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GI- WK 1-3 > Structure of GI tract & Motility > Flashcards

Structure of GI tract & Motility Flashcards

1
Q

What are the important structures of the alimentary canal?
(6)

A
  1. Mouth + oropharynx
  2. Oesophagus
  3. Stomach
  4. Small intestine
  5. Large intestine
  6. Rectum & Anus
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2
Q

What are the accessory structures of the alimentary canal? (3)

A
  • Salivary glands
  • Pancreas
  • Liver & Gall bladder
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3
Q

What are the layers (inwards going out) of the digestive tract wall? (4)

A
  1. Mucosa
  2. Submucosa
  3. Muscularis externa
  4. Serosa
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4
Q

Main cells type found in mucosa?

A

Epithelial cells

Lamina propria

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5
Q

Main cells type found in Sub-mucosa?

A

Connective Tissue

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6
Q

Main cells type found in Muscularis externa?

A

Connective tissue. Consists of circular and longitudinal muscle layer.

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7
Q

Main cells type found in Serosa?

A

Connective tissue

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8
Q

What are the main smooth muscle layers involved in GI motility?

A

Circular muscle layer
Longitudinal muscle layer
muscularis Mucosa

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9
Q

What are the effects of Circular muscle contraction on Lumen?

A

Narrower & Longer

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10
Q

What are the effects of Longitudinal muscle contraction on Lumen?

A

Fatter & Shorter

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11
Q

What is the role of muscularis Mucosa?

A

change in secretory/ absorptive Area of Mucosa (folding).

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12
Q

What is the function of gap junctions in smooth muscle cells?

A

Allows electrical conduction between adjacent cells.

Smooth muscle- contracts as a unit

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13
Q

Are the waves of depolarisation in the stomach, small & large intestine Fast or Slow?

A

Slow.

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14
Q

Which cells are these slow electrical impulses driven by?

A

Interstitial cells of Cajal. Pacemaker cells of the GI tract.

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15
Q

Where are the interstitial cells of Cajal found?

A

Between circular and longitudinal muscle layer.

And in Submucosa

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16
Q

Why don’t all slow waves lead to smooth muscle contraction?

A

Not all of them reach the threshold for the AP.

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17
Q

What factors affect the slow wave impulse?

A
  • Hormonal stimuli
  • Neuronal stimuli
  • Mechanical stimuli
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18
Q

What is the significance of the duodenum having a faster slow wave impulse than the terminal lieum?

A

Drives luminal contents in Aboral direction

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19
Q

What is the significance of the slow rate of the proximal colon being half of the distal colon?

A

Favours retention of luminal contents

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20
Q

Where are the neurones of the enteric nervous system located?

A

Ganglia of-

  1. Myenteric Plexus
  2. Sub-mucous plexus
21
Q

Function of myenteric plexus?

A

Maintains motility and sphincter.

22
Q

Function of sub mucous plexus?

A

Modulates epithelia and blood vessels

23
Q

Is the Enteric nervous system an intrinsic or extrinsic stimulation?

A

Intrinsic. Found in GI tract.

24
Q

How does the ENS coordinate muscular, secretive & absorptive activities?

A
  1. Sensory neurones
  2. Inter- neurones (Main ones. Coordinates reflexes & motor programme)
  3. Effector neurones
25
Q

Where does parasympathetic innervation of the GI tract synapse?

A

Preganglionic fibres synapse with ganglionic cells at the ENS.

26
Q

What are the excitatory effects of parasympathetic stimulation?

A
  • Increased gastric, pancreatic
  • ” small intestinal secretion
  • ” SM contraction and blood flow
27
Q

What are the inhibitory effects of parasympathetic stimulation?

A

Relaxation of

  1. Stomach
  2. Sphincter.
28
Q

Where does sympathetic innervation synapse?

A

Preganglionic synapse at pre-vertebral ganglia

Post-ganglionic– synapse neurones in ENS

29
Q

What is the excitatory effect of sympathetic stimulation

A

Increased sphincter tone

30
Q

What is the inhibitory effect of sympathetic stimulation

A

Reduced motility, secretion and blood flow

31
Q

Example of local Reflex in GI tract?

A

Peristalsis

32
Q

Example of short reflex?

A

Intestino-intestinal inhibitory reflex

33
Q

Example of long reflex?

A

Gastro-ileal reflex

34
Q

What is peristalsis?

A

Wave of relaxation followed by contraction which travels in aboral direction.

35
Q

What factor triggers peristalsis?

A

Distension of gut wall

36
Q

How does distension cause peristalsis?

A
  1. Distension
  2. Sensory neurones activated
  3. Altered activity of motoneurons and interneurones.
  4. Either causes contraction or relaxation via circular or longitudinal SM.
37
Q

What is segmentation?

A

Rhythmic contractions of Circular muscle layer that mixes and churns luminal contents.

38
Q

What is colonic mass movement?

A

Sweeping contraction forces faeces into rectum

39
Q

What is the migrating motor complex (MMC)

A

Powerful contraction stretching from stomach to terminal ileum

40
Q

Where are tonic (sustained) contractions low and high pressure?

A

Low- organs w major storage functions

High- Sphincter

41
Q

What are the major 6 Sphincters of the body?

A
  1. Upper Oesophageal
  2. Lower “
  3. Pyloric
  4. Ileocaecal valve
  5. Internal Anal
  6. External Anal
42
Q

The above sphincters are generally composed of smooth muscle except?

A

Upper oesophageal sphincter. Composed of skeletal muscle.

43
Q

What are the important structures of the mouth?(5)

A
  1. Lips
  2. Teeth
  3. Pallate
  4. Tongue
  5. Pharynx
44
Q

What are the 3 phases of swallowing?

A
  1. Oral/ Voluntary
  2. Pharyngeal
  3. Oesophageal
45
Q

What happens in oral phase?

A

Tongue pushes food upwards & Backwards into the pharynx.

  1. Mechanoreceptors stimulated
  2. Afferent nerve impulses via CN IX, X sent to pons & medulla.
  3. Efferent nerve impulses via CN VIII, IX, X, XI to laryngeal pharyngeal skeletal muscle.
46
Q

What happens in the pharyngeal phase? (4)

A

Involuntary phase

  1. Epiglottis closes over larynx/trachea. Breathing is stopped
  2. Vocal folds closed.
  3. Soft palate flicks up to block access to nasopharynx..
  4. Tongue blocks off food from going back into oral cavity
47
Q

What happens in the oesophageal phase?

A

Closure of the upper oesophageal Sphincter.

Primary peristalsis triggered

48
Q

What happens if food remains in the oesophagus after this?

A

Second wave of contraction pushes them down.

49
Q

Which nerves stimulate the process of swallowing? (3)

A
  1. Trigeminal
  2. Glossopharyngeal
  3. Vagus

GI- WK 1-3 (25 decks)

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