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The Digestive System
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The Digestive System Overview Functional anatomy Motility function
Secretory function Digestive and absorptive function Liver functions 12-Nov-18 Digestive System
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Functional Anatomy The digestive system include Glands
Mouth, oesophagus Gastro-intestinal tract Stomach Small intestine Colon Glands Salivary, liver and pancreas 12-Nov-18 Digestive System
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Digestive System 12-Nov-18 Digestive System The middle portion
Duodenum inches Jejunum Ileum m The lower segment Large Int 1.5m 6-7 cm diameter 12-Nov-18 Digestive System
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Function of the Digestive System
Transfer nutrients from External environment to internal environment To receive, digest and absorb Chemical substances which constitute the ingested food 12-Nov-18 Digestive System
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Musculature of GIT Smooth muscle with the exception of:
Mouth, pharynx, upper 1/3 of oesophagus External anal sphincter 12-Nov-18 Digestive System
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Musculature of GIT Arranged in three coats Inner muscularis mucosa
Longitudinal Serves as base for mucosa Circular muscle layer Outer longitudinal muscle layer 12-Nov-18 Digestive System
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12-Nov-18 Digestive System Muscularis mucosa Submucosa Mucosal glands
Large gland (pancreas) Meissner’s Plexus Glands of Brunner (duodenum) Muscle layers Myenteric plexus. (Auerbach’s) Mucous Membrane Submucosa Villi Submucous plexus Myenteric plexus Serosa Glands outside gut but developing from it. Mesentry From Physiology book by H.T Sherrief 12-Nov-18 Digestive System
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From Physiology Book by H.T. Sherrief
12-Nov-18 Digestive System
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Sphincters Divide the tract into functional compartments
Cricopharyngeal Upper oesophageal sphincter Prevent entry of air into oesophagus Lower oesophageal sphincter Prevent irritant gastric content from entering into oesophagus 12-Nov-18 Digestive System
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Sphincters Pyloric sphincter Ileocecal Anal sphincter
Separate the acid environment of stomach from alkaline environment of duodenum Ileocecal Limit reflux of materials from colon Anal sphincter Necessary for continence 12-Nov-18 Digestive System
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Sphincters Cricopharyngeal Lower oesophageal Pyloric Ileocecal Anal
12-Nov-18 Digestive System Anal
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Nerve Supply Intrinsic Myenteric Plexus (Auerbachs)
Available starting From lower oesophagus to the rectum Provided by intrinsic nerve plexuses (intra-mural) Myenteric Plexus (Auerbachs) Between outer longitudinal muscle layer and circular muscle layer Affect motility 12-Nov-18 Digestive System
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Intrinsic Nerve Supply
Submucosa plexus (Meissners) Between circular muscle layer and muscularis mucosa Affect motility and secretion 12-Nov-18 Digestive System
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Intrinsic Nerve Supply
Nerves from these plexuses supply Smooth muscles, longitudinal,circular,Muscularis Secretory cells in epithelium Receptors in epithelium (chemo, stretch, pressure) 12-Nov-18 Digestive System
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Extrinsic Nerve Supply
Autonomic nervous system Parasympathetic Sympathetic Parasympathetic nerves terminate on Nerve cells of myenteric and submucosa plexuses Post-ganglionic cholinergic nerves Post-ganglionic purinergic nerve 12-Nov-18 Digestive System
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Parasympathetic Stimulation of parasympathetic
Excitation of GIT smooth muscles Relaxation of sphincters Increased overall activity Peristalsis Glandular secretions Neurotransmitters Acetylcholine (ach) - cholinergic Purinergic ATP, 5HT, CCK, substance-p 12-Nov-18 Digestive System
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Sympathetic Sympathetic nerve fibres terminate on
Post-ganglionic cholinergic nerves Cause pre-synaptic inhibition On blood vessels Vasoconstriction On smooth muscle GIT Inhibition 12-Nov-18 Digestive System
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Sympathetic Sympathetic stimulation causes Increase tone of sphincters
Inhibit GIT motility 12-Nov-18 Digestive System
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Control of GIT Motility
Motility of GIT is controlled by a combination of factors Myogenic Neurogenic Humoral Intrinsic Myogenic control based on Intrinsic rhythmic fluctuation of membrane potential of muscle cells Leads to rhythmic depolarization 12-Nov-18 Digestive System
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Intrinsic myogenic Control
Rhythmic fluctuation of resting of memb. Pot. Is known as Control activity, Slow wave, basic electric activity (BER), pace- setter potent. 12-Nov-18 Digestive System
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Slow wave Potential Spike potential associated with muscle contraction
Threshold Pot. - 35 Depolarization - 50mv RMP Hyper-polarization 12-Nov-18 Digestive System
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Neurogenic Intramural plexuses Extrinsic neural control STIMULATION
Myenteric Submucosal Extrinsic neural control Parasympathetic Sympathetic STIMULATION Stretch Acetylcholine, Certain specific GIT hormones 12-Nov-18 Digestive System
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Neurogenic Parasympathetic stimulation causes Membrane to depolarize
At -35 mv Spike potential develop Spike potential Associated with muscle contraction Frequency Increases as depolarization increases 12-Nov-18 Digestive System
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Neurogenic INHIBITION Causes hyperpolarization Noradrenalin
Sympathetic Certain GIT hormones Causes hyperpolarization 12-Nov-18 Digestive System
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Humoral Control Certain hormones secreted by the cells of GIT have profound effects on motility of GIT Gastrin Secretin Cholecystokinin GIP gastro-inhibitory peptide 12-Nov-18 Digestive System
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Gastrin Secreted by stomach antrum Gastrin increases Entry of food
Vagus Gastrin increases Constriction of LES Stomach motility Small intestine motility Gall bladder motility Gastrin 12-Nov-18 Digestive System
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Cholecystokinin Secreted by mucosa Inhibit stomach motility
Duodenum Jejunum In response Fatty substance, fatty acid, AA, acidic chyme Inhibit stomach motility Slows gastric emptying Increase contractility of gall bladder Increase pancreatic enzyme secretion 12-Nov-18 Digestive System
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Secretin Mucosa of duodenum in response to
Acidic chyme from stomach Mild inhibition of most of GIT 12-Nov-18 Digestive System
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Gastro-inhibitory Peptide GIP
From mucosa of upper small intestine in response Fat, carbohydrate Causes decrease in motor activity of stomach Slowing the emptying of gastric contents into duodenum 12-Nov-18 Digestive System
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Excitation of Smooth Muscles
Contraction occurs in response to spike potential Slow wave potential do not cause contraction Smooth muscles have Myosin, Actin Arrangement not orderly Contraction occur by sliding action of filaments like in skeletal muscles 12-Nov-18 Digestive System
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Molecular Basis of Contraction
Stimulation Nerves, hormones, stretch Voltage gated ca++ channels open Influx of ca++ Ca++ bind to Calmodulin Phosphorylation of myosin head Actin bind to myosin Contraction 12-Nov-18 Digestive System
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Molecular Basis of Contraction
Cessation of contraction De-phosphorylation of myosin Cross-bridges remain attached to actin Produces sustained contraction Relaxation of smooth muscle Occurs when Dissociation of calcium- Calmodulin complex 12-Nov-18 Digestive System
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Tonic Contraction Continuous Caused by Lasting for minutes or hours
Increasing or decreasing in intensity Caused by Series of spike pot Frequency of spike pot Determine degree of tonic contraction 12-Nov-18 Digestive System
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Rhythmic Contraction Occur at frequency of 3 to 12 per min
Responsible for Phasic function of the GIT Peristalsis Mixing of food 12-Nov-18 Digestive System
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Types of Movements in GIT
Mixing movements and propulsive movement MIXING movement Caused by either Peristaltic contractions or Constrictive contractions of small segments of the gut 12-Nov-18 Digestive System
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Propulsive Movement Intramural plexuses
Contact of the bolus with mucosa Stimulates receptors Through interneurones Excites orad segment Inhibition of analward segment Contractile ring appears around the gut and then moves forwards Inhibition excitation Receptors Bolus Peristaltic contraction Leading wave of distension 12-Nov-18 Digestive System
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