Intro to GI Physiology Flashcards
main function of GI tract
digestion and absorption of nutrients
Functional layers of SI
mucosal
submucosa
muscle layers - circular and longitudinal m.
serosa
extrinsic NS - ANS
cell bodies outside gut wall
intrinsic NS - ENS
cell bodies located within the wall of the gut
parasympathetic innervations
via the vagus and pelvic n. pre ganglionic - brainstem and sacral spinal cord post ganglionic - wall of organ Ach to nAchR - ganglion Ach to mAchR - target organ
sympathetic innervations
via n that run b/w the spinal cord and prevertebral ganglia and b/w these and the organs pre ganglionic - w/in spinal cord post ganglionic - inn ENS Ach to nAchR - ganglion NE to ADR alpha or beta - target organ
ENS
cell bodies within gut wall
innervated by myenteric and submucosal plexuses
integrating center - stimuli in wall of gut
can have effect w/o CNS input
CNS
vago-vagal reflex
modulate ENS responses
centers that control food intake are located in the brain
paracrine regulation
acts locally, diffusion over short distances
released by enteroendocrine cells or sensing cells
examples - somatostatin and histamine
somatostatin
secreted: by D cells of the GI mucosa
released: due to decrease in luminal pH
actions: inhibits gastric H secretion and secretion of other GI hormones
also secreted by hypothalamus and gamma cells of the exocrine panceas
histamine
stored and secreted: by enterochromaffin-like (ECL) cells in gastric glands in stomach
target: parietal cells
action: stimulate acid production
endocrine regulation
hormone peptides w/in EECs are released after stimulation
hormones enter portal circulation to liver to systemic circulation to target cells
gastrin
hormone family: gastrin-CCK
site of secretion: G cells of stomach
secretion stimuli: small peptides, AA, distention of stomach, vagal stimulation
actions: increase gastric H, stimulate growth of gastric mucosa
cholecystokinin (CCK)
hormone family: gastrin-CCK
site of secretion: I cells of duodenum and jejunum
secretion stimuli: small peptides, AA, FFA
actions: increase pancreatic enzymes and HCO3, contraction of the gallbladder, growth of exocrine pancreas and gallbladder, inhibit gastric emptying, paracrine signaling
secretin
hormone family: secretin-glucagon
site of secretion: S cells of duodenum
secretion stimuli: H in duodenum, FFA in duodenum
actions: increase pancreatic and biliary HCO3, decrease gastric H secretion, inhibit trophic effects of gastrin, paracrine signaling
Glucose-dependent insulinotropic peptide (GIP)
hormone family: secretin-glucagon
site of secretion: duodenum and jejunum
secretion stimuli: FFA, AA, oral glucose
actions: increase insulin release from pancreatic beta cells and decrease gastric H secretion
neural regulation
action of NT
requires an AP to release NT
NT binds to R on post synaptic cell
Ach
source: cholinergic neurons
action: smooth m contraction, sphincter relaxation, increase salivary, gastric and pancreatic secretions
NE
source: adrenergic neurons
action: smooth m contraction, sphincter relaxation, increased salivary secretions
VIP
source: n of mucosa and smooth m
action: relaxation of smooth m, increase intestinal and pancreatic secretions
GRP
source: n from gastric mucosa
action: increase gastric secretions
Enkephalins
source: n mucosa and smooth m
action: smooth m contraction, decrease intestinal secretions
Neuropeptide Y
source: n of mucosa and smooth m
action: relaxation of smooth m, decrease intestinal secretion
Substance P
source: co release w/ Ach
action: contraction of smooth m, increase salivary secretion
alpha melanocortin pathway
inhibit food intake and increase metabolism
alpha MSH released by POMC binds to MCR - 4 in second order neurons
neuropeptide Y pathway
increase feeding and storage of calories
hunger stimulates NPY which binds to Y1R
AGRP will act as antagonist to MCR - 4
ghrelin
initiate feeding response
source: endocrine cells in stomach
action: release of NPY, increase appetite, gastric motility, acid secretion, adipogenesis, insulin secretion
insulin
function: moves across BBB binds to POMC and NPY systems
action: decrease appetite and increase metabolism
CCK
source: I cells of duodenum
action: elicits satiety by decrease ghrelin and gastric emptying, increased gastric distention
PYY
appetite suppressor
source: L cells of ileum and coon
action: Y2 R on hypothalamus will inhibit NPY allows release of POMC
Leptin
appetive-supressing, negative feedback for regulation of food intake
source: cells in adipose tissue and endocrine cells in stomach binds to POMC and NPY systems
action: inhibition NPY pathway and stimulates POMC pathway, decrease appetite, increase metabolism, decreased ghrelin release
