Motility in the GI Tract Flashcards
What are the main functions of the motor activity of the GI tract
Non-propulsive movements (segmentation)
Peristaltic movements
Reservoir function
What are two types of muscularis externa contractions
Phasic
Tonic
What’s the time scale for phasic muscle contractions ?
Seconds
What’s the time scale for tonic muscle contractions ?
Minutes- hours
What are non-propulsive movements (segmentation)
churn up contents of the GI tract to promote digestion and absorption
What are peristaltic movements
process of moving material along the gastrointestinal tract
What is the reservoir function
isolating different section of the GI tract for storage
How is the reservoir function performed
by sphincter
Give examples of sphincters and what they are reservoirs for?
Stomach- after meal
Large Intestine- waste
What of the motor activity of the GI tract functions are phasic contractions
Non-propulsive movements (segmentation)
Peristaltic movements
What of the motor activity of the GI tract functions are tonic contractions
Reservoir function
What type of contraction does the Non-propulsive movements (segmentation) carry out
Phasic
What type of contraction does the Peristaltic movements carry out
Phasic
What type of contraction does the reservoir function carry out
Tonic
What type of muscle is the muscularis externa 1/3 of the way of the oesophagus to the rectum
Smooth muscle
What type of muscle is the muscularis externa in the upper 1/3 of the oesophagus
skeletal muscle
When is the muscularis externa smooth muscle
1/3 of the way of the oesophagus to the rectum
When is the muscularis externa skeletal muscle
upper 1/3 of the oesophagus
What is a single muscular unit?
Muscle fibres act together as a functional unit
How is the smooth muscle of the muscularis externa organised? How is this beneficial?
Two smooth muscle cells connected to three varicosities connecting the nerve to the smooth muscle fibre
So that there is signalling from the nerve to the smooth muscle cell
Innovated smooth muscle cells connected to other muscle cells to other smooth muscle cells by gap junctions
coordinated activity of the muscle fibres
What is a special feature of the membrane voltage within the smooth muscle cells of the muscularis externa of the GI tract
Slow waves
Oscillations of the membrane voltage within the smooth muscle cells of the muscularis externa of the GI tract
When action potential fired membrane becomes very negative
reaches a hyperpolarisation threshold
starts to make it positive but doesn’t reach action potential threshold
becomes more positive again after modulation where it reaches action potential
Action potential fires again
Slower than skeletal muscle action potential
What is the resting potential of the muscularis externa of the GI tract
Depolarised ( -40 ~ -60mV)
How is slow waves within the smooth muscle cells of the muscularis externa of the GI tract modulated
Hormones and nerves e.g Acetycoline Cholecystokinin Make waves more positive to reach action potential threshold
How is the frequency of muscle contractions dictated?
Frequency of action potential firing which is determined by slow waves
What are sphincters
Specialised builging of the inner circular muscles from the muscularis externa
What do sphincters do?
separate two adjacent compartments of the GI tract
Maintain positive resting pressure
Regulate antegrade and retrograde movement
Effectively serve as one-way valves
What does antegrade mean
Forward moving
What does retrograde mean
Backward moving
What are the sphincters ogf the GI tract
Upper oesophageal sphincter (UES) Lower oesophageal sphincter (LES) Pyloric sphincter Sphincter of Oddi Ileocecal sphincter Internal and external anal sphincters
Where is the Upper oesophageal sphincter (UES) located?
The top of the oesophagus
Where is the Lower oesophageal sphincter (LES) located?
At the bottom of the oesophagus
Where is the Pyloric sphincter located?
At the bottom of the stomach
Where is the Ileocecal sphincter located?
At the bottom of the small
Where is the Internal and external anal sphincters located?
At the rectum
How is the stomach isolated as a reservoir?
By the action of the Pyloric sphincter at the bottom and Lower oesophageal sphincter (LES) at the top
How is the action of the pyloric sphincter important
Regulating release of partially digested food from the stomach into the small intestine after a meal
How is the small intestine isolated as a reservoir?
By the action of the Pyloric sphincter at the top and Lower oesophageal sphincter (LES)
How is the small intestine isolated as a reservoir?
By the action of the Pyloric sphincter at the top and ileocecal sphincter at the bottom
How is the large intestine isolated as a reservoir?
By the action of the internal and external anal sphincter at the bottom and ileocecal sphincter at the top
Which sphincter is made of skeletal muscle and why is this important
External anal sphincter
As for voluntary movement
so don’t automatically discharge. Go to the toilet
Where is the Sphincter of Oddi located
Wrapped around two ducts coming into the dduodenum:
- Pancreatic
- biliary/ bile
What is the contraction of Sphincter of Oddi role
regulating delivery of pancreatic juice and bile from biliary system into duodenium
What is the epithelium of the oesophagus and why?
Stratified squamous epithelium
Protective mechanism from acid reflux from stomach
What are the type of sphincters are sphincters normally?
Anatomical
Which type of sphincter is the lower oesophageal sphincter
Physiological
What is the difference between an Anatomical and physiological sphincter?
Anatomically - bulging of the inner circular muscular layer
Physiological- no bulging but different in physiology
How is closure of the lower oesophageal sphincter achieved?
Contraction of the diaphragm
intra-abdominal pressure is greater than the intra- gastric pressure
anatomical organization of the gastrointestinal tract
What movement is more common in the GI tract antegrade or retrograde
Antergrade
How are the contraction of the sphincters cordinated?
smooth muscle contractions of adjacent compartments
What of the GI reflexes are voluntary
Swallowing reflex
Process of swallowing
Initiated voluntarily
then entirely under reflex control
tongue is gonna push a bolus of food to the back of the mouth
In the pharynx that bolus of food is going to activate touch receptor
Touch receptors communicate with medulla and lower pons
By cranial nerves swallowing reflex is going to control the pharynx and the upper oesophagus
By vagal nerves the rest of the oesophagus
What is a bolus of food
Food mixed with saliva
Where is the bolus of food is going to activate touch receptor
In the pharynx
When in the swallowing reflex does the reflex become involuntary
When medulla and pons is activated
Swallowing reflex- Once medulla and lower pons activated what controls the pharynx and upper oesophagus
cranial nerves
Swallowing reflex- Once medulla and lower pons activated what is controlled by the cranial nerves
pharynx and upper oesophagus
Swallowing reflex- Once medulla and lower pons activated what is controlled by the vagal nerves
Th rest of the oesophagus that is not the upper oesophagus
Swallowing reflex- Once medulla and lower pons activated what controls the rest of the oesophagus that is not the upper oesophagus
Vagal nerves
What are the three phases of swallowing
Oral phase/ Voluntary phase
Pharyngeal phase
Oesophageal phase
Process of swallowing: Oral phase/ Voluntary phase
The tongue presses the food against the hard palate
The bolus is forced into the pharynx and stimulates touch receptors
Signal to medulla and pons
Process of swallowing: Pharyngeal phase
soft palate elevates
epiglottis closes trachea
Only when epiglottis closes-
Upper oesophageal sphincter relaxes
What is the purpose of each part of the pharyngeal phase?
Protect the respiratory system
soft palate elevates- to protect the nasal passages
epiglottis closes trachea- protects trachea passages
Process of swallowing: Oesophageal phase
Upper oesophageal sphincter closed
peristalsis starts
getting food from oesophagus to stomach
What is peristalsis
sequential contraction of ring of muscle
Inner circular muscle of the muscularis externa contracting behind the bolus of food and relaxed smooth muscle in front
How is the upper and lower oesophageal sphincters coordinated?
When upper opens lower closes
vice versa
How is the stomach distinguished by mobility?
Orad
Orad and Caudad
What is the Orad of the stomach used for?
Accommodation of food
What is the Orad and Caudad of the stomach used for?
Gastric emptying
Where is the Orad of the stomach located?
Top of the stomach
Where is the Caudad of the stomach located?
Bottom of the stomach
What happens to either Orad or caudad during swallowing and what is this known as?
Relaxing of the Orad
Receptive relaxation
What is receptive relaxation and its function
Relaxing of the Orad of the stomach
to accomodate food coming down the oesophagus
Process of vomiting
Reverse peristalsis Pyloric sphincter and stomach relaxes forced inspiration occurs against a closed epiglottis This gives a Sharply elevated intra abdominal pressure with forceful contraction of abdominal muscles vomit propels up the oesophagus reflex relaxation of upper oesophagus sphincter Induces vomiting
What does a forced inspiration against closed epiglottis achieve in vomitting?
Lowering of the diaphragm
Decreases intrathoracic pressure
intra abdominal pressure goes up
Motility in the stomach
Peristalsis
Contractions begin in the corpus and travel toward the pylorus (propulsion)
They increase in force and velocity as they approach the gastroduodenal junction
Grinding occurs mainly in the antrum
Retropulsion is very effective at mixing and breaking down gastric contents
What is propulsion
wave s of contractile activity in the muscularis externa
What is grinding in the stomach?
Mixing of foodstuff into smaller and smaller parts
What is retropulsion
Where after contractile waves hit pylorus sphincter it returns and travels through lumen of the stomach
Motility in the Small Intestine
Non-propulsive movements-The most frequent type of movement in the small intestine
Caused by rhythmic contraction and relaxation of the muscularis externa
Effectively mixes chyme and brings digested nutrients into contact with the mucosal surface
Aids digestion more than moving it
Peristalsis-
Occurs at low frequency
Caused by contraction of successive sections of muscularis externa
Propels chyme for a short distance, allowing time for digestion and absorption
Motility of the large intestine
Mixing the chyme, to improve the absorption of water and salts from the colon
Kneading the semisolid contents
Segmentation
Mass movement or mass peristalsis
What is segmentation
Moving contents towards anus slowly
What is Moving contents towards anus slowly termed as?
segmentation
What is the rate that contents are moved towards the anus?
5-10cm/hour
How is motility of the large intestine controlled?
Directly controlled by enteric nervous system except for control of defecation
Where is the absorption of salt and water predominately done?
Ascending and transverse column of the large intestine
How many times does mass peristalsis happen per day in the large intestine? Why?
1-3/ day
to move waste material to the rectum
What is the special movement that moves colonic content towards the anus?
Mass of peristalsis
How much does contents are moved towards the anus with mass peristalsis?
20cm
What is the gastrocolic reflex
distention of the wall of the stomach initiates a mass peristalsis
What is duodenocolic reflex
distention of the wall of the duodenum initiates a mass peristalsis
Defaecation
distention of the wall of the rectum
rectosphincteric reflex happening
Relaxation of the internal anal sphincter (Contraction of external anal sphincter if not wanting to defaecate)
Relaxation of external anal sphincter
Contraction of abdominal wall muscles and relaxation of pelvic wall muscles
flexure of hips and descent of pelvic floor
What is defaecation also known as?
Retcosphincteric reflex
How do you initiate the rectosphincteric reflex
By filling of the rectum with faeces
Distention of the rectum wall
Putting a balloon in the rectum and inflating that balloon
Retcosphincteric reflex
Activated stretch receptors in the rectum
signalling by the afferent pelvic nerves back to the sacral spinal cord
signalling back to the rectum esp. external anal sphincter via pudendal somatic motor nerve fibres
