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1、动物生理学消化与吸收(2)第1页，共28页，编辑于2022年，星期五Hydrochloric acid Hydrochloric acid produced in stomach is also called gastric acid.有两种形式：游离酸和结合酸（与蛋白质结合）胃酸排出量：基础酸排出量05mmol/h 最大排出量 2025mmol/h 胃酸的生理作用胃酸的生理作用激活胃蛋白酶原，为胃蛋白酶提供酸性环境杀灭细菌促进Ca2+和Fe2+的吸收进入十二指肠后，可促进secretin和CCK的释放 第2页，共28页，编辑于2022年，星期五Mechanism of hydrochlori
2、c acid secretion parietal cell第3页，共28页，编辑于2022年，星期五第4页，共28页，编辑于2022年，星期五Proton pumpMechanism of hydrochloric acid secretion 第5页，共28页，编辑于2022年，星期五Pepsinogen pp,sndnPepsin的最适pH为2.03.5，当pH5.0时便 失活主要作用于蛋白质及多肽分子中含苯丙氨酸或酪氨酸的肽键上，主要分解产物是眎和胨以及少量的多肽和氨基酸。Pepsinogen pepsinHCl第6页，共28页，编辑于2022年，星期五Mucus and bicarb
3、onateMucus 由粘膜表面的上皮细胞、粘颈细胞、贲门、幽门的腺细胞产生。作用：润滑 保护胃粘膜免受机械损伤 降低胃酸的酸度、降低胃蛋白酶活性防止酸和胃 蛋白酶对胃粘膜的损害 减慢H+向胃壁的扩散Mucus bicarbonate barrierGastric mucosal barrier第7页，共28页，编辑于2022年，星期五第8页，共28页，编辑于2022年，星期五Gastric Mucus-Bicarbonate Barrier第9页，共28页，编辑于2022年，星期五View of a bleeding ulcer by using an endoscope(a tubular
4、 instrument bearing a tiny lens and a light source)that can be inserted into the abdominal cavity.第10页，共28页，编辑于2022年，星期五Intrinsic intrinsik factorIntrinsic factor is a glycoprotein produced by the parietal cells of the stomach.It is necessary for the absorption of vitamin B12 in the terminal ileum.第
5、11页，共28页，编辑于2022年，星期五6.3.1.3 Regulation of gastric secretion 消化间期胃液分泌 消化期胃液分泌 Endogenous substances promoting gastric secretion Acetylcholine (vagus reflexes)Stimulates smooth muscle contraction Also stimulates Chief,Parietal,ELC and G cells Ach M receptor ECL cells Histamine H2 receptor第12页，共28页，编辑
6、于2022年，星期五Gastrin(endocrine)Effects Stimulates chief,parietal cells StimulatesECL cells Stimulates the growth of GI mucosa,and the synthesis of protein Stimulates the motility of GI tract,contraction of gallbladder,and the secretion of bile and pancreas.Big gastrin G34Small gastrin G17 Artificial G5
7、第13页，共28页，编辑于2022年，星期五Histamine(paracrine)Produced by ECL cells Strongly stimulates gastric secretionBind to H2 receptorBe Controlled by Ach and gastrin第14页，共28页，编辑于2022年，星期五协同作用协同作用第15页，共28页，编辑于2022年，星期五Endogenous substances inhibiting gastric secretionSomatostatin SS(过去也称GHIH)生长抑素Secretin 促胰液素pros
8、taglandin 前列腺素第16页，共28页，编辑于2022年，星期五Cephalic phase 头期 Neural regulationGastric phase胃期 Both neural and humoral Intestinal phase 肠期 mainly humoralGastric secretion in digesting phase第17页，共28页，编辑于2022年，星期五Cephalic phaseConditioned reflexUnconditioned reflexAccount for 10%-15%total volume of secretionL
9、arge amount of HL and pepsinogen,high digestive ability 第18页，共28页，编辑于2022年，星期五第19页，共28页，编辑于2022年，星期五Gastric PhaseDistensionof stomach(arrival of food)Vagal/EntericreflexesParietalcellsAChPeptidesin lumenG cellsGastrinGastrin/AChECLcellsHistamine第20页，共28页，编辑于2022年，星期五Starts when food reaches the stom
10、ach Provides 2/3 of the juice releasedThere are two parts(neural and chemical)to this phaseNeural partActivated by stretch receptorsInitiates both local neural reflexes as well as the longer vago-vagal reflexBoth reflexes result in release of ACh at stomach synapses which stimulates secretory cellsT
11、his branch is inhibited by Sympathetic action(emotional upset)Gastric Phase第21页，共28页，编辑于2022年，星期五Chemical partAn increase in pH(thus,less acidity),presence of peptides,and caffeine activate the G-cellsThis results in Gastrin being releasedGastrin acts on Parietal cells that start secreting HClGastri
12、n also stimulates Histamine release,which in turn stimulates Parietal cellsThe increase in HCl promotes pepsin production and protein degradationThe release of Gastrin is partly regulated by acidity,Increased acidity inhibits the G-cells.Increased presence of proteins in a meal tends to buffer proto
13、n.This in turn keeps the pH from becoming too acidic and allows more gastrin to be released第22页，共28页，编辑于2022年，星期五第23页，共28页，编辑于2022年，星期五Intestinal PhaseAccount for about 5%of secretionPrimarily hormonal denervated stomach will be stimulated to secrete acid by protein in duodenumHormone still unknownV
14、ery smalll number of G-cells in duodenum also release gastrin in response to amino acids第24页，共28页，编辑于2022年，星期五第25页，共28页，编辑于2022年，星期五Regulation of Gastric Secretions occurs via 3 phases第26页，共28页，编辑于2022年，星期五第27页，共28页，编辑于2022年，星期五Factors inhibiting gastric secretion during digesdtionAcid inhibit release of gastrin stimulates release of SS in anrum stimulates release of secretin and bulbogastrone球抑胃素 in doudenumFat stimulates release of enterogastrone(not isolated)Hypertonic solution高张溶液（高渗溶液）(duodenal)osmotic receptor enterogastric reflex第28页，共28页，编辑于2022年，星期五