1. Chapter 6 DIGESTION & ABSORPTION § 1. Introduction  Concept of digestion & absorption  Concept of digestion & absorption * Mechanical & chemical digestion * Mechanical & chemical digestion  Characteristics of digestive smooth muscles  Characteristics of digestive smooth muscles * General characteristics * General characteristics * Electrophysiological characteristics * Electrophysiological characteristics Resting potential (RP) Resting potential (RP) Slow wave or basic electrical rhythm (BER) Slow wave or basic electrical rhythm (BER) Action potential (AP) Action potential (AP)

2. Electrical activities & contraction of digestive smooth muscles

3.  Secretion of digestive glands * Main functions of digestive fluids * Main functions of digestive fluids  Gastrointestinal innervation * Intrinsic (or enteric) nervous system * Intrinsic (or enteric) nervous system Submucosal & myenteric plexus Submucosal & myenteric plexus * Extrinsic nervous system * Extrinsic nervous system Parasympathetic & sympathetic nerves Parasympathetic & sympathetic nerves  Gastrointestinal hormones * General functions * General functions * Brain-gut peptides * Brain-gut peptides

4. Intrinsic (or enteric) (or enteric)nervoussystem

5. Extrinsic nervous system

6. § 2. Digestion in the mouth & esophagus  Saliva & its function  Saliva & its function * Nature & Composition of saliva * Nature & Composition of saliva pH 6.6~7.1, 99% water pH 6.6~7.1, 99% water Salivary amylase, lysozyme, salt, etc. Salivary amylase, lysozyme, salt, etc. * Functions of saliva * Functions of saliva Moisten the cavity & solve food; keep the Moisten the cavity & solve food; keep the mouth clean; anti-bacteria; digest starch mouth clean; anti-bacteria; digest starch * Regulation of salivary secretion * Regulation of salivary secretion Pure neuroregulation Pure neuroregulation Conditioned & unconditioned reflex Conditioned & unconditioned reflex

7.  Mastication or chewing & its effects * Definition * Definition * Effects * Effects Break up large food particles; mixes the Break up large food particles; mixes the food with saliva; aid swallowing food with saliva; aid swallowing  Deglutition or swallowing * Definition * Definition * Process * Process 1st, 2nd & 3rd phase 1st, 2nd & 3rd phase Peristalsis & lower esophageal sphincter Peristalsis & lower esophageal sphincter

8. Peristalsis of the esophagus

9. § 3. Digestion in the stomach  Gastric juice & its secretion  Gastric juice & its secretion * Nature, Compositions & functions * Nature, Compositions & functions pH 0.9~1.5, colorless, 1.5~2.5 L/day pH 0.9~1.5, colorless, 1.5~2.5 L/day Hydrochloric acid (HCl) Hydrochloric acid (HCl) Secreted by parietal cells Secreted by parietal cells Basic secretion: 0~5 mmol/h Basic secretion: 0~5 mmol/h Max secretion: 20~25 mmol/h Max secretion: 20~25 mmol/h Mechanism of HCl secretion Mechanism of HCl secretion Functions: see next page Functions: see next page

10. Relationship between max volume of HCl secretion & the number of parietal cells

11. Functions of HCl: Functions of HCl: Turn pepsinogen into pepsin & provide a Turn pepsinogen into pepsin & provide a medium of low pH favoring pepsin action; medium of low pH favoring pepsin action; Kill many swallowed virulent organisms; Kill many swallowed virulent organisms; Promote the secretion of pacreas & bile; Promote the secretion of pacreas & bile; Promote the absorption of calcium & ferrum Promote the absorption of calcium & ferrumPepsinogen Secreted by chief cells & activate by HCl Secreted by chief cells & activate by HCl Function: digest proteins into proteoses, peptones, Function: digest proteins into proteoses, peptones, polypeptides, with little free amino acids polypeptides, with little free amino acids

12. Mucus Mucus Secreted by neck & surface mucous cells, Secreted by neck & surface mucous cells, cardiac & pyloric glands cardiac & pyloric glands Function: form mucus-bicarbonate barrier Function: form mucus-bicarbonate barrier Intrinsic factor Intrinsic factor Secreted by parietal cells Secreted by parietal cells Function: Promote the absorption of Vit B 12 Function: Promote the absorption of Vit B 12 * Regulation of gastric secretion Endogenous releasing substances Endogenous releasing substances Acetylcholine (ACh), gastrin & histamine Acetylcholine (ACh), gastrin & histamine Somatostatin (SST) (release-inhibiting) Somatostatin (SST) (release-inhibiting)

13. Mucus-bicarbonate barrier

14. Action of acetylcholine, gastrin & histamine on the perietal cells

15. Gastric secretion in the digestive phase Cephalic phase Cephalic phase Mechanisms: Mechanisms: Conditioned & Unconditioned reflex Conditioned & Unconditioned reflex Vagal efferent & with Gastrin secretion Vagal efferent & with Gastrin secretion through gastrin-releasing peptide (GRP) through gastrin-releasing peptide (GRP) Experiment: Sham feeding by Pavlov Experiment: Sham feeding by Pavlov Characteristics: Characteristics: Large quantity (30%) Large quantity (30%) High acidity & digestive power High acidity & digestive power

16. Experiment of Sham feeding by Pavlov

17. Gastric phase Mechanisms: Mechanisms: Distension of gastric fundus & body initiating Distension of gastric fundus & body initiating vagovagal & local plexus reflexes vagovagal & local plexus reflexes Distension of pylorus initiating a release of Distension of pylorus initiating a release of gastrin through intrinsic plexus gastrin through intrinsic plexus Chemical stimulation of G cells initiaying a Chemical stimulation of G cells initiaying a release of gastrin release of gastrin Experiment: Pavlov pouch Experiment: Pavlov pouch Characteristics: Characteristics: Large quantity (60%) Large quantity (60%) High acidity & digestive power High acidity & digestive power

18. Heidenhain (R) & Pavlov (L) pouch

19. Intestinal phase Mechanisms: Mechanisms: Mainly humoral regulation Mainly humoral regulation Chemical & Mechanical stimulation Chemical & Mechanical stimulation initiating releases of Gastrin, Entero- initiating releases of Gastrin, Entero- oxyntin & Other humoral factors oxyntin & Other humoral factors Experiment: Pavlov pouch Experiment: Pavlov pouch Characteristics: Characteristics: Small quantity (10%) Small quantity (10%) Lower acidity & digestive power Lower acidity & digestive power

20. Cephalic, gastric, & intestinal phase of gastric juice secretion

21. Summary of cephalic, gastric, & intestinal phase of gastric juice secretion

22. Inhibitory regulation Hydrochloric acid (HCl) Hydrochloric acid (HCl) A typical example of negative feedback A typical example of negative feedback Conditions & Mechanisms: Conditions & Mechanisms: pH ≤ 1.2~1.5 in the gastric antrum pH ≤ 1.2~1.5 in the gastric antrum Inhibition of G cells, Release of SST Inhibition of G cells, Release of SST pH ≤ 2.5 in the duodenum pH ≤ 2.5 in the duodenum Release of secretin, bulbogastrone Release of secretin, bulbogastrone Fat: Initiating release of enterogastrone Fat: Initiating release of enterogastrone Hypertonic solution: Entero-gastric reflex Hypertonic solution: Entero-gastric reflex

23.  Gastric motility & emptying * Main types of gastric motility * Main types of gastric motility Tonic contraction Tonic contraction Maintaining the shape & place of stomach, Maintaining the shape & place of stomach, as well as the intragastric pressure as well as the intragastric pressure Receptive relaxation Receptive relaxation Definition & its innervation Definition & its innervation Peptide or NO –ergic vagal fibers Peptide or NO –ergic vagal fibers Gastric peristalsis Gastric peristalsis Initiate from middle stomach, 3 times/min Initiate from middle stomach, 3 times/min Mix & grind food into chyme & help empty Mix & grind food into chyme & help empty

24. * Gastric emptying & its control * Gastric emptying & its control Definition & some rules Definition & some rules Carbohydrate > proteins > lipids, Mix 4~6 h Carbohydrate > proteins > lipids, Mix 4~6 h Discontinuous emptying Discontinuous emptying Adapting for digestion & absorption Adapting for digestion & absorption Control of emptying Control of emptying Promotion in stomach: vagovagal & plexus Promotion in stomach: vagovagal & plexus reflex, gastrin release reflex, gastrin release Inhibition in duodenum: entero-gastric Inhibition in duodenum: entero-gastric reflex & enterogastrone reflex & enterogastrone

25. * Gastric motility in the digestive interphase * Gastric motility in the digestive interphase Migrating motor complex (MMC) Migrating motor complex (MMC) Phase I: resting phase, 90~120 min Phase I: resting phase, 90~120 min Phase II: irregular spike & sporadic Phase II: irregular spike & sporadic peristalsis, 30~45 min peristalsis, 30~45 min Phase III: large amount of spikes & regular Phase III: large amount of spikes & regular strong contraction, 5~10 min strong contraction, 5~10 min Phase IV: transition period, about 5 min Phase IV: transition period, about 5 min Significance: act as a street cleaner Significance: act as a street cleaner Vomiting Vomiting Definition: a reflex, benefit & harm Definition: a reflex, benefit & harm

26. Migrating motor complex (MMC)

27. § 4. Digestion in the intestine  Pancreatic juice & its secretion  Pancreatic juice & its secretion * Nature, Compositions & functions * Nature, Compositions & functions pH 7.8~8.4, colorless & odourless, 1~2 L/day pH 7.8~8.4, colorless & odourless, 1~2 L/day Bicarbonate (HCO 3  ) Bicarbonate (HCO 3  ) Neutralize HCl & provide a weak basic Neutralize HCl & provide a weak basic medium favoring digestive enzyme action medium favoring digestive enzyme action Pancreatic enzymes: amylase, lipase, colipase, Pancreatic enzymes: amylase, lipase, colipase, trypsinogen & chymtrypsinogen, etc. trypsinogen & chymtrypsinogen, etc. Turn trypsinogen into trypsin by entero- Turn trypsinogen into trypsin by entero- kinase, turn chymtrypsinogen into chym- kinase, turn chymtrypsinogen into chym- trypsin by trypsin trypsin by trypsin Trypsin inhibitor: a polypeptide Trypsin inhibitor: a polypeptide

28. * Regulation of pancreatic secretion Nervous regulation Nervous regulation Vagus nerve: ACh, gastrin Vagus nerve: ACh, gastrin Characteristics: H 2 O & HCO 3  , enzymes  Characteristics: H 2 O & HCO 3  , enzymes  Sympathetic nerve: ACh, NA Sympathetic nerve: ACh, NA Characteristics: weak effect Characteristics: weak effect Humoral reulation Humoral reulation Secretin: H 2 O & HCO 3  , enzymes  Secretin: H 2 O & HCO 3  , enzymes  Cholecystokinin (CCK): Cholecystokinin (CCK): Characteristics: H 2 O & HCO 3  , enzymes  Characteristics: H 2 O & HCO 3  , enzymes  Feedback: CCK-releasing peptide Feedback: CCK-releasing peptide

29.  Bile secretion & gallbladder emptying  Bile secretion & gallbladder emptying * Nature, Compositions & functions * Nature, Compositions & functions Hepatic bile: pH 7.4, golden yellow Hepatic bile: pH 7.4, golden yellow Bladder bile: pH 6.8, color become darker Bladder bile: pH 6.8, color become darker Compositions: H 2 O, ions, bile acid, bile Compositions: H 2 O, ions, bile acid, bile pigment, fatty acid, cholesterol, lecithin, pigment, fatty acid, cholesterol, lecithin, mucoprotein, etc., but no enzyme mucoprotein, etc., but no enzyme Functions of bile (mainly by bile salt): Functions of bile (mainly by bile salt): Fat emulsification; lipid absorption; Fat emulsification; lipid absorption; Promote the absorption of fat-soluble Vits Promote the absorption of fat-soluble Vits

30. * Control of bile secretion & gallbladder emptying Nervous regulation Nervous regulation Vagus nerve: ACh, gastrin Vagus nerve: ACh, gastrin Hepatic bile secretion  (small amounts) Hepatic bile secretion  (small amounts) Gallbladder contraction  (slightly) Gallbladder contraction  (slightly) Humoral reulation Humoral reulation Gastrin: direct to hepatic cells & gallbladder; Gastrin: direct to hepatic cells & gallbladder; indirect to stomach  HCl  secretin  indirect to stomach  HCl  secretin  Secretin: act to bile duct & not to hepatic cells, Secretin: act to bile duct & not to hepatic cells, so: H 2 O & HCO 3  , bile salt (  ) so: H 2 O & HCO 3  , bile salt (  ) Cholecystokinin (CCK): gallbladder Cholecystokinin (CCK): gallbladder contraction & Oddi’s sphincter dialation contraction & Oddi’s sphincter dialation Bile salt: enterohepatic circulation of bile salt Bile salt: enterohepatic circulation of bile salt

31. Enterohepatic circulation of bile salt

32.  Secretion of the small intestine * Intestinal glands * Intestinal glands Brunner’s gland (basic mucus) Brunner’s gland (basic mucus) Lieberkuhn Crypt (main part) Lieberkuhn Crypt (main part) * Nature, Compositions & functions * Nature, Compositions & functions pH 7.6, iso-osmotic solution, 1~3 L/day pH 7.6, iso-osmotic solution, 1~3 L/day Enterokinase, the only one secreted Enterokinase, the only one secreted Oligopeptidase, oligosaccharidase those Oligopeptidase, oligosaccharidase those contained in the epithelial cells contained in the epithelial cells * Regulation of secretion of small intestine * Regulation of secretion of small intestine Mainly through plexus reflex initiated by Mainly through plexus reflex initiated by inflation of the intestine inflation of the intestine

33.  Movements of the small intestine  Movements of the small intestine * Movement in the digestive interphase * Movement in the digestive interphase MMC similar to that in the stomach MMC similar to that in the stomach * Main movement forms in digestive phase * Main movement forms in digestive phase Tonic contraction: the same as in stomach Tonic contraction: the same as in stomach Segmentation: peculiar to the small intestine Segmentation: peculiar to the small intestine Peristalsis: 0.5~2.0 cm/s Peristalsis: 0.5~2.0 cm/s Peristaltic rush: 2~25 cm/s Peristaltic rush: 2~25 cm/s * Regulation of small intestinal movement * Regulation of small intestinal movement

34. Segmentation of the small intestine

35. * Regulation of small intestinal movement * Regulation of small intestinal movement Intrinsic plexus: receive mechanical & Intrinsic plexus: receive mechanical & chemical stimuli and then cause peristalsis chemical stimuli and then cause peristalsis Extrinsic plexus: parasympathetic nerve  Extrinsic plexus: parasympathetic nerve  intestinal activities  ; sympathetic never  intestinal activities  ; sympathetic never  intestinal activities  intestinal activities  Humoral factors: gastrin, CCK, Enk, 5-HT, etc. Humoral factors: gastrin, CCK, Enk, 5-HT, etc.  Functions of the ileocecal sphincter * Permit some of chyme to squirt into the cecum * Permit some of chyme to squirt into the cecum each time when a peristalsis wave reaches it each time when a peristalsis wave reaches it * Prevent reflux of colonic contents into the ileum * Prevent reflux of colonic contents into the ileum

36. § 5. Digestion in the colon  Main function of the colon  Main function of the colon Absorb water Absorb water Absorb Vit B & K synthesized by bacteria Absorb Vit B & K synthesized by bacteria Formation & temporarily storage feces Formation & temporarily storage feces  Secretion of the colon  Secretion of the colon pH 8.3~8.4, Mucus & HCO 3  pH 8.3~8.4, Mucus & HCO 3  Protect mucosa against injuries & lubricate feces Protect mucosa against injuries & lubricate feces  Movements of the colon  Movements of the colon Haustral to and fro movement, Segmentation or Haustral to and fro movement, Segmentation or Polyhaustral pushing movement, Peristalsis, Polyhaustral pushing movement, Peristalsis, Mass peristalsis Mass peristalsis

37.  Feces & Defecation * Feces: contain inorganic material, undigested * Feces: contain inorganic material, undigested plant fibers, bacteria, water, etc. plant fibers, bacteria, water, etc. * Defecation: a reflex initiated by distension of * Defecation: a reflex initiated by distension of the rectum with feces the rectum with feces Reflex process, Primary & higher centers Reflex process, Primary & higher centers  Action of colonic bacteria * Benefit: synthesis Vit. B co & K * Benefit: synthesis Vit. B co & K * Harm: produce some poisonous substances * Harm: produce some poisonous substances  Action of dietary fibers on the intestinal function Reduce absorption of water; Enhance colonic Reduce absorption of water; Enhance colonic movement; Increase the volume of feces; Low movement; Increase the volume of feces; Low the caloric ratio of the food the caloric ratio of the food

38. § 6. Absorption in the small intestine  Sites of absorption  Sites of absorption Oral cavity & Stomach: little Oral cavity & Stomach: little Duodenum & Upper jejunum: most nutrients Duodenum & Upper jejunum: most nutrients Ileum: bile salts & Vit. B 12 Ileum: bile salts & Vit. B 12 Colon: water & electrolytes Colon: water & electrolytes  Proofs as the main absorptive region  Proofs as the main absorptive region Huge absorptive surface (200 m 2 ) Huge absorptive surface (200 m 2 ) Plenty of capillaries & lymph capillaries Plenty of capillaries & lymph capillaries Large quantity of digestive fluid (6~8 L/day) Large quantity of digestive fluid (6~8 L/day) Food has almost completely been digested Food has almost completely been digested

39. Sites of absorption

40. Enlargement of the surface area of the intestine

41.  Absorption of main nutrients  Absorption of main nutrients * Water * Water 8 L/day, passive & iso-osmotic absorbed 8 L/day, passive & iso-osmotic absorbed Different absorbability in different parts Different absorbability in different parts * Inorganic slats * Inorganic slats Sodium: 95%~99%, jejunum>ileum>colon Sodium: 95%~99%, jejunum>ileum>colon active transport active transport Ferrum: 1/10, mainly in duodenum & jejunum, Ferrum: 1/10, mainly in duodenum & jejunum, transferrin dependent, active transport transferrin dependent, active transport Calcium: promote by Vit. D, active transport Calcium: promote by Vit. D, active transport Anions: mainly Cl  & HCO 3 , passive transport Anions: mainly Cl  & HCO 3 , passive transport

42. * Carbohydrate Absorptive form: monosarccharide Absorptive form: monosarccharide Mechanism: secondary active transport Mechanism: secondary active transport * Protein * Protein Absorptive form: amino acid Absorptive form: amino acid Mechanism: secondary active transport Mechanism: secondary active transport * Fats * Fats Absorptive form: glycerol, monoglyceride, Absorptive form: glycerol, monoglyceride, fatty acid, cholesterol fatty acid, cholesterol Mechanism: passive diffusion Mechanism: passive diffusion Pathway: blood & lymph Pathway: blood & lymph

43. Digestion & absorption of fats in the intestine