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GI 2018 > Introduction to the GI tract and motility > Flashcards

Introduction to the GI tract and motility Flashcards

1
Q

What is the function of the mouth and oropharynx?

A

chops and lubricates food, starts carbohydrate digestion, propels food to oesophagus

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2
Q

What is the function of the oesophagus?

A

Muscular tube- propels food to the stomach

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3
Q

What is the function of the stomach?

A

Stores/churns food, continues carbohydrate and protein digestion, regulates delivery of chyme to the duodenum

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4
Q

What is the function of the small intestine?

A

Principle site of digestion and absorption of nutrients

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5
Q

What is the function of the large intestine?

A

Colon reabsorbs fluid and electrolytes, stores faecal matter before delivery to the rectum

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6
Q

What is the function of the rectum and anus?

A

Storage and regulated expulsion of faeces

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7
Q

What are the accessory structures of the alimentary canal?

A

Salivary glands, pancreas, liver and gall bladder

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8
Q

Define motility

A

Mechanical activity mostly involving smooth muscle

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9
Q

Define secretion?

A

Into the lumen of the digestive tract occurs from itself and accessory structures in response to the presence of food, hormonal and neural signals

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10
Q

What is secretion required for?

A

Digestion
Protection
lubrication

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11
Q

Define digestion

A

Chemical breakdown baby enzymatic hydrolysis of complex foodstuffs to smaller, absorbable units

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12
Q

Define absorption

A

Transfer of the absorbable products of digestion from the digestive tract to the blood or lymph

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13
Q

What is present in the mucosa of the digestive tract wall?

A 
Epithelial cells
Exocrine cells
Endocrine gland cells
Lamina propria (capillaries, enteric neurones, immune cells)
Muscularis mucosae
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14
Q

What is present in the submocosa of the digestive tract wall?

A

Connective tissue
Larger blood and lymph vessels
Glands
Nerve nerwork (sub mucous plexus)

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15
Q

What is present in the muscularis external of the digestive tract wall?

A

Circular muscle layer
Myenteric plexus
Longitudinal muscle layer

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16
Q

What is the serosa?

A

Connective tissue

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17
Q

What is GI motility largely due to?

A

Activity of smooth muscle

Skeletal muscle activity in the mouth, pharynx, upper oesophagus and external anal sphincter

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18
Q

What does circular muscle contraction causes?

A

Lumen becomes narrower and longer

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19
Q

What does longitudinal muscle contraction cause?

A

Intestine becomes shorter and fatter

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20
Q

What does contraction of the muscularis mucosae cause?

A

Change in absorptive and secretory area of mucosa (folding), mixing activity

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21
Q

What are adjacent SMC coupled by?

A

Gap junctions

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22
Q

What do gap junctions form?

A

Functional syncytium

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23
Q

How are cells depolarised in the smooth muscle of the GI tract?

A

By one synchronous wave

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24
Q

What is spontaneous activity across the syncytium driven by?

A

Pacemaker cells

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25
Q

What is spontaneous activity across the syncytium modulated by?

A

Intrinsic (enteric) and extrinsic (autonomic) nerves

Numerous hormones

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26
Q

How does electrical activity occur in the stomach, small intestine and large intestine?

A

Spontaneous activity occurs as slow waves

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27
Q

What does slow wave electrical activity determine?

A

Max frequency, direction and velocity of rhythmic contractions

28
Q

What drives slow wave electrical activity?

A

Interstitial cells of cajal, pacemaker cells interspersed between the far more numerous SMCs

29
Q

When does contraction occur?

A

If the slow wave amplitude is sufficient to trigger SMC acton potentials

30
Q

What is force of contraction related to?

A

The number of action potentials discharged

31
Q

What do slow waves determine?

A

Basic electrical rhythm

32
Q

What does slow wave reaching threshold depend upon?

A

Neuronal stimuli

Hormonal stimuli

Mechanical stimuli

33
Q

What is the BER frequency in the stomach?

A

3 slow waves per minute

34
Q

What is the BER frequency in the small intestine?

A

approx 12 and 8 waves per minute respectively

35
Q

What is the BER frequency in the large intestine?

A

approx 8 and 16 waves per minute

36
Q

Describe the autonomic parasympathetic innervation of the GI tract?

A

Preganglionic fibres (releasing ACh) synapse with ganglion cells (in essence post-ganglionic neurones) within the ENS

37
Q

What are the excitatory influences upon the parasympathetic innervation?

A

Increased gastric, pancreatic and small intestinal secretion, blood flow and smooth muscle contraction

38
Q

What are the inhibitory influences upon the parasympathetic innervation?

A

Relaxation of some sphincters, receptive relaxation of stomach

39
Q

Describe the autonomic parasympathetic innervation of the GI tract?

A

Preganglionic fibres (releasing ACh) synapse in the prevertebral ganglia. Postganglionic fibres (releasing NA) innervate mainly enteric neurones, but also other structures

40
Q

What are the excitatory influences of the sympathetic system?

A

Increased sphincter tone

41
Q

What are the inhibitory influences of the sympathetic innervation of the GI tract?

A

Decreased motility, secretion and blood flow

42
Q

What are the preverterbal ganglia in the GI tract?

A
  1. Celiac
  2. Superior mesenteric
  3. inferior mesenteric

Superior cervical ganglion

43
Q

What is the role of the myenteric (auerbach) plexus?

A

Regulated motility and sphincters

44
Q

What is the role of the submucous (meissner’s) plexus?

A

Modulates epithelia and blood vessels

45
Q

How does the ENS operate?

A

Intrinsic to GI tissue- reflex circuits can operate independently but hormones and extrinsic nerves have a strong regulatory influence

46
Q

How does the ENS co-ordinate muscular, secretive and absorptive activities?

A

Via

  • sensory neurones
  • interneurones
  • effector neurones
47
Q

Give examples of sensory neurones of the GI tract?

A

Mechanoreceptors
Chemoreceptors
Thermoreceptors

48
Q

What do interneurones do?

A

Co-ordinate reflexes and motor programmes

49
Q

What do effector neurones do?

A

Excitatory or inhibitory motor neurones supplying both smooth muscle layers, secretory epithelium, endocrine cells and blood vessels

50
Q

Give an example of a local reflex?

A

Peristalsis

51
Q

Give and example of a short reflex?

A

Intestino-intestinal inhibitory reflex (local distension activated sensory neurones, exciting sympathetic pre-ganglionic fibres that cause inhibition of muscle activity in adjacent areas

52
Q

Give and example of a long reflex?

A

Gastroileal- increase in gastric activity causes increased propulsive activity in the terminal ileum

53
Q

Define peristalsis

A

A wave of relaxation, followed by contraction that normally proceeds along the gut in an aboral direction- triggered by distension of the gut wall

54
Q

Describe the altered activity of motoneurons in the oral direction?

A

Longitudinal muscle relaxes
(release of VIP and NO from inhibitory motoneurone)

Circular muscle contracts
(release of ACh and substance P from excitatory motoneurone)

55
Q

Describe the altered activity of motoneurons in the aboral direction?

A

Longitudinal muscle contracts (release of ACh and substance P from excitatory motoneurone)

Circular muscle relaxes (release of VIP and NO from inhibitory motoneurone)

56
Q

Define segmentation?

A

(mixing, or churning, movements) – rhythmic contractions of the circular muscle layer that mix and divide luminal contents
-occurs in the small intestine (in the fed state) and in the large intestine (where it is called haustration) (greater detail in subsequent lectures)

57
Q

Define colonic mass movement?

A

powerful sweeping contraction that forces faeces into the rectum – occurs a few times a day

58
Q

Define migrating motor complex?

A

powerful sweeping contraction from stomach to terminal ileum (greater detail in subsequent lectures)

59
Q

Define tonic contractions

A

sustained contractions

low pressure - organs with a major storage function (e.g. stomach)

high pressure - sphincters

60
Q

What are sphincters?

A

One way valve by maintaining a positive resting pressure

61
Q

What does pressure distally to a sphincter cause?

A

Closing

62
Q

Describe the upper oesophageal sphincter?

A

skeletal muscle

(i) relaxes to allow swallowing
(ii) closes during inspiration

63
Q

Describe the lower oesophageal sphincter?

A

Smooth muscle

(i) relaxes to permit entry of food to the stomach
(ii) closes to prevent reflux of gastric contents to the oesophagus

64
Q

Describe the pyloric sphincter?

A

Smooth muscle

(i) regulates gastric emptying
(ii) usually prevents duodenal gastric reflux

65
Q

Describe the ileocaecal valve?

A

Smooth muscle

regulates flow from ileum to caecum

(i) distension of ileum opens, distension of proximal colon closes

66
Q

Describe the anal sphincters?

A

Internal (smooth muscle) and external (skeletal muscle) anal sphincters

are regulated by the defaecation reflex

67
Q

What is the 7th valve?

A

Sphincter of oddi

GI 2018 (10 decks)

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