Intro to GI Physiology

Question 1

main function of GI tract

Answer 1

digestion and absorption of nutrients

Question 2

Functional layers of SI

Answer 2

mucosal
submucosa
muscle layers - circular and longitudinal m.
serosa

Question 3

extrinsic NS - ANS

Answer 3

cell bodies outside gut wall

Question 4

intrinsic NS - ENS

Answer 4

cell bodies located within the wall of the gut

Question 5

parasympathetic innervations

Answer 5

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

Question 6

sympathetic innervations

Answer 6

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

Question 7

ENS

Answer 7

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

Question 8

CNS

Answer 8

vago-vagal reflex
modulate ENS responses
centers that control food intake are located in the brain

Question 9

paracrine regulation

Answer 9

acts locally, diffusion over short distances
released by enteroendocrine cells or sensing cells
examples - somatostatin and histamine

Question 10

somatostatin

Answer 10

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

Question 11

histamine

Answer 11

stored and secreted: by enterochromaffin-like (ECL) cells in gastric glands in stomach

target: parietal cells
action: stimulate acid production

Question 12

endocrine regulation

Answer 12

hormone peptides w/in EECs are released after stimulation

hormones enter portal circulation to liver to systemic circulation to target cells

Question 13

gastrin

Answer 13

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

Question 14

cholecystokinin (CCK)

Answer 14

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

Question 15

secretin

Answer 15

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

Question 16

Glucose-dependent insulinotropic peptide (GIP)

Answer 16

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

Question 17

neural regulation

Answer 17

action of NT
requires an AP to release NT
NT binds to R on post synaptic cell

Question 18

Ach

Answer 18

source: cholinergic neurons
action: smooth m contraction, sphincter relaxation, increase salivary, gastric and pancreatic secretions

Question 19

NE

Answer 19

source: adrenergic neurons
action: smooth m contraction, sphincter relaxation, increased salivary secretions

Question 20

VIP

Answer 20

source: n of mucosa and smooth m
action: relaxation of smooth m, increase intestinal and pancreatic secretions

Question 21

GRP

Answer 21

source: n from gastric mucosa
action: increase gastric secretions

Question 22

Enkephalins

Answer 22

source: n mucosa and smooth m
action: smooth m contraction, decrease intestinal secretions

Question 23

Neuropeptide Y

Answer 23

source: n of mucosa and smooth m
action: relaxation of smooth m, decrease intestinal secretion

Question 24

Substance P

Answer 24

source: co release w/ Ach
action: contraction of smooth m, increase salivary secretion

Question 25

alpha melanocortin pathway

Answer 25

inhibit food intake and increase metabolism

alpha MSH released by POMC binds to MCR - 4 in second order neurons

Question 26

neuropeptide Y pathway

Answer 26

increase feeding and storage of calories
hunger stimulates NPY which binds to Y1R
AGRP will act as antagonist to MCR - 4

Question 27

ghrelin

Answer 27

initiate feeding response

source: endocrine cells in stomach
action: release of NPY, increase appetite, gastric motility, acid secretion, adipogenesis, insulin secretion

Question 28

insulin

Answer 28

function: moves across BBB binds to POMC and NPY systems
action: decrease appetite and increase metabolism

Question 29

CCK

Answer 29

source: I cells of duodenum
action: elicits satiety by decrease ghrelin and gastric emptying, increased gastric distention

Question 30

PYY

Answer 30

appetite suppressor

source: L cells of ileum and coon
action: Y2 R on hypothalamus will inhibit NPY allows release of POMC

Question 31

Leptin

Answer 31

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