Download - GI Physiology
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GI Physiology
Regulation Neural
Hormonal
Neural Regulation Involuntary except
oesophagus & rectum
Rest AutonomicENS
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Extrinsic Innervation
Somatic / Autonomic
Somatic Pharynx & prox. Oe. (Motorlower cranial nerves
Anal canal pudendal nerve
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Autonomic NS
PSNS Vagus Increases GI motility (A
SNS Inhibit GI activity (Norad)
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Intrinsic Innervation
By ENS
Afferents from gut
Response with or without ANS
little brain of gut
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Hormonal Regulation
1. Gastrin (Antrum) Increase of LESpressure, stim of small bowel and GB
2. CCK (Duo & Jej) - Stim of GB, slowsmotility of small bowel & stomach
3. Secretin (Duo & Jej) Increases pyloricpressure, inhibits small & large bowel
4. Motilin (Duo) increase of gastricemptying
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Hormonal Regulation
5. Somatostatin (Islets) Increasesgastric emptying, inhibits secretions
6. GIP (small intestine) Delays gastricemptying
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Oesophagus
Sphincters prevent regurg. and keep oe.empty between swallows
UES prevents regurg to pharynx
LES - prevents regurg
maintains HPZ
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Stomach Functions
1. Reservoir : 200 1500ml
2. Mix and grind food
3. Chemically breakdown food 4. Kill microbes
5. Control emptying into duodenum
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Stomach Glands
Mucous cells mucous for protection
Parietal cells HCl & IF
Chief cells - Pepsinogen
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Stomach Innervation
Vagus Increased motility & secretions
Relax fundus on food intake
Sympathetics Decreased activity ofsmooth muscle
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Small Bowel
Mucosal surface increased by plicae, villiand microvilli (500 fold)
Motility influenzed by ANS,ENS andhormones
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Functions of Colon
1. Absorption of water and electrolytes
2. Transportation of waste
3. Storage of waste
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Anal Canal
Internal sphincter Involuntary,Responsible for resting pressure
External sphincter Voluntary,Responsible for pressure on voluntarysqueeze
Innervated by somatic nerves
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Gall bladder
Concentrates bile and works as reservoir
Empties in relation to meals in response tohormones
Sphincter of Oddi several parts HPZ
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Pancreas
1. Exocrine function
2. Secretion of HCO3
3. Endocrine function Insulin, Glucagon,
Somatostatin Hormonal mechanisms for regulation
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Physiology of Swallowing
1. Oral stage tongue voluntary control
2. Pharyngeal stage Reflex
Food stimulates swallow receptors
Swallow centre inhibits respiration
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3. Oesophageal stage
Peristalsis + Gravity
7-10 sec
LES pressure 20mmHg over intra-gastricpressure at rest
Pressures equal during swallowing
LES opens until bolus and contractionhave passed through
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Factors affecting LES Pressure
Increase Gastrin, Motilin, Vasopressin
Protein
Prokinetics
Decrease Proges.,Secretin,CCK,Glucagon
Fat, alcohol, chocolate
Ca blockers, Benzodiazepines,Theophylline, Atropine
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Disorders of Swallowing
1. Mechanical eg. Ca, FB
2. Neuromuscular incoordination eg.Achalasia, DES, Bulbar palsy
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Achalasia
Autoimmune/ Genetic/ Infective
Loss of ganglion cells in myenteric plexus
Degenerative changes in vagus & DMN
Chagas is aquired achalasia
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Manometry in Achalasia
Absence of peristalsis
Elevated LES pressure
Incomplete relaxation of LES
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GERD
Gastric acid pH 1.5 2
Oesophageal pH 6 7
Physiological reflux After meals, shortduration, not during sleep
Pathological reflux long duration, D/N,symptomatic
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Aetiology of GERD
1. Incompetent LES
2. Deficient/delayed acid clearance
3. Gastric abnormalities
4. Transient LES relaxation
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Incompetent LES
1. Hormonal factors eg. Progesterone inpregnancy
2. Length of LES exposed to higherintragastric pressure Hiatus hernia
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Delayed acid clearance
1. Primary peristalsis D/N = 60/6
2. Secondary peristalsis absence ofswallow
3. Salivation neutralises acid
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Gastric abnormalities
1. GOO
2. Delayed emptying eg. DM, vagotomy
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Basis of tests
Manometry LES pressure & length
24 hr oesophageal pH Quantify,frequency, timing
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Physiology of defaecation
Distension of rectum registered in cortex
RAIR IAS relaxes
Faeces in contact with upper anal receptors Receptors determine quality and content
(sampling reflex)
Contraction of rectum, relaxation of EAS,pelvic floor & puborectalis sling
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Anorectal Manometry
Resting pressure autonomic neuropathy,MDA
Squeeze pressure Trauma, surgery
RAIR absent in Hirshprungs
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