Digestion: What Governs Digestion; The Enteric Nervous System

Question 1

The enteric nervous system

Answer 1

The enteric nervous system is the ‘Brain of the gut’ and extends from the mouth to the anus.
* The key components of the enteric nervous system are two nerve plexuses, which are embedded in the wall of the digestive tract: this includes the myenteric and submucosal plexus.
Enteric = intestines, plexus = network of nerves, sub = below, mucosal = mucosal layer, my(o) = muscle

Question 2

The enteric nervous system: Autonomic regulation

Answer 2

The enteric nervous system function independently but is regulated by the ANS.
* The myenteric plexus governs GIT peristalsis
* The submucosal plexus controls the release of digestive secretions such as gastric juice and digestive enzymes
o M for my enteric = motility
o S = Submucosal = secretion
Parasympathetic (Rest and digest): Vagus nerve
* Increase muscular activity (Peristalsis = Myenteric plexus)
* Increase glandular Secretions (Submucosal plexus)
Sympathetic (fight or flight) i.e. stress
* Decrease muscular activity (Peristalsis = Myenteric plexus)
* Decrease glandular Secretions (Submucosal plexus)

Question 3

The Vagus Nerve

Answer 3

The Vegas nerve is crucial in stimulating activity in the digestive system (the enteric nervous system).
* The Vegas nerve, or the 10th cranial nerve, extends from the head and travels through the thorax and diaphragm, where it innervates the digestive organs, connecting the brain and gut
* Vagus nerve activity has suppressed during periods of chronic stress and is enhanced with diaphragmatic breathing. This explains how stress inhibits digestion
* Vagus nerve activity directly stimulates the myenteric & submucosal plexus & hence increases digestive motility & digestive secretions
Motility = independent movement

Question 4

The Gut– Brain Axis

Answer 4

The brain and gut develop from the same part of human embryonic tissue and therefore share many nerve endings and chemical transmitters.
* Nearly every chemical that controls the brain’s been identified in the GIT
* Serotonin plays a role in peristalsis, secretion, sensation with over 95% of it produced in that GIT. Furthermore, due to its association with mood, this explains a possible link between poor gut health & depression
* Dysbiosis can also influence serotonin manufacture in the gut through affecting the availability of tryptophan and co-factors (needed for its production). For example, antibiotic use can affect mood negatively