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Digestive System > Smooth Muscle and Motility > Flashcards

Smooth Muscle and Motility Flashcards

1
Q

What are the types of muscle in the GIT and what is the distinction between the 2

A
  • Smooth - Involuntary
  • Skeletal - Voluntary
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2
Q

Where in the GIT are smooth and skeletal muscle found

A
  • Smooth muscle - most regions
  • Skeletal muscle - Pharynx, top third of oesophagus, external and sphincter
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3
Q

What are the 2 types of smooth muscle and what is the major distinction between the 2

A
  • Phasic - Rapidly contracts
  • Tonic - Allows for sustained contraction
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4
Q

Where in the GIT is phasic smooth muscle found

A
  • Body of oesophagus
  • Stomach of antrum
  • Small and large intestines
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5
Q

Where in the GIT is tonic smooth muscle found

A
  • Lower oesophageal sphincter
  • Ileocecal valve
  • Internal anal sphincter
  • Upper stomach (orad)
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6
Q

PACE MAKEING??

A
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7
Q

What causes the contraction of smooth muscle

A
  • An increase in the oscillating membrane potential of the ICC above the threshold
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8
Q

What stimulates depolarisation of smooth muscle cells in muscle contraction

A
  • Stretch
  • ACh
  • Parasympathetic innervation
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9
Q

What causes the relaxation of smooth muscle in the GIT

A
  • The movement of the oscillating membrane potential away from the threshold value.
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10
Q

What stimulates hyperpolarisation of smooth muscle cells in smooth muscle relaxation

A
  • Noradrenaline
  • Sympathetic innervation
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11
Q

What intrinsically innervates the gastrointestinal tract

A
  • Enteric nervous system
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12
Q

What extrinsically innervates the gastrointestinal tract

A
  • Autonomic nervous system
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13
Q

What are the 2 divisions of the enteric nervous system

A
  • Submucosal plexus
  • Myenteric plexus
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14
Q

Where is the submucosal plexus found

A
  • Between submucosa and circular muscle
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15
Q

Where is the myenteric plexus found

A
  • Between longitudinal and circular muscle
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16
Q

What divisions of the autonomic nervous innervate smooth muscle contraction and smooth muscle relaxation

A
  • Parasympathetic - contraction
  • Sympathetic - relaxation
17
Q

What are the effects of activating the myenteric plexus

A
  • Increase in tonic contraction
  • Increase in intensity/rate of phasic contractions
  • Increase in velocity of conduction
18
Q

What are the effects of activating the submucosal plexus

A
  • Increase in secretory activity
  • Modulation of intestinal absorption
19
Q

What are the 3 main levels of organisation in the enteric nervous system

A
  • Receptors
  • Sensory neurones
  • Motor neurones
20
Q

What are the 2 types of receptors in the enteric nervous system

A
  • Mechanoreceptors
  • Chemoreceptors
21
Q

What are the 2 types of motor neurones in the enteric nervous system

A
  • Inhibitory
  • Excitatory
22
Q

What are the effects of stimulating the sympathetic and parasympathetic nervous system in extrinsic innervation

A
  • Sympathetic - Motility is inhibited (due to hyperpolarisation)
  • Parasympathetic - Motility is increased (due to depolarisation)
23
Q

What is the supply of parasympathetic innervation to the digestive organs

A
  • Vagus nerve (oesophagus to transverse colon)
  • Pelvic nerves (descending colon to rectum)
24
Q

What causes an excitatory reflex in the gut wall

A
  • Stimulation of sensory neurones that activate an excitatory motor neurone
25
Q

Give some examples of excitatory reflexes in the gut

A
  • Gastro-colic reflex
  • Gastro-enteric reflex
  • Gastro-ileal reflex
  • Duodeno-colic reflex
26
Q

Explain the gastro-colic reflex

A
  • Distension caused by having a big meal
  • Mechanoreceptors detect this
  • Signals are sent to colon via excitatory motor neurones (increases colon motility)
  • This makes room for chyme that will enter the colon from the stomach
27
Q

What causes an inhibitory reflex in the gut wall

A
  • Stimulation of sensory neurones that cause activation of inhibitory motor neurones
28
Q

Give some examples of inhibitory reflexes in the gut wall

A
  • Ileo-gastric reflex
29
Q

Explain the ileo-gastric reflex

A
  • Distension of ileum activates the mechanoreceptors that are present
  • As chyme in ileum is not yet digested or absorbed inhibitory signals are sent to the stomach
30
Q

Name 3 pathologies of GIT motility

A
  • Hirschsprung disease - congenital lack of neuronal ganglionic cells in ENS plexuses
  • Chagas disease - Parasitic infection that causes reduction in number of neuronal ganglionic cells
  • Achalasia- Reduction of neuronal cell numbers in lower oesophageal segment
31
Q

What can Hirschsprung disease cause and what is a treatment for it

A
  • Megacolon (above the point where the neurones are missing)
  • Treatment - removal of aganglionic section and joining the 2 healthy ends
32
Q

14:26

A

Digestive System (7 decks)

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