Enteric Nervous System Flashcards
Where does the ENS run from?
Runs from oesophagus to rectum
What does intrinsic innervation of the GIT mean?
All essential components are in the GIT, dont need connection elsewhere
What are Nuclei in the GIT
Neurones axons clumped together
Why is ENS known as a little brain?
Has network of neurones (80-100 million)
What are the 2 major plexuses?
- Submucosal (Meissners) plexus
- Myenteric (Auerbachs) plexus
Location of submucosal plexus
Stomach and intestine only
Location of myenteric plexus
Full length of GIT
Myenteric is sandwiched between two …… layers
Muscle
Longitudinal muscle
Circular muscle
Submucosal plexuses between
Circular muscle
Submucosa
Types of neurones found in the plexuses
Afferent (sensory) neurones
Interneurones
Efferent (secretomotor) neurones
Effectors
What receptors are associated with afferent neurones
Sensory
Mechano
Chemo
What are is the function of interneurones?
Coordinate input and output
Excitatory + inhibitory
What effectors do efferent neurones?
Smooth muscle
Secretory glands
What NTs does the efferent neurones use
ACh
Various peptides
What do enteric reflexes do?
Control:
Motility
Secretion
Blood flow
What plexus does the motor reflex involve?
Myenteric plexus
What do mechanoreceptors detect?
Detect physical presence of food in GIT
What do chemoreceptors detect?
Detect sensory chemicals released by food
What is an example of a motor reflex
Peristalsis
Movement of food in a rhythmic Ashton along GIT
How is bolus (food) pushed along the GIT via sensory info
- Sensory receptors (mechano/ chemo) detect contents of lumen
- Info from receptors transported into myenteric plexus
- Info distributed via interneurones to alter impact of efferent neurones that interact with muscle layers
Mechanism used to push food down GIT
- Bolus stimulates mucosal sensory receptors
- Infro to Myenteric plexus
- Excitatory interneurones prod effect
- Effect = smooth musce contraction, decreases size of lumen, pushes bolus forward
- In front of bolus inhibitory interneurones = smooth muscles relax
- Occurs simultaneously so smooth movement
What is secretory reflex?
Food stimulates sensory receptors
Bring info to submucosal plexus
Interneurones - efferent fibres - secretory cells
Secrete into lumen helping digestion and lubrication
(Enzymes, mucus, acid)
Is blood flow to gut adjusted by the ENS
Yes involves both plexuses
Blood flow matches to activity of the gut
How is the CNS integrated with the ENS
Symp/ parasymp is an intermediate
Brain can override the ENS
How does CNS influence vary along GIT
Once food swallowed ENS cant stop food travelling
CNS controls sphincters so can control faeces
What causes dysfunction in the GIT (associated with ENS)
- Age
- Congenital absence of ENS neurones (genetic) - peristalsis stopped
- Abolition of rectoanalreflex
What range of diseases can affect ENS
Specific diseases
General disease
Specific Diseases associated with ENS:
- Changas disease
- Achalasia
- Hirschprungs disease
What is Changas disease?
Endemic in South America
Parasite transferred into blood via insect bite
Toxins prod that kills ENS neurones
ENS shutdown so cant eliminate toxin
What is Achalasia disease?
Affects oesophagus and oral cavity - hard to swallow
Nutritional status decreased
More common in elderly bc loss of inhibitory neurones in Myenteric plexus in
- sphincter at opening of stomach
- oesophagus
General neurological conditions that affect ens
- Parkinson’s disease
- Peripheral neuropathies
- Myasthenia Gravis
How is irritable bowel syndrome caused?
Dysfunctional interaction between brain and ENS
Are there opioid receptors in ENS?
Yes bcs ENS releases opoid NT
Target opoid receptors to change function of ENS and so GIT
What is the active ingredient in anti- diarrhoeal agents and how they work
Loperamide that act at opioid receptors to reduce gut motility
How do some pain meds (morphine/ codeine) cause constipation as a side effect
They are also opioids so thy can act on opioid receptors in the gut and reduce gut activity
What are the 4 layers of small intestine superficial to deep
Serosa
Longitudinal muscle
Circular muscle
Submucosa
Mucosa
Function of myenteric plexus
Increase tone of the gut
Control velocity and strength of gut contractions via inhibitory and excitatory interneurones
Controls GIT motility
Function of submucosal plexus
Controls secretions
Controls local muscles
Controls absorption
What are the two ways ENS works?
- Autonomously (reflexes)
- Via para/ symp NS
What are the causes of the symp ns overriding the ENS
- fight or flight
- inhibits both plexuses
- causes decrease in peristalsis, blood flow, absorption, secretion
What are the causes of para NS overriding ENS
- rest and digest
- stimulates both plexuses
- causes increase in peristalsis, blood flow, absorption, secretion
Difference between short and long reflex of ENS
Short more common, can act fast and only involve neurones of GIT
Long uses integration of CNS
Examples of long and short reflexes
Inhibition of stomach secretions and motility is an example of short reflexes, while the internal digestion of food and chemical secretions stimulation by senses are example of long reflexes.
Other causes of dysfunction of ENS
Congenital absence of ENS neurones - genetic mutation
Peristaltic wave halts at section missing ENS neurones - faeces cant pass and builds up, (distending colon) breeding ground for infection
Abolition of rectoanalreflex - affects defection, manifests after birth
