Regulation of GI functions Nerves and smooth muscle (Choudhury)

Question 1

where are some locations of multi-unit smooth muscle

Answer 1

eye (Ciliary body- iris)
vas deferens
skin (piloerector muscle
some blood vessels

Question 2

where are some locations of single-unit smooth muscle

Answer 2

GI tract
uterus
ureter
bladder

Question 3

what are the pacemaker cells of the GI system

Answer 3

Interstitial cells of cajal

Question 4

what are the two ions that are ressponsible for the slow wave action potential in GI tract

Answer 4

Ca 2+ influx

K+ eflux

Question 5

what parts of the GI system use phase contractions and which part use tonic contractions

Answer 5

phasic- GI tract

tonic -sphincters

Question 6

what are three sources of calcium for activation of smoth muscle contraction

Answer 6

Voltage-gated Ca2+channels
Extracellular source
Depolarization (graded, slow-wave, AP: Electromechanical coupling) opens L-type Ca2+channels

2. Sarcoplasmic reticulum
   a. Ca2+-induced Ca2+ release (CICR) via ryanodine receptor
   b. IP3 Ca2+ channel*
   Pharmacomechanical coupling: hormones & neurotransmitters can initiate increased [Ca2+]i via G-protein coupled receptors (voltage independent)
3. Store-operated Ca2+channels (SOCs)
   Extracellular source
   Opening linked to depletion of SR Ca2+ stores
   Voltage independent

Question 7

what is pharmacomechanical coupling

Answer 7

hormones & neurotransmitters can initiate increased [Ca2+]i via G-protein coupled receptors (voltage independent)

causing release of Ca from SR in smooth muscle

Question 8

what are the 4 GI regulatory mechanisms

Answer 8

1. Autonomous Smooth muscle
   
   • Single-unit smooth m. with gap junctions: Electrical Syncytium
   • Slow wave potentials: Interstitial cells of Cajal = pacesetters
2. Extrinsic Nerves
   
   • Sympathetic and Parasympathetic
   • Coordinate activity in different regions
3. Intrinsic Nerve Plexuses
   
   • Submucosal and Myenteric plexuses
   • Local coordination of motility & secretions
4. Gastrointestinal Hormones
   -Gastrin, Secretin, CCK, GIP
   -Paracrines:
   Somatostatin, Histamine

Question 9

what does increased parasympathetic activity do for the gut

Answer 9

promotes digestive and absorptive processes; increases motility and secretions***

Question 10

what are the outcomes of increased ACh

Answer 10

increased:
salivation
defecation
lacrimation
GIT motility
urination
muscle contraction

Question 11

what are the outcomes of decreased ACh

Answer 11

dry mouth
increased constipation
increased urine retention

Question 12

what is the other name for the myenteric plexus and where is it located

Answer 12

(Auerbach’s plexus):

-Between the outer longitudinal and inner circular muscle layers of the
muscularis externa throughout the GI tract

Question 13

what is another name for the submucosal plexus and where is it located

Answer 13

(Meissner’s plexus):

-In the submucosa of the small and large intestines

Question 14

what does the myenteric plexus control

Answer 14

motility of smooth muscle

Question 15

what does the submucosal plexus control

Answer 15

secretions and blood flow

Question 16

what are the submucosal and myenteric plexuses part of?

Answer 16

enteric NS