETYLCHOLINE,28,Gastric secretion during digesting food,29,Mechanisms Stimulating Gastric Acid Secretion in Cephasic Phase,Cephalic Phase,GRP,30,Cephalic PhaseUnconditioned and con
15、ditioned reflex Only occurs when we want fooddepression 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,Gastrin/ACh,32,Intestinal PhaseAccount for abou
16、t 5% of secretionPrimarily hormonal denervated stomach will be stimulated to secrete acid by protein in duodenumHormone still unknownVery small number of G-cells in duodenum also release gastrin,33,Regulation of Gastric Secretions occurs via 3 phases,34,Regulation of gastric secretion,Secretion of A
17、ch or other transmittersby nerve endings,D,Mechanical stimulationEntero-oxyntin,Fatty 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
18、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,Responsible for digestive function of pancreas,FunctionSecretion of bicarbonate by duct cellsSecre
19、tion of digestive enzymes by acinar cells,40,Zymogens (酶原）,Acinar cells contain digestive enzymes stored as inactive zymogen granulesPrevents autodigestion of pancreasEnterokinase (bound to brush border of duodenal enterocytes) converts trypsinogen to trypsin Trypsin converts all other zymogens to a
20、ctive forms,41,Cleave peptide bondsHydrolyze DNA/RNACollagen digestionPhospholipidsto fatty acidsTriglycerides to fatty acids+ glycerolStarch to maltose + glucose,Categories of Pancreatic Enzymes,ProteasesNucleasesElastasesPhospholipasesLipases Amylase,42,Activation of pancreatic proteases,43,H2O,Bi
21、carbonate secretion,Lumen,Blood,44,Bicarbonate function,Function 1. Neutralize gastric acid emptied into the duodenum 2. Provide a favorable alkaline environment for optimal activity of pancreatic enzymes,45,Control of Pancreatic Function,Bicarbonate secretion stimulated by secretinSecretin released
22、 in response to acid in duodenum,Zymogen secretion stimulated by cholecystokinin (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 in 3 phasesC
23、ephalic 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 - majority of secretionCombination of hormones CCK and secretin and neuronal reflex Results in maximal enzyme a
24、nd bicarbonate release,47,Control of pancreatic secretion,Key hormones in stimulation of secretion:Cholecystokinin (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,Secr
25、etin,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/Function of Liver,Liver lobule,Portal triad,Bilecanaliculus,Hepaticartery,Hepaticportal vein,Centralvein,54,55,Secretion and storage of bil
26、e,Constituents of bile Liver GallbladderWater98%92%Bile salts1%6%Bilirubin(胆红素）0.04%0.3%Cholesterol（胆固醇）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 into enterocytes (include vitamin A, D, E, K)Increased synthes
27、is and secretion of bileCholesterol excretion (only route)Excretion of breakdown products of haemoglobin (bilirubin，胆红素),Functions of bile,57,(a)A molecular 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 emuls
28、ify fats, The polar surface promotes water solubility.,Bile Salt,58,Bile 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 enough lipase en
29、zymes 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 readily break down.,60,Regulation of bile secretion and empty of gallbladder,1. Nervous regulation: Vagu
30、s-vagus reflex2. Humoral regulation: CCK , Gastrin, Secretin, SS3. Bile salt: Enteroheptic circulation (Def.),61,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,Ga
31、llbladder-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 “recycled” by reabsorption along the intestine. Inhibition of reabsorption results in
32、 synthesis of new bile acids and lowering of cholesterol levels.Increasing dietary fiber could trap a greater percentage of the bile in the fibrous feces.,65,Regulation of Bile Release,Acidic, fatty chyme causes the duodenum to release:Cholecystokinin (CCK) and secretin into the bloodstreamBile salt
33、s and secretin transported in blood stimulate the liver 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 function,Digestive enzymes not secret
34、ed from small intestine - from pancreas or found on enterocytesexcept enterokinase secreted from duodenal mucosa Mucus/alkali secretions - mucosal protection Aqueous 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 small intestinal secretion,Local stimuli The presence of chyme in the intestineHormonal regulation Secretin CCKNeuronal regulation Vagus nerve excitatory Sympathetic nerve - inhibitory,
