Regulstion of gut Flashcards
What is the enteric nervous system?
Intrinsic nervous system
- wall of the GI tract contains millions of neurons
- independently controls GI
- integrates motor and secretory activities of GI
What might arise as a result of enteric dysfunction?
What might cause it?
Inflammation
Irritable bowel syndrome
Post-operative injury
Ageing
What does the enteric nervous system regulate?
Motility
Blood flow
Water and electrolyte transport
Secretion
Absorption
Which neurons are used?
Standard
- Sensory
- Motor
- Interneurons
- Decides magnitude of stimulus - not just a refluex
Where are the main nerve plexuses located?
Cuts through layers
- Myenteric plexus
- between longitudinal and circular muscle
- for gut motor function
- between longitudinal and circular muscle
- Submucosal plexus
- underneath epithelia
- for epithelial, blood flow and endocrine function
- underneath epithelia
- Deep muscular plexus
- in the circular muscle
What does the autonomic nervous system regulate?
Smooth muscle, cardiac muscle and glands
How are the foregut and midgut sympathetically innervated?
Thoracic splanchnic nerves
How is the hindgut sympathetically innervated?
Lumbar splanchnic nerves
What is the point of sympathetic nerve activation?
Inhibit GI system activity
How are the foregut and midgut parasympathetically innervated?
Cranial nerves
How is the hindgut sympathetically innervated?
Pelvic nerves
What are the main autonomic neurotransmitters?
NA - symp
ACh - para
How does the autonomic nervous system interact with the GI?
Synapses to myenteric plexuses via enteric system
What is the point of parasympathetic nerve activation?
Stimulate GI activity
WHat is intramural plexus?
Intramural plexus
- plexus found in ENS
What is intrinsic and extrinsic innervation of GI?
Intrinsically?
- neurons of the ENS
Extrinsically
- afferent - pain, nausea
- efferent - coordination of para and symp
The nerve fibres of the PNS and SNS are long or short? - pre synapse and post
PNS
- LONG PREGANGLIONIC
- SHORT POSTGANGLIONIC
SNS
- SHORT PREGANGLIONIC
- LONG POSTGANGLIONIC
What is the function of the GI endocrine system?
Not necessarily endocrine organ but contains endocrine cells that can produce hormones
Hormone production which can act as neurocrine or paracrine factors
- released by nuclei
Regulation of the mechanical, chemical and enzymatic processes of digestion
How might hormones be released?
Apical membrane of cell has sensors that check contents of gut lumen and then allow stimulation of hormone release from basal.
Which hormones do L-cells secrete?
GLP-1 - glucagon like peptide
- satiety
What is GLP-2 required for?
Growth and development of GI tract
Give an example of paracrine action within the GI system
Histamine released form stomach wall cells is s key stimulus for HCl secretion by parietal cells
What is the function of gastrin? What stimulates and inhibits it?
Stimulates gastric acid release
- stimulated by
- AA and peptides ins tomach
- Gastric distension
- Vagus nerve
- inhibited by
- fall of stomach pH to below 3
Function of somatostatin and
Synthesised in D cells of gastric duodenal mucosa
Stimulated by
- mixed meal entry
Inhibits
- gastric secretion
- motility
- hormone release
- growth and proliferation
Why is an analogue used instead of somatostatin?
What is somatostatin used for?
Neuroendocrine tumours
- ## longer half life - longer effect
Function of secretin and where made?
S cells of upper duodenum
Stimulus
- pH drop
Causes
- bicarbonate secretion by pancreas
- inhibits gastric acid and emptying
Function of CCK and where?
Cells in the small intestine
Stimulated by
- fat and peptides in upper small intestine
Independent of vagus
stimulates
- pancreatic enzyme release
- delays gastric emptying
- gallbladder contraction
- decreases food intake
GIP function and made>
Mucosal K cells
Made when meal ingested
Stimulates insulin secretion and antagonists cause lower insulin release
PYY function and where made?
Made in ileum
- released from L cells
Reduces intestinal motility, gallbladder contraction
exocrine secretion of pancreas
Inhibits intestinal fluid and electrolyte secretion AND food intake
