L22: Neuroendocrine Control

Question 1

how do ENS neurons connect to other neurons inside and outside of the ENS

Answer 1

interneurons and afferent neurons

Question 2

ENS sample gut content through ________

Answer 2

receptors

Question 3

____ ENS neurons innervate target cells: smooth muscle, secretory and absorptive cells

Answer 3

efferent

Question 4

T/F: In monogastric animals, the ENS can still coordinate digestion even after being severed from the brain

Answer 4

T

Question 5

macronutrients are sensed by receptors expressed in ________ cells of the gut via their microvilli that extend into the gut lumen

Answer 5

enteroendocrine

Question 6

afferent neurons of the ENS are ______ neurons and innervate muscle receptors in the ….

Answer 6

cholinergic
mucosa - chemoreceptors, mechanoreceptors
muscle layer - mechanoreceptors

Question 7

what are the target organs of the efferent neurons of the ENS (inhibitory and excitatory)

Answer 7

smooth muscles
secretory cells
endocrine clles

Question 8

what are the excitatory neurons of the ENS and what do they stimulate

Answer 8

ACh and Substance P
stimulate contraction of smooth muscles, secretion and enteroendocrine cell degranulation

Question 9

what are the inhibitory neurons of the ENS and what do they inhibit

Answer 9

VIP, NO, ATP
- inhibit smooth muscle cells
- cause vasodilation

Question 10

what does the myenteric (Auerbach’s) plexus innervate

Answer 10

longitudinal and circular smooth muscle layers; concerned with control of gut movements

Question 11

what does the submucosal (Meissner’s) plexus innervate

Answer 11

glandular epithelium, intestinal endocrine cells and submucosal blood vessels; primarily concerned with control of intestinal secretion

Question 12

_____ integrate extrinsic and intrinsic input and communicate bw myenteric and submucosal plexus

Answer 12

interneurons

Question 13

what is post-operative ileus and what are the 3 categories of mechanism that can cause it

Answer 13

hypomotility or amotility of the GI tract in the absence of an obstruction

• neurogenic, inflammatory and pharmacologic

Question 14

what are the pharmacological causes of post-operative ileus

Answer 14

• opioid peptides modulate GI motility through receptors on myenteric and submucosal ganlia that inhibit enteric neuron function
• exogenous administered opioids decrease transit in GI tract through mu 2 (opioid) receptors in myenteric plexus causing hypomotility

Question 15

what is the main function of parasympathetic innervation within the ENS

Answer 15

promote digestion
- motility patterns
- net fluid secretion
- vasodilation
- entertoendocrine cell degranulation

Question 17

what is the dominant extrinsic neural tone of the alimentary tract controlled by

Answer 17

parasympathetic innervation

Question 18

what is the main function of the sympathetic innervation of the ENS

Answer 18

inhibit digestion & recover fluid volume
- stops motility
- increases net fluid abs
- vasoconstriction

Question 19

ENS can operate w/out CNS input in ______ animals

Answer 19

monogastric

Question 20

what is the release stimulus for gastrin

Answer 20

• anticipation of food, stomach distension, presence of proteins/peptides in stomach

Question 21

what inhibits gastrin release

Answer 21

• HCl
• somatostatin
• secretin
• GIP

Question 22

what are the functions of gastrin

Answer 22

• stimulates K+/H+ ATPase pump activity of parietal cells
• stimulates release of histamine from enterochromaffin like cells
• histamine stimulates cAMP mediated insertion of K+/H+ ATPase pumps into the apical membrane of parietal cells
• effects gastric motility
• minor effect on pancreas acinar cells

Question 23

somatostatin is a peptide hormone synthesized by enteroendocrine ____ cells of the _____, ____ cells in the endocrine pancreas and in the hypothalamus

Answer 23

D cells of stomach
endocrine

Question 24

function of somatostatin

Answer 24

directly and indirectly inhibits gastric acid secretion

Question 25

how does somatostatin directly vs indirectly inhibit gastric acid secretion

Answer 25

Directly: inhibits adenylyl cyclase of parietal cells which antagonizes the stimulatory effects of histamine

Indirectly: inhibits G cells, ECL cells and parietal cells

Question 26

what is the release stimuli for somatostatin

Answer 26

very low pH in antrum and CCK

Question 27

somatostatin does the opposite of ?

Answer 27

gastrin

Question 28

when is somatostatin release blocked and how

Answer 28

• during cephalic and gastric phase, the release is blocked by vagal stimulation

Question 29

what are the two main functions of secretin

Answer 29

• pH regulation by promoting pancreatic and biliary bicarbonate secretion and bicarbonate secretion in duodenum epithelial cells
• reduces gastric secretions by blocking G cells

Question 30

secretin release stimuli

Answer 30

entry of fat and acid (protons) into duodenum, stimulates S cells

Question 31

what inhibits Cholecystokinin (CCK)

Answer 31

somatostatin

Question 32

what cells produce CCK and where

Answer 32

enteroendocrine I cells of dudodenal and jejunal mucosa and neurons in the ileum and colon

Question 33

what are the functions of CCK

Answer 33

• enzyme secretion from pancreas
• contraction of gall bladder to release bile
• activation of D cells (somatostatin)

Question 34

what causes the release of Cholecystokinin (CCK)

Answer 34

presence of FAs/AAs/peptides in chyme entering the duodenum

Question 35

what cells produce Gastric inhibitory peptide (GIP) and where

Answer 35

neuroendocrine K cells of duodenal and jejunal mucosa

Question 36

what stimulates the release of GIP

Answer 36

glucose and FAs in chyme entering duodenum

Question 37

what are the functions of GIP

Answer 37

• inhibit parietal acid secretion
• increase insulin release from endocrine pancreas

Question 38

what are the functions of motilin

Answer 38

increase gastric emptying and somatostatin release from pancreas

Question 39

what cells produce motilin and where

Answer 39

neuroendocrine Mcells of duodenal and jejunal mucosa

Question 40

what is the release stimuli for Motilin

Answer 40

increased pH in duodenum
also spontaneously released during interdigestive phase

Question 41

what is Erythromycin

Answer 41

a motilin receptor agonist; marolide antibiotic

Question 42

what are the side effects of the antibiotic Erythromycin

Answer 42

enhances gastric emptying
side effects: D+, nausea, abdominal pain, V+

Question 43

what happens to salivary gland activity during the intestinal phase

Answer 43

cease activity

Question 44

what happens to gastric secretion activity during the inestinal phase

Answer 44

secretions decrease, caused by neural and humoral control
* neural: removal of stimuli from stomach
* humoral: somatostatin is synthesized and released from D cell, gastrin and CCK activate D cells, further increasing somatostatin
somatostain inhibits activity of parietal and ECL cells

Question 45

how do endocrine control systems affect secretions into the GI tract during the interdigestive phase (when stomach & SI are empty)

Answer 45

• gastrin release reduced
• somatostatin inhibits gastric and pancreatic secretions and CCK release
• motilin stimulates contraction of gut smooth muscle

Question 46

what is Gastrinoma/Zollinger-Ellison Syndrome

Answer 46

rare neuroendocrine tumor that arises from malignant transformation of somatostatin secreting delta cells of the endocrine pancrease to gastrin producing cells

gastrin stimulates secretion of gastric acid –> gastrinoma –> peptic ulcers, D+/steatorrhea/hypokalemia

steatorhhea = abnormal amount of lipids in feces