juices . The ENS instead co-ordinates highly complex dynamics that create digestive fluids of different composition and ph levels throughout different stages of the digestive tract .( 5 )
IN ADDITION TO THE KEY ROLE IT PLAYS IN FOOD ABSORPTION , THE ENTIRE DIGESTIVE TRACT IS ALSO A VERY IMPORTANT PART OF OUR IMMUNE SYSTEM . THE DIGESTIVE TRACT IS ESSENTIALLY AN OPEN TUBE FROM THE MOUTH TO THE ANUS THAT PERMITS THE EXTERNAL WORLD TO FLOW RIGHT THROUGH US .
The ENS further co-ordinates the activation of smooth muscle to create life-essential peristalsis .( 5 ) This finely tuned synchronicity orchestrated by the so-called second brain is so essential that the first brain could not function adequately without it . The enteric nerve cells are buried deep within the tubular structure of the digestive tract , which includes the mouth cavity , the oesophagus , stomach , small intestine , and the large intestine , with its rectum and anus completing the digestive passage .
The anatomical organisation of the GIT from the lower third of the oesophagus to the rectum can be simplified into four primary layers :
1 . The most internal layer enfolding the GIT lumen is the mucosa , which has three layers in itself : the epithelium , the lamina propria and the muscularis mucosa . This layer is responsible for direct and immediate contact with all substances entering the GIT .
2 . The mucosa in turn is enfolded by the submucosa , which accommodates the complex pathways of the submucosal plexus . This plexus controls local intestinal secretion and blood flow , electrolyte and water transport and absorption and regulates the configuration of the luminal surface including local contraction . It is primarily innervated by afferent sensory neurons .
3 . The submucosal layer is surrounded by the muscularis propria incorporating the myenteric plexus and the circular and longitudinal muscular layers of the GIT . Fascinatingly , the myenteric plexus arises from the vagal trigone — also known as the nucleus ala cinerea within the floor of the fourth ventricle . It gives rise to the parasympathetic fibres of the vagus nerve innervating the smooth musculature and glands of the respiratory and intestinal tracts as well as the heart muscle . This in itself creates a highly significant link between the ENS and the ANS .( 1 ) The myenteric plexus provides motor innervation to both muscular layers of the GIT from parasympathetic and sympathetic fibres , whereas the submucosa is only innervated by parasympathetic fibres . The myenteric plexus regulates GIT motility . Approximately 70 % of myenteric neurons are efferent motor neurons ; 30 % are sensory and thus responsible for feedback into the CNS .
4 . The fourth layer of the GIT is the serosa and adventitia , both protective and anchoring .
Localised regions of the GIT have become highly specialised to function at optimum efficiency from the oral cavity right through to the anal exit . Autonomous ENS function is to a large degree made possible by the prominent presence of interneurons . ‘ Interneurons are cells that add layers of complexity and sophistication that distinguish the central and enteric nervous systems from the … peripheral ganglia found outside the bowel .’( 1 , p45 )
This autonomous dynamic is to a significant degree affected by the microorganisms resident within our digestive realm and particularly within the large intestine . The microbiome of the gut wields a powerful influence on the balance and health of our digestive system as well as the health of our emotional landscape .( 5 ) This highlights the importance of encouraging our clients to consider healthy , wholefood nutrition . Interneurons make it possible for the ENS to process the information it receives in a similar manner to the brain . The nerves of the gut do not simply pass signals from sensory receptors via motor nerves to muscles , glands and blood vessels ; they also engage with significant message processing that directly influences the function of the GIT without involving the CNS .
JATMS | Autumn 2022 | 19