Upper GI Physiology/Gut Motility

Question 1

what areas of the GI tract are under voluntary control?

Answer 1

upper oesophageal sphincer - swallowing
external anal sphincter - defacation

Question 2

what are the 2 main components of the enteric nervous system?

Answer 2

submucosal (meissners) plexus
myenteric (auerbachs) plexus - inbetween CM and LM

Question 3

what do the CM and LM do?

Answer 3

CM - allows squeezing/increased pressure allowing contents to be moved around
LM - squeezes to shorten diameter to allow forward movement

Question 4

what are the interstitial cells of cajal?

Answer 4

pacemaker function
lies in myenteric plexus
produce basic electrical rhythm (BER) determining how often a gut area can contract
higher BER in proximal than distal

Question 5

what is the function of the enteric nervous system?

Answer 5

mediates reflex activity in absense of CNS input (interprandial period)

Question 6

what is the enteric nervous system influenced by?

Answer 6

extrinsic factors:
vagal control - excitatory to non-sphincteric muscle
sympathetic control - inhibitory to non-sphincteric muscle (excitatory to sphincter muscle)
neurohormonal influences (opioid receptors, motilin)

Question 7

describe the measurement of motility function

Answer 7

pressure (circular muscle function)
transit (radiolabelled isotopes, breath tests, scintigraphy, dynamic contrast radiology)

Question 8

what is the innervation of the oesophagus?

Answer 8

sympathetic - sympathetic trunk
parasympathetic - vagus nerve

Question 9

describe the muscular structure of the oesophagus?

Answer 9

prox 2/3 - striated voluntary muscle
dist 1/3 - smooth muscle

Question 10

what is a hiatus hernia?

Answer 10

weakness of diaphragmatic hiatus allowing stomach to partially move into the chest resulting in increased reflux

Question 11

what diseases can be diagnosed by manometry in the oesophagus?

Answer 11

achalasia - lower oesophageal sphincter less responsive, lower peristaltic function
oesophagus in scleroderma - weak LOS, absent peristalysis, severe oesophagitis
jackhammer oesophagus - pain on swallowing (still functional)

Question 12

what is the interprandial period controlled by?

Answer 12

migrating motor complex

Question 13

what is the interprandial period?

Answer 13

cleansing of gut in preparation for next meal
cyclic contraction sequence occuring every 90 minutes
regulated by motilin

Question 14

what are the 4 phases of the interprandial period?

Answer 14

• prolongued quiescence
• increased frequency of contractility
• a few minutes of peak electrical/mechanical activity
• declining activity merging to next phase 1

Question 15

what is motilin?

Answer 15

polypeptide hormone produced by M cells in small intestine
secreted in 90 minute intervals
cleanses gut
stimulates contraction of gastric fundus and enhances gastric emptying

Question 16

name a motilin agonist

Answer 16

erythromycin

Question 17

how can the gastric fundus/body accomodate large volumes?

Answer 17

volume increases up to 1.5l
due to receptive relaxation

Question 18

explain the process of gastric mixing

Answer 18

upper stomach muscles contract weakly (3 per minute) beginning in the middle of the gastric body and travelling to pylorus
occurs due to BER from pacemaker cells in stomach
contractions increase in force distally (major mixing - antrum)
contents form layers based on density (fats floating to top/emptying last)

Question 19

explain the process of gastric emptying (meal related motility stage 3)

Answer 19

liquids rapidly leave (20 minutes)
solid emptying is reguated (duodenal acid exposure can be harmful)
solids mixed/churned with gastric juice and can empty when rize reduced to 2mm

Question 20

what are the 3 phases of meal related motility?

Answer 20

cephalic
gastric
intestinal

Question 21

what is the cephalic stage of meal related motility?

Answer 21

secretory phase (vagally mediated)
sight/smell of food increases gastric secretion (20% of total)

Question 22

explain the gastric phase of meal related motility

Answer 22

stomach expands without pressure increase
MMC replaced by contractions of variable amplitude/frequency allowing mixing/digestion
frequency/direction of contractions controlled by gastric pacemaker (rhythmic depolarisations at 3 per minute triggering SM contractions with neurohumeral input)

Question 23

how much food is delivered to duodenum per hour?

Answer 23

200kcal

Question 24

explain the physiology of gastric emptying

Answer 24

antral pressure higher than gastric body/duodenum
as intra-gastric pressure rises, pylorus opens briefly
small amount of chyme passes to duodenum
most gastric content propelled back to stomach (more mixing)

Question 25

what can the duodenal mucosa sense from the stomach?

Answer 25

acidity osmotic pressure fat/AA presence (fat in duodenum inhibits gastric emptying)

Question 26

name some disorders associated with accelerated gastric emptying?

Answer 26

dumping syndrome diarrhoea

Question 27

name some disorders associated with delayed gastric emptying?

Answer 27

abdominal pain vomiting poorly controlled gastro-oesophageal reflux malnutrition