GIT Motility

Question 1

What are Intramural Plexuses?

Answer 1

• Consist of Submucosal (Meissner’s) Plexus and Myenteric (Auerbach’s) Plexus.
• Have cell bodies receiving input from extrinsic nerves, other cell bodies and gut wall receptors.
• Output: to muscle and gland cells.

Question 2

What is the role of Aurbach’s plexus in motility and secretion?

Answer 2

• Myenteric, located on muscularis interna

Question 3

What is the role of Meissner’s plexus in motility and secretion?

Answer 3

• Submucosal.

Question 4

Discuss parasympathetic innervation of GI.

Answer 4

• Vagal innervation to oesophagus and stomach.
• Sparser innervation to small intestines and colon.
• Pelvic nerves to distal colon and rectum.
• ^ motility and relaxes sphincters.

Question 5

Discuss sympathetic innervation of GI.

Answer 5

• Efferent activity via NA decreases motility and contracts sphincters.

Question 6

What is Basal/Basic Electrical Rhythm (BER) and what causes it?

Answer 6

• Continual slow waves that facilitate intrinsic electrical activity along muscle fibre membrane of the GI smooth muscle.
• Generated by Interstitial Cells of Cajal (ICC) pacemaker cells. Get info from ENS to smooth muscle cells & generates the BER.

Question 7

What is the resting membrane potential of GI smooth muscle?

Answer 7

• Unstable between -50mV to -60mV.
• Slow wave potential rises above -40mV and becomes spike potential.
• ?BER caused by increase in intracellular calcium which leads to depolarisation and smooth muscle contraction.

Question 8

Describe the migrating motor complex.

Answer 8

• 5-10 minute phase of intense contractions which migrates from stomach to ileum in 1.5 hrs during fasting.
• Clears stomach and SI and keeps bacterial counts low in SI.
• 4 phases: I- IV.

Question 9

What is Segmentation (mixing)?

Answer 9

• Circular muscle of SI contracts and mixes chyme and spreads it over the entire length of the intestine.
• Slightly propulsive, similar frequency to BER, due to close constriction of circular muscle.

Question 10

What is peristalsis?

Answer 10

• Contraction taking place behind the bolus of chyme and relaxation ahead.
• Mediated by stimulation of excitatory and inhibitory motor neurons.
• Rushes may occur in presence of irritant or bacteria. Can cause diarrhoea.

Question 11

What are the enterogastric reflexes of GI function?

Answer 11

• Enterogastric reflex: a feedback mechanism to regulate the rate at which chyme leaves the stomach and enters the small intestine.
• When reflex stimulated in duodenum results in inhibition of gastrin release by G cells.
• Delays emptying: Stretching and distension.

Question 12

Describe how hormonal influences affect gastrointestinal function.

Answer 12

• CCK, gastrin, somatostatin

Question 13

What is Hirschsprung disease?

Answer 13

• Also called Congenital aganglionic megacolon.
• An enlargement of the colon, caused by bowel obstruction resulting from an aganglionic section of bowel.
• Normal enteric nerves are absent.
• Results in severe constipation and megacolon.