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GI > Alimentary Canal > Flashcards

Alimentary Canal Flashcards

1
Q

What is the alimentary canal?

A

Series of organs from mouth to anus separated by sphincters

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2
Q

Orally?

A

Moving towards mouth

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3
Q

Aborally?

A

Moving towards anus

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4
Q

List of organs in alimentary canal?

A

Mouth & oropharynx, oesophagus, stomach, small intestine, large intestine, rectum & anus

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5
Q

What are the accessory structures of alimentary canal?

A

Salivary glands, pancreas, liver and gallbladder

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6
Q

What is the function of each part of canal?

A

Mouth & oropharynx - chops & lubricates food, starts carb digestion, propels food to oesophagus

Oesophagus - muscular tube that propels food to stomach

Stomach - stores/churns food, continues carb and starts protein digestion, regulates delivery of chyme to duodenum

Small intestine - Duodenum, jejunum, ileum, main site of digestion and absorption

Large intestine - Caecum, appendix, colon, colon reabsorbs fluids and electrolytes and stores faecal matter

Rectum & anus - storage and expulsion of faeces’

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7
Q

Superior to inferior parts of the colon?

A

Descending, ascending, sigmoid.

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8
Q

Activities of alimentary canal?

A

Motility
Secretion
Digestion
Absorption

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9
Q

Motility?

A

Mechanical activity mostly involving smooth muscle except pharynx, upper oesophagus and external anal sphincter which is skeletal muscle

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10
Q

Secretion?

A

Occurs in presence of neural, hormonal or mechanical stimuli.

Required for digestion, protection and lubrication

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11
Q

Digestion?

A

Chemical breakdown of food by enzymatic hydrolysis to smaller absorbable units

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12
Q

Absorption?

A

Transfer of absorbable units from GI tract to blood or lymph

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13
Q

Generalised structure of digestive tract wall?

A

Refer to slide

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14
Q

How does motility arise?

A

Activity of smooth muscle (skeletal in some cases)

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15
Q

Types of smooth muscle involved in motility?

Effects of contraction of these?

A

Circular - contraction narrows lumen and lengthens muscle

Longitudinal - contraction shortens intestine and fattens it

Muscularis mucosae - contraction causes change in absorptive and secretory area of mucosa by folding

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16
Q

What is GI smooth muscle coupled by?

A

Electrically coupled by gap junctions

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17
Q

What is the role of gap junctions in GI smooth muscle?

A

Allow spread of electrical currents forming functional syncytium - synchronised contraction to act as single unit SM

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18
Q

How is the excitation generated?

A

Spontaneously by pacemaker cells - Interstitial cells of cajal (ICCs)

Modulated by:

Intrinsic (enteric) and extrinsic (autonomic) nerves

Hormones

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19
Q

How is this excitation described in stomach and small/large intestine?

A

Slow waves

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20
Q

When does contraction of SM occur?

A

When slow wave amplitude reaches threshold to trigger AP

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21
Q

Where are ICCs found and how do they link?

A

Between longitudinal and circular muscle layers and in submucosa

Form gap junctions with each other and SMC

22
Q

What determines if a slow wave reaches threshold?

What does slow wave determine?

A

Neural, hormonal or mechanical (food) stimuli

Basic electrical rhythm

23
Q

BER Frequency for stomach, small intestine and large intestine

A

Stomach - 3 slow waves per min

Small intestine - 12 in duodenum and 8 in terminal ileum

Drives contents in aboral direction

Large intestine - 8 in proximal colon and 16 in sigmoid

Favours retention of luminal contents

24
Q

Parasympathetic Stimulation of GI tract?

A

Preganglionic fibres (releasing ACh) synapse with ganglia (in essence post ganglionic neurones) within enteric nervous system

25
Q

Parasympathetic excitatory influences?

A

Increases gastric, pancreatic and small intestinal secretion, blood flow and SM contraction

26
Q

Parasympathetic inhibitory influences?

A

Relaxation of some sphincters, receptive relaxation of stomach

27
Q

Sympathetic stimulation of GI tract?

A

Preganglionic fibres synapse in the prevertebral ganglia

Postganglionic fibres (releasing NA) innervate mainly enteric neurones

28
Q

Sympathetic excitatory influences?

A

Increased sphincter tone

29
Q

Sympathetic inhibitory influences?

A

Decreased motility, secretion and blood loss

30
Q

What make up the prevertebral ganglia?

A

Celiac, Superior and inferior mesenteric

31
Q

What is the enteric nervous system?

A

Approx 100 million neurones in which the bodies are located in ganglia connected by fibre tracts in either;
Myenteric plexus or Submucous plexus

32
Q

Other name for myenteric plexus and its function?

A

Auerbach’s

Regulates motility and sphincters

33
Q

Other name for submucous plexus and function?

A

Meissner’s

Mainly modulates epithelia and blood vessels

34
Q

What does the ENS do?

A

Co-ordinates muscular, secretive and absorptive activities via sensory neurones, interneurons and effector neurones

35
Q

Sensory neurones?

A

Mechanoreceptors, chemoreceptors, thermoreceptors

36
Q

Effector neurones?

A

Excitatory and inhibitory motor neurones

37
Q

Types of nerve reflex and examples?

A

Local reflex - peristalsis

Short reflex : intestine-intestinal inhibitory reflex

Long reflex - gastroileal reflex

38
Q

What is peristalsis?

What is it triggered by?

A

Wave of relaxation followed by contraction along gut in aboral direction

Distension of gut wall

39
Q

What causes circular muscle to contract?

A

Release of ACh and substance P from excitatory motor neurone

At the same time relaxation of longitudinal muscle by release of VIP and NO from inhibitory motor neurones occurs

40
Q

What causes circular muscle to relax?

A

Release of VIP and NO from inhibitory motorneurone

At same time longitudinal muscle contracts due to release of ACh and substance P from excitatory motorneurone

41
Q

What is segmentation?

A

Mixing/churning - Rhythmic contractions of circular muscle layer that mix and divide contents

Occurs in small intestine (fed) and large intestine (haustration)

42
Q

Colonic mass movement?

A

Powerful sweeping contraction forcing faeces to rectum

43
Q

Migrating motor complex (MMC)?

A

Powerful sweeping contraction from stomach to ileum

44
Q

Tonic contractions?

A

Sustained contractions

Low pressure - organs with major storage function (stomach)

High pressure - sphincters

45
Q

How many sphincters in GI tract?

Purpose?

A

6 excluding sphincter of oddi

Act as one way valves maintaining positive resting pressure relative to 2 adjacent structures (usually smooth circular muscle)

46
Q

What is the UOS and what does it do?

A

Upper oesophageal sphincter

Relaxes to allow swallowing

Closes during inspiration

47
Q

What is the LOS and what does it do?

A

Lower oesophageal sphincter

Relaxes allowing food to move to stomach

Closes preventing reflux

48
Q

Pyloric sphincter function?

A

Regulates gastric emptying

Prevents duodenal gastric reflux

49
Q

Ileocaecal valve?

A

Regulates flow from ileum to caecum

Distension of ileum opens and distension of proximal colon closes

50
Q

Internal and external anal sphincters muscle type and function?

A

Internal - smooth
External - skeletal

Regulated by defaecation reflex

GI (2 decks)

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