1、Gastrointestinal Physiology,YU Yanqin, PhDZhejiang University, School of Medicine,Digestive system,Digestion:Alimentary tract (消化道) Mechanical digestion Digestive gland (消化腺) Chemical digestion Absorption:,The four processes carried out by the GI tract: digestion, secretion,absorption, and motility.
2、,Functions of the digestive system,Components of the digestive system,Structure of the alimentary canal,（肠系膜）,General properties of gastrointestinal smooth muscle,Low excitabilityHigh distensibility （扩张性）Tonic contractionAutorhythmicityHigh sensitivity to temperature, stretch and chemical stimulatio
3、n,Electrophysiological properties of gastrointestinal smooth muscle,Resting membrane potential-40-80 mVIonic basisEm (selective membrane permeability to K+, Na+, Cl- and Ca2+)Electrogenic Na+-K+ pump,The spontaneous rhythmic, subthreshold depolarizations of the cell membrane (slow wave) of the gastr
4、ointestinal tract that characterizes the underlying electrical activity of the bowel （肠）Initiated in the interstitial cells of Cajal (ICC) (pacemaker cell),Slow wave (basic electrical rhythm，基本电节律),Santiago Ramon Y Cajal,He and Camillo Golgi received the Nobel Prize in 1906 for introduction of the s
5、ilver-chromate （铬酸银） stain,Slow wave (basic electrical rhythm,BER)Intensity: 1015 mVFrequency: 312 cpmIonic mechanism? spontaneous rhythmic changes in Na+-K+ pump activity,Normal BER frequencies in the gastrointestinal system,Jejunum：空肠Ileum：回肠,Spike potential (Action potential)Duration: 1020 msIoni
6、c mechanism:Depolarization: Ca2+ influxRepolarization: K+ efflux,Neural control of gastrointestinal function,Enteric nervous system (intrinsic)Autonomic nervous system (extrinsic),Enteric (Intrinsic) nervous systemMyenteric plexus (Auerbachs plexus)Submucosal plexus (Meissners plexus),Neurotransmitt
7、ers secreted by enteric neuronsAch, NE, ATP, serotonin, dopamine, cholecystokinin（胆囊收缩素）, substance P, vasoactive intestinal polypeptide（血管活性肠肽）, somatostatin（生长抑素）, etc.,Roles of enteric nervous system,Sympathetic nerveNEInhibitory (-),Autonomic nervous system,Parasympathetic nerveMainly AChStimula
8、tory (+),Three typesReflexes that are integrated entirely within the enteric nervous systemReflexes from the gut to the prevertebral sympathetic ganglia and then back to the gastrointestinal tractReflexes from the gut to the spinal cord or brain stem and then back to the gastrointestinal tract,Gastr
9、ointestinal reflexes,Gastrointestinal hormones（胃肠激素）,The hormones synthesized by a large number of endocrine cells within the gastrointestinal tractPhysiological functionsControl of the digestive functionControl of the release of other hormonesTrophic action,Gastrointestinal hormones,Four main types
10、Gastrin促胃液素Secretin促胰液素Cholecystokinin (CCK)胆囊收缩素Gastric inhibitory peptide (GIP) 抑胃肽,Brain-gut peptide（脑-肠肽）,Definition:the peptide which is found in the brain and the gut also. Classification:Gastrin 促胃液素CCKP substance,Digestion in the stomach,Gastric juice（胃液）,PropertiespH 0.91.51.52.5 L/dayMajor
11、 componentsHydrochloric acid 盐酸Pepsinogen 胃蛋白酶原Mucus 粘液Intrinsic factor 内因子,Gastric juice,Secreted by parietal cells壁细胞Chief cells主细胞Mucous neck cells粘液颈细胞,Hydrochloric acid,Secreted by the parietal cellsOutputBasal: 05 mmol/hMaximal: 2025 mmol/h,Mechanism of HCl secretionActive transportH+ pump (pr
12、oton pump)Cl-HCO3- exchange,FOOD,Acid production by the parietal cells in the stomach depends on the generation of carbonic acid; subsequent movement of hydrogen ions into the gastric lumen results from primary active transport.,Acid sterilization 杀菌Activation of pepsinogenPromotion of secretin促胰液素s
13、ecretionAssisted effect of iron and calcium absorption,Role of HCl,One inhibitory andthree stimulatory signals that alteracid secretion byparietal cellsin the stomach.,Proton pump inhibitors and histamine blockers,Pepsinogen,MW: 42,500Secreted by the chief cells as an inactive precursor of pepsinAct
14、ivated in the stomach, initially by H+ ions and then by active pepsin, autocatalytic activationActive pepsin (MW: 35,000),Effect of pepsinPepsin is an endopeptidase, which attacks peptide bonds in the interior of large protein molecules,Mucus,Secreted by the epithelial cells all over the mucosa and
15、by the neck mucus cells in the upper portion of the gastric glands and pyloric glandsRoleLubrication of the mucosal surfaceProtection of the tissue from mechanical damage by food particles,gastric pit: 胃小凹,Mucus-HCO3- barrier,Intrinsic factor,A high molecular weight glycoprotein, synthesized and sec
16、reted by the parietal cellsThe intrinsic factor binds to Vit B12 and facilitates its absorption,Vit B12,Regulation of gastric secretion,Basic factors that stimulate gastric secretionAcetylcholine (+ all secretory cells)Gastrin (+ parietal cells)Histamine (+ parietal cells),Regulation of gastric secr
17、etion,Nervous regulationShort reflex pathways Short excitatory reflexes: mediated by cholinergic neurons in the plexusesShort inhibitory reflexes: mediated by non-adrenergic non-cholinergic (NANC) neurons,Regulation of gastric secretion,Nervous regulationLong autonomic pathwaysLong excitatory reflex
18、es: parasympatheticLong inhibitory pathways: sympathetic,Regulation of gastric secretion,Humoral regulation,ExcitatoryAChHistamineGastrin,InhibitorySomatostatin Secretin5-hydroxytryptamine (5-HT) Prostaglandin前列腺素,Phases of gastric secretion,Cephalic phase 头相Gastric phase 胃相Intestinal phase 肠相,Inhib
19、ition of gastric secretion,The functional purpose of the inhibition of gastric secretion by intestinal factors is presumably to slow the release of chyme 食糜 from the stomach when the small intestine is already filled or overactive,Inhibition of gastric secretion,stimulated by the presence of acid, f
20、at, protein breakdown products, hyperosmotic or hypo-osmotic fluids, or any irritating factors in the upper small intestine,Motor function of the stomach,Proximal stomachcardia 贲门fundus 胃底corpus (body)胃体Distal stomachantrum 胃窦pylorus 幽门pyloric sphincter 幽门括约肌,Motor function of the stomach,Receptive
21、relaxation 容受性舒张Storage function (1.01.5 L)Vago-vagal reflexPeristalsis 蠕动BER in the stomach,Rhythmic waves of smooth muscle contraction in the gut are the result of waves of action potentials moving along via gap junctions.,Waves of smooth muscle contraction mix and propel theingested contents of t
22、he gastric lumen, but only a small amount of the material enters the small intestine (duodenum) as a result of each wave cycle.,Emptying of the stomach 排空,Emptying of the stomach,Emptying rateSmall particle large particleIsosmotic hyper- & hypo-osmoticCarbohydrates Protein FatRegular meal 46 hrs,Reg
23、ulation of stomach emptyingGastric factors that promote emptyingGastric food volumeGastrinDuodenal factors that inhibit stomach emptyingEnterogastric nervous reflexesFat Cholecystokinin,Delivery of acid and nutrients into the small intestine initiates signaling that slows gastric motility and secretion which allows adequate time for digestion and absorption in the duodenum.Enterogastrone-肠抑胃素,
