Enteric Nervous System

Question 1

What are the layers in the gut in order from the lumen

Answer 1

Mucosa
- epithelial tissue
- lamina propria
- muscularis mucosa
Submucosa
Submucosal plexus
Muscularis externa
- Inner circular layer
- Myenteric plexus
- Outer longitudinal layer
Serosa

Question 2

What is the difference between intraperitoneal and retro peritoneal

Answer 2

Intraperitoneal - has serosa and a mesentery
Retro peritoneal - no serosa or mesentery. Attached to the posterior abdominal wall by adventitia

Question 3

Where are the stretch receptors that detect distension found?

Answer 3

Muscularis externa

Question 4

What do the two muscular layers of the gut do when stimulated by distension

Answer 4

Circular - contracts and pushes the bolus forwards
Longitudinal - relaxes so that the lumen behind the bolus doesnt increase in size
Because when longitudinal muscle contracts - it opens the lumen

Question 5

How does distension lead to contraction of circular muscle and relaxation of longitudinal muscle?

Answer 5

Stretch receptors in muscularis externa stimulate ascending fibres
Ascending fibres give axons to circular layer. Ach and substance P stimulates the muscles to contract
Ascending fibres give axons to longitudinal layer. NO and VIP inhibit muscle - relax

Question 6

What happens to the muscle layers when the stretch receptors stimulate the descending fibres

Answer 6

Descending gives axons to circular muscle. VIP and NO inhibit layer -> relax
Descending gives axons to longitudinal muscle. Ach and substance P stimulate layer to contract

Question 7

What is the process by which distension causes relaxation and contraction that leads to the bolus moving

Answer 7

Receptive relaxation

Question 8

What do chemoreceptors in the submucosa respond to

Answer 8

Fatty acids
Glucose
H+
Peptides
Ect

Question 9

What happens when the submucosal plexus is stimulated by the chemoreceptors

Answer 9

Submucosal plexus can stimulate glands which increases secretion of things such as HCO3-
Submucosal plexus can stimulate vessels to dilate which increases blood flow and therefore absorption

Question 10

What happens to bile and pancreatic juice sectretion when you eat a fatty meal

Answer 10

Chemoreceptors sense fatty acids
Stimulates Submucosal plexus which stimulates S cells
Increase secretion of secretin
- stimulates the liver to increase bile synthesis
- stimulates pancreatic acinar cells to release bicarbonate rich pancreatic juice

Question 11

What do S cells secrete

Answer 11

Secretin

Question 12

What do i cells secrete

Answer 12

CCK

Question 13

What are some actions of CCK

Answer 13

Gall bladder contractions
Increase secretin’s action on liver
Pancreas to secrete enzymes
Relaxes sphincter of oddi

Question 14

What do K cells secrete

Answer 14

GIP

Question 15

How does GIP affect the pancreas

Answer 15

Pancreas to secrete insulin

Question 16

How does the sympathetic nervous system affect the GI tract

Answer 16

Decrease motility
Decrease secretions
Decrease absorption
Decrease blood flow
Constrict sphincters

Question 17

How does the sympathetic nervous system inhibit the GI tract

Answer 17

Nerves go to prevertebral ganglia
Splanchnic nerves to submucosal and myenteric plexi
Inhibit both

Question 18

How does the parasympathetic nervous system stimulate the enteric nervous system

Answer 18

Efferent vagal fibres from dorsal nucleus of vagus
Go to both submucosal and myenteric plexi

Question 19

How does the parasympathetic nervous system affect the GI tract

Answer 19

Increase motility
Increase secretions
Increase absorption
Relax sphincters

Question 20

What is the difference between long and short reflexes in the GI tract

Answer 20

Short - receptors cause effects within plexuses
Long - afferent vagal - efferent vagal - stimulate / signals sent to prevertebral ganglion - inhibit
The long is the vago-vagal reflex / enterogastric reflex