动物生理学6.消化与吸收(二).ppt

6.3.1.2 Composition and function of gastric juice 纯净的胃液是一种无色而呈酸性反应的液体。pH 0.9-1.5 正常人每日分泌的胃液量约为1.5-2.5 L。 胃液的成分 无机物，如盐酸、钠和钾的氯化物等， 有机物，如粘蛋白、胃蛋白酶原等。 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0~5mmol/h 最大排出量 20~25mmol/h 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 Mechanism of hydrochloric acid secretion Pepsinogen [p?p,s?n?d??n] Pepsin的最适pH为2.0~3.5，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。 Mucus and bicarbonate Mucus 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：① 润滑 ② 保护胃粘膜免受机械损伤 ③ 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 ④ 减慢H+向胃壁的扩散 Mucus bicarbonate barrier Gastric mucosal barrier Intrinsic [in’trinsik] factor Intrinsic 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. 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 Gastrin (endocrine) Effects① Stimulates chief , parietal cells② Stimulates　ECL cells ③ Stimulates the growth of GI mucosa, and the synthesis of protein ④ Stimulates the motility of GI tract, contraction of gallbladder, and the secretion of bile and pancreas. Big gastrin G34 Small gastrin G17 Artificial G5 Histamine (paracrine) Produced by ECL cells Strongly stimulates gastric secretion Bind to H2 receptor Be Controlled by Ach and gastrin Endogenous substances inhibiting gastric secretion Somatostatin SS (过去也称GHIH) 生长抑素 Secretin 促胰液素 prostaglandin 前列腺素 Gastric secretion in digesting phase Cephalic phase 头期 Neural regulation Gastric phase胃期 Both neural and humoral Intestinal phase 肠期