Lecture 8: Gut mobility Flashcards
What two areas of the GI tract are under voluntary control and which functions does this participate in?
Upper oesophageal sphincter- swallowing
External anal sphincter- defecation
Which branch of the nervous system does the enteric nervous system come up?
Autonomic nervous system
Can and does work independently to the brain and spinal cord
Known as the “Second brain”
What is the function of the enteric nervous system?
Governs the function of the gastrointestinal tract
What makes up the enteric nervous system?
Consists of mesh-like system of neurones
Is the enteric nervous system a part of the sympathetic or parasympathetic innervation?
Neither
Capable of working independently
Can be influenced by both sympathetic and parasympathetic
What is the enteric nervous system derived from?
Neural crest cells
Which parts of the GI system does the enteric nervous system innervate?
Begins at the oesphagus
Ends at the anus
Name the two ganglias of the enteric nervous system?
Collected into two ganglia: Myenteric and submucosal plexus
Where is the myenteric plexus located?
In the muscularis externa layer
Between the circular and longitudinal layer
Where is the submucosal plexus located?
Between the submucosa and the muscularis externa layer
Which muscle layer in the muscularis externa is most inner?
Circular
What is the function of the interstitial cells of cajal?
Function as the pacemaker cells for the enternic nervous system
Drives the electrical and mechanical activities of the smooth muscle cells via slow wave oscillations
What are the two ways to measure the mobility of the gut?
Pressure: measure the pressure of the muscle
Transit: measure how long it takes for a substance to go from one area to another
The pressure measurement of the gut mobility measures the ability of which muscle(s)?
Circular muscle only
Not able to measure the longitudinal muscle
Describe how the type of muscle changes in the oesophagus as it decends?
Superior third: Stratied Skeletal muscle
Middle: Mixed
Lower third: Smooth muscle
What do the two bands of this HRM trace represent?
Upper and lower sphincter
When the pressure trace goes blue at the upper and lower oesphageal sphincter- what does this tell us?
This tells us the pressure is reduced
Due to the circular muscle being relaxed
What is the significances of the EGJ relaxation phase on the HRM trace?
Significant as it allows the bolus to enter the stomach
The lower oesphageal sphincter is relaxed
Why does the trace show a curvature change at the P zone of the HRM trace?
This is the area of the oesphagus where the epithelium goes from stratied skeletal to smooth
Define a hiatus hernia?
This is when the cardia region of the stomach moves superiorly through the diaphragm- now located in the chest cavity
What are the symptoms of an hiatus hernia?
Can lead to food and gastric acid being backed up in the oesphagus
Why does food and gastric acid build up in the oesphagus in the hiatus hernia?
How to diagnosis
This is because the lower oesphageal sphincter cannot work correctly anymore and thus no longer prevents backflow from the stomach
Diagnosed by HRM trace- can see the pressure in the LOS is not strong.
Define dysphagia?
Medical term for swallowing difficulties
Briefly describe nutcracker oesphagus?
Oesphagus mobility disorder
Characterised by oesphageal spasms of the muscles of the oesphagus
Pain on swallowing
Briefly describe diffuse oespageal spasm?
Characterised by uncoordinated contractions of the oesphagus
Results in difficulties swallowing or regurgiation
What is scleroderma? and possible effects in the oesphagus
Medical condition in which the immune system starts to attack the connective tissue under the skin and around internal organs and blood vessels
Weak/absent lower oesphagus sphincter
At what period of time would you want the circular muscles to be relaxed in the upper and lower oesphageal sphincter?
For UOS: at the start of swallowing to allow the food to enter the oesphagus
LOS: when the food has entered the oesphagus, the LOS should be relaxed to allow the food to pass and enter the stomach
What is achalasia and what causes it?
Clinical symptoms of achalasia
Medical condition that is the result of the lower oesphageal sphincter failing to open- constantly contracted (can see on the HRM trace)
Food cannot move from the oesphagus to the stomach
Regurgitation is associated with the condition leading to severe weight loss.
Can view on the HRM trace
What two measured can you use to detect achalasia?
HRM trace
Barium swallow
What do you call this appearance on the barium swallow test?
Bird’s peak appearance
Describe the bird’s peak apperance of a barium swallow test and what condition does it indicate?
Narrowing at the lower oesphageal sphincter
Diliation of the oesphagus
Stasis of barium in the oesphagus
What are the two states of gut mobility in the stomach and small intestine?
Interprandial aka Fasting period
Fed aka meal related period
What is the name of the distinct pattern of electromechanical activity observed in gastrointestinal smooth muscle during the interprandial (fasting) period?
Migrating motor complex (MMC)
The migrating motor complex has its cyclic contractions occuring every __ minutes?
90 minutes
The migrating motor complex is regulated by which hormone?
Motilin
What is the signficiance of the the migrating motor complex?
Acts to cleanse the stomach and the intestine
What are the 4 phases of the migrating motor complex?
- Prolonged period of quiescence (inactivity)
- Increased frequency of contractility (light squeeze)
- Short period of peak contractility (tight squeeze)
- Decline activity (relaxation)
During an Interprandial (Fasting) State, what is the name of the electrical activity that controls contractile behaviour?
Migrating motor complex (MMC)
What, where and when is motilin secreted?
Secreted by M cells in the mucosa of the proximal small intestine
Secreted at 90 min intervals during fasting state
What is the function of motilin?
“housekeeper” of the gut
Regulates the migrating motor complex: a cyclic contraction sequence to cleanse the stomach and small intestine in time for the next meal.
Give an example of a drug that acts on motilin?
Erythromycin is a motilin agonist
For this reason a common side effect is diarrhoea
What are the 3 phases of the fed aka meal related state of mobility?
- Cephalic
- Gastric
- Intestinal
**Called because stimuli of the brain, stomach and small intestine influence the acid secretion **
Describe the cephalic phase of gut mobility?
- This occurs before food enters the stomach.
- Phase is triggered by the thought, smell, taste or sight of food.
- These triggers stimulate the cerebral cortex which sends signals via the vagus nerve to the stomach (parasympathetic innervation).
- The vagus nerve releases acetyl choline (ACh), which triggers parietal and G cells (respectively releasing HCL and gastrin).
- ACh also inhibits D cells (thus inhibiting the release of somatostatin).
- Accounts for around 20% of total gastric secretion.
Describe the gastric phase of gut mobility?
- Stomach expands without increasing the pressure
- Frequency and direction of gastric muscular contractions controlled by the interstitial cells of cajal- triggering gastric smooth muscle contractions at around 3 cycles per minute.
- The period in which swallowed food and semi-digested proteins activate gastric activity.
- Accounts for around 2/3rds (67%) of total gastric secretion.
- Solids and liquids leave the stomach at different periods of time as solids have to undergo mixing and churning to make sure the particles are small enough to get into the crevices of the small intestine
What is the gastric emptying time for solids and liquids?
Liquids empty faster than solids
Liquids: over 20 mins
Solids: over 3-4 hours
What are the two properities of the chyme that effect the rate of gastric emptying?
- Particle state: liquids empty faster than solids
- Nutrient content: fatty meals take longer to leave the stomach
How do we measure gastric emptying?
Patient is given scrambled eggs which is mixed with radioactive material.
Once eaten, the clearing of this food is seen on a nuclear medicine camera
Name an example of accelerated gastric emptying?
Dumping syndrome: patient is lightheaded after a meal
Diarrhoea
Name an example of delayed gastric emptying?
Idiopathic: condition is unknown
Longstanding diabetes
Opioid analgesic drugs e.g. codeine
Post viral
Define Gastroparesis
a disease in which the stomach cannot empty itself of food in a normal fashion
What are some common symptoms of delayed gastric emptying?
Abdominal pain
Nausea and vomiting
Weight loss
Describe ways to manage gastroparesis?
Dietary:
- Small meals frequently
- Liquid food is tolerated better
- Nutritional support if required
Attention to underlying cause:
- Limit use of opioid analgesic drugs
- Improve diabetic control
- For post viral: will improve with time
Medicine:
- Motilin agonist e.g. erthryomycine
Endoscopic treatment
- Botulinum toxic injection to the pyloric sphincter to relax it allowing gastric emptying.
Gastric electrical stimulation
- Electrical device that prove high frequency and low amplitude contractions.
- Improves the nausea and vomiting symptom only
What is the rate of mobility of solids and liquids in the small intestine?
Same rate
But liquids are transports to the caecum more rapidly because they enter the small intestine first (due to faster gastric emptying)
Give an example of a disorder of the small bowel mobility?
- Chronic intestinal pseudo-obstruction
- Acute post-operative ileus
Define chronic intestinal pseudo-obstruction?
A condition where the intestines appear to be blocked but in fact is caused by nerve and/or muscle problems stopping food being squeezed through the small bowel
Tends to be a conseuqnece of other disease (secondary condition)
Define acute post-operative ileus?
This happens after surgery in the abdomen.
The abdomen is “stunned”
Results in the constipation and intolerance of oral intake in the absence of mechanical obstruction after surgery.
What is the main way to reduce the risk of acute post-operative ileus?
Introduce food immediately= If delays can prolong the intolerance
Another risk is the type of surgery: Open surgery the risk is greater than laparoscopic surgery
Define acute colonic pseudobstruction?
Acute dilatation of the colon that obstructs the flow of intestinal contents
Large bowel parsympathetic dysfunction
Common after cardiothoracic or spinal surgery
Give an example of a disorder of the large bowel mobility?
Acute colonic pseudobstruction
Describe colonic mobility?
No typical pacemaker activity
Mixture of short duration and long duration contractions
Marked increase in colonic motility after a meal (gastrocolic reflix)
Transit from caecum to rectum takes 1-2 days
Name some drugs that reduce colonic motility?
Opiates
Anticholinergics
Loperamide aka immodium
Name some drugs that increase colonic activity?
Stimulant laxatives
Name and describe some problems with anorectal function?
Excessive rectal distension
- Acute or chronic diarrhoeal illness
- Chronic constipation
Anal sphincter weakness
- Sphincter weakness due to damage to pudendal nerve
Hirschrung’s Disease
- Lack of congenital development of nerve plexi and
ganglia, resulting in a lack of nervous control of the colon.
