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AEU (CLB) > Gut motility > Flashcards

Gut motility Flashcards

1
Q

Why do we need motility within the GI tract

A
  • To propel ingesta along the tract
  • To retain ingesta at a given site for digestion/ absorption/ storage
  • To physically break up food material and mix it with digestive secretions
  • To circulate ingesta so that it comes into contact with absorptive substances
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2
Q

How is motility achieved in the GI tract (3 ways)

A

1) Peristalsis
2) Mechanical digestion
3) Mixing

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3
Q

What does mechanical digestion mean?

A

Involuntary contractions and relaxations of muscles in the tract to help break down food.

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4
Q

What are the 3 regulations of motility in the GI tract?

A

1) Neural
2) Hormonal
3) Myogenic

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5
Q

What parts of the nervous system are responsible for motility (in a neural sense)

A
  • ANS (inc sympathetic and parasympathetic)
  • ENS (this uses the myenteric plexus and the submucosal plexus)
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6
Q

What 3 types of hormone are responsible for motility in the GI tract?

A
  • Classical hormones (endocrine)
  • Local hormones (paracrine)
  • Neurohormone (neurocrine)
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7
Q

How are endocrine substances transported?

A

Classical hormones are carried by the blood from endocrine cells to target cells

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8
Q

How are paracrine substances transported?

A

Local hormones diffuse through interstitial fluid and act on target cells in the immediate vicinity of the secretory cell

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9
Q

How are neurocrine substances transported?

A

Neurohormones are released from neurones and transported by blood to target cells.

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10
Q

What does myogenic control of motility refer to?

A

The intrinsic/ natural rhythm of the GI muscularate

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11
Q

How is the parasympathetic nervous system involved in the motility of the GI tract?

A
  • Relies on the vagus nerve down to the level of the transverse colon and then pelvic nerves to the rest of the tract
  • Activation of parasympathetic nervous system usually stimulates activity of the GI tract
  • Contributes to rest and digest response
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12
Q

How is the sympathetic nervous system involved in the motility of the GI tract?

A
  • Relies on pathway via postganglionic adrenergic fibres which terminate in the submucosal and myenteric plexus
  • Activation of the sympathetic nervous system inhibits activity of the the GI tract
  • Contributes to fight/ flight response
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13
Q

What are interneurones?

A

Interneurones are nerves that connect the myenteric plexus and the submucosal plexus

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14
Q

What is the role of interneurones?

A

Interneurones within the plexus connect affect neurones with efferent neurones to smooth muscle (forming reflex arcs within the wall of the GI tract).

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15
Q

What do axons from neurones in the plexus innervate?

A
  • Smooth muscle cells in the muscularis externa and muscularis mucosae
  • Secretory cells in the mucosa and submucosa
  • Intramural endocrine cells
  • Blood vessels
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16
Q

What happens during the short reflex arc of the GI tract?

A
  • Chemoreceptors and mechanoreceptors in the wall of the GI tract send signals to the myenteric plexus and submucosal plexus via local afferents
  • The myenteric plexus and submucosal plexus send signals to the muscularis externa, the muscularis mucosae, endocrine cells, secretory cells and blood vessels via local efferents.
17
Q

What happens during the long reflex arc of the GI tract?

A
  • Taste and smell senses send signals to the CNS
  • Chemoreceptors and mechanoreceptors send signals to CNS via splanchnic and vagal afferents
  • CNS interacts with submucosal and myenteric plexus via sympathetic and parasympathetic pathways (efferent nerves).
  • These efferents also send signals to the muscularis external, muscularis mucosae, endocrine cells, secretory cells and blood vessels.
18
Q

How are endocrine cells stimulated within the GI tract?

A
  • Stimulated by long + short reflex arcs
  • Stimulated by composition of luminal contents
  • Stimulated by stretch
19
Q

What are the 8 different hormones that act in the GI tract?

A

1) Gastrin
2) Cholecystokinin
3) Secretin
4) Gastric Inhibitory Peptide
5) Vasoactive Intestinal peptide
6) Gastrin releasing peptide
7) Histamine
8) Serotonin
Some Say Good Girls Can Go Very Hormonal

1-4 = Endocrine. 5-6 = Neurocrine. 7-8 = Paracrine

20
Q

Where are the interstitial cells of Cajal located?

A

Within the smooth muscle of the GI tract

21
Q

What is the function of the interstitial cells of cajal?

A

They exhibit slow oscillations in membrane potentials to make the basic electrical rhythm of the GI tract

22
Q

How does the oesophagus move food from the pharynx to the stomach?

A

Via peristalsis (specifically the primary peristaltic wave)

23
Q

What is the secondary peristaltic wave?

A

A wave of peristalsis further down the oesophagus that is mediated by local reflexes originating in the enteric nervous system at the site of distention

24
Q

What is the interdigestive motility complex?

A

Alternating periods of quiescence and peristaltic contractions

25
Q

What is receptive relaxation and how is it controlled?

A
  • Receptive relaxation = when smooth muscle in the proximal part of the stomach relaxes to allow food to enter
  • Controlled/ regulated by the swallow centre as the vagus nerve carries information from the swallow centre to the stomach
26
Q

How does muscle contraction occur in the stomach?

A
  • Contraction begins in the fundus, narrowing the lumen and forcing food down into the pyloric region.
  • Pyloric region contracts, some food goes down into the duodenum but most of it is circulated back up to the fundus region
27
Q

What are the 2 types of muscle contraction in the small intestine?

A

1) Segmentation = mixing movements
2) Peristalsis = propulsive movements

28
Q

What is the migrating motility complex?

A

Myoelectric waves that sweep through the intestine in a regular cycle during the interdigestive state

29
Q

What are the 4 types of contraction possible in the large intestine?

A

1) Haustration (sacs which store and propel contents)
2) Peristalsis
3) Antiperistalsis (in opposite direction)
4) Mass movements (peristaltic contraction) moving from transverse colon to rectum

AEU (CLB) (11 decks)

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