L22: Neuroendocrine Control Flashcards
how do ENS neurons connect to other neurons inside and outside of the ENS
interneurons and afferent neurons
ENS sample gut content through ________
receptors
____ ENS neurons innervate target cells: smooth muscle, secretory and absorptive cells
efferent
T/F: In monogastric animals, the ENS can still coordinate digestion even after being severed from the brain
T
macronutrients are sensed by receptors expressed in ________ cells of the gut via their microvilli that extend into the gut lumen
enteroendocrine
afferent neurons of the ENS are ______ neurons and innervate muscle receptors in the ….
cholinergic
mucosa - chemoreceptors, mechanoreceptors
muscle layer - mechanoreceptors
what are the target organs of the efferent neurons of the ENS (inhibitory and excitatory)
smooth muscles
secretory cells
endocrine clles
what are the excitatory neurons of the ENS and what do they stimulate
ACh and Substance P
stimulate contraction of smooth muscles, secretion and enteroendocrine cell degranulation
what are the inhibitory neurons of the ENS and what do they inhibit
VIP, NO, ATP
- inhibit smooth muscle cells
- cause vasodilation
what does the myenteric (Auerbach’s) plexus innervate
longitudinal and circular smooth muscle layers; concerned with control of gut movements
what does the submucosal (Meissner’s) plexus innervate
glandular epithelium, intestinal endocrine cells and submucosal blood vessels; primarily concerned with control of intestinal secretion
_____ integrate extrinsic and intrinsic input and communicate bw myenteric and submucosal plexus
interneurons
what is post-operative ileus and what are the 3 categories of mechanism that can cause it
hypomotility or amotility of the GI tract in the absence of an obstruction
- neurogenic, inflammatory and pharmacologic
what are the pharmacological causes of post-operative ileus
- opioid peptides modulate GI motility through receptors on myenteric and submucosal ganlia that inhibit enteric neuron function
- exogenous administered opioids decrease transit in GI tract through mu 2 (opioid) receptors in myenteric plexus causing hypomotility
what is the main function of parasympathetic innervation within the ENS
promote digestion
- motility patterns
- net fluid secretion
- vasodilation
- entertoendocrine cell degranulation
what is the dominant extrinsic neural tone of the alimentary tract controlled by
parasympathetic innervation
what is the main function of the sympathetic innervation of the ENS
inhibit digestion & recover fluid volume
- stops motility
- increases net fluid abs
- vasoconstriction
ENS can operate w/out CNS input in ______ animals
monogastric
what is the release stimulus for gastrin
- anticipation of food, stomach distension, presence of proteins/peptides in stomach
what inhibits gastrin release
- HCl
- somatostatin
- secretin
- GIP
what are the functions of gastrin
- stimulates K+/H+ ATPase pump activity of parietal cells
- stimulates release of histamine from enterochromaffin like cells
- histamine stimulates cAMP mediated insertion of K+/H+ ATPase pumps into the apical membrane of parietal cells
- effects gastric motility
- minor effect on pancreas acinar cells
somatostatin is a peptide hormone synthesized by enteroendocrine ____ cells of the _____, ____ cells in the endocrine pancreas and in the hypothalamus
D cells of stomach
endocrine
function of somatostatin
directly and indirectly inhibits gastric acid secretion
how does somatostatin directly vs indirectly inhibit gastric acid secretion
Directly: inhibits adenylyl cyclase of parietal cells which antagonizes the stimulatory effects of histamine
Indirectly: inhibits G cells, ECL cells and parietal cells
what is the release stimuli for somatostatin
very low pH in antrum and CCK
somatostatin does the opposite of ?
gastrin
when is somatostatin release blocked and how
- during cephalic and gastric phase, the release is blocked by vagal stimulation
what are the two main functions of secretin
- pH regulation by promoting pancreatic and biliary bicarbonate secretion and bicarbonate secretion in duodenum epithelial cells
- reduces gastric secretions by blocking G cells
secretin release stimuli
entry of fat and acid (protons) into duodenum, stimulates S cells
what inhibits Cholecystokinin (CCK)
somatostatin
what cells produce CCK and where
enteroendocrine I cells of dudodenal and jejunal mucosa and neurons in the ileum and colon
what are the functions of CCK
- enzyme secretion from pancreas
- contraction of gall bladder to release bile
- activation of D cells (somatostatin)
what causes the release of Cholecystokinin (CCK)
presence of FAs/AAs/peptides in chyme entering the duodenum
what cells produce Gastric inhibitory peptide (GIP) and where
neuroendocrine K cells of duodenal and jejunal mucosa
what stimulates the release of GIP
glucose and FAs in chyme entering duodenum
what are the functions of GIP
- inhibit parietal acid secretion
- increase insulin release from endocrine pancreas
what are the functions of motilin
increase gastric emptying and somatostatin release from pancreas
what cells produce motilin and where
neuroendocrine Mcells of duodenal and jejunal mucosa
what is the release stimuli for Motilin
increased pH in duodenum
also spontaneously released during interdigestive phase
what is Erythromycin
a motilin receptor agonist; marolide antibiotic
what are the side effects of the antibiotic Erythromycin
enhances gastric emptying
side effects: D+, nausea, abdominal pain, V+
what happens to salivary gland activity during the intestinal phase
cease activity
what happens to gastric secretion activity during the inestinal phase
secretions decrease, caused by neural and humoral control
* neural: removal of stimuli from stomach
* humoral: somatostatin is synthesized and released from D cell, gastrin and CCK activate D cells, further increasing somatostatin
somatostain inhibits activity of parietal and ECL cells
how do endocrine control systems affect secretions into the GI tract during the interdigestive phase (when stomach & SI are empty)
- gastrin release reduced
- somatostatin inhibits gastric and pancreatic secretions and CCK release
- motilin stimulates contraction of gut smooth muscle
what is Gastrinoma/Zollinger-Ellison Syndrome
rare neuroendocrine tumor that arises from malignant transformation of somatostatin secreting delta cells of the endocrine pancrease to gastrin producing cells
gastrin stimulates secretion of gastric acid –> gastrinoma –> peptic ulcers, D+/steatorrhea/hypokalemia
steatorhhea = abnormal amount of lipids in feces
