Enteric Nervous System and Gut Hormones Flashcards
Describe the myelination pattern of the enteric nervous system fibres.
Unmyelinated
What do interneurons do?
Integrates lots of sensory inputs to generated a coordinated response.
State the two plexuses of the enteric nervous system and what they regulate.
Myenteric (Auerbach’s) Plexus - located between circular and longtudinal muscle - controls activity of muscularis externa- controls gut motor function
Submucosal (Meissner’s) Plexus - senses the environment of the lumen and controls blood flow, endothelial and endocrine function
*There are also minor plexuses including the deep muscular plexus inside circular muscle, and the ganglia supplying the biliary system and pancreas.
Where are the cell bodies of the sympathetic preganglionic fibres found?
In the thoracic and lumbar spinal cord
Describe where the sympathetic innervation of the gut comes from.
Midgut and foregut are innervated by thoracic splanchnic nerves
Rest of the gut is innervated by lumbar splanchnic nerves
Where are the cell bodies of the parasympathetic preganglionic fibres found?
In the brainstem and sacral spinal cord
Describe where the parasympathetic innervation of the gut comes from.
Most of the gut is innervated by branches of the vagus nerve (down to the level of the transverse colon)
The rest of the gut receives parasympathetic fibres from the pelvic nerves
In general, the ANS controls gut function via the enteric nervous system (through the two plexuses). What is an exception to this?
Sympathetic nervous system has direct control over blood flow to the GI tract. It does not have to go through the ENS to regulate blood flow.
Which afferents take information from the chemo and mechanoreceptors in the GI tract to the CNS?
Vagal and splanchnic afferents
Describe the structure of enteroendocrine cells.
They have a finger like protrusion that detects the environment of the lumen. They are located near blood vessels so they can release hormones into the blood. They can also talk directly to neurons via projections called neuropods.
Which cells release GIP-1, GLP-1, GLP-2, PYY and CCK?
GIP-1 = K cells
GLP-1 + GLP-2 + PYY = L cells
CCK = I cells
State some functions of the gastrointestinal endocrine system.
Regulation of mechanical processes of digestion
Regulation of chemical and enzymatic processes
Control of post-absorptive processes involved in the assimilation of digested food
Effects on growth and development of the GI tract (e.g. GLP-2 promotes small intestine growth)
What is the incretin effect?
Release of insulin following oral glucose is much greater than the release with IV glucose because of the incretins (e.g. GIP-1). The incretins potentiate the insulin response.
Describe paracrine actions of the GI hormones.
Somatostatin from the stomach can inhibit acid secretion by paracrine mechanisms.
Histamine release from stomach wall cells is a key physiological stimulus for the release of HCl from gastric parietal cells
Where is gastrin synthesised?
Pyloric Antrum and upper small intestine
