GI Physiology

7/29/2019 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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GI Physiology

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