general introduction and oral eosphageal response to a meal Flashcards
General tract from mouth to anus
- mouth and esophagus - 8-10 sec 2. stomach - 1-3 hours 3. small intestine - 7-9 hours 4. large intestine - 25-30 hours 5. rectum and anus - 30-120 hours
Bristol stool scale
7 types of stool assessment of transit time in GI tract
optimal delivery rate, maintaining barrier function the above are mediated by
- extrinsic nerves 2. intrinsic nerves 3. neurocrines 4. paracrines 5. hormones
Extrinsic nerves
autonomic nervous system (ANS) - sympathetic - parasympathetic
intrinsic nerves
enteric nervous system (ENS)
neurocrine
signals released from nerve endings
paracrine
released from specialized mucosal cell some are involved in immune modulation
endocrine hormones
released into systemic circ. - return to exert action
parasympathetic and sympathetic effect on: motility sphincter tone secretion vascular resistance
Para - increase motility - decrease the sphincter tone - increase secretion - no effect on vascular resistance (blood flow to gut) sym - decrease motility - increase sphincter tone - decrease secretion (except salivary glands) - increase vascular resistance (vasocontrict blood flow to gut)
two major nerve plexuses
- myenteric (Auerbach’s) plexus 2. submucosal (Meissner’s) plexus these are collections of neuronal ganglia and their fibers the above is Enteric Nerve System (ENS) and can be viewed as third branch of AUTOMATIC NERVOUS SYSTEM
nuerotransmitters of ENS
- acetylcholine 2. norepinephrine 3. peptides
NANCs
non adrenergic, non cholinergic neurons
parasympathetic and sympathetic nerve innervation of the gut
postganglionic sympathetic fiber - direct projection to smooth muscle of gut wall, b-vessel, and enteric neurons in both plexus parasympathetic fiber - project to enteric neuron, myenteric plexus - indirect (para affect via ENS neurons para and sym modulate each other through ENS
3 types of neurons in ENS
- sensory neurons 2. interneurons 3. motor neurons
sensory neuron
monitor changes, input to interneurons and CNS
interneurons
relay signal - activate or inhibit motor neurons interneurons of both plexuses synapse
motor neurons
simulate or inhibit smooth m. and secretion
program libraries
ENS neuronal circuits operate autonomously
short reflex
peristaltic reflex program library based
long reflex
i.e. Vago-vagal reflex autonomic input modify program libraries to produce long reflex
vago-vagal reflex
sensory input -> vagal afferent fiber -> CNS -> resulting coordinated alteration -> vagal efferent fibers -> affect all regions of the gut
major neurotransmitters of GI
- acetylcholine (ACh) - parasympathetic and enteric 2. substance P - parasympathetic and enteric 3. nitric oxide (NO) - parasympathetic and enteric 4. norepinephrine (NE) - sympathetic 5. neuropeptide Y - sympathetic and enteric 6. vasoactive Intestinal polypeptide (VIP) - enteric
acetylcholine (ACh) (GI nervous sys, and function)
- parasympathetic and enteric - increase motility - increase secretion released from autonomic fibers -> effect activity of enteric neuron -> release different NT
substance P (GI nervous sys, and function)
- parasympathetic and enteric - increase motility
nitric oxide (NO) (GI nerve sys, and function)
- parasympathetic, enteric - muscle relaxation
norepinephrine (NE) (GI nerve sys, and function)
- sympathetic - decrease motility, blood flow and secretion released from autonomic fibers -> effect activity of enteric neuron -> release different NT