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Body systems 2 > control of gut motility > Flashcards

control of gut motility Flashcards

1
Q

aim of G.I. tract control

A

to maximise absorption of nutrients, whilst minimising damage from toxins

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2
Q

how is control of GI tract achieved

A

-achieved by regulating motility
- controlling secretion of digestive juices

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3
Q

senses the lumen contains

A

the intestinal epithelium is the largest sensory organ in the body

senses the lumen contents:
- distention = mechanoreceptors
- osmolality = osmoreceptors
- acidity = chemoreceptors
- digestive products = chemoreceptors

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4
Q

receptor activation causes

A

nerves: a) long reflexes (brain), b) short reflexes (enteric NS)

hormones

paracrine transmission

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5
Q

what regulates movement of food through the G.I tract

A

smooth muscle (and sphincters) regulate movement of food
- circular muscle - narrows
- longitudinal muscle - shortens

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6
Q

mucosa of the gut wall

A

epithelium
lamina propria
muscularis mucosae

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7
Q

serosa of gut wall

A
  • areolar connective tissue
  • epithelium
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8
Q

muscularis of gut wall

A
  • circular muscle
  • longitudinal muscle
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9
Q

extrinsic nerves

A

parasympathetic (preganglionic) -> increased motility, increased secretion (integrates with ENS many transmitters released)

sympathetic (postganglionic) -> decreased motility (decreased blood flow)

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10
Q

G.I smooth muscle

A
  • irregular arrangement of actin/ myosin -> still generates tension when stretched
  • cells grouped into bundles of 5000 cells
  • cells are electrically coupled (gap junctions) = functional units
  • unstable membrane potential (5-15 mV) = slow waves
  • slow waves determines frequency of contraction
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11
Q

slow waves of depolarisation

A
  • resting Vm = -40 to -60 mV
  • slow waves superimposed on resting Vm
  • size of slow wave modulated by nerves and hormones
  • contraction only if slow wave reaches threshold Vm
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12
Q

modulation of slow waves

A
  • food stimulates nerve and hormonal activity: increases or decreases the size of the maximum depolarisation
  • nerves (intrinsic and extrinsic)
    • ACh -> depolarisation (increased contraction)
    • NO, VIP, NA, Ade -> hyper pol ( decreased contraction

hormones
- gastrin, motilin -> depolarisation
- secretin, GIP -> hyperpolarisation

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13
Q

G.I hormones

A
  • all short chain peptides
  • secreted by the enteroendocrine cells (found in the mucosa) into the blood
  • target various regions of G.I. and glanfs
  • may have effects on CNS
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14
Q

enteroendocrine cells

A
  • microvilli on lumen side - sense lumen contents or movement
  • 90% of EE cells - enterochromaffin cells
  • remaining 10% = hormones
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15
Q

enterochromaffin cells

A

stimulation -> release of serotonin (5-HT)

released serotonin stimulates afferent neurons via 5-HT3 receptors

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16
Q

SERT

A

removes serotonin to terminate signal

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17
Q

PIEZO 2 channel

A

mechanosensor

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18
Q

paracrine transmission

A
  • short hormones do not enter blood; diffuse through interstitial fluid
  • histamine best example (gastric secretion)
  • prostaglandins, bradykinin ( released in response to irritation of gut wall
19
Q

the mouth

A
  • chewing (mastication)
  • decrease size of food
  • increase surface area
  • increase exposure to saliva
20
Q

oral stage of swallowing

A

voluntary
- food pushed towards pharynx by tongue

21
Q

pharyngeal stage of swallowing

A

swallowing reflex - involuntary
- elevation of soft palate
- contraction of pharyngeal muscles
(inhibition of respiration and closure of glottis)
- opening of upper oesophageal sphincter

22
Q

oesophageal stage of swallowing

A

involuntary
- peristalsis in oesophagus
- opening of lower oesophageal sphincter

23
Q

stomach function

A
  1. storage
    adaptive and receptive relaxation
  2. peristalsis
    nerves and hormones (modulate force)
    - 3 contractions/ min
    -churning action
  3. pyloric S. closed by wave of contraction
    - limits emptying (3ml/min)
    -retains particles over 2 mm in diameter
24
Q

regulation of emptying

A
  1. increased distention of the stomach detected by gastrin/nerves, causes increased emptying
  2. products of digestion in duodenum -> decreased emptying
    a) enterogastric reflex: peptides and HCl in duodenum -> decreased mixing and decreased emptying

b) hormones e.g. CCK, G.I.P and secretin
food in duodenum -> decreased motility

25
Q

small intestine

A

transit = 2-4 hours
functions:
1. mixing (increased digestion and absorption
2. propulsion (minor role)

26
Q

main types of movement in the small intestine

A
  • segmentation (mixing and propulsion
  • peristalsis (propulsion)
27
Q

segmentation

A
  • contractions of circular muscle
  • contractions occur at different sites -> mixing
  • basal electrical rhythm and local distension -> myenteric plexus = local contractions
  • gradually moves chyme forward
28
Q

BER in duodenum and ileum

A

12 min-1 in duodenum
ileum = 8 min -1

29
Q

peristalsis

A

ring of contraction forms behind chyme
-> pushes chyme forward
- occurs at any point in small intestine
- initiated by distension and coordinated by myenteric plexus
- travels on a few cm
- influenced by neural/ hormonal factors
- peristaltic rush -> diarrhoea

30
Q

gastro-ileal reflex in small intestine

A

increased gastric distension -> increased ileal motility and ileocaecal valve relaxes

31
Q

ileogastric reflex in small intestine

A
  • distention of ileum -> decreased gastric motility
32
Q

ileocaecal valve

A

between small and large intestine
- normally closed

opens when:
- peristaltic wave reaches it
- as part of gastro ileal reflex

33
Q

large intestine functions

A

absorption of water and sodium

storage of feacal matter

transmit time 33h - range 5-45 hour

34
Q

mixing in large intestine

A
  • haustration = segmentation
  • constriction of circular muscle
  • longitudinal muscle arranged in 3 strips (taeniae coli and does not prevent bulging of wall -> ovoid segments = haustra)
  • contractions occur at different sites -> gradual ‘digging over’ of faecal material
35
Q

propulsion in colon
ileocaecal valve -> transverse colon

A

gradual forward movement by HAUSTRAL contractions

36
Q

propulsion in colon
descending colon -> rectum

A

mass movements (gastrocolic/ duodenocolic reflexes)
- occur 3 or 4 times per day for 10-30 min
- initiated by distension
- ring of contraction propel chyme 30-80% length of the colon
- often after meals

37
Q

rectum

A
  • usually empty - segmental contraction impedes filling
  • mass movements - faecal matter into rectum
  • distends rectum -> rectospincteric reflex
38
Q

anal sphincters

A

internal sphincter - smooth muscle - 80-85% resting anal sphincter tone
(involuntary

external sphincter - skeletal muscle (voluntary)

39
Q

defaecation reflex - short reflex

A
  • peristalsis in colon and rectum
  • relaxation of internal anal sphincters
  • propels faeces through anus
40
Q

defaecation reflex - long reflex

A

-strengthens peristalsis
- increased intra abdominal pressure
- pelvic floor descends

41
Q

defaecation

A

puborectalis contracts to choke rectum or relaxes to straighten pathway to anus

42
Q

inter digestive motility

A

presence of food -> increased nerves and hormones = motility

43
Q

peristaltic waves housekeeping functions

A
  • empties stomach of large particles
  • removes sloughed off epithelial cells
  • prevents bacteria in colon moving into small intestine

Body systems 2 (19 decks)

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