Motility of the gut

Question 1

Definition of latch bridge mechanism

Answer 1

Force generating state of dephosphorylated, slowly detaching cross bridges

Question 2

Definition of plasticity

Answer 2

Smooth muscle when it is able to function over a wide range of lengths

Question 3

Definition of gastrointestinal motility

Answer 3

Functional expression of smooth muscle contraction

Question 4

Definition of pacemaker potentials

Answer 4

Slow +ve increase in voltage across cell membrane that occurs between the end of 1 AP and the beginning of the next one

Question 5

Definition of basal electrical rhythm

Answer 5

Spontaneous depolarization and depolarization of pacemaker cells in smooth muscle

Question 6

What is the main function of motility

Answer 6

Mixing

Churning

Question 7

Describe the stomach’s contractile activity

Answer 7

Vigorous peristalsis near pylorus, initiated by ICC

Deliver small amounts of chyme to duodenum

Question 8

Describe the regulation of gastric activity

• secretin
• CCK
• GIP
• sympathetic
• parasympathetic (vagus/pelvic splanchnic)
• ENS
• motilin
• chyme contents

Answer 8

Secretin

• via S cells => HCO3 and bile prod/sec
• inhibitory

CCK

• via I cells => enzyme sec, GB contraction
• inhibitory

GIP

• via K cells => insulin sec
• inhibitory

Increased SNS/decreased PNS

• via duodenal chemoreceptors/stretch receptor
• long reflex => layers of GI system
• short reflex => via ENS
• inhibitory

ENS

• via CNS input
• inhibitory

Motilin
-via intestinal M cells => stimulatory

Chyme contents

• fatty => inhibitory
• carbohydrates => stimulatory

Question 9

Describe the activity of smooth muscle in the GI tract

What is the function

Answer 9

Single unit SM via latch bridges
ICC = pacemakers
-duodenum has the fastest rate of activity

Results in

• peristalsis
• segmentation
• mass movement
• sphincter tone control

Question 10

Activity of GI smooth muscle and contractile activity

Answer 10

Visceral smooth muscle, rhythmic activity cycles (Interstitial cells of Cajal)

Peristalsis, move bolus

Segmentation, churn, fragment bolus

Sphincter tone and relaxation (pyloric)

Question 11

Name the 4 layers of the GI tract

Name the ENS plexuses found here

Answer 11

Mucosa
Submucosa => Meissners
Muscular externa => Auerbach
Adventitia/serosa

Question 12

Describe the importance of the ENS

Answer 12

Can regulate Gi independently from CNS
However, always has CNS input

Acts on

• SM
• secretory cells
• endocrine cells
• blood vessels