Digestive System - Physiology


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Digestive System - Physiology

  1. 1. Digestive SystemDigestive System PhysiologyPhysiology
  2. 2. The digestive system is formed of 1. Alimentary canal 2. Digestive glands
  3. 3.  Mucosa  submucosa  circular m layer  longtudinal m layer  serosa Structure of alimentary canalStructure of alimentary canal
  4. 4. Gastrointestinal wall
  5. 5. Types of movement of GIT Peristalsis Stretch circular contraction behind & relaxation in front→ Stretch serotonin sensory nerves myenteric plexus→ → -Retrograde cholinergic neurons (subs P & a.ch) → contraction -Antegrade cholinergic neurons (VIP, NO & ATP) → relaxation Mixing movement •Peristaltic wave in blocked sphincter •Constrictive movement
  6. 6. Innervation of the GIT 1. Intrinsic innervation: Enteric Nervous System. 2. Extrinsic innervation: Parasympathetic and sympathetic innervations.
  7. 7.  Myenteric plexus (Auerbach's plexus).  Submucous plexus (Meissner's plexus). Enteric nervous systemEnteric nervous system
  8. 8. Submucous plexus Myenteric plexus between the circular layer and the mucosa. between the outer longitudinal and inner circular muscle layers Exocrine and endocrine functions of the GIT Motor function of the GIT Mainly excitatory, some inhibitory Enteric nervous systemEnteric nervous system
  9. 9.  The plexuses are interconnected.  They contain motor neurons; secretory neuron sensory neurons that respond to stretc tonicity, glucose, or amino acids; an interneurons.  Substances secreted by the ENS: acetylcholin serotonin, GABA, and vasoactive intestin peptide.
  10. 10. 2. Extrinsic Innervation:  Parasympathetic: Cranial (Abdominal viscera) Preganglionic : vagus Relay: terminal ganglia on the wall of the viscera Postganglionic : in the myenteric and submucosal plexus Sacral:2nd , 3rd , 4th (pelvic viscera) Preganglionic : pelvic nerves. Relay: terminal ganglia on the wall of the viscera Postganglionic ends on : in the myenteric and submucosal plexus Increase in the activity of ENS
  11. 11. 2. Extrinsic Innervation:  Sympathetic: (Abdominal viscera) Preganglionic : lower 6th thoracic Run as greater splanchnic nerve. Relay: coeliac and superior mesenteric ganglia Postganglionic: pass with blood vessels to all parts of the gut (Pelvic viscera) Preganglionic : T12 , L1, 2, 3. Run as lesser splanchnic nerve. Relay: inferior mesenteric ganglia Postganglionic: pass with blood vessels to all parts of the gut Inhibition of GIT function: directly Inhibition of enteric nervous system
  12. 12. Regulation of the GIT 1. Nervous control of GIT:  Reflexes that occur inside the ENS: self regulation (local enteric reflexes)  Reflexes from the gut to symp ganglia then back to GIT (enterogastric reflex)  Reflexes from the gut to parasymp n. in BS or sc back to GIT (conditioned and unconditioned reflexes).
  13. 13. 2. Hormonal control: Polypeptides secreted by APUD cells (amine precursors uptake and decarboxylation). Hormones fall into one of 2 families: Gastrin family: the primary members of which are gastrin and cholecystokinin (CCK). Secretin family: the primary members of which are secretin, glucagon, VIP, and gastrin inhibitory polypeptide (GIP). Others: motilin and somatostatin
  14. 14. Mastication (Chewing)Mastication (Chewing) •Mechanical breakdown of large food particles into smaller ones in the mouth. •Increase exposed surface area to enzymes and help swallowing.
  15. 15.  Center: pons  Mastication muscles: motor branch of trigeminal.  May be voluntary or involuntary (autonomic reflex) Mastication (Chewing)Mastication (Chewing)
  16. 16. Swallowing (Deglutition)Swallowing (Deglutition) •Propelling of food from mouth to stomach through pharynx and oseophagus
  17. 17. Salivary Secretion Saliva is secreted primarily by three pairs of glands: 1. the parotid glands: 20% 2. the submandibular: 75%. 3. the sublingual glands: 5%. 4. many small buccal glands in mouth cavity.
  18. 18. 99.5% water 0.5% Solids: a. organic: K+ , Na+ , HCO- 3, Cl- , Na2HPO4. b.Organic: Ptyalin enzyme Mucin Lysozymes Immunoglobulin A Composition of saliva: 1500ml/dayComposition of saliva: 1500ml/day
  19. 19. Salivary Secretion Saliva •800- 1500 ml/day with proteins & electrolytes •pH→ 6- 7.0 ( 8.0 during active secretion) •Hypotonic ( Na+ & Cl- less , K+ & HCO3 more than plasma •Contains IgA, lysozyme, lactoferrin, mucin prolin rich proteins
  20. 20.  The parotid glands acini are serous.  The sublingual glands acini are mucous.  The submandibular glands acini are mixed.  The buccal glands secrete only mucous. Types of Salivary glands:Types of Salivary glands:
  21. 21. Stages of Salivary Secretion: I-Primary secretion in the acini: contains ptyalin and/or mucin in a solution of ions which shows no great difference from extracellular fluid. II- Modification of Primary secretion in the ducts: the following occur under effect of aldosterone. Sodium ions (Na+) are actively reabsorbed. Potassium ions (K+) are actively secreted. Sodium reabsorption is higher than potassium secretion in the salivary ducts Chloride ions (Cl-) to be passively reabsorbed. Therefore, the sodium ion and chloride ion concentrations of the saliva are markedly reduced whereas the potassium ion concentration becomes increased during passage through the ducts.
  22. 22.  Bicarbonate ions (HCO3- ) are actively secreted into the lumen of the duct.  The ducts are relatively impermeable to water. Therefore, the saliva that reaches the mouth is hypotonic and alkaline (pH= 8.0).
  23. 23. Salivary secretion
  24. 24. Functions of Saliva: Protection of oral mucosa:  Cooling hot foods.  Neutralizing acid.  Lysozyme attacks the walls of bacteria.  Antibodies (immune globulin IgA) destroy oral pathogenic bacteria.
  25. 25. Teeth protection:  The buffers in saliva: bicarbonate, phosphate buffers, mucin, help to keep the oral pH at about 7.0. At this pH, the saliva is saturated with calcium and so the teeth do not lose calcium. Loss of Ca2+ from the teeth enamel leads to dental caries. Digestion:  Saliva contains the digestive enzyme ptyalin (salivary α-amylase) that digests starch into disaccharides.
  26. 26.  Lubrication and Wetting:  Swallowing: Saliva contains mucin (glycoproteins) that lubricates the food  Speech: Keeping mouth moist facilitates movements of the lips and tongue during speech.  Taste: Saliva acts as (a solvent for the molecules that stimulate taste receptors.
  27. 27. Innervation of salivary glands Parasympathetic efferent Increase secretion & VD ( Ach & VIP) Sublingual & submandibular glands Superior salivary nucleus →facial ( corda tympani) Parotid gland Inferior salivary nucleus → glossopharyngeal nerve
  28. 28. Sympathetic efferent Small amount of saliva rich in organic constituents- VC Superior & inferior salivary nuclei → T 1 & 2 → superior cervical ganglion → all salivary glands Both sympathetic & parasympathetic are complementary in salivary secretion
  29. 29. Submandibular and sublingual Parotid gland Superior salivary nucleus in medulla inferior salivary nucleus in medulla Preganglionic fibers arise Chorda tympani (facial) Glossopharyngeal n. Run as Submandibular ganglon Otic ganglion relay Supply Submandibular and sublingual Supply parotid gland Postganglionic fibers Innervation of salivary glands:Innervation of salivary glands: parasympathetic fibersparasympathetic fibers
  30. 30. Sympathetic efferent fibres:  Preganglionic fibres arise from the lateral horn cells of the upper 2 thoracic segments of the spinal cord.   They relay in the superior cervical ganglion.  Postganglionic fibres arising from this ganglion reach all the salivary glands along the wall of their blood vessels.  Stimulation of the sympathetic nerve supply to the salivary glands causes vasoconstriction, and secretion of a small amount of saliva rich in mucin.
  31. 31. Control of Salivary secretion:  Stimulation of salivary secretion is entirely under neural control in response to conditioned or unconditioned stimuli.
  32. 32. Unconditioned reflexes: Mechanical and chemical stimulation of taste buds in mouth causes reflex secretion of large amount of watery saliva:
  33. 33. Conditioned reflexes:  Salivary secretion is easily conditioned as shown in Pavlov's original experiment. Sight, smell, hearing, preparation of food, or even thinking of food, result in reflex increase in the secretion of saliva. The impulses arrive to the salivary nuclei from the cerebral cortex, in response to any conditioned stimulus.
  34. 34. Swallowing (Deglutition)Swallowing (Deglutition) •Buccal (oral phase) •Pharyngeal phase •Oesophageal phase. Involuntary Voluntary
  35. 35.  Tongue is elevated upwards and backwardsTongue is elevated upwards and backwards with bolus of food on its dorsum.with bolus of food on its dorsum.  Bolus of food is rolled backwards to back ofBolus of food is rolled backwards to back of tongue.tongue.  Bolus is forced to pharynx by contraction ofBolus is forced to pharynx by contraction of mylohyoid muscle.mylohyoid muscle. Buccal phaseBuccal phase
  36. 36.  Receptor:Receptor: swallowing receptor area on theswallowing receptor area on the tonsillar pillars at the oropharyngealtonsillar pillars at the oropharyngeal junction.junction.  Afferent:Afferent: glossopharyngeal nerve.glossopharyngeal nerve.  Centre:Centre: swallowing centre in medulla andswallowing centre in medulla and lower pons.lower pons.  Efferent:Efferent: 55thth , 9, 9thth , 10, 10thth , 12, 12thth nerves.nerves. Pharyngeal phasePharyngeal phase
  37. 37.  Actions:Actions: 1.Rapid peristaltic1.Rapid peristaltic wave:wave: cont. of superior,cont. of superior, middle & inferiormiddle & inferior pharyngeal muscles.pharyngeal muscles. Pharyngeal phasePharyngeal phase
  38. 38.  Actions:Actions: 2. Protective reflexes:2. Protective reflexes:  Nose: elevation of soft palateNose: elevation of soft palate  Mouth: elevation of tongue, cont. of myelohyoid muscle.Mouth: elevation of tongue, cont. of myelohyoid muscle.  Larynx: elevation of larynx to be covered by epiglottis,Larynx: elevation of larynx to be covered by epiglottis, inhibition of respiration.inhibition of respiration. Pharyngeal phasePharyngeal phase
  39. 39. Actions:Actions: 3. Relaxation of pharyngeoesophageal sphincter3. Relaxation of pharyngeoesophageal sphincter Opening way for bolus of food to oesophagusOpening way for bolus of food to oesophagus Pharyngeal phasePharyngeal phase
  40. 40. Swallowing ( deglutition) Oral voluntary stage Food is rolled posteriorly by pressure of tongue upward Pharyngeal stage ( involuntary) Soft palate close nares , vocal cords approximate Epiglottis close larynx, upper esophageal sphincter relaxes, pharynx contract( peristalsis) -respiration stops Esophageal stage ( involuntary) Primary peristalsis→ pharynx to stomach Secondary peristalsis from distention of esophagus by food ( enteric nervous system & vago-vagal reflex)
  41. 41. Peristaltic waves:Peristaltic waves: 1. 1ry peristaltic wave:1. 1ry peristaltic wave: Continuation of peristaltic wave in pharynx.Continuation of peristaltic wave in pharynx. Start in upper part of oesophagus and travels wholeStart in upper part of oesophagus and travels whole length in 9 sec.length in 9 sec. Oseophageal phaseOseophageal phase If failedIf failed 2ry peristaltic wave2ry peristaltic wave
  42. 42. Peristaltic waves:Peristaltic waves: 2. 2ry peristaltic wave:2. 2ry peristaltic wave: As a result of distension of oesophagus by retainedAs a result of distension of oesophagus by retained food (bolus).food (bolus). A 2ry wave at site of bolus empty all contentsA 2ry wave at site of bolus empty all contents into the stomachinto the stomach.. Oseophageal phaseOseophageal phase
  43. 43.  Upper half of oesophagus: vagovagal reflex.Upper half of oesophagus: vagovagal reflex. Bilateral vagotomy: ???Bilateral vagotomy: ???  Lower half of oesophagus: local reflex.Lower half of oesophagus: local reflex. Control of oseophageal phaseControl of oseophageal phase
  44. 44. Oesophageal musclesOesophageal muscles
  45. 45. Lower Esophageal Sphincter LES • Remains tonically contracted • Receptive relaxation (relaxes LES ahead of peristaltic waves) → easy propulsion • Between meals LES prevent reflux of gastric content into esophagus • Tone of LES Ach→ contraction of LES NO & VIP → relax LES • ↓ tone of LES → gastro esophageal reflux
  46. 46.  It is a physiological sphincter at the lowerIt is a physiological sphincter at the lower end of oesophagus.end of oesophagus.  Tonically contracted to prevent regurgitationTonically contracted to prevent regurgitation of acidic gastric contents to oesophagus.of acidic gastric contents to oesophagus.  During swallowing, it relaxesDuring swallowing, it relaxes Lower Oesophageal sphincter (LES)Lower Oesophageal sphincter (LES)
  47. 47. StomachStomach
  48. 48. Stomach Functional anatomy
  49. 49. - Parietal cells secret HCl & intrinsic factor - Cheif cells secret pepsinogen - Entero-Chromafin-Like cells secret histamin -mucous cells
  50. 50.  FundusFundus  BodyBody  AntrumAntrum  PylorusPylorus Stomach is divided anatomicallyStomach is divided anatomically
  51. 51. Cardia Lesser curvature Duodenum Pylorus Esophagus Fundus Body Greater curvature Antrum
  52. 52. Function of the StomachFunction of the Stomach 1.Motor function of stomach 2.Secretory function of stomach
  53. 53. Secretory function of stomachSecretory function of stomach Gastric gland
  54. 54.  H2OH2O  Ions:Ions: HH++ , Cl, Cl-- , Na, Na++ , K, K++  Enzymes:Enzymes: pepsin, gelatinase, lipasepepsin, gelatinase, lipase  MucousMucous  Intrinsic factorIntrinsic factor Composition of acid secretionComposition of acid secretion
  55. 55. Acid secretionAcid secretion H2O OH- H2O 1 2 3 5 4 6 7 8
  56. 56. Acid secretionAcid secretion 1 2
  57. 57. Functions of HCl • Killing bacteria • Dissolve food into chyme • Activate pepsinogen • Iron & calcium absorption • Stimulate secretin hormone & bile flow
  58. 58. Stimuli of HCl secretion: • Histamine: acts via H2 receptors increases intracellular cAMP. • Acetylcholine: acts via M3 muscarinic receptors increases intracellular Ca+ +. • Gastrin: it acts either directly on oxyntic cells by increasing intracellular Ca++ (like acetylcholine) or indirectly through stimulating the secretion of histamine from enterochromaffin-like cells (ECL
  59. 59. Mechanism of action of HCl stimuli: •Parietal cells contain receptors for these stimuli. Binding of these stimuli with their receptors release 2nd messengers which transfer the H+/K+ ATPase proteins from the membranes of intracellular vesicles to the plasma membrane thus increasing the number of pump proteins in the plasma membranes.
  60. 60.  Acetyl choline.Acetyl choline.  Gastrin hormone.Gastrin hormone.  HistamineHistamine. Stimulation of acid secretionStimulation of acid secretion
  61. 61. Phases of gastric secretionPhases of gastric secretion Cephalic phase ( nervous)- Condition & unconditioned reflexes → vagus nerve → acetylcholine & gastrin → ↑HCl, pepsinogen & mucous ( one third of secretion) Gastric phase ( nervous & hormonal) 2/3 of secretion Long vagovagal reflexes Local enteric relexes Gastrin secretion Intestinal inhibitory phase ( nervous & hormonal) Presence of food in intestine → entero gastric reflex & secretion of GIP, VIP, CCK & secretin which inhibit secretion
  62. 62. Cephalic phase: (nervous):Cephalic phase: (nervous): Conditioned & unconditionedConditioned & unconditioned Gastric phase: (nervous and hormonal):Gastric phase: (nervous and hormonal): Vagovegal reflexVagovegal reflex Local enteric reflexesLocal enteric reflexes Gastrin mechanismsGastrin mechanisms Intestinal phase: (nervous and hormonal):Intestinal phase: (nervous and hormonal): Entergastric reflexEntergastric reflex Hormones: GIP, VIP, CCK, secretinHormones: GIP, VIP, CCK, secretin Regulation of acid secretionRegulation of acid secretion
  63. 63. Gastric motility Physiologically- based the stomach is divided into - Proximal motor unit ( fundus & body) responsible for storage of food ( receptive relaxation) - Distal motor unit ( antrum & pylorus) responsible for • mixing & partial digestion of food • gastric peristaltic waves & emptying food
  64. 64. 1- storage function of stomach ( receptive relaxation) Gastric distention relaxation of stomach to→ increase capacity to 1- 1.5 L from 50 ml ( efferent fibers in vagus, sympathetic & ENS) 2- Mixing & propulsion of food Gastric slow waves start at mid point of greater curvature ( 3-5 cycles/min) spiks peristaltic→ → waves contraction of antrum followed by pyloric→ region & duodenum 3- stomach emptying
  65. 65. Regulation of gastric evacuation 1- gastric factors Distention of stomach & gastrin hormone increase→ gastric emptying 2- intestinal factors Enterogastric relex ( acid, irritation, distention, fats & proteins inhibit gastric emptying→ Fat in duodenum CCK, GIP & secretin inhibit→ → gastric emptying 3- Liquids are evacuated more rapidly, carbohydrates more than fats or proteins 4- Pain inhibits & emotions increase or decrease gastric emptying
  66. 66.  Proximal motor unit:Proximal motor unit: fundus bodyfundus body  Distal motor unit:Distal motor unit: Antrum PylorusAntrum Pylorus Stomach is divided physiologicallyStomach is divided physiologically
  67. 67. Innervation of the Stomachnnervation of the Stomach  1. Parasympathetic (vagus nerve): Cholinergic excitatory fibers •Distal motor unit Purinergic inhibitory fibers • Proximal motor unit
  68. 68. Innervation of the Stomachnnervation of the Stomach 2. Sympathetic Fibers:  Origin: Lower 6th thoracic segments  Preganglionic: greater splanchnic nerve.  Relay in: Celiac ganglion  Postganglionic: pass to stomach to inhibit PMU
  69. 69. 1.Motor function of stomach1.Motor function of stomach  Storage of food.  Mixing and partial digestion of food to form chyme.  Slow empting of the chyme into duodenum.
  70. 70. 1.Motor function of stomach1.Motor function of stomach Storage of food (receptive relaxation): Reflex initiated by the arrival of food into the stomach to increase its capacity for food. 50ml 1-1.5L (So stomach bulge outwards while pressure remains low).
  71. 71. Storage of food (receptive relaxation):Storage of food (receptive relaxation): Gastric distension. Afferent fibers Vagal nucleus Sympathetic ganglia Local enteric plexus Purinergic vagal fibers Myenteric inhibitory fibers Adrenergic sympathetic
  72. 72. Motor function of stomachMotor function of stomach 2. Mixing of food and empting of stomach: Weak peristaltic wave start in the middle of the body towards pylorus (stronger and faster at pyloric antrm). Antral contents to be forced back to the proximal part leads to mixing of food
  73. 73. Motor function of stomachMotor function of stomach 2. Mixing of food and empting of stomach: Antrum, pylorus and upper duodenum function as one unit contraction of antrum followed by contraction of pylorus and duodenum gastric contents prevented from entering duodenum but mixed and crushed.
  74. 74. Motor function of stomachMotor function of stomach 2. Mixing of food and empting of stomach: Strong peristaltic wave at pylorus (pyloric pump) Toniccontractionof pyloricsphincter Slow gastric emptingSlow gastric empting
  75. 75. Motor function of stomachMotor function of stomach Factors affecting gastric empting: 1. Gastric factors: Gastric distension Gastric empting ( ++ Pyloric pump , -- pyloric sphincter)  Nervous reflexes  Gastrin hormone
  76. 76. Motor function of stomachMotor function of stomach Factors affecting gastric empting: 2. Intestinal factors (entergastric reflex): Presence of the following factors inhibits gastric empting (-- pyloric pump, cont. pyloric sphincter):  fats and proteins.  Increased pH.  Distension of duodenum.
  77. 77. Entergastric reflexEntergastric reflex Fats and proteins. Increased pH. Distension of duodenum. Afferent fibers Vagal nucleus Sympathetic ganglia Purinergic vagal fibers Adrenergic sympathetic Secretin CCK GIP Secretin CCK GIP
  78. 78. Motor function of stomachMotor function of stomach Factors affecting gastric empting: 3.Consistency of food: Liquids > solids
  79. 79. Vomiting Reflex abnormal emptying of gastric content through esophagus & mouth Causes of vomiting 1.Reflex mechanical stimulation of posterior→ tongue – irritation of gastric mucosa- intestinal obstruction- sever pain – coronary thrombosis 2.central stimulation of CTZ by drugs,→ hypoxia, acidosis, morning sickness of pregnancy & motion sickness
  80. 80. Mechanism of vomiting - Relaxation of stomach & LES – contraction of pyloric sphincter - Deep inspiration , strong contraction of diaphragm& abdominal muscles to increase intra-abdominal P squeeze the contents of→ stomach up - Protection of air passages
  81. 81. Pancreatic secretion It is the most important digestive juice because it contains enzymes for digestion of most of food stuffs • Volume → 1500 ml / day • pH → 8-8.3, Alkaline ( HCO3) • Pancreatic Digestive enzymes
  82. 82. Pancreatic Digestive enzymes 1. Proteolytic enzymes trypsin, chymotrypsin, carboxypeptidase, ribonuclease & deoxyribonuclease 2. Pancreatic amylase 3- Pancreatic lipase. 4- cholesterol esterase 5- phospholipase
  83. 83. Regulation of pancreatic secretion Nervous regulation Vagal stimulation (conditioned &unconditioned reflex) → acetyl choline → pancreatic enzymes Hormonal regulation Secretin Acid in intestine → secretin → pancreatic juice rich in HCO3 Cholecystokinin CCK Polypeptides, amino acids & fats → CCK → pancreatic juice rich in enzymes
  84. 84. Liver & Biliary system
  85. 85. Functions of the liver Liver acts as a chemical factory, an excretory system, an exocrine and an endocrine gland 1- Vascular Functions for Storage and Filtration of Blood: store 200-400 ml. of blood Kupffer cells(remove 90% of bacteria in the portal venous blood (the colon bacilli)
  86. 86. 2- Metabolic Functions: Carbohydrate metabolism: (glucostat" ) Glycogenesis- glycogenolysis- gluconeogenesis- Cori cycle ( formation of glycogen from lactic acid) Lipid metabolism: oxidation of fatty acids - Formation of lipoproteins - lipogenesis Protein metabolism: Deamination of amino acids - Formation of urea , plasma proteins, most of coagulation factors & non-essential amino acids Storage of vitamins: Such as vitamin A, D, E, K and B12. & iron Detoxification or excretion of drugs, hormones and other substances  
  87. 87. 3- Secretory and excretory functions: Formation of bile: • Bile is required for the digestion and absorption of fats ( bile salts) and for the excretion of water-insoluble substances such as cholesterol and bilirubin • Secretion is continuous through all the day & is stored in gall bladder
  88. 88. Composition of bile • 500-1500 ml/day • Fresh bile is alkaline • Becomes acidic during storage in gall bladder to prevent precipitation of calcium
  89. 89. Water 97.00 % Bile salts 0.70 % Bile pigments 0.20 % Cholesterol 0.06 % Inorganic salts 0.70 % Fatty acids 0.15 % Lecithin 0.10 % Fat 0.10 %
  90. 90. Bile salts•  sodium and potassium salts of bile acids conjugated to glycine or taurine ( glycocholic & taurocholic acids) - The bile acids are synthesized from cholesterol.•  – Primary bile acids: cholic acid and chenodeoxycholic acid.•  – Secondary bile acids: In the colon, bacteria convert cholic acid to deoxycholic acid and chenodeoxycholic acid to lithocholic acid.  
  91. 91. Function of bile salts 1- Digestion of fat a-activation of pancreatic lipase b- emulsification of fat preparatory to its digestion and absorption by - detergent action reduce surface→ tension between fat globules - hydrotropic action
  92. 92. 2-Absorption of fat & fat soluble vitamins- form micelles micelles are bile acid-lipid water-soluble complexes that play an important role in keeping lipids in solution and transporting them to the brush border of the intestinal epithelial cells, where they are absorbed.
  93. 93. Phospholipids Free fatty acids, cholesterol Bile acids Bile acids OH group Peptide bond Carboxyl group
  94. 94. The Gallbladder   Functions of the Gallbladder: Storage of Bile Concentration of Bile removal of sodium by the gallbladder mucosa through an active transport mechanism, which passively draws chloride, bicarbonate and water. Prevention of marked rise in the Intrabiliary pressure Secretion of white bile Acidification of Bile: (absorption of bicarbonate)
  95. 95. Control of Gallbladder Emptying = Cholagogues Cholecytokinin (CCK) major stimulus for gallbladder contraction and sphincter of Oddi relaxation. Vagal stimulation cephalic stage of digestion and vago-vagal reflex during the gastric phase of digestion
  96. 96. Types of movement of GIT Peristalsis Stretch circular contraction behind & relaxation in front→ Stretch serotonin sensory nerves myenteric plexus→ → -Retrograde cholinergic neurons (subs P & a.ch) → contraction -Antegrade cholinergic neurons (VIP, NO & ATP) → relaxation Mixing movement •Peristaltic wave in blocked sphincter •Constrictive movement
  97. 97. Movement of small intestine Segmentation movements & peristalsis help mixing & propagation of the contents down the intestine 1- Segmentation ( mixing) contractions Divide the chyme, increase blood &lymph fow & mix food with secretion Duodenum & jejunum → 12/min Ileum → 8-9/min Controlled by slow wave ( basic electrical rhythm – myenteric nerve plexus)
  98. 98. 2- Peristalsis • Faster in proximal part & slower in distal part • Progression of the chyme 1-2 cm/min ( 3-5hr for travel from pylorus to ileocecal valve) Stretch contraction behind (subs P &→ → a.ch) & relaxation in front VIP, NO & ATP→ • Increased after meal by stretch of duodenum, gastro enteric reflex & hormones (gastrin- CCK-insulin • Inhibited by secretin & glucagone
  99. 99. Thank Thank youyou