Gut motility Flashcards
What is the role of the upper oesophageal sphincter?
Controls entry of food bolus into GI tract (initiated by the process of swallowing)
What is the role of the External anal sphincter?
allow defecation
what are the 2 main areas of innervation of GI tract?
o Myenteric plexus – most important
o Submucosal plexus
Role of the Interstitial cells of Cajal?
These are cells located within the muscle layers of the alimentary tract.
They mediate communication between the autonomic nervous system and smooth muscle
When is the enteric nervous system active?
all the time
what are the extrinsic factors that influence the enteric nervous system?
what effect do they each have on non-sphincteric muscle ?
o Parasympathetic (Vagal) – excitatory to non-sphincteric muscle o Sympathetic – inhibitory to non-sphincteric muscle, excitatory to sphincteric muscle
What are the neurohormonal influences on the enteric nervous system?
o 5 hydroxy tryptamine (serotonin)
o Motilin
o Opioid receptors
what does interprandial mean?
between meals
Describe the difference between the muscular layers found in the 1/3 of the oesophagus versus the lower 2/3
upper 1/3: striated voluntary muscle
Lower 2/3: smooth muscle, circular and longitudinal layers (involuntary)
When does the migrating motor complex occur and what is its role?
occurs in interprandial period (between meals)
It is a cyclic contraction sequence which cleanses stomach and intestine of any remaining food in between meals
How often does the migrating motor complex occur? what is it regulated by ?
Every 90 minutes
Regulated by Motlin
Describe the 4 stages of the migrating motor complex
1) prolonged period of quiescence
2) increased frequency of contractility
3) a few minutes of peak electrical and mechanical activity
4) declining activity merging to next phase 1
What is motilin and what is it produced by?
A Polypeptide hormone
Produced by M cells in the small intestine
How often is motilin secreted and what effect does it have?
Secreted every 90 minutes
It stimulates contraction of gastric fundus and enhances gastric emptying
Name a motilin agonist and what is a common side effect of it?
Erythromycin: common side effect = diarrhoea as there is too much cleansing of the gut
During mealtime, what replaces the migrating motor complex?
MMC is replaced by contractions of variable amplitude and frequency, allowing mixing and digestion
What does the gastric pacemaker do?
It generates rhythmic depolarisations and
Controls the FREQUENCY and DIRECTION of gastric muscular contractions
How frequently does the gastric pacemaker generate rhythmic depolarisations?
at a frequency of 3 cycles per minute
what size do Digestible food particles become before they leave the stomach?
when size is reduced to 2mm
How long do liquids take to leave the stomach ?
20 minutes
How long do solids take to leave the stomach ?
3-4 hours
define Gastroparesis
disease which causes delayed Gastric emptying
List some causes of Gastroparesis
- Idiopathic/ unknown
- Longstanding diabetes with macrovascular disease
- Drugs – e.g. opiates
- Post viral
Describe motility in the colon
No pacemaker activity
Colon mixes material without prpulsion (moving it forward) - for water absorption
Acts as a temporary storage site and expels faeces
How long is the transit from caecum to rectum ? IS the transit shorter in men or women?
1-2 days
Shorter duration in men (they have increased faecal content)
How is colon transit measured?
USing Serial X-Rays with radio-opaque markers
If there are no markers left, what does this mean?
normal transit
If there are markers left in rectosigmoid, what does this mean?
pelvic outlet obstruction
If there are markers scattered throughout colon, what does this mean?
slow transit constipation
which drugs reduce gut motility (reduce diarrhoea)?
Opiates
Anti-cholinergic
Loperamide = Imodium
which drug increase gut motility (reduce constipation)?
Laxatives
Describe the internal anal sphincter in terms of muscle, control and when it is used?
Smooth muscle
Involuntary control
Remains contracted in resting conditions
Describe the external anal sphincter in terms of muscle, control and when it is used?
Striated muscle
Voluntary control
recruited in reflex reaction to coughing/sneezing
What happens in Hirschsprung’s disease ?
Nerves are missing from part of the intestine – causes constipation
