Gastrointestinal tract Slow waves Basic Electrical Rhythm Tonic

Gastrointestinal tract

Slow waves & Basic Electrical Rhythm Tonic contractions

• Functional syncytium • AP propagation through gap junctions • Basal electrical activity → slow movement • Varying RMP • Slow wave – 5 -15 m. V (resting) – Frequency (Stomach 3, Duodenum 12, Illeum 9) – interstitial cells of Cajal (pace maker) • Spikes (Stimulated) – Frequency – Slow Na-Ca channels – 20 ms duration

• Depolarizing factors – Parasympathetic (A. Ch) – Strech – GI hormones • Tonic contraction – Continues – Spike freq. – Ca entry • Hyperpolarizing factors – Sympathetic – Epi, NE

Enteric Nervous System

ENS • Myenteric plexus or Auerbach’s plexus – GIT motility – Tonus, rhythmic contraction, frequency, velocity of peristalsis – VIP (inhibitory) • pyloric sphincter, sphincter of the ileocecal valve • Submucosal plexus or Meissner’s plexus – Blood flow & secretion – Local secretion, absorption, – Local contraction of the submucosal muscle

• Sensory nerve endings (Epithelium) – Mynert & meissner – GI reflexes – SC, Brain stem, Prevertebral ganglia, Vague, • • A. Ch NE, Epi 5 HT, DA, ATP, CCK, VIP, SS, Sub P, Enk, Bombesin

GI reflexes • ENS • ﺣﺮکﺎﺕ ﺩﻭﺩی • ﻣﺨﻠﻮﻁ کﻨﻨﺪﻩ • ﺗﺮﺷﺤﺎﺕ گﻮﺍﺭﺷی • GIT → Sympathetic Ganglia → different GIT location – Gastrocolic reflex – Enterogastric reflex – Colonoilleal reflex • GIT → Spinal cord/Brain stem → different GIT location – Defication

Hormonal control Gastrin • “G” cells of the antrum (stomach) – distention, – AA, – Gastrin Releasing Peptide (vagal stimulation) • Gastric acid secretion • Growth of mucosa

CCK • “I” cells (mucosa of the duodenum and jejunum) – FA, – Monoglyceride • Bile secretion • inhibits stomach contraction • Inhibits appetite

Secretin • “S” cells in duodenum – Acid • Inhibits motility • Pancreatic secretion of HCO 3

Gastric inhibitory peptide (GIP) • upper small intestine – FA – AA – CH – ↓stomach motor activity – slows emptying – Insulin

Motilin • upper duodenum – fasting, GIT motility. – interdigestive myoelectric complexes – increases

GI motility • propulsive movements – Peristalsis – Intestinal distention – Chemical/physical stimulation – Parasympathetic stimulation (blocked by atropin) – Myentric plexus – Unidirectional – Receptive relaxation – Peristaltic Reflex and the “Law of the Gut. ” • mixing movements – blocked by a sphincter – local intermittent constrictive contractions

Gastrointestinal Blood flow

Splanchnic Circulation Reticuloenduthelial cells - Bac, - AA, CH

GI circulation Mesentric Arcuate Celiac

Microvasculature of the villus • Counter current • O 2 shunt Parasympathetic Sympathetic (escape)

Propulsion & Mixing of Food

Hunger & Appetite • Lateral HT • Venteromedial HT • Orexin, Ghrelin, NPY • Leptin

Mastication (Chewing) • Incisors/molars – Rhythmic movement – Fruits, Veg. • Cortex, amygdala, HT • motor branch of trigeminal nerve • Reflexes • indigestible cellulose membranes • Increases the surface

Swallowing (Deglutition) • Voluntary stage • Pharyngeal stage(involuntary) • Epithelial sensors • NTS • swallowing center • esophageal stage

Pharyngeal stage • ﻣﻬﺎﺭ ﻣﺮکﺰ ﺗﻨﻔﺲ • Esophageal stage – primary peristalsis – secondary peristalsis • remained bolus • Myentric plexus • Reflex – Transsection of vague – Receptive Relaxation of the Stomach http: //www. linkstudio. info/images/portfolio/medani/Swallow. swf

Lower Esophageal Sphincter • Normal pressure • Prevents reflux • Abdominal pressure • Receptive relaxation • achalasia

The Stomach • Storage • Mixing (Chyme) • slow emptying • Body – Antrum • Rostral –Caudal – Food form concentric circles – Vagovagal reflex

• basic electrical rhythm (constrictor waves) • Constrictor rings force toward the pylorus • Retropulsion – Gastric glands – Chyme fluidity • Pyloric Pump – Regulation of emptying – Gastric / Duodenal signals • Hunger Contractions

Gastric factors promote emptying – Stretched wall (myentric reflex) – Gastrin (acid, motor activity, Pyloric pump) Duodenal factors prevent emptying – Distention – Mucosal irritation – Chyme acidity/ osmolality / AA → ENS →perivertebral Gang → vague → Brainstem inhibit pyloric pump (Enterogastric Reflex)

Hormonal inhibition • Lipid in duodenum → CCK – Contraction of pyloric sphincter – Inhibits pyloric pump • Secretin (acid) • GIP (FA, AA, CH)

GI motility • Propulsive movements – Peristaltic movements – Mass movements • Mixing movements – Segmentation – Haustration

• Segmentation • Peristaltic rush – Myentric & autonome • muscularis mucosae • ileocecal valve • 1. 5 -2 L/d • Cecal distension • appendix

Colon • Water & electrolytes absorption • storage • Haustrations – teniae coli – 2. 5 cm • Mass Movements – 1 -3 times/day 20 cm, 10 -30 min – Gastrocolic, Duodenocolic • Ulcerative colit

Defecation Reflexes Internal reflex parasympathetic

Secretory Functions of GIT

• Digestive enzymes • Mucous glands ، ﻟﻐﺰﻧﺪگی ، • چﺴﺒﻨﺪگی • ﺧﺎﺻیﺖ آﻤﻔﻮﺗﺮیک • single-cell mucous glands (Goblet cells) • crypts of Lieberkühn • Deep tubular glands • complex glands The salivary glands, pancreas, and liver

Acini and salivary ducts Parasympathetic stimulation

Regulation of salivation Parasympathetic Kallikrein

ﺗﺮﺷﺤﺎﺕ ﻣﻌﺪﻩ • Mocous neck cell • Oxyntic (Parietal) cell Hcl 160 m. M • Peptic (chief) cell • Pyloric cell Body/antrum

Oxyntic (Parietal) cell

Stimulation of Hcl secretion • A. Ch • Gastrin • Histamin • Enterochromaffin-like cell (ECL) – Chyme in antrum – Gastrin

• Pepsinogen – Hcl (1. 8<p. H<3. 5) – Stimulation (Hcl, A. ch) • Internal Factor – B 12 – Pernicious anemia • Gastric barrier • Pyloric (chief) cell – Mocous – Gastrin (G cells, protein)

Pancreatic secretion

ﺗﺮﺷﺤﺎﺕ ﺭﻭﺩﻩ • Brunner glands – Vagus / Secretin – Sympathetic inhibition (Peptic Ulcer) • Lieberkuhn crypts – Goblet cells – Enterocytes • 1. 8 L/d • Digestive Enzymes

Digestion & absorption in the GIT

ﻫﻴﺪﺭﻭﻟﻴﺰ ﻛﺮﺑﻮﻫﻴﺪﺭﺍﺕ • Starch • Ptyalin • Pancreatic amylase • Maltase & dextrinase • Lactase • Sucrase

ﻫﻴﺪﺭﻭﻟﻴﺰ پﺮﻭﺗﺌﻴﻦ ﻫﺎ • Pepsin (collagen), p. H , %10 -20 • Proelatase (elastin) • Trypsin, chymotrypsin, • Carboxypeptidase • Enterocyte (aminopeptidase, Dipeptidase) • Cytosolic peptidase

ﻫﻴﺪﺭﻭﻟﻴﺰ چﺮﺑﻲ ﻫﺎ • TG, • Lingual lipase (%10) • Pancreatic lipase

Emulsification of Fat by Bile Acids and Lecithin • Reversible hydrolysis • Bile salts, lecithin (micelle formation) • cholesterol ester hydrolase • phospholipase A 2