Introduction to GI Function & Regulation Flashcards
main functions of the GI system
conveys nutrients, water, and electrolytes into the body
boundary between external and internal environment
oropharyngeal cavity function
prehension/initial intake
reduction (mechanical and enzyme)
mix with saliva
transport/swallow
esophagus main function
transport
stomach function
storage/delivery rate control
digestion
small intestine function
digestion and absorption
monitor luminal content
large intestine function
absorption
fermentation
storage
what are the 5 main functions of the GI tract as a whole
motility, storage, secretion, digestion, absorption
cleft palate renders ___ movement during suckling ineffective
oropharyngeal
what occurs if the nasopharynx is not closed off (cleft palate)?
nasal regurgitation
how does the palate normally form?
progressive fusion between lateral palatine processes
what is atresia ani?
congenital abnormality where the anus is closed off (stenosis)
describe the types of atresia ani/coli
list the layers of the esophagus, stomach, SI, and large intestine
mucosa
submucosa
2 muscle layers
serosal layer
what does the mucosa layer consist of?
epithelium, lamina propria, muscularis mucosa
describe morphology of epithelium at different GI segments
esophagus = multilayer stratified squamous
stomach, SI, LI = columnar single layer
how is accumulation of defects prevented in the GI tract?
constant and fast renewal of epithelium
where do stem cells originate?
neck/crypt area to migrate up/down for differentiation
what do stem cells differentiate into?
enterocytes, goblet cells, enteroendocrine, paneth cells
GI functions are controlled by a ___ and ___ control system
intrinsic and extrinsic
what is the ENS?
intrinsic nervous system
where are ENS neurons located?
between inner circular and outer longitudinal layer of muscularis externa (myenteric)
AND
within submucosa (submucosal)
myenteric plexus innervation
N to longitudinal and circular smooth muscle layers
mainly gut movement
submucosal plexus innervation
N to glandular epithelium, intestinal endocrine cells, and submucosal blood vessels
mainly intestinal secretions
what are circuits?
synaptically interconnected networks of neurons that connect receptors with target organs
receptors of mucosa
mechano-
chemo-
temperature receptors
gut wall receptors
mechanoreceptors
muscosa target organs
glands, enteroendocrine cells
gut wall target organs
muscle, blood vessels
what are varicosities?
structures located on axons, release neurotransmitter
what’s an advantage of varicosities in ENS?
activates a broader area around axons vs focused at end of axon
describe the motor function of ENS
N muscles and sphincters
causes contract/relaxation, controlling motility through the system
describe the sensory ENS function
detect lumen pH, temperature, pressure
interstitial cells of cajal (ICC)
specialized smooth muscle cells
act as pacemaker to modulate phasic contractile activity
have gap junctions
what are the “slow waves” of the GI tract?
regular oscillations in membrane potential due to ICC’s self generating depolarizing rhythm
what nervous system makes up the intrinsic system?
ENS
what nerves make up the extrinsic system?
vagus and splanchnic nerves
sympathetic nervous system effect on GI
NOR = decrease motility, increase sphincters, decrease secretions
NO and VIP (vasoactive intestinal peptide)
parasympathetic nervous system effect on GI
N secretory cells in glands, smooth muscle of blood vessels, myenteric plexus
VAGUS NERVE
ACh increases motility, decreases sphincters, increase secretions
what’s involved in the sympathetic NS for GI?
NO
VIP (vasoactive intestinal peptide)
splanchnic nerve
what’s involved in the parasympathetic NS for GI?
ACh
substance P
vagus nerve
the splanchnic nerve contains sympathetic ___ and spinal ___
sympathetic efferent
spinal afferent
what do splanchnic afferents carry?
info about distension of gut wall, presence of noxious chemicals, inflammation
splanchnic efferents are ___ in nature
INHIBITORY
what hormone decreases motility and glandular secretions?
norepinephrine
what does the vagus nerve contain?
sensory afferents
motor efferents
what does vagus innervate?
abdominal viscera and pharyngeal mucosa
vagus/parasympathetic control is typically ___ in nature
STIMULATORY
what hormone increases gut blood flow, motility, and gland secretions>
ACh
what is a vagotomy?
Sx where one or more branches of the vagus nerve are cut
vagotomy usually ___ rate of gastric secretion and motility
reduces
vagotomy can reduce problems related to ___ gastric acid production in ___ animals
excessive
monogastric
damage to the vagus causes malfermentation in ___
ruminants
what are the endocrine secretions of the intrinsic system?
CCK, gastrin, secretin, GIP, motilin
enteroendocrine cells sense ___ on their ___ side
sense gut content on their apical side
what do enteroendocrine cells release from their basal side?
hormones, neuroactive substances (neurocrines), paracrines, autocrines
what are the four routes of intrinsic endocrine control of the GI tract?
endocrine
neurocrine
paracrine
autocrine
which intrinsic endocrine route is this?
endocrine
which intrinsic endocrine route is this?
neurocrine
which intrinsic endocrine route is this?
paracrine
which intrinsic endocrine route is this?
autocrine
enteroendocrine cells of the stomach and SI produce which hormones?
gastrin, secretin, CCK, GIP, motilin
which endocrine cell produces gastrin?
G cell
which endocrine cell produces CCK?
I cells
which endocrine cell produces secretin?
S cells
which endocrine cell produces motiliin?
M cells
which endocrine cell produces GIP?
K cells
what are some examples of neuroactive substances?
NO
substance P
VIP
enkephalines
where are neuroactive substances released?
near afferent nerve terminals into lamina propria
which endocrine secretions are part of extrinsic system?
aldosterone
what does aldosterone do regarding GI?
stimulates Na and water reabsorption in colon via ENac sodium channels
increases reabsorption in salivary glands
aldosterone ___ Na absorption in the colon and salivary duct
increases
glucocorticoids ___ activity of Na/K ATPase
increase
