S1: Introduction to the Control of the Alimentary Tract

Question 1

What ANS innervates the GI system?

Name 2 main supplies

Answer 1

The extrinsic parasympathetic : vagal
The sympathetic: splanchnic
Intrinsic enteric NS

Question 2

Role of sympathetic and parasympathetic nervous system in the GI tract

Answer 2

Sympathetic:

• inhibits digestive activity
• stimulates glucose release by liver

Parasympathetic:

• stimulates digestive activity
• relaxes rectum
• stimulates gallbladder

Question 3

What neurotransmitter causes ascending contraction of GI tract?

Answer 3

Acetylcholine is involved in smooth muscle contraction

Question 4

What neurotransmitters cause descending relaxation of GI tract?

Answer 4

VIP and NO

Question 5

What fibre links the gut muscle and mucosa to the brain?

Answer 5

Afferent vagus fibre

Question 6

What links brain to ENS?

Answer 6

Vagus efferent fibre

Question 7

What links the gut muscle and mucosa to the spinal cord?

Answer 7

Splanchnic fibres

Question 8

What volume does an empty stomach have compared to accommodation?

Answer 8

50ml when resting

1.5L upon receptive relaxation of fundus and body of the stomach

Question 9

What happens to the pyloric sphincter upon the arrival of a peristaltic eve?

Answer 9

The sphincter closes

Question 10

Name the 4 types is factors controlling the GI tract

Answer 10

Endocrine
Paracrine
Neural (vago-vagal reflex, enteric/local reflex)
Metabolic

Question 11

What type of hormones are produced by the GI tract?

Answer 11

Peptides

Question 12

What produces gastrin?

Answer 12

The atrium of the stomach which has a thick muscle wall important for contractions

Question 13

What is the site of action of gastrin?

Answer 13

The gastrin acts on the body of the stomach (thinner muscle layer).

Question 14

Where is the fundus and it’s function?

Answer 14

It is the top bit of the stomach.
This acts as a pacemaker zone as the cells can spontaneously depolarise and produce pacemaker potentials. It therefore initiated peristalsis.

Question 15

List the gastrin mediated effects

Answer 15

• Gastrin released from G cells when stimulates from a neurone releasing GRP (gastrin releasing peptide)
• G cells travels in the blood circulation and binds to ECL
• The ECL then releases histamine
• Histamine acts on H2 receptors on parietal cells stimulating the release of HCl

Gastrin can also have a direct effect in parietal cells stimulating release of HCl.

Question 16

What cells release HCl?

Answer 16

Parietal Cells

Question 17

What cells release Gastrin?

Answer 17

G cells

Question 18

What stimulates G cells?

Answer 18

Gastrin releasing peptide (GRP) is released when stimulated by a parasympathetic neurone

Question 19

What is the ECL?

Answer 19

A neuroendocrine cell found in the gastric glands and gastric mucosa
(Enterochromaffin)

Question 20

What stimulates ECL?

Answer 20

1. GRP binding to ECL

2. ECL cells can be stimulated by acetyl choline released from neurones

Question 21

What three things stimulate HCl release?

Answer 21

1. Gastrin mediated effects
   G cells - GRP- ECL- Histamine- H2 receptor - Parietal cells
2. Gastrin having a direct effect on parietal cells
3. Acetylcholine acting directly in parietal cells

Question 22

Where do hormones (endocrine) travel?

Answer 22

They go to target tissue via blood

Question 23

Where do Paracrine agents travel?

Answer 23

They travel via the interstitial fluid

Question 24

Mechanism of somatostatin on G cells

Answer 24

Presence of H+ will mean they bind to D cells.
This stimulates D cells to release somatostatin which binds to G cells
This inhibits Gastrin release and controls the acid production if the stomach

Question 25

What cells release somatostatin?

Answer 25

D cells

Question 26

What does the afferent vagus innervate?

Answer 26

Lower oesophagus Fundic region Duodenal area

Question 27

What is the vago-vagal reflex?

Answer 27

A reflex in which afferent (sensory) and efferent (motor) axons are in the vagus trunk Vagal afferents from the gut enter the medulla and synapse at the NTS (nucleus tractus solitaries) . There is then processing of this information and vagal efferents originate and leave the medulla at the DMVN (dorsal motor vagal nucleus)

Question 28

What pathway does the vagus nerve trunk take?

Answer 28

The pathway is via the brain stem (medulla)

Question 29

What are the functions of the vago-vagal reflex?

Answer 29

Controls contraction of GI muscle layers in response to distension of tract by food Allows accommodation of large amounts of food in GI

Question 30

What neurotransmitter does the short post-ganglionic vagal nerve release?

Answer 30

Acetylcholine which affects secretion and motility of the gut

Question 31

Which 2 nerve plexus are intrinsic to the gut?

Answer 31

1. Myenteric plexus | 2. Submucosal plexus

Question 32

Function of Myenteric plexus

Answer 32

Controls motor function

Question 33

Function of submucosal plexus

Answer 33

Control intestinal secretions

Question 34

The myenteric plexus and submucosal plexus are connected to the CNS by parasympathetic and sympathetic fibres? What happens if they are disconnected?

Answer 34

They are able to function autonomously without these connections

Question 35

What nervous system (specific subdivision!) mediated the myenteric plexus and submucosal plexus?

Answer 35

The enteric nervous system which is a part of the ANS

Question 36

What is the most prominent plexus of the GI tract?

Answer 36

Myenteric plexus

Question 37

What does the cholinergic innervation of the myenteric plexus do?

Answer 37

It increases gastric motility and secretion Parasympathetic system - ‘rest and digest’ therefore increases GI activity

Question 38

What does the adrenergic innervation of the myenteric plexus do?

Answer 38

It will decrease gastric motility and secretion

Question 39

What does the rate of emptying depend on?

Answer 39

The materials ability to be absorbed

Question 40

What type of food is quickest and slowest to be emptied into the duodenum?

Answer 40

Carbohydrates are emptied quickly into the duodenum Proteins are slower emptying Fatty acids are the slowest

Question 41

How does fatty acids in the duodenum cause decrease in gastric emptying?

Answer 41

It increases the contractility of the pyloric sphincter. | The pyloric sphincter is usually open so increasing the contractility keeps it closed more often

Question 42

Is peristalsis slower in the large intestine or small intestine?

Answer 42

It is slower in the large intestine

Question 43

What controls movement of peristalsis?

Answer 43

Vagal inhibitory and excitatory fibres

Question 44

What is the purpose of peristalsis?

Answer 44

The wave of propulsive contraction nice content of the gut towards the anus