Chapter 5 Digestion and Absorpion Teachering Hours 7 hours Intensive Teaching:Gastric secretion and it's regulation;gastrointestinal motility and it's regulation;digestion in small intestine;the role of pancreatic juice,bile and small intestine juice:digestion in rumen;the absorption ofnutrients Nodi for student:1.The properties and electrical activity of gastrointestinaltract smooth muscle 2.Environmental properties in rumen;microorganism and it's role in rumen;digestion in rumen; 3.The exchange of nutrient between digestive canal and blood. Seaction 1 Introduction Digestion:Digestion is a process essential for the conversion of food into a small and simple form. Absorption Absorption is the process of transporting small molecules from the lumen of the gut into blood. 1 Types of digestion: (1)Mechanical Digestion (2)Chemical Digestion (3)Bacterial Digestion 2 Properties of gastrointestinaltract smooth muscle 2.1 General Functional characteristics ofgastrointestinaltract smooth muscle 1)Lower excitability,slower contraction and relaxation 2)Higher extensibility
Chapter 5 Digestion and Absorpion Teachering Hours ：7 hours Intensive Teaching：Gastric secretion and it’s regulation; gastrointestinal motility and it’s regulation;digestion in small intestine; the role of pancreatic juice,bile and small intestine juice;digestion in rumen;the absorption of nutrients. Nodi for student：1. The properties and electrical activity of gastrointestinaltract smooth muscle 2. Environmental properties in rumen; microorganism and it’s role in rumen;digestion in rumen； 3. The exchange of nutrient between digestive canal and blood. Seaction 1 Introduction Digestion: Digestion is a process essential for the conversion of food into a small and simple form. Absorption :Absorption is the process of transporting small molecules from the lumen of the gut into blood. 1 Types of digestion: (1)Mechanical Digestion (2)Chemical Digestion (3) Bacterial Digestion 2 Properties of gastrointestinaltract smooth muscle 2.1 General Functional characteristics of gastrointestinaltract smooth muscle 1)Lower excitability, slower contraction and relaxation 2) Higher extensibility
3)Tonic contraction 4)Autorhythmicity 5)More sensitive to stretch,chemicals,cold and warm stimulation but not to electric stimulation 2.2 Electrical activity of gastrointestinaltract smooth muscle (1)Resting potential:-55~-60mv.Mainly determined by K+equilibrium potential, Related also with Na+and Ca2+ (2)Slow wave or basic electric rhythm (BER):Basic electrical rhythm is the spontaneous rhythmic,subthreshold depolarization of the cell membrane in the gastrointestinal tract.BER are not action potential,but show undulating changes in the resting membrane potential. (3)Action potential:(i)Action potential can only be generated on the background of slow wave potential. (ii)The ionic basis ofaction potential is determined by Ca2+influx. (iii)The amplitude of smooth muscle contraction depends on number of action potential generated Slow waves are changes in resting membrane potential.Always present but do not always cause contractions. 3 Regulation of gastrointestinal function 3.1 Automic nervous system (1)Sympathetic nerveamd Parasympathetic nerve (2)Intrinsic nervous system:myenteric plexus;submucosal plexus
3) Tonic contraction 4) Autorhythmicity 5) More sensitive to stretch, chemicals, cold and warm stimulation but not to electric stimulation 2.2 Electrical activity of gastrointestinaltract smooth muscle (1)Resting potential：-55～-60mv. Mainly determined by K+ equilibrium potential, Related also with Na+ and Ca2+ (2)Slow wave or basic electric rhythm (BER): Basic electrical rhythm is the spontaneous rhythmic, subthreshold depolarization of the cell membrane in the gastrointestinal tract. BER are not action potential, but show undulating changes in the resting membrane potential. (3)Action potential: (i) Action potential can only be generated on the background of slow wave potential. (ii)The ionic basis of action potential is determined by Ca2+ influx. (iii)The amplitude of smooth muscle contraction depends on number of action potential generated Slow waves are changes in resting membrane potential. Always present but do not always cause contractions. 3 Regulation of gastrointestinal function 3.1 Automic nervous system (1)Sympathetic nerve amd Parasympathetic nerve (2) Intrinsic nervous system: myenteric plexus; submucosal plexus
3.2 Humoral regulation Seaction2 Ingestion 1.Types of ingestion 2.Regulation of ingestion 2.1 center (1)feeding center (2)satiety center 2.2 reflex regulation (1Regulation by nutrients: i)Blood glucose:The concentration ofblood glucose decreased induce starvation i）Amino acid: amino acid appetite ii）Fatty acld: fatty acid appetite (2)Nonmetabolic regulation Seaction3 Digestion in Mouth 1.Salivary secretion (1)Compositionofsaliva Water;mucin;lysozyme;bicarbonate (2)Functions Dmoistening and lubricating the food; 2contains the enzyme amylase,partially digests polysaccharides. ③antibacterial role ④heat elimination
3.2 Humoral regulation Seaction2 Ingestion 1. Types of ingestion 2. Regulation of ingestion 2.1 center (1) feeding center (2) satiety center 2.2 reflex regulation (1)Regulation by nutrients: i) Blood glucose: The concentration of blood glucose decreased induce starvation ii) Amino acid: amino acid appetite iii) Fatty acid: fatty acid appetite (2) Nonmetabolic regulation Seaction3 Digestion in Mouth 1. Salivary secretion (1) Composition of saliva Water;mucin; lysozyme; bicarbonate (2)Functions ①moistening and lubricating the food; ②contains the enzyme amylase ,partially digests polysaccharides. ③antibacterial role ④ heat elimination
(3)Regulation ofsalivary secretion The secretion of saliva is controlled by both sympathetic and parasympathetic neurons.Both of them stimulate salivary secretion,with the parasympathetic producing the greater response. There is no hormonal regulation of salivary secreation, 2.Chewing During chewing,food is broken down into small particles and mixed with saliva 3.Swallowing Seaction4 Digestion in Stomach 1.Gastric secretion 1.1 The location of gastric secretion (1)Cardiac gland:secret mucus (2)Fundus gland:i)parietal cell:secret HCl and intrinsicfactor ii)Chief cell:pepsinogen iii)Mucous neck cell:secret mucus (3)Pyloric gland:secret base mucus 1.2 character,constituent and function of gastric juice (1)HCI:i)activates pepinogen ii)kills bacteria iii)assisted effect of iron and Ca absorption iv)promotes pancreatic secretion and billiary,intestinal secretion (2)Pepsinogen:HCI Pespinogen pepsin
(3)Regulation of salivary secretion The secretion of saliva is controlled by both sympathetic and parasympathetic neurons.Both of them stimulate salivary secretion ,with the parasympathetic producing the greater response. There is no hormonal regulation of salivary secreation, 2. Chewing During chewing ,food is broken down into small particles and mixed with saliva. 3. Swallowing Seaction4 Digestion in Stomach 1. Gastric secretion 1.1 The location of gastric secretion (1)Cardiac gland: secret mucus (2) Fundus gland: i) parietal cell: secret HCl and intrinsicfactor ii) Chief cell: pepsinogen iii) Mucous neck cell: secret mucus (3)Pyloric gland: secret base mucus 1.2 character, constituent and function of gastric juice (1) HCl: i) activates pepinogen ii)kills bacteria iii) assisted effect of iron and Ca absorption iv) promotes pancreatic secretion and billiary, intestinal secretion (2)Pepsinogen: Pespinogen pepsin HCl
Hydrolyze protein (3)Mucus:lubrication,protection Mucus-HCO3 barrier:Mucus-HCO3-barrier is an alkaline gel layer of mucus which is mainly insoluble and coats the stomach mucosa.The importance functions of the mucus-HCO3-barrier are protecting the gastric mucosa against injury by acid or pepsin,and contributing to lubrication offood transport. (4)intrinsicfactor:forming complex with B12,combined with the receptor in ileum to promote B12 absorption 1.3 Regulation ofgastricjuice secretion (1)Cephalic phase:The cephalic phase is initiated when receptors in the head are stimulated by sight,smell,taste,and chewing.There are nervous and humoral mechanisms involved in this phase. Vagus什 release Ach↑ gastric secretion stimulate G cells secretion Characteristics:Approximately 30%of total gastric juice with higher acidity and pepsinogen is secreted in cephalic phase. (2)Gastric phase:Once food enters the stomach,it excites i)long vagovagal reflexes,ii)local enteric reflexes,and iii)the gastrin mechanism,all of which in turn cause secretion of gastric juice during several hours while the food remains in the stomach.. (3)Intestinal phase:
Hydrolyze protein (3)Mucus: lubrication, protection Mucus-HCO3 barrier: Mucus-HCO3- barrier is an alkaline gel layer of mucus which is mainly insoluble and coats the stomach mucosa. The importance functions of the mucus- HCO3- barrier are protecting the gastric mucosa against injury by acid or pepsin, and contributing to lubrication of food transport. (4) intrinsicfactor: forming complex with B12, combined with the receptor in ileum to promote B12 absorption 1.3 Regulation of gastric juice secretion (1)Cephalic phase: The cephalic phase is initiated when receptors in the head are stimulated by sight, smell, taste, and chewing.There are nervous and humoral mechanisms involved in this phase. Vagus (+) release Ach gastric secretion stimulate G cells secretion Characteristics: Approximately 30% of total gastric juice with higher acidity and pepsinogen is secreted in cephalic phase. (2) Gastric phase: Once food enters the stomach, it excites i) long vagovagal reflexes, ii) local enteric reflexes, and iii) the gastrin mechanism, all of which in turn cause secretion of gastric juice during several hours while the food remains in the stomach.. (3) Intestinal phase:
Lower secretory volume;acidity and pepsinogen 2.Gastric motility 2.1 Types ofgastric motility (1)Castric receptive relaxation: Receptive relaxation is a reflex in which the gastric fundus dilates when food passes down the pharynx and the esophagus.When food enters the stomach,a "vagovagal reflex"from the stomach to the brain stem and then back to the stomach reduces the tone in the muscular wall of the body of the stomach so that the wall bulges progressively outward,accommodating greater and greater quantities of food up to a limit in the completely relaxed stomach. (2)Tonic contraction (3)Gastric peristalsis: 2.2 regulation ofgastric motility 2.3 Gastricemptying:to empty gastric contents into the duodenum 1)Characteristics of food:viscosity,size of food particles,isotonia,solidity; carbohydrate>protein>fat 2)the promoting factors in stomach quantity offood,gastrin 3)the inhibitory factors in duodenum entero-gastric reflexes:The enterogastric reflex is initiated by the pressure of food in the small intestine.It inhibits stomach by transmitting through the enteric and extrinsic nervous systems. 3.Microbial digestion in rumen
Lower secretory volume; acidity and pepsinogen. 2. Gastricmotility 2.1 Types of gastric motility (1)Castric receptive relaxation: Receptive relaxation is a reflex in which the gastric fundus dilates when food passes down the pharynx and the esophagus. When food enters the stomach, a “vagovagal reflex” from the stomach to the brain stem and then back to the stomach reduces the tone in the muscular wall of the body of the stomach so that the wall bulges progressively outward, accommodating greater and greater quantities of food up to a limit in the completely relaxed stomach. (2) Tonic contraction (3)Gastric peristalsis: 2.2 regulation of gastric motility 2.3 Gastric emptying: to empty gastric contents into the duodenum 1) Characteristics of food: viscosity, size of food particles, isotonia, solidity; carbohydrate>protein>fat 2) the promoting factors in stomach quantity of food, gastrin 3) the inhibitory factors in duodenum entero-gastric reflexes: The enterogastric reflex is initiated by the pressure of food in the small intestine. It inhibits stomach by transmitting through the enteric and extrinsic nervous systems . 3. Microbial digestion in rumen
3.1 condition for existence ofmicroorganism (1)temperature:38~41 C (2)pH:(3 )water content is relative stability (4) anaerobic interspace 3.2 microorganism in rumen (1)infusorium (2)bacteria(3)anaerobiceumycetes 3.3 Digestion in rumen (1)carbohydrate: Cellulose cellobiose glucose pyruvic acid,lactic acid VFA+CH4+CO2 (2)Proteins Protein amino acid 一NH tropina (3)Lipid (4)Vit:microorganism in rumen could synthesize VitB and VitK (5)Belching Section5 Digestion in Small Intestine 1.Pancreatic secretion (1)Compositionofpancreatic juice Water:90% NaHCO3: pancreatic enzymes:trypsinogen chymotrypsinogen pancreatic amylase Pancreatic lipase,etc (2)Functionofpancreatic juice
3.1 condition for existence of microorganism (1)temperature:38~41 ℃ (2)pH: (3 )water content is relative stability (4) anaerobic interspace 3.2 microorganismin rumen (1) infusorium (2) bacteria (3) anaerobic eumycetes 3.3 Digestion in rumen (1) carbohydrate: Cellulose cellobiose glucose pyruvic acid, lactic acid VFA+CH4+CO2 (2) Proteins Protein amino acid NH3 tropina (3) Lipid (4)Vit: microorganism in rumen could synthesize VitB and VitK (5) Belching Section5 Digestion in Small Intestine 1. Pancreatic secretion (1) Composition of pancreatic juice Water: 90% NaHCO3: pancreatic enzymes: trypsinogen、chymotrypsinogen、pancreatic amylase、 Pancreatic lipase, etc (2)Function of pancreatic juice
i)pancreatic juice is an alkaline solution,neutralize gastric acid and provided alkaline environment for pancreatic enzymes; ii)the most important digestive juice:hydrolyze food to small and simple form. (3)Control ofpancreatic juice secretion i)）Neural regulaton Vagus excitation mainly stimulates enzyme secretion. ii)Humoral regulation Secretin stimulates mainly HCO3 and H2O secretion Acidic chime Cholecystokinin (CCK) Mainly stimulate acinar cell to secrete pancreatic enzymes 2.Bile secretion (1)Compositionofbile Water:bile salt;bile pigment,etc (2)Function ofbile Facilitate the digestion and absorption oflipid. (3)Control ofbile section i)Neural regulaton:Vagus excitation increases the bile secretion and sympathetic nerve excitation decrease the bile secretion. ii)Humoral regulation Bile salt and secretin are the major stimulators. 3.Secretion ofsmall intestine
i)pancreatic juice is an alkaline solution, neutralize gastric acid and provided alkaline environment for pancreatic enzymes; ii) the most important digestive juice: hydrolyze food to small and simple form . (3) Control of pancreatic juice secretion i) Neural regulaton: Vagus excitation mainly stimulates enzyme secretion. ii) Humoral regulation Secretin stimulates mainly HCO3 - and H2O secretion Acidic chime Cholecystokinin (CCK) Mainly stimulate acinar cell to secrete pancreatic enzymes 2. Bile secretion (1) Composition of bile Water; bile salt; bile pigment, etc (2) Function of bile Facilitate the digestion and absorption of lipid. (3)Control of bile section i) Neural regulaton: Vagus excitation increases the bile secretion and sympathetic nerve excitation decrease the bile secretion. ii) Humoral regulation Bile salt and secretin are the major stimulators. 3. Secretion of small intestine
4.Motility ofsmall intestine (1)Types ofsmall intestine movement i)Tonic contraction: ii)segmentation:This is a special way movement for small intestine. The significance of segmentation includes:1 Mixing intestinal contents with digestive juices to facilitate digestion;2Making chymecontacts closely to the wall of intestine to facilitate absorption. iii)Peristalsis (2)Control ofsmall intestine movement i)Neural regulaton:Vagus(+) stimulate small intestine movement Sympathetic nerve(+) inhibit small intestine movement ii)Humoral regulation:CCK Section6 Digestion in Large Intestine 1.Large intestine juice secretion The large intestine juice is an alkaline solution.It almost has not digestive eenzymes but mucus,bicarbonate and result in a weak ability of digestion. Function oflarge intestine juice:protect intestinal mucosa and lubricate defecation 2.Bacterial digestion in large intestine The bacteria in large intestine cloud produce small amounts of VitB and VitK 3.Motility oflarge intestine 4.Defecation Section7 Absorption
4. Motility of small intestine (1) Types of small intestine movement i) Tonic contraction: ii)segmentation: This is a special way movement for small intestine. The significance of segmentation includes: ① Mixing intestinal contents with digestive juices to facilitate digestion;②Making chymecontacts closely to the wall of intestine to facilitate absorption. iii) Peristalsis (2)Control of small intestine movement i) Neural regulaton:Vagus(+) stimulate small intestine movement Sympathetic nerve (+) inhibit small intestine movement ii) Humoralregulation: CCK Section6 Digestion in Large Intestine 1. Large intestine juice secretion The large intestine juice is an alkaline solution.It almost has not digestive eenzymes but mucus, bicarbonate and result in a weak ability of digestion. Function of large intestine juice:protect intestinal mucosa and lubricate defecation 2.Bacterial digestion in large intestine The bacteria in large intestine cloud produce small amounts of VitB and VitK. 3. Motility of large intestine 4.Defecation Section7 Absorption
1.Location ofabsorption (1)Absorption in stomach 1)Simplex stomach:small amounts of water;ethanol;glucose 2)Stomachus compositus:VFA;Water;NH3;CO2 (2)Absorption in small intestine:Most nutrients are absorbed in small intestine. The reasons of small intestine as main absorptive region: DThe large absorptive surface area formed by valvulae connivent,villi and microvilli; 2Chyme stays in small intestine for longer time; 3There are abundant capillaries and lymphatic capillaries in intestinal mucosa 4Food has already been digested into small and absorbable molecules. (3)Absorption in large intestine:Only water and salt are absorbed in large intestine of carnivorous animal.To herbivore,a great deal of nutrients can be absorbed in large intestine. 2.Mechanisms ofabsorption (1)Passivetransport;(2)Active transport;(3)endocytosis 3.Absorption ofmain substances (1)Carbohydrate 1)glucose:secondary activetransport; 2)VFA:simple diffusion (2)Protein:secondary active transport.absorbed after digested to amino acids. (3)Fat:diffusion facilitated by bile salt
1. Location of absorption (1)Absorption in stomach 1) Simplex stomach: small amounts of water; ethanol; glucose 2) Stomachus compositus: VFA; Water; NH3; CO2 (2)Absorption in small intestine: Most nutrients are absorbed in small intestine. The reasons of small intestine as main absorptive region: ①The large absorptive surface area formed by valvulae connivent,villi and microvilli; ②Chyme stays in small intestine for longer time; ③There are abundant capillaries and lymphatic capillaries in intestinalmucosa ④Food has already been digested into small and absorbable molecules. (3)Absorption in large intestine: Only water and salt are absorbed in large intestine of carnivorous animal.To herbivore, a great deal of nutrients can be absorbed in large intestine. 2.Mechanisms of absorption (1) Passive transport; (2) Active transport; (3) endocytosis 3.Absorption of main substances (1) Carbohydrate 1) glucose: secondary active transport; 2) VFA: simple diffusion (2)Protein: secondary active transport.absorbed after digested to amino acids. (3)Fat: diffusion facilitated by bile salt