,Chapter 6,DIGESTION & ABSORPTION, 1. Introduction Concept of digestion & absorption * Mechanical & chemical digestion Characteristics of digestive smooth muscles* General characteristics* Electrophysiological characteristicsResting potential (RP)Slow wave or basic electrical rhythm (BER)Action potential (AP),Electrical activities & contraction of digestive smooth muscles, Secretion of digestive glands * Main functions of digestive fluids Gastrointestinal innervation* Intrinsic (or enteric) nervous systemSubmucosal & myenteric plexus* Extrinsic nervous systemParasympathetic & sympathetic nerves Gastrointestinal hormones* General functions* Brain-gut peptides,Intrinsic(or enteric) nervous system,Extrinsic nervous system, 2. Digestion in the mouth digest starch* Regulation of salivary secretionPure neuroregulationConditioned & unconditioned reflex, Mastication or chewing aid swallowing Deglutition or swallowing* Definition* Process1st, 2nd & 3rd phasePeristalsis & lower esophageal sphincter,Peristalsis of the esophagus, 3. Digestion in the stomach Gastric juice & its secretion * Nature, Compositions & functionspH 0.91.5, colorless, 1.52.5 L/dayHydrochloric acid (HCl)Secreted by parietal cellsBasic secretion: 05 mmol/hMax secretion: 2025 mmol/hMechanism of HCl secretionFunctions: see next page,Relationship between max volume of HCl secretion & the number of parietal cells,Functions of HCl: Turn pepsinogen into pepsin Promote the absorption of calcium & ferrum PepsinogenSecreted by chief cells & activate by HClFunction: digest proteins into proteoses, peptones, polypeptides, with little free amino acids,MucusSecreted by neck & surface mucous cells, cardiac & pyloric glandsFunction: form mucus-bicarbonate barrierIntrinsic factorSecreted by parietal cellsFunction: Promote the absorption of Vit B12 * Regulation of gastric secretionEndogenous releasing substancesAcetylcholine (ACh), gastrin & histamineSomatostatin (SST) (release-inhibiting),Mucus-bicarbonate barrier,Action of acetylcholine, gastrin & histamine on the perietal cells,Gastric secretion in the digestive phaseCephalic phaseMechanisms:Conditioned & Unconditioned reflexVagal efferent & with Gastrin secretionthrough gastrin-releasing peptide (GRP)Experiment: Sham feeding by PavlovCharacteristics: Large quantity (30%)High acidity & digestive power,Experiment of Sham feeding by Pavlov,Gastric phaseMechanisms: Distension of gastric fundus & body initiatingvagovagal & local plexus reflexesDistension of pylorus initiating a release of gastrin through intrinsic plexusChemical stimulation of G cells initiaying arelease of gastrinExperiment: Pavlov pouchCharacteristics: Large quantity (60%)High acidity & digestive power,Heidenhain (R) & Pavlov (L) pouch,Intestinal phaseMechanisms: Mainly humoral regulationChemical & Mechanical stimulationinitiating releases of Gastrin, Entero-oxyntin & Other humoral factorsExperiment: Pavlov pouchCharacteristics: Small quantity (10%)Lower acidity & digestive power,Cephalic, gastric, & intestinal phase of gastric juice secretion,Summary of cephalic, gastric, & intestinal phase of gastric juice secretion,Inhibitory regulationHydrochloric acid (HCl)A typical example of negative feedbackConditions & Mechanisms:pH 1.21.5 in the gastric antrumInhibition of G cells, Release of SSTpH 2.5 in the duodenumRelease of secretin, bulbogastroneFat: Initiating release of enterogastroneHypertonic solution: Entero-gastric reflex, Gastric motility & emptying * Main types of gastric motilityTonic contractionMaintaining the shape & place of stomach, as well as the intragastric pressure Receptive relaxationDefinition & its innervationPeptide or NO ergic vagal fibersGastric peristalsisInitiate from middle stomach, 3 times/minMix & grind food into chyme & help empty,* Gastric emptying & its controlDefinition & some rulesCarbohydrate proteins lipids, Mix 46 hDiscontinuous emptying Adapting for digestion & absorptionControl of emptying Promotion in stomach: vagovagal & plexus reflex, gastrin release Inhibition in duodenum: entero-gastric reflex & enterogastrone,* Gastric motility in the digestive interphaseMigrating motor complex (MMC)Phase I: resting phase, 90120 minPhase II: irregular spike & sporadic peristalsis, 3045 min Phase III: large amount of spikes & regular strong contraction, 510 minPhase IV: transition period, about 5 minSignificance: act as a street cleanerVomiting Definition: a reflex, benefit & harm,Migrating motor complex (MMC), 4. Digestion in the intestine Pancreatic juice & its secretion * Nature, Compositions & functionspH 7.88.4, colorless & odourless, 12 L/dayBicarbonate (HCO3)Neutralize HCl & provide a weak basic medium favoring digestive enzyme actionPancreatic enzymes: amylase, lipase, colipase,trypsinogen & chymtrypsinogen, etc.Turn trypsinogen into trypsin by entero-kinase, turn chymtrypsinogen into chym-trypsin by trypsinTrypsin inhibitor: a polypeptide,