第四节小肠内消化digestioninthesmallintestine一、胰液.ppt

大肠内有许多细菌。细菌主要来自食物和空气，它们由口腔入胃，最后到达大肠。大肠内的酸碱度和温度对一般细菌的繁殖极为适宜，细菌便在这里大量繁殖。细菌中含有能分解食物残渣的酶。糖及脂肪的分解称为发酵，其产物有乳酸、醋酸、二氧化碳、沼气、脂肪酸、甘油、胆碱等。蛋白质的细菌分解称为腐败，其产物有胨、氨基酸、氨、硫化氢、组胺、吲哚等，其中有的成分由肠壁吸收后到肝中解毒。大肠内的细菌能利用肠内较为简单的物质合成维生素B复合物和维生素K，它们由肠内吸收后，对人体有营养作用。 Cholecystokinin (CCK) stimulates the gallbladder, which responds by contracting and delivering more bile to the duodenum through the sphincter of Oddi, which relaxes (opens) in response to CCK. Summary: regulation of bile secretion Small intestinal juices Secreted by: Brunners glands(十二指肠腺) Crypts of Lieberkuhn（小肠腺或李氏腺） 1~3 L/day pH 7.6 Isosmotic Small intestinal juices Components H2O Electrolytes (Na+, K+, Ca2+, Cl-) Mucus IgA Enterokinase 肠致活酶 Small intestinal juices Function: Completing the digestion of peptides, carbohydrates fat Regulation: Secretion by intestinal glands is mainly due to the local effects of chyme 食糜 in the intestine and is regulated by both neural and hormonal factors Movement of small intestine during digestion Segmentation 分节运动 Peristalsis 蠕动 Tonic contraction: maintaining a basal state of intestinal smooth muscle contraction Movement of small intestine Segmentation Segmentation The most common type of activity in the intestine during digestion absorption Consisting of the alternate contraction relaxation of adjacent bands of circular smooth muscle Function: Mixing food digestive secretions facilitating both digestion absorption of digestive products by the mucosal epithelium Regulated by excitatory inhibitory neurons in the plexuses Peristalsis Regulation of intestinal motility Autoregulation: Regulated by BER Neural Reflexes: mainly by ‘short’ reflexes in the intrinsic plexuses which are responsible for peristalsis and segmentation also by extrinsic nerves (sympathetic vagal nerves) which mediate ‘long’ reflexes Regulation of intestinal motility Hormonal controls: Gastrin, CCK, motilin（胃动素）, 5-HT (+) Secretin, VIP, glucagon（胰高血糖素） (-) Function of large intestine The principle functions of