Enteric Nervous System Flashcards
Enteric nervous system fxn
Sites with preganglionic parasympathetic fibers synapse with post neurons that innervate smooth muscel
Many of the symp post gnaglionic synapse onto neurons in wall of the gut
Different types of regulation
Hormonal - from entero-endocrine cells
Neuroendocrine regulation - NT/hormones from neurons
Neural - from ANS and PNS
Serotonin and Motilin
Serotonin - stimulates intrinsic afferents which send impulses into intrinsic nervous system and activate motor neurons
Motilin - stimulates constraction of duodenum and stomach antrum
Cephalic
Gastric
Intestinal
Interdigestive phases
What predominates
Extrinsic/nerual
Mostly intrinsic/hromone gastrin
Mostly intrinsic/secretin and CCK
Intrinsic and local reflexes ENS
Waves of contraction initiated by pacesetter cells
Interdigestive phase
Post-prandial
Low levels of secretions
Minimal phasic contractions but low level tone EXCEPT for spincters where tone is high
Cephalic phase
Facial and GP nerves for salivation
Vagus - chief cells for pepsinogen, G cells for gastrin, ECL for histamine, parietal for HCL
Minimal effects on lower GI tract but some weak motility and scretory
Gastric phase
Arrival of food in stomach
Mostly hormonal control
Gastric secretion inc by distension and chemical nature of chyme (AA and short polypeptides)…stimule G cells for gastrin, chief cells pepsinogen, ECL cells histamine which in turn inc HCL
Positive feedback - as more HCl and pepsinogen secreted, more polypeps and AA release
Negative - as pH dec, inhibits G cell release of gastrin
Intestinal phase
Inhibits gastric activity when chyme enters SI
Mostly hormonal
Arrival of chyme inc osmolality nd distension
Activates sensory neurons of vagus and produces inhib neural reflex upstream - inhibit gastric motility and secretion
Downstream excitatory responses and inc secretions of pancrea,s liver, and intestine
Hormones - inhibit gastric activiy…CCK has week effect on gastrin
Contractions of GI smooth muscle
Occur automatically in response to endogenous pacemaker activity
Depolarizations of interstitial cells of Cajal control rhythm of contracyion
Featurees of smooht muscle
Myogenic rhythm that generates cyclic depolarization
Small cells interconnect by gap jxns (nexus)
Depolarization and spread for coordinated contraction
High actin/myosin ration allows smooth muscle to wokr over very wide lengths
Structure of smooth muscle cells
Dense bodies of the intracellular skeleton
Small fibers so EC calcilum works
Inc SA/V ratio
inc Actin/myosin
Varicosities
Mech of smooth muscle
More neergy eff Always some cross-bridge maintenace Myosin-linked regulation Not a fast velocity and no twitch Stress relaxation
Electricla smooth muscle
BER influenced by ANS innervation of interstitial cells of Cajal
EPSPS are long acting
SNS and PNS influence
SNS
Mostly adrenergic and catecholaminergic
Most terminate and intramural plexus and cause inhibition EXCEPT those that activate muscularis mucosa and inc scretion of mucus for protection
PNS
Vagus nerve
Pelvic nerve from hypogastric plexus
Mostly cholinergic
Excist muscle contraction and inc secretoary
Inhibit LES and stomach (VIP and NO)
Inhibit pyloric sphincter and IAS (non-cholinergic)
