2. GI Part 7 Flashcards
GI tract functions (5)
- secretion
- digestion
- absorption
- motility
- storage
what does the GI tract supply the body with (3)
- nutrients
- electrolytes
- water
how does the GI tract coordinate its functions (2)
- intrinsic control system
2. extrinsic control system
what is the intrinsic control system
located in wall of GI tract
enteric nervous system, GI hormones
what is the extrinsic control system
located outside the GI tract
vagus and splanchnic nerves, non-GI hormones
describe the enteric nervous system
a component of the autonomic nervous system
located within the GI wall
enables autonomic regulation of GI functions
describe plexus submucosa (Meissner)
located between submucosa and circular musculature
regulates mucus secretion and food absorption
describe plexus myenteric (Auerbach)
located in muscularis external, between longitudinal and circular musculature
control of the muscular activity (tone and contractions rhythm)
how are cells arranges in the enteric nervous system
how are cells connected
how do cells work together
cells are arranged in bundles of as many as 1000 parallel fibers (longitudinal or circular arrangement)
within each bundle, msucle fibers are electrically connected with one another through gap junctions
each bundle of smooth msucle fibers is partially separated from the next by loose connective tissue, but the bundles fuse with one another at many points and works as a syncytium
how are enteric neurons different from typical neurons
unlike typical neurons, enteric neurons secrete their neurotransmitter from varicosities or bulge like structures on often lengthy axonal collaterals or branches
the effect of an enteric neuron is spread to affect a wide area
what do sensory nerve cells do in ENS
detect changes and stimuli and regulate function
axons go to other enteric nerve cells and to the CNS
mechanosensitive cells (mechanoreceptors) in the ENS
recognize stretching of intestinal wall or volume changes (intraluminal pressure)
induce a response – gastric phase of gastric acid secretion
chemo sensitive cells (chemoreceptors) in the ENS
detect presence of nutrients in the GI lumen, changes in osmolarity, changes in pH
induce a response – sensibilization of enteroendocrine cells
interneurons in the ENS
process signals coming from other nerve cells or form the CNS and propagate them to other neurons
motor neurons of the ENS
induce a change in the GI tract in response to a stimulus
types of motor neurons in the ENS and their locations
muscle motor neurons – primarily located in myenteric plexus
secreto motor neurons – primarily located in submucosa plexus
vaso motor neurons – located in both plexuses
what does NANC mean
non-adrenergic, non-cholinergic neurotransmitters secreted by enteric neurons
examples of NANC (3)
nitric oxide – inhibitory substance that reduces motility of GI tract
VIP – inhibits gastric secretion and causes vasodilation and relaxation of smooth muscle sphincters
Substance P – excitatory substance, increases secretion and motility of the GI tract
interaction of CNS and ENS – outer (extrinsic) innervation comprises (3)
parasympathetic fibers
sympathetic fibers
visceral afferent fibers
ENS – parasympathetic neurotransmitter and what it does
uses Ach which stimulates many GI functions
ENS – sympathetic neurotransmitter and what is does
uses noradrenaline which has an inhibitory effect on the GI tract
neurons with origin in medulla oblongata through the vagus nerve go where
oesophagus stomach small intestine ascending colon pancreas gallbladder liver
neurons with origin in the sacral spinal cord through the pelvic nerve go where
descending colon
distal parts of the GI tract
ENS parasympathetic postganglionic neurotransmitters
excitatory – acetylcholine
inhibitory – NANC substances, VIP, NO
where do sympathetic nerve fibers of the ENS exit
thoracal and lumbar segments of the spinal cord
length of sympathetic pre and post ganglionic axons of the ENS
preganglionic neurons have short axons
postganglionic neurons have long axons extending to target organs
what is the sympathetic ganglion chain
on either side of the spinal cord, many sympathetic ganglia are arranged like a string
what is the sympathetic postganglionic neurotransmitter
noradrenaline – inhibitory
what are the 2 types of electrical waves and which one produces contractions
slow waves – don’t produce contractions
spikes – produce contractions
describe slow waves
not action potentials
slow undulating changes in the resting membrane potential
frequency – 3-12 per minute (depending on location)
where do slow waves originate
specialized smooth msucle cells – interstitial cells of Cajal (ICC)
what as ICC considered to be
electrical pacemakers for smooth msucle cells
similar to Purkinje cells in the heart
what do ICC form
networks with each other and are interposed between the smooth msucle cells
what is the origin of the slow wave
ICC undergo cyclic changes in membrane potential due to unique ion channels that periodically open and produce currents
what are spike potentials and when do they occur
true action potentials
occur automatically when the resting membrane potential of the GI smooth msucle becomes more positive than -40 mV
when do slow waves induce an action potential
only when they reach smooth muscle cells that are (or were previously) sensitized
when do spike potentials appear
each time the peaks of the slow waves become more positive than -40 mV
what makes the frequency of the spike waves greater, how does this affect contractions
the higher the slow wave potential rises, the greater the frequency of the spike potentials and the higher the contractions
