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MD3002 GI > GIT motility > Flashcards

GIT motility Flashcards

1
Q

what are the main functions of the GIT?

A
  • propel ingested food along the entire length of the GIT
  • mixing and grinding of the contenets of the GIT
  • aid absorption of nutrients and water
  • clear the stomac and intestines of luminal contents
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2
Q

what is GIT motility?

A

this is the ability of the alimentary canal (tract) to contract and propel ingested substances along its length

timing of food movement is important for optimum processing

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3
Q

what things does mastication aid in??

chewing

A
  • teeth (incisors and molars)
  • mixing food with saliva (lubrication - mucin is a glycoprotein that acts as a lubricant)
  • reduces food size (facilitates swallowing)
  • mixes food components with digestive enzymes (carbohydrate with salivary amylase for carbohydrate digestion and fat with lipases for lipid digestion)
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4
Q

the muscles of the teeth are innervated by which nerve

A

trigeminal nerve

cranial nerve V

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5
Q

what is the process of mastication controlled by?

A

it is controlled by brain stem nuceli
- reticular areas for rythmical chewing
- additional involvement from the hypothalamus/amygdala/cerebral cortex

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6
Q

what are the 3 stages of Deglutition (swallowing)

A

1) voluntary stage = initaites the swalloing process
2) pharyngeal phase = involuntary passage of food through the pharynx into the esophagus
3) oesophageal phase = involuntary transport of food from the pharynx to the stomach

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7
Q

what does deglutition require?

A

it requires the pharynx to be a tract for propulsion of food
- this is important so that respiration is not compromised

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8
Q

describe the steps/movement of mouth muscles/ tongue in the voluntary phase (phase1)?

A

1- food is voluntarily moved posteriorly into the pharynx by the tongue
2- the trachae is closed
3- the oesophagus is opened
4- a fast peristaltic wave is initiated by the nervous system of the pharynx forces the bolus of food into the upper esophagus

happen in < 2 seconds

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9
Q

the pharyngeal phase is a reflex arc (automatic), what is it initiated by?

A

it is initaited by the voluntary movement of food into the back of the mouth
- detected in a ring area around the pharyngeal opening.
- excitation of the involuntary pharyngeal sensory receptors to elicit the swallowing reflex.

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10
Q

how is the oesophageal phase initiated?

A

This stage is iniated automatically by neuronal areas of the medulla and lower pons
- the motor impulses from the swalloing centre to the pharynx and upper eosophagus that causes swallowing are transmitted successively by CN V, CN IX, CN X, CN XII

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11
Q

what is the effect of pharyngeal stage of swallowing on respiration?

A
  • the pharyngeal stage occurs in < 6 seconds
  • interuption of respiration is for a fraction of usual respirator cycle
  • the swallowing centre will specifically inhibit the respiratory centre of the medulla during this time (respiration is arrested very breifly)
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12
Q

stage 1 peristalsis?

A
  • continuation of the peristaltic wave that begins in the pharynx and spreads into the eosphagus during the pharyngeal stage of swallowing
  • this is a continous wave tht passes from the pharynx to the stomach in about 8-10 seconds
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13
Q

stage 2 peristalsis?

A
  • this is a result from distention of the oesophagus by retained food
  • the waves continue until all food has emptied into the stomach
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14
Q

what is stage 2 of peristalsis iniated by?

A
  • intrinsic neural circuits in the myenteric nervous system
  • reflexes that begin in the pharynx
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15
Q

what are th 2 different types of muscle that are found in the oesophagus?

A

1) straited muscle in the upper 1/3rd. (they creates peristaltic waves)
2) smooth muscle in the lower 2/3rds

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16
Q

what controls the 2 different types of muscle in the oesophagus?

A

straited = controlled by skeletal nerve impulses from the glosspharyngeal and vagus nerves

smooth = vagus nerve that acts through connections with the oesophageal myenteric nervous plexus.

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17
Q

under normal circumstances, what hsould happen in the oesophageal phase and peristalsis?
what happens in abnormal circumstances?

A

primary peristalsis should happen, this is an automatic and singular wave of contraction that does not stop until food is in the stomach.

in abnormal circumstances, if there is a blockage, a second wave will occur= secondary peristalsis.

18
Q

what is receptive relaxation?

A

this is relaxation wave that precedes peristalsis
- it opens the oesophageal sphincter in preparation for food to allow the stomach to relax. for the stomach to expand it has to relax.
- it occur ahead of the peristaltic wave
- it allows easy propulsion of food into the stomach.

19
Q

what controls receptive relaxation

A

myenteric inhibitory neurons.

20
Q

in the last 3cm of the oesophageal circular muscle, what does it act as?

A

it acts as a lower oesophageal sphincter called the gastroesophageal sphincter
- it is normally tonically constricted.

21
Q

what happens to the food entering the stomach?

storage motor function of stomach

A

the food entering the stomach will form concentric circles in the stomach.
- newest food lying closest to the oesophageal sphincter
- oldest food lying nearest the outer wall of the stomach

22
Q

what are the 3 motor functions of the stomach?

A

storage
mixing
emptying

23
Q

describe the ‘vagovagal reflex’?

A

this reflex is initated by food stretching the stomach.
- stomach -> brain stem -> back to the stomach

  • this will cause a decrease in tone in stomach muscular wall
  • the wall will then bulge outwards
  • greater quantities of food will be accomated for.

limit = 0.8-1.5 litres

24
Q

describe the motor function ‘mixing’ of the stomach?

mixing motor function of stomach

A
  • mixing of the food with gastric secretions forms a semifluid micture (chyme)
  • there are mixing waves = peak peristaltic constrictor waves which begin in mid/upper portions of the stomach wall, they move forward every 15-20 secs.
  • these waves become more intense
25
Q

describe how you get segmentation of the small intestine

mixing contractions and segmentation contractions

A
  • chyme induced extension of the GI wall -> stretch -> localised concentric contractions (spaced along intestine, short lasting) -> segmentation
  • the frequency of segmentation will be determined by the frequnecy of the slow waves
26
Q

how can segmentation become weaker?

A

it can become weak when the excitator activity of the enteric nervous system is blocked by atropine

27
Q

what causes segmentation of the small intestine

A

slow waves in the smooth muscle
however,
it is not effective without the background excitation from the myenteric nerve plexus

28
Q

describe the activity of peristalsis after a meal?

A
  • chyme entry into duodenum -> duodenal wall stretch
  • gastroenteric reflex (from stomach distension via the myenteric plexus)
  • gastrin, CCK, insulin, motilin, serotonin increases motility
  • secretin, glucagon decreases motility

activity is increased after a meal

29
Q

describe the propulsive movement of peristalsis?

A
  • occurs in any part of the small intestine
  • moves towards anus at 0.5-2cm/s
  • it becomes weak and dies out after 3-5cm
  • the net movement of chyme is slow:1cm/min
  • the chyme movement from pylorus to iliocecal valve takes about 3-5 hrs
30
Q

where is the ileocecal valve?
how does it close?

A
  • it protudes into the lumen of the cecum
  • it forcefully closs when excess pressure builds up in the cecum.
31
Q

describe the structure of the ileocecal sphincter?

A

the wall of the terminal ileum is thickened circular muscle and this creates a sphincter
- it normally remains mildly constricted and slows emptying of ileal contents into the cecum

32
Q

what happens to the ileocecal valve immediatly after a meal?

A

the gastroileal reflex intensifies peristalsis in the ileum and there will be emptying of ileal contents into the cecum

33
Q

what is the ileocecal sphincter regulated by?

A

the cecum to ileocecal sphncter and cecm ileum reflex is mediated by the myenteric plexus and extrinsic autonomic nerves.

34
Q

what are the mixing movements in the colon aided by?
what are these?

A

mixing movemets in colon = haustrations
- these are similar to segmentation movements in the small intestine
- there is combined contraction of circular and longitudinal smooth muscle
- it generates bag like sacs (30 seconds peak, then 60 secs disappear)

35
Q

what is the differance in function for the proximal and distal half of the colon?

A

proximal half = absorption
distal half = storage

36
Q

what happens in modified peristalsis

mass movements

A
  • a constrictive ring occurs (usually in the transverse colon) in response to distension
  • 20cm of colon distal to constrictive ring lose haustrations and contract as a unit
  • fecal material move in mass down the colon.
37
Q

describe the time frame for propulsive movements?

A
  • contraction develops progressivly over 30 secs
  • relaxation occurs over the next 2-3 mins
  • another mass movement then occurs
  • a series of mass movements persists for 10-30 mins, then it stops.
  • it will return at variable time points (usually every 12 hrs- straight after breafast)
  • sensation oif need to poo is felt when poo is in the rectum.

this is our body getting rid of excess food in preparation for more meals.

38
Q

describe gastrocolic and duodenal colic reflexes?

A

gastrocolic = reflex as food moves into stomach
duodenal colic = movement as food moves into duodenum

  • this is facilaited mass movement after meals
  • due to distention of the stomach and duodenum
39
Q

describe the innervation of gastrocolic and duodenal colic reflexes?
and how are they inhibited?

A

reflex from GIT to prevertebral sympathetic ganglia and back to GIT
- the reflex will be inhibited when extrinsic autonomic nerves of the colon are removed

40
Q

what is the effect of iritation of the colon?

A

irritation of the colon can also cause mass movemnts
eg - ulcerated condition of colon mucosa, mass movement persists almost all the time.

41
Q

describe defication and how does the anal canal change?

A
  • the rectum is usually empty of faeces
  • the anal canal is tightly closed via the contraction of anal sphincters
  • gas or faeces in the rectum will stimulate stretch receptors in its wall initating the rectosphincteric reflex
  • defication is a reflex activity but it is subject to conscious control.
42
Q

describ the rectosphincteric reflex?

A

this reflex relaxation of the smooth muscle of the internal anal sphincter and contraction of the striated muscle of the external anal sphincter (this is what stops us from pooing ourselves all the time)

MD3002 GI (10 decks)

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