case 4 - cellular aspects of motility and interaction with commonly used drugs Flashcards
what are the principles of control
maximise absorption of nutrients
Achieved by:
regulating motility
Controlling secretion of digestive juices
(Very little control of absorption)
= excellent ‘scavenger,’ evolved when food was in short supply
what do mechanoreceptors sense
distension
what do osmoreceptors sense
osmolality
what do chemoreceptors sense
acidity and digestive productd
what does receptor activation cause
Hormones
Nerves: a) short reflexes and b) long reflexes
Paracrine transmission
You can’t compartmentalise these responses, these responses all happen together
what are the main sensory cell
enteroendocrine cells
what do microvilli do
sense lumen contents or movement
where do you have stored hormone transmitter
on the blood side of the lumen
what are incretins and what are exampls
GIP and GLP-1 are incretins which enhance insulin release by endocrine pancreas
what is motililin
important in inter-digestive motility
what are all GI hormones
all short chain peptides
Secreted by enteroendocrine cells found in the mucosa into the blood
Target various regions of the GI and glands
Many have effects on nervous system
what is CCK
secreted by the intestine
Affects the pancreas, gall bladder, stomach
Affects CNS - satiety
what is the enteric nervous system
100 million neurones in the myenteric and submucosal plexus
what are the excitatory substances in the ENS
substance P, gastrin releasing peptide and ACH
what are the inhibitory substances in the ENS
nitric oxide, vasoactive intestinal peptide
what is the short reflex
all neurones involved are part of the ENS
what are the extrinisic nerves
the autonomic nervous systems
features of the parasympathetic
preganglionic fibres synapse with ENS (which can release: ACH, SP, GRP, NO, VIP)
involved in long reflexes e.g vago-vagal (vagus = both afferent and efferent - 80% vagal fibres are sensory)
features of the sympathetic
post-ganglion fibres —> noradrenaline = decreased motility and decreased blood flow
- No major role in ‘day to day’ motility
what does CCK do
CCK causes contraction of the gall bladder
It also stimulates nerves and travels up to the dorsal vagal complex which can stimulate release of ACh - also cause contraction of the gall bladder
what happens at the Sphincter of Oddi
relaxes - NO/VIP
what is the main mechanoreceptor and chemoreceptor sensory cell of the GI tract
enterochromaffin cells - serotonin
what happens if these cells are stimulated
they release serotonin - 5HT
what does SERT do
removes 5HT to terminate signal
SERT mutations also linked to IBS
