Flashcards in Functions and Dysfunctions of GIT motility Deck (33):
How is relaxation of the fundus regulated?
- Vagovagal reflex
- If vagal innervation is interrupted then intragastric pressure increases
- Receptive relaxation allows folds to relax and open up, you get to a point where folds are fully open and then intraluminal pressure will increase
When will intraluminal pressure increase?
- You have fully opened all the rugae, folds, so you have maxed out the vagovagal receptive relaxation
What happens when someone has a vagotemy?
- You do not have the vagovagal, so these folds will not open up
Functions of the stomach?
- Phase of propulsion, rapid flow of liquids with suspended small particles and delayed flow of large particles
- Phase of grinding, emptying of liwuids with small particles
- Phase of retropulsion, large particles are retropulsed back up and then go through propulsion etc
- Propulsion, grinding, retropropulsion
What is the function of the pylorus?
- Allow carefully regulated emptying of gastric contents
- Prevents regurgitation of duodenal contents into stomach (innervated by vagus, relaxation and sympathetics)
What are the controls of gastric emptying?
- Cephalic, gastric and intestinal
- Cephalic, approach of food or food in mouth
- Gastric, food in stomach
- Intestinal, food is intestines
What is the gastric phase in gastric emptying?
- excitory phase in which the stomach empties at a rate proportional to the volume within it
- due to myogenic reflex, stretching smooth muscle causes reflex contraction
- activation of pressure receptors sending impulses in local nerve plexi and vagus
- gastrin released in response to peptides
What is the intestinal phase in gastric emptying
- inhibitory, mainly, duodenum adapts work load as the intestines need time
- controlled through hormonal and paracrine
- low pH activates secretin secretion
- high levels of amino acids increases gastrin secretion
- high levels of carbohydrates increased GIP
What is the cephalic phase in gastric emptying?
- Inhibitory phase, allows stomach to act as a resevour
- Results in relaxation of stomach enabling it to store
What are the functions of the motor activity in the GIT ?
1) It produces segmental contractions, these are associated with nonpropulsive movement of luminal contents that enhances mixing or churning
2) Produces peristaltic contractions that causes propulsion or propagated movement of food
3) Some hollow organs act as resevoirs for holding luminal content
- Segmental contractions, peristalsis contraction, reservoir
What is the types of motility in the small intestine in the fed state?
- Retrograde peristaltic contractions, this includes segmentation and peristalsis
What is involved in Segmentation?
- Rings of circular muscle at intervals contract and then relax
- Adjacent rings then contract and relax
What is peristalsis of the small intestine?
- Sequential conractions of rings of circular muscle behind the bolus, followed by sequential relaxation
- Combination of activity between muscular layers with sequential activity in each of them
- Contraction of circular muscle behind bolus, contraction of longitudinal muscles ahead of food mass
- Contraction of circular muscle forces food mass forward
What is the Migratory Motor Complex, MMC?
- This is present in the fasted state of the GIT
- In the fasting state the small bowel is quiescent but the MMC does show exhibit rhythmic changes in both electrical and motor activity
- It has four stages, a prolonged quiescent period
- A period of increasing action potential frequency and contractility
- Period of peak electrical and mechanical activity lasting a few minutes
- Period of declining activity that emerges into the quiescent period
What is the role of the MMC?
- To propel particles greater than 2mm in diameter from the stomach into the duodenum
- Clear the small intestine of its residual content
- Stops colonic bacteria from migrating into the terminal ileum
- They start in the stomach and then travel into the terminal ileum
- Terminated and fed by feeding
What is the major determinant of the MMC pattern?
- Hormone motilin, 22 amino acid peptide synthesized in the duodenal mucosa and released just before the initiation of phase 3 of the MMC cycle
How is smooth muscle contraction controlled?
- Acetylcholine is the neurotransmitter
- Motilin and somatostatin stimulate smooth muscle contraction
- VIP relaxes smooth muscle
- Stretch, myogenic reflex, produces a reflec contraction mediated by opening of calcium channels
- ENS which can be modulated by the ANS
What does somatostatin do?
- Stimulate smooth muscle contraction
- Inhibits gastric acid release
What does Vasoactive intestinal peptide do?
relax smooth muscle
What motility is in the ileum?
- Iliogastric reflex, ilial distention leads to decreased gastric motility
- Gastroileal reflex, increased gastric activity causes increased ileal motility and increased movement of chime through the ilealcaecal valve
- Mediated through the enteric nervous system
What causes sphincteric relaxation?
- Stimuli proximal to the sphincter causes sphincteric relaxation and distal to the sphincter causes sphincteric contraction
- Distention of the ileum results in relaxation of the sphincter
- Distention of the proximal colon causes contraction
What regulates ileal flow into the colon?
- Distention of the ileum causes relaxation of the sphincter, distention of the colon results in contraction
- Ileal flow is regulated by luminal contents and pressure proximal and distal to the sphincter
What is different about the colon?
- It has no villi! But does have microvilli
What happens to the longitudinal muscle layer in the colon?
- Thickens to form 3 muscular bands which run the length of the colon called taeniae coli
- taenia coli extend and retract and gather to form haustra
What are the functions of the colon?
1) Absorbs large quantities of fluid and electrolytes thus converting liquid content of ileocecal material to solid, as the osmotic flow will follow the ions for example so they will be absorbed, removing the water rendering the remaining product as solid
2) Avidly absorb SCFA (this is a product of carbohydrate fermentation_
3) Storage/reservoir function
4) Regulated release of faecal material
5) Provides environment for beneficial bacteria which synthesises vitamins, this vitamins are K and B
6) Secretes mucus and ions
What ions does the colon secrete?
What is involved in colonic motility?
- Colonic rhythmic phasic contractions
- Giant migrating conrtactins
What is a colonic rhythmic phasic contraction?
- The fluid contents of the ascending colon are gradually becoming solid as water is absorbed, this creates a challenge met by the colon- it generates two types of RPCs; one short duration (2-3 seconds) and one long duration (15-20 seconds)
- The short duration has no propagation and has varying amplitude
- The long duration contractions may propagate over short distances, enabling turn over and properl the semi solid to solid contents more effectively
What are colonic RPCs?
- Short and long duration (2-3, 15-20 seconds respectively)
- Short has is not propagated and has varyimg amplitude
- Long duration allows semi solid to solid to be turned over and propelled more effectively and propagation happens over short distances
- They are highly disorganised in space and vary in amplitude and duration
- Equivalent to segmentation, random mixing within the colon
- Enhance fermentation and defecation
What is a colonic giant migrating contraction?
- GMCs, large amplitude lumen occluding contractions
- Propagate very rapidly in distal direction over larger distances to produce mass movements
- Spontaneous GMCs occur around 2-10 times a day
- Occur in both fastin and postprandial state
How can you stimulate motility in the colon?
- Bulk, inducing myenteric plexus
- Indigestible material passes through quickly activating pressure receptor
How is motility in the colon controlled?
- Autonomic control, vagus innervates ascending and some transverse
- When vagus stimulated you are mediating rhythmic contractions
- Synmpathetic inhabits
- Distal colon is innervated by pelvic nerve, stimulating induces expulsive movents