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

Introduction to the GI tract and motility Flashcards

(67 cards)

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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
What is spontaneous activity across the syncytium modulated by?
Intrinsic (enteric) and extrinsic (autonomic) nerves Numerous hormones
26
How does electrical activity occur in the stomach, small intestine and large intestine?
Spontaneous activity occurs as slow waves
27
What does slow wave electrical activity determine?
Max frequency, direction and velocity of rhythmic contractions
28
What drives slow wave electrical activity?
Interstitial cells of cajal, pacemaker cells interspersed between the far more numerous SMCs
29
When does contraction occur?
If the slow wave amplitude is sufficient to trigger SMC acton potentials
30
What is force of contraction related to?
The number of action potentials discharged
31
What do slow waves determine?
Basic electrical rhythm
32
What does slow wave reaching threshold depend upon?
Neuronal stimuli Hormonal stimuli Mechanical stimuli
33
What is the BER frequency in the stomach?
3 slow waves per minute
34
What is the BER frequency in the small intestine?
approx 12 and 8 waves per minute respectively
35
What is the BER frequency in the large intestine?
approx 8 and 16 waves per minute
36
Describe the autonomic parasympathetic innervation of the GI tract?
Preganglionic fibres (releasing ACh) synapse with ganglion cells (in essence post-ganglionic neurones) within the ENS
37
What are the excitatory influences upon the parasympathetic innervation?
Increased gastric, pancreatic and small intestinal secretion, blood flow and smooth muscle contraction
38
What are the inhibitory influences upon the parasympathetic innervation?
Relaxation of some sphincters, receptive relaxation of stomach
39
Describe the autonomic parasympathetic innervation of the GI tract?
Preganglionic fibres (releasing ACh) synapse in the prevertebral ganglia. Postganglionic fibres (releasing NA) innervate mainly enteric neurones, but also other structures
40
What are the excitatory influences of the sympathetic system?
Increased sphincter tone
41
What are the inhibitory influences of the sympathetic innervation of the GI tract?
Decreased motility, secretion and blood flow
42
What are the preverterbal ganglia in the GI tract?
1. Celiac 2. Superior mesenteric 3. inferior mesenteric Superior cervical ganglion
43
What is the role of the myenteric (auerbach) plexus?
Regulated motility and sphincters
44
What is the role of the submucous (meissner's) plexus?
Modulates epithelia and blood vessels
45
How does the ENS operate?
Intrinsic to GI tissue- reflex circuits can operate independently but hormones and extrinsic nerves have a strong regulatory influence
46
How does the ENS co-ordinate muscular, secretive and absorptive activities?
Via - sensory neurones - interneurones - effector neurones
47
Give examples of sensory neurones of the GI tract?
Mechanoreceptors Chemoreceptors Thermoreceptors
48
What do interneurones do?
Co-ordinate reflexes and motor programmes
49
What do effector neurones do?
Excitatory or inhibitory motor neurones supplying both smooth muscle layers, secretory epithelium, endocrine cells and blood vessels
50
Give an example of a local reflex?
Peristalsis
51
Give and example of a short reflex?
Intestino-intestinal inhibitory reflex (local distension activated sensory neurones, exciting sympathetic pre-ganglionic fibres that cause inhibition of muscle activity in adjacent areas
52
Give and example of a long reflex?
Gastroileal- increase in gastric activity causes increased propulsive activity in the terminal ileum
53
Define peristalsis
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
Describe the altered activity of motoneurons in the oral direction?
Longitudinal muscle relaxes (release of VIP and NO from inhibitory motoneurone) Circular muscle contracts (release of ACh and substance P from excitatory motoneurone)
55
Describe the altered activity of motoneurons in the aboral direction?
Longitudinal muscle contracts (release of ACh and substance P from excitatory motoneurone) Circular muscle relaxes (release of VIP and NO from inhibitory motoneurone)
56
Define segmentation?
(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
Define colonic mass movement?
powerful sweeping contraction that forces faeces into the rectum – occurs a few times a day
58
Define migrating motor complex?
powerful sweeping contraction from stomach to terminal ileum (greater detail in subsequent lectures)
59
Define tonic contractions
sustained contractions low pressure - organs with a major storage function (e.g. stomach) high pressure - sphincters
60
What are sphincters?
One way valve by maintaining a positive resting pressure
61
What does pressure distally to a sphincter cause?
Closing
62
Describe the upper oesophageal sphincter?
skeletal muscle (i) relaxes to allow swallowing (ii) closes during inspiration
63
Describe the lower oesophageal sphincter?
Smooth muscle (i) relaxes to permit entry of food to the stomach (ii) closes to prevent reflux of gastric contents to the oesophagus
64
Describe the pyloric sphincter?
Smooth muscle (i) regulates gastric emptying (ii) usually prevents duodenal gastric reflux
65
Describe the ileocaecal valve?
Smooth muscle regulates flow from ileum to caecum (i) distension of ileum opens, distension of proximal colon closes
66
Describe the anal sphincters?
Internal (smooth muscle) and external (skeletal muscle) anal sphincters are regulated by the defaecation reflex
67
What is the 7th valve?
Sphincter of oddi

GI 2018 (10 decks)

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