functions of GIT
- reduce food size
- absorption and excretion
layers of the gut wall lumen outwards
- mucosal
- submucos
- muscularis
- aerosol
gut muscularis layers
inner circular
outer longitudinal
gut epithelial shedding
replaces every 5d
absorptive cells in gut
near surface
in contact with intestinal crypts
secretory cells in gut
in crypts or glands
outflow of fluid protects from infection
macroscopic gut blood supply
~25% of CO at rest
microscopic gut blood supply
dense capillary networks
ENS structures
- submucosal plexus
- myenteric plexus
submucosal plexus
controls mucosa
- secretion
- absorption
- villi movement
myenteric plexus
controls muscularis/motility
why is GIT regulation phased
it has different functions at different phases of digestion.
cephalic phase
preparation
- detect: food
- prepare: the GIT lumen
gastric phase
digestive
- detect: distension, pH, nutrients
- prepare: send signals via ENS, CNS, hormones
intestinal phase
controlled release
- detect: stretch, acid, osmolarity, nutrients
- prepare: ENS, CNS, hormones
neurotransmitters in the GIT
stimulatory: Acetylcholine
inhibitory: NO
how big are GIT smooth muscle cells
5-20uM diameter
~500uM long
how many GIT smooth muscle cells interact with each other
each with ~10 surrounding cells via gap and adherens junctions
interstitial cells of cajal membrane potential
-40 to -80mV
pacemakers of the GIT
interstitial cells of cajal membrane
where are interstitial cells of cajal located in the stomach and small intestine
in the smooth muscle layer close to the myenteric plexus
where are interstitial cells of cajal located in the colon
in the boundary between the muscle layer and submucosal layer
mechanisms of GIT phasic contraction upregulation
- depolarisation of cell membrane
- pharmochemical contraction
mechanisms of GIT phasic contraction downregulation
- hyperpolarisation of smooth muscle cell membrane
- increased MLCP
- inhibition of ENS and CNS
