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1、动物生理学消化与吸收(2)第1页，本讲稿共28页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，本讲稿共28页Mechanism of hydrochloric acid secretion par
2、ietal cell第3页，本讲稿共28页第4页，本讲稿共28页Proton pumpMechanism of hydrochloric acid secretion 第5页，本讲稿共28页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，本讲稿共28页Mucus and bicarbonateMucus 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
3、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，本讲稿共28页第8页，本讲稿共28页Gastric Mucus-Bicarbonate Barrier第9页，本讲稿共28页View of a bleeding ulcer by using an endoscope(a tubular instrument bearing a tiny lens and a light source)that can be inserted into the abdominal
4、 cavity.第10页，本讲稿共28页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11页，本讲稿共28页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
5、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，本讲稿共28页Gastrin(endocrine)Effects Stimulates chief,parietal cells StimulatesECL cells Stimulates the growth of GI muco
6、sa,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第13页，本讲稿共28页Histamine(paracrine)Produced by ECL cells Strongly stimulates gastric secretionBind to H2 receptorBe Control
7、led by Ach and gastrin第14页，本讲稿共28页协同作用协同作用第15页，本讲稿共28页Endogenous substances inhibiting gastric secretionSomatostatin SS(过去也称GHIH)生长抑素Secretin 促胰液素prostaglandin 前列腺素第16页，本讲稿共28页Cephalic phase 头期 Neural regulationGastric phase胃期 Both neural and humoral Intestinal phase 肠期 mainly humoralGastric secreti
8、on in digesting phase第17页，本讲稿共28页Cephalic phaseConditioned reflexUnconditioned reflexAccount for 10%-15%total volume of secretionLarge amount of HL and pepsinogen,high digestive ability 第18页，本讲稿共28页第19页，本讲稿共28页Gastric PhaseDistensionof stomach(arrival of food)Vagal/EntericreflexesParietalcellsAChPep
9、tidesin lumenG cellsGastrinGastrin/AChECLcellsHistamine第20页，本讲稿共28页Starts when food reaches the stomach 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-vaga
10、l reflexBoth reflexes result in release of ACh at stomach synapses which stimulates secretory cellsThis branch is inhibited by Sympathetic action(emotional upset)Gastric Phase第21页，本讲稿共28页Chemical partAn increase in pH(thus,less acidity),presence of peptides,and caffeine activate the G-cellsThis resu
11、lts in Gastrin being releasedGastrin acts on Parietal cells that start secreting HClGastrin 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 a
12、cidity inhibits the G-cells.Increased presence of proteins in a meal tends to buffer proton.This in turn keeps the pH from becoming too acidic and allows more gastrin to be released第22页，本讲稿共28页第23页，本讲稿共28页Intestinal PhaseAccount for about 5%of secretionPrimarily hormonal denervated stomach will be s
13、timulated to secrete acid by protein in duodenumHormone still unknownVery smalll number of G-cells in duodenum also release gastrin in response to amino acids第24页，本讲稿共28页第25页，本讲稿共28页Regulation of Gastric Secretions occurs via 3 phases第26页，本讲稿共28页第27页，本讲稿共28页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，本讲稿共28页