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Metabolism > GI motility > Flashcards

GI motility Flashcards

1
Q

describe how movement of stomach smooth muscle is initated? at which cells?

A

human stomach movement:

  • random depolarisation of interstitial cells of cajal is communicated to smooth muscle cells, via gap junctions
  • slow waves of electrical activity propagte from dominant pacemake in corpus (see photo)
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2
Q

fill the blanks bestie

A
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3
Q

the stomach movements are spontaneous, but are modulated by which NS?

A

= by enteric NS

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4
Q

overall function of the enteric system? (3)

what are two plexi find in enteric nervous system?
what are their locations?
functions?

A
  • *enteric system function:**
  • controls GI motility
  • controls local blood flow
  • controls transmucosal movement of fluids
  • *mytenric plexus:
  • location: between theinner and outer layers of the muscularis externa**
  • function: primary motility controller
  • *submucosal plexus:
  • location:submucosa**
  • function: primarly fluid exchange controller
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5
Q

GI tract dominant nervous control systems:

which (out of CNS, myogenic and ENS) controls:

a) oesphagus?
b) stomach? (3)
c) small intestine
d) colon? (2)
e) anus? (2)

A

a) oesphagus: CNS contrl (vagus)
b) stomach: myogenic (ICC), ENS & CNS (vagus)
c) small intestine: ENS
d) colon: ENS and myogenic control
​e) anus: ENS and CNS (spinal)

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6
Q

what is the migrating motor complex?

where can it originate?

what is its functions? (2)

A

migrating motor complex: propagating contractions every 90-120 mins. 3 phases

originates:

  • *a) stomach -** vagus dependent
  • *b) small intestine -** _vagus independent

functions:_

a) clear undigested material
b) prevents bacteria overgrowth

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7
Q

what are the three stages of the migrating motor complex?

A
  • Phase 1 is fairly quiet,
  • Phase 2 occurs after an hour or so with small changes in amplitude
  • Phase 3 is a great high amplitude contraction - makes u hungry
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8
Q

what two things specifically make u hungry?

A
  • release of hormone ghrelin
  • phase three of migrating motor complex
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9
Q

what are 3 stages of digestion?

A

Cephalic phase: Thought, sight, smell, taste (learned responses). MMCs abolished. Prepares GI tract: saliva, gastric acid, pancreatic secretion, gastrin, ghrelin secretion

Gastric phase: Satiation, early digestion, gastric emptying. This is triggered by mechanical effect. Triggered by mechanical effect.

Intestinal phase: Feedback and satiation. Triggered mainly by chemoreceptor activation within the small bowel.

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10
Q

how does peristalsis occur in oesophagius ? (primary / secondary waves?)

A

peristalsis:

  • bolus enters striated muscle, initiates primary peristaltic wave. pressures changes / waves of contraction push bolus down.
  • this stimulates stretch receptors = secondary peristaltic wave of smooth muscle (back up secondary wave) pushes the bolus into the stomach
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11
Q
  • *functions of the proximal stomach:**
  • what happens when bolus enters stomach? (2 steps)
  • what is each step innervated by?
  • what method can u do to relieve pressure of stomach? - how does this occur?

functions of the distal stomach? (3)

A

functions of the proximal stomach:

  • *- receptive relaxation:** makes proximal stomach stretch so not immediatly full (vagal-vagal relflex, causes release of CCK)
  • *- adaptive relaxation:** ENS releases NO to allow relaxation
  • can relieve pressure by _burping (_lets gas out of stomach) via relaxation of LOS
  • *functions of the distal stomach:**
  • propulsion, retropulsion and further grinding and mixing (propels food agaisnt closed pylorus)
  • gastric acid digestion
  • only particles of 1-2 mm empty into duodenum
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12
Q

fyi

A
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13
Q

describe the speed of gastric empty of:

a) liquids?
b) large solid particles
c) viscous chyme?

what is rate of emptyin regulated by?

A

a) liquids: fast and exponential
b) large solid particles: lag phase - only after sufficient grinding
c) viscous chyme: linear fashion

get slow gastric emptying and promotes satiety

= maintains a constant flow of nutrients into the intestine !!

rate of emptyin regulated by: intestine - neural and hormonal

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14
Q

what are the dudenal and jejunal brakes?

A

dudenal and jejunal brakes:

  1. food goes into the duodenum, might be too big - like long chain fatty acids / amino acids. causes the release of CCK
  2. release of CCK activates vagal efferents
  • *3. as a result of vagal efferents:**
  • reduces opening of pyloric sphincte
  • reductions contractions in corpus
  • enhances relaxation of fundus
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15
Q

what is the ileal brake?

A
  • fats reach the ileum (even tho theyre meant to have been absorbed in duodenum)
  • causes release of peptide YY & **glucagon-like peptide-1 (GLP-1) by enteroendocrine cells

= slows gastric emptying**

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16
Q

describe how the ENS and peristaltic reflex works:

  1. how this reflex activated? (2)
  2. describe the difference between the different motor neurons causing ascending and descending wave of peristalsis:
  • what type of NT released?
  • what does that cause?
A

1. Activation of enteric reflexes: can be chemical or mechanical.

  • Chemical activation can be through substances from endocrine cells (e.g. 5-HT), nutrients or low Ph
  • mechanical via muscle deformation or stretch

motor neurons:
Ascending wave of peristalsis:excitatory neuro-transmission to muscle, mostly by the release of acetylcholine. This causes the contraction and initiate the push.

Descending wave of peristalsis: Inhibitory neurotransmission to muscle, mostly by release of the gas nitric oxide

17
Q

role of ascending (3), transverse (1) and descending colon? (2)

A
  • *Ascending colon:**
  • *-**mixing
  • absorption of water / ions / nutrients
  • fermentation due to rich no. of living bacteria
  • *Transverse colon**:
  • Absorption, with relatively rapid transit
  • *Descending colon**:
  • Storage.
  • Partly voluntary transit when defecation needed.
18
Q

what anatomical features of the colon ensure that peristalsis is modified?

A
  • get bulges of outer circular muscle (haustra), which are held together by three bands of circular muscle: taenia

- taenia can contract in either direction

19
Q

what are the movements of the ascending colon? (3)

A

propulsion

retropulsion

segmentation (mixes contenet and increases exposure to mucosa)

20
Q

how does bolus move along colon? (2)

A
  • constrictive ring occurs (giant migrating concentration) and haustra disappear from a portion of the ascending colon

~20cm of the colon distal to the constrictive ring lose their haustrations and contract as a unit, propelling faecal material into the transverse colon

21
Q

what happens when bolus goes into rectum?

A
  • Contents continue to enter rectum
  • Triggers conscious urge to defecate due to increased pressures
  • As contents distend the rectum, the pressure increases passively - active contraction may increase pressure further
  • Accompanied by relaxation of internal anal sphincter & contraction of external sphincter
22
Q

what normally prevents defecation? (2) what changes when u defecate

A
  • *defecation prevented by:**
  • Tone of internal anal sphincter & puborectalis
  • Mechanical effects of acute anorectal angle. The pubic symphysis and angle act as a mechanical obstruction to defecate moving to the anus.
  • *defecate:**
  • Puborectalis muscle and external anal spinchter relax
  • Intraabdominal pressure increase
  • squatting facilaites

Metabolism (35 decks)

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