Alimentary Canal

Question 1

What is the alimentary canal?

Answer 1

Series of organs from mouth to anus separated by sphincters

Question 2

Orally?

Answer 2

Moving towards mouth

Question 3

Aborally?

Answer 3

Moving towards anus

Question 4

List of organs in alimentary canal?

Answer 4

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

Question 5

What are the accessory structures of alimentary canal?

Answer 5

Salivary glands, pancreas, liver and gallbladder

Question 6

What is the function of each part of canal?

Answer 6

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’

Question 7

Superior to inferior parts of the colon?

Answer 7

Descending, ascending, sigmoid.

Question 8

Activities of alimentary canal?

Answer 8

Motility
Secretion
Digestion
Absorption

Question 9

Motility?

Answer 9

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

Question 10

Secretion?

Answer 10

Occurs in presence of neural, hormonal or mechanical stimuli.

Required for digestion, protection and lubrication

Question 11

Digestion?

Answer 11

Chemical breakdown of food by enzymatic hydrolysis to smaller absorbable units

Question 12

Absorption?

Answer 12

Transfer of absorbable units from GI tract to blood or lymph

Question 13

Generalised structure of digestive tract wall?

Answer 13

Refer to slide

Question 14

How does motility arise?

Answer 14

Activity of smooth muscle (skeletal in some cases)

Question 15

Types of smooth muscle involved in motility?

Effects of contraction of these?

Answer 15

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

Question 16

What is GI smooth muscle coupled by?

Answer 16

Electrically coupled by gap junctions

Question 17

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

Answer 17

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

Question 18

How is the excitation generated?

Answer 18

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

Modulated by:

Intrinsic (enteric) and extrinsic (autonomic) nerves

Hormones

Question 19

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

Answer 19

Slow waves

Question 20

When does contraction of SM occur?

Answer 20

When slow wave amplitude reaches threshold to trigger AP

Question 21

Where are ICCs found and how do they link?

Answer 21

Between longitudinal and circular muscle layers and in submucosa

Form gap junctions with each other and SMC

Question 22

What determines if a slow wave reaches threshold?

What does slow wave determine?

Answer 22

Neural, hormonal or mechanical (food) stimuli

Basic electrical rhythm

Question 23

BER Frequency for stomach, small intestine and large intestine

Answer 23

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

Question 24

Parasympathetic Stimulation of GI tract?

Answer 24

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

Question 25

Parasympathetic excitatory influences?

Answer 25

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

Question 26

Parasympathetic inhibitory influences?

Answer 26

Relaxation of some sphincters, receptive relaxation of stomach

Question 27

Sympathetic stimulation of GI tract?

Answer 27

Preganglionic fibres synapse in the prevertebral ganglia Postganglionic fibres (releasing NA) innervate mainly enteric neurones

Question 28

Sympathetic excitatory influences?

Answer 28

Increased sphincter tone

Question 29

Sympathetic inhibitory influences?

Answer 29

Decreased motility, secretion and blood loss

Question 30

What make up the prevertebral ganglia?

Answer 30

Celiac, Superior and inferior mesenteric

Question 31

What is the enteric nervous system?

Answer 31

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

Question 32

Other name for myenteric plexus and its function?

Answer 32

Auerbach's Regulates motility and sphincters

Question 33

Other name for submucous plexus and function?

Answer 33

Meissner's Mainly modulates epithelia and blood vessels

Question 34

What does the ENS do?

Answer 34

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

Question 35

Sensory neurones?

Answer 35

Mechanoreceptors, chemoreceptors, thermoreceptors

Question 36

Effector neurones?

Answer 36

Excitatory and inhibitory motor neurones

Question 37

Types of nerve reflex and examples?

Answer 37

Local reflex - peristalsis Short reflex : intestine-intestinal inhibitory reflex Long reflex - gastroileal reflex

Question 38

What is peristalsis? What is it triggered by?

Answer 38

Wave of relaxation followed by contraction along gut in aboral direction Distension of gut wall

Question 39

What causes circular muscle to contract?

Answer 39

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

Question 40

What causes circular muscle to relax?

Answer 40

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

Question 41

What is segmentation?

Answer 41

Mixing/churning - Rhythmic contractions of circular muscle layer that mix and divide contents Occurs in small intestine (fed) and large intestine (haustration)

Question 42

Colonic mass movement?

Answer 42

Powerful sweeping contraction forcing faeces to rectum

Question 43

Migrating motor complex (MMC)?

Answer 43

Powerful sweeping contraction from stomach to ileum

Question 44

Tonic contractions?

Answer 44

Sustained contractions Low pressure - organs with major storage function (stomach) High pressure - sphincters

Question 45

How many sphincters in GI tract? Purpose?

Answer 45

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

Question 46

What is the UOS and what does it do?

Answer 46

Upper oesophageal sphincter Relaxes to allow swallowing Closes during inspiration

Question 47

What is the LOS and what does it do?

Answer 47

Lower oesophageal sphincter Relaxes allowing food to move to stomach Closes preventing reflux

Question 48

Pyloric sphincter function?

Answer 48

Regulates gastric emptying Prevents duodenal gastric reflux

Question 49

Ileocaecal valve?

Answer 49

Regulates flow from ileum to caecum Distension of ileum opens and distension of proximal colon closes

Question 50

Internal and external anal sphincters muscle type and function?

Answer 50

Internal - smooth External - skeletal Regulated by defaecation reflex