Motility of GI tract Flashcards
Gastrointestinal tract
Mouth Oesophagus Stomach Small intestine Large intestine
Accessory glands
Salivary glands
Liver
Gallbladder
Pancreas
Sphincters
Made up of smooth muscle and act as ‘valve of reservoir’
Hold luminal content adequately before emptying to next segment
Dysregulation of sphincters
Results in GI motility disorders
- achalasia
- gastroparesis
Mucosa layers
Epithelial layer
Lamina proporia
Muscularis mucosa
Epithelial layer
Exocrine cells and endocrine cells
Lamina propria
Small blood vessels
Nerve fibres
Lymphatic cells/ tissue (GALT)
Loose connective tissue
Muscularis mucosa
Think layers smooth muscle
Responsible for controlling mucosal blood flow and GI secretion
Submucosa
Loos CT, large BVs, lymphatic vessels
Glands in some GI regions
Submucosal nerve plexus (Meissners plexus)- regulates blood flow and secretion
Muscularis externa
Circular muscle
Myenteric nerve plexus
Longitudinal muscle
Myenteric nerve plexus
Auerbach’s
Lies between muscle layers and regulates motility
Serosa
CT connects to abdominal wall
Supports GI tract in the abdominal cavity
Blood vessels, extrinsic nerves and ducts of large accessory exocrine glands enter through
GI innervation
Intrinsic pathway
- enteric nervous system
- functionally organised by submucosal and myenteric plexus
- myenteric involved in control of gut motility
- submucosal coordinates intestinal absorption and secretion
Extrinsic pathway
- the gut brain axis
- ENS linked to CNS via sensory and motor nerve
- parasympathetic and sympathetic nervous system
Extrinsic innervation
Parasympathetic
- preganglionic vagus nerve innervates oesophagus, stomach, small intestine, liver, pancreas, caecum, appendix, ascending colon, transverse colon
- pelvic nerve innervates remainder of colon via hypogastric plexus
- stimulates motility and secretion
Sympathetic
- preganglionic fibres from T8-L2
- postganglionic cell bodies in celiac, IM and SM ganglia
- inhibits gut motility and secretion
- constricts sphincters
Intrinsic innervation
Myenteric plexus
- between circular and longitudinal muscle layers
- thin layer of ganglia, ganglion cells and inter-ganglionic nerve tracts
- innervate longitudinal and outer lamella of circular
- control of gut motility
Submucosal plexus
- between submucosal layer and circular layer
- functionally distinct from myenteric plexus
- project mainly into inner lamella of circular
- coordinates intestinal absorption and secretion
Hirschsprung’s disease
Congenital absence of myenteric plexus in portion of distal colon
Lacks peristalsis and undergoes continuous spasms
Leads to functional obstruction and severe constipation
Smooth muscle in motility
Act as functional syncytium
Pacemaker activity- slow waves- BER
Spike potentials of BER depolarises membrane to threshold (caused by opening of Ca2+ channels)
Ca2+ in spike potential triggers muscle contraction
Regulation of smooth muscle contraction
Greater the number of spikes per BER the greater the degree of muscular contraction
Excitatory transmitters depolarise membrane potential
Inhibitory transmitters hyperpolarise membrane potential
Types of gastrointestinal movement
Segmentation
- mainly small intestine for mixing food with enzymes
- closely spaced contractions of circular smooth followed by relaxation
Tonic contraction
- sphincters
- separation
Peristalsis
- longitudinal contracts first then circular
- leads to progressive wave
- distension of gut by food triggers peristalsis
Migrating motor complex
Pattern of motility every 90 minutes between meals
Strong propulsive contractions down distal stomach and small intestine
Sweep indigestible materials
Does not require external innervation
Paralytic ileus
Temporary cessation of gut motility most commonly caused by abdominal surgery
Also caused by infection or inflammation of abdominal cavity, electrolyte abnormality and drug ingestion
Nausea, vomiting, abdominal distention, absent bowel sounds
Swallowing- deglutition
Bolus of food formed in mouth by mastication then propelled to oropharynx as tongue moves up and back against hard palate (V)
Bolus stimulates mechanoreceptors in parynx
Efferent impulses from vagus to pharynx, oesophagus and palate for muscle contraction
Soft palate elevates, superior constrictor of pharynx contacts to close nasopharynx
Larynx rises so epiglottis covers trachea
Peristalsis initiated in pharynx continues down oesophagus
Oesophagus
~25cm
Upper 1/3 skeletal striated muscle, lower 2/3 smooth
On swallowing
- UOS briefly relaxes, allows food to pass to oesophagus
- contractile wave sweeps down oesophagus
- LOS and proximal stomach relax to allow bolus to enter
Achalasia
Dysphagia results from failure of LOS to relax, causing functional obstruction
Loss of peristalsis of oesophageal body
Lose ganglionic cells of myenteric plexus or natural defects in vagal dorsal nucleus of brainstem
GORD
LOS is incompetent, allows flow of gastric juices and content back into oesophagus
Gastric juices are corrosive so distal oesophagus becomes inflamed and sometime ulcerated
3 functions of the stomach
- Storage- ingest food faster than can be digested, aided by receptive relaxation
- Physical and chemical disruption- mixing
- Deliver resultant chyme to intestine at optimal rate- gastric emptying
Receptive relaxation
Increases in stomach pressure triggers dumping and reflux
Relaxation of muscle- increase in fibre length without change in tone
Increase in size without increase in intragastric pressure
Receptive relaxation mediated by vagus as part of end of swallowing reflex
Pressure sensors maintain pressure at abdominal levels
Occurs in proximal unit
Mixing
Peristalsis through strong coordinated contraction of three muscle layers in distal
Cells in longitudinal act as pacemakers
Activity originates mid stomach
Spreads distally and force and speed increases
Little chyme forced to duodenum, most content returns to distal regions
Emptying
Terminal part- pyloric antrum markedly thickened muscle layer
Pyloric sphincter controls exit
Increase of chyme induces antral contractions and opening of sphincter as peristaltic wave approaches
Small amounts of cyme enters duodenum, sphincter contracts
Liquids leave first
Control of stomach emptying
Small intestine has limited capacity so only accept small amounts of chyme
Gastric contents empties at rate proportional to volume, pH, physical and chemical natire
- volume in stomach promotes emptying
- more isotonic, empties more rapidly
Enterogastric reflex stimulates pyloric contraction to prevent emptying and prevent overfilling over small intestine
Dumping syndrome
Rapid emptying of gastric contents into small intestine
Nausea, pallor, sweating, vertigo, fainting after meal
Gastroparesis
Impaired of absent ability of stomach to empty
Occasionally in severely diabetic patients
Early satiety, abnormal bloating, nausea
Motility along small intestine
Mixing: multiple short contractions, frequency varies
Peristalsis: short range contractions
Stimulated by extrinsic and intrinsic factors
Villus movements mix and drain lymphatics of fat absorption
Small intestine motility dysfuntions
Impaired small intestine peristalsis can lead to abnormally high bacteria
Lead to diarrhoea/ steatorrhoea
Intestinal blind loop syndrome
Motility in large intestine
Slow, irregular movements increase contact with absorbing surface
lacks longitudinal muscle, instead has 3 thick bands for accordion like movement
Contractions of circular muscle divide colon to haustrations
Mixing movement
Propulsive movement
Rectum and defecation
Mass movement propels faeces into rectum and distends stretch receptors to provoke defecation reflex
Internal anal sphincter- involuntary
External anal sphincter- voluntary
Afferent stimulation leads to parasympathetic signal to relax internal sphinter
