GI Intro To The Struct Of GI tract and motility Flashcards
What are the compartments of the ailment are canal separated by
Sphincters
What su the motility and what are some types
Mechanical activity mostly involving smooth muscle
( except skeletal muscle at mouth, pharynx, upper oes and external anal sphincter)
Propulsive movements oral to aboral
Mixing movements -
Tonic contractions
What are secretion required for
Digestion
Protection
What do some sec contain
Water ‘borrowed’ plasma
Electrolytes - sodium, pottasium, chloride
Organic compounds - bile salts, mucus, enzymes
What is digestion
Chemical breakdown by enzyme hydrolysis of complex foodstuffs to smaller absorbable units
What is carb digestion usually mediated by and what is it broken down to
Polysacc –> monosacs such as glucose or galactose
What is the digestion of proteins mediated by and what are they broken down to
Mediated by proteases, dipeptides
Broken to amino acids, dipeptides see
What mediates fat digestion and what is it broken down to
Mediated by lipases
Conv to monoglycerides and free fatty acids
What are the layers on the digestive tract wall
Mucosa
Su mucosa
Muscular is external
Serosa
What is the mucosal layer
Epi cells
Exocrine cells
Endocrine gland cells
Lamina propria
What is in the sub mucosa layer
Connective tissue
Larger blood and lymp vessels
Glands
Myenteric nerve network
What is the muscularis external layer
Circular muscle layer
Myentericplexus
Longitudinal muscle layer
What is the Serosa layer
Connective tissue
Forms thin and sticky fluid lubricates outer surface
What is the gastrointestinal motility largely due to
Activity of smooth muscle (circular, longitudinal layers and muscularis mucosal)
Skeletal muscle imp - mouth, pharynx, upper oes, external anal sphincter
What action does the circular and longitudinal muscle do
Circular - lament narrow and longer
Longitudinal- shorter and fatter
How are adjacent smooth muscle cells coupled
Via gap junctions whic allow spread of electrical activity
How is the rhythm of the GI muscle cells
Intrinsic - enteric su mucosa plexus
Extrinsic autonomic nerves
Numerous hormones sec by endocrine cells of GI tract
How does spontaneous electrical activity portray in the intestines
Slow waves - rhythmic patterns of mem depo and repo that spread from cell to cell via gap junctions
What does the slow wave activity determine
Maximum frequency, direction and velocity of rythmic contractions
What are the slow waves driven by
Pacemaker cells interstitial cells of Cajal
Contraction only occurs if the slow waves…..
Amplitude sufficient trigger action potential in smooth muscle
Force is related to whatn
Number of action potentails discharged
Where are ICC’s found
Between longitudinal and circular muscle layers and in the submucosa
What do the slow waves determine
The basal electrical rhythm
Not all slow waves trigger
Contraction
Whether slow wave amplitude aches threshold depends upon
Neural stimuli
Hormonal stimuli
Mechanical stimuli
How many slow waves/min are in the
Stomach
Small intestine
Large intestine
Stomach - 3 slow waves
Small intestine - 10-12 waves in duo, 8 in ileum
Large intestine - 8 in proximal colon, 16 distal colon
Where are the neurones of the gut found
In ganglia in the Myenteric and submucous plexuses
What connects the ganglia of the gut
Interganglionic fibre tracts
What is the alternative name for Myenteric and submucous plexuses
Myenteric - auerbachs
Submucous - meissners
What dos the enteric nervous system do
Coordinates muscular, secretive and absorptive activities
How does the enteric nervous system do what it does
Via Sensory neurones specialised (mechanorecpe) Inter neurones (majority, coordinating reflexes) Effector neurones (excitatory and inhibitory Motor neurones supplying longitudinal and circular smooth muscle layers, sec epi, endocrine cells and blood vessels)
What so the parasympathetic innervation of the GI tract
Preganglionic (ACh) synapse in ENS
Excitatory - increased gastric, pans and small intestine sec, blood flow and smooth muscle contraction
Inhibitory - relaxation of some sphincters, receptive relaxation of stomach
What is the sympathetic innervation like in the GI tract
Preganglionic fibres (ACh) synapse at prevertebral ganglion Postganglionic releasing (NA) innervate mainly enteric structures also other structures
Functionally less lmp than parasymp
Inhibitory - decreases motility, secretion and blood flow
What is an example of a local reflex
Peristalsis
What is an example of a short reflex
Intestino-intestinal inhibitory reflex
Local distension and command adjacent smooth muscle to relax
What is an example of a long reflex
Increase gastric activity
Increase propulsive activity in terminal ileum
Food detected and causes contraction of terminal ileum propelled to large intestine
What so peristalsis
A wave of contraction that normally proceeds along gut in a aboral direct triggered by distension of gut wall
Contraction behind bolus and relaxation in front
What is segmentation
Mixing or churning movements
Rhythmic contractions of the circular muscle layer that mix and divide luminal contents
Where does segmentation occur
In small intestine and large intestine in fed state where called haustration
What are tonic contractions
Sustained contractions found in the sphincters of the GI tract
How many sphincters of the GI tract
6
What does a sphincter consist of
Specialised circular general smooth muscle
Are exceptions
What do sphincters act as
one way valves maintaining a positive resting pressure relative to two structures (eg oes and stomach)
What is the upper esophageal sphincter made of and what does it do
Skeletal and relaxes to allow swallowing and closes during inspiration
What does the lower esophageal sphincter do
Relaxes to permit food into stomach
Closes to prevent reflux of gastric contents to esophagous
What dos the pyloric sphincter do
Regulates gastric emptying
Usually prevents duodenal gastric reflux
What does the illeocecal sphincter do
Regulates the flow of ileum to colon
Distension of ileum opens
Distension of proximal colon closes
What so the difference between the internal and external anal sphincters
Internal - smooth muscle
External - skeletal muscle
How are the two anal sphincters regulated
By the defecation reflex
What is the direction of the food bolus
Oral to aboral
