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1、1,VII GI SECRETIONS,2,Exocrine of the GI tract,Composition Function Digest food Dilute the food into iso-osmotic fluid Provide a favorable pH for the digestive enzymes Provide mucus for lubrication and protection of the alimentary tract Regulation,Saliva 1.5 l/d pH 6.8-7.0,Ingest 2 l/d water,Gastric
2、 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 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,A
3、cinar Cells: 腺泡细胞,6,Functions of Salivary Secretion,1. Moisten food 2. Begin chemical digestion (amylase, 淀粉酶) 3. Adjust appetite 4. 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 recept
4、or) (water secretion) and sympathetic (NA, receptor) (enzyme) lead to increased secretion,Fear Sleep Tired Dehydration,Nausea,Secretion Vasodilation Cell contraction Metabolism,PNS(IP3),SNS (cAMP),8,VII.2 Gastric secretion,9,Temporary store of ingested material Dissolve food particles and initiate d
5、igestive process Control delivery of contents to small intestine Sterilize ingested material Produce 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,S
6、torage Mucus HCl Pepsinogen Intrinsic factor,Mixing/Grinding Gastrin,11,Gastric gland cells,1. Oxyntic gland (泌酸腺）Parietal cellChief cellMucous neck cell 2. Pyloric glandMucus cell 3. Cardiac glandMucus cell 4. Endocrine cells (G, D, ECL) ECL:enterochromaffin-like cell (肠嗜铬样细胞）,12,Composition and fu
7、nction of gastric secretions,1. HCl converts pepsinogen to pepsin for chemical digestion provides optimal pH environment for pepsin destroys some bacteria stimulates the small intestinal mucosa to release secretin and CCK promotes the absorption of Ca2+ and Fe2+ in small intestine,13,Composition and
8、 function of gastric secretions,2. Pepsinogen (precursor of pepsin)digestion of proteins 3. Mucusforms a protective barrier: Mucus-bicarbonate barrier 4. 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 prec
9、ursor of pepsin which initiates protein digestion Is not necessary for complete digestion of dietray protein pancretic enzymes are sufficient Active only when the pH 3.5,18,Physical/chemical barrier to attack by gastric juice Stimulated by: Ach Mechanical Stim Chemicals (ethanol) If breached e.g. hy
10、persecretion of acid - ulceration,19,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 layer protect the stomach mucosa from injury by hydrochloric acid and pepsin,21,Intr
11、insic Factor,The only gastric secretion that is essential for health Secreted from parietal cells in humans, chief cells in other species Forms a complex with vitamin B12 in the gut Resistant to digestion and enables absorption of vitamin B12 Lack of intrinsic factor causes Vit B12 deficiency (perni
12、cious anaemia),22,VII.3 Regulation of Secretion,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 secretiongastrin and pepsin releasepancreatic exocrine sec
13、retions,Stimulates acid secretion,25,stimulatory signals of Gastric Secretions,Autonomic nervesRelease Ach, stimulatessmooth muscle contractionChief , Parietal , ELC and G cells secretion,GastrinStimulates Chief , Parietal , ELC cells secretion,HistaminStimulates Parietal cells secretin,Protein prod
14、ucts such as peptides, A.AsStimulates G-cells,AcidsStimulate 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,C
15、ephalic Phase Unconditioned and conditioned reflex Only occurs when we want food depression dampens this reflex Account for 10% - 15% total volume of secretion Large amount of HCl and pepsinogen, high digestive ability,31,Gastric Phase,Distension of stomach (arrival of food),Peptides in lumen,Gastri
16、n/ACh,32,Intestinal Phase Account for about 5% of secretion Primarily hormonal denervated stomach will be stimulated to secrete acid by protein in duodenum Hormone still unknown Very 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 Ach or other transmitters by nerve endings,D,Mechanical stimulation Entero-oxyntin,Fatty acids,
