113 - Neural and Hormonal Control of GIT Function 1

Question 1

Basic function of GIT
1
2
3
4
5

Answer 1

1) Digestion of food
2) Absorption of nutrients
3) Excretion of waste
4) Prevention of invasion by pathogens
5) Contains microbiome

Question 2

Key requirements of GIT regulation 
1
2
3
4

Answer 2

1) Control intestinal smooth muscle contractions.
2) Regulate secretion of digestive enzymes, solvents for enzymatic function
3) Control reabsorption of water from lumen to prevent dehydration
4) Coordinate widely separated regions (EG: regulation of gastric emptying by gat in duodenum)

Question 3

Pacemaker cells of the enteric nervous system, regulating contractile activity of intestinal smooth muscle

Answer 3

Interstitial cells of Cajal. Modified smooth muscle cells.

Question 4

Interstitial cells of Cajal function

Answer 4

Regulate contractile activity and secretion of water and salt over mm to cm distances
Contain elements needed for complex motor programs

Question 5

Two systems that interact for GIT function

Answer 5

Enteric nervous system, endocrine system.

Question 6

Segmentation

Answer 6

Mixing function of enteric nervous system

Question 7

Peristalsis

Answer 7

Propulsive motor pattern, mediated by enteric nervous system

Question 8

Function of GIT endocrine system

Answer 8

Signal from intestinal mucosa to ancillary organs like brain, pancreas, gall bladder.

Question 9

Arrangement of the enteric nervous system in the GIT?
1
2
3

Answer 9

1) Ganglia between the longitudinal (outer) and circular (internal) smooth muscle layers in the GIT (myenteric plexus).
2) Submucosal plexus. Innervate mucosa.
3) Interstitial cells of Cajal, all joined with gap junctions (to coordinate). Sit within circular smooth muscle layer.

Question 10

Number of neuron types in murine enteric nervous system

Answer 10

~22

Question 11

Mucosal enteroendocrine cells
1
2
3

Answer 11

1) Often span epithelium
2) Many defined by mediators they release (EG: serotonin-releasing enterochromaffin cells)
3) Also enterochromaffin-like cells that release histamine

Question 12

Number of enteroendocrine cells in GIT

Answer 12

Over 20

Question 13

Where is majority of body’s serotonin produced?

Answer 13

In gut wall (over 90%) (serotonin-containing enterochromaffin cell)

Question 14

Examples of hormonal factors released by enteroendocrine cells

Answer 14

Serotonin, CCK, secretin, somatostatin, glucagon-like peptides 1 and 2

Question 15

Roles of vagus in GIT function
1
2
3

Answer 15

1) Vagus pathway for control of swallowing
2) Vagus regulates acid secretion in stomach.
3) Co-ordination of contraction of stomach, duodenum

Question 16

Part of GIT that vagus controls

Answer 16

First part. Vagal control wanes as you go towards colon.

Question 17

Neural aspects responsible for intestino-intestinal reflexes
1
2

Answer 17

1) Vagus (often excitatory)

2) Dorsal root ganglia (often inhibitory)

Question 18

Function of sympathetic neurons in the GIT

Answer 18

Often inhibitory

Question 19

Viscerofugal neurons
1
2
3

Answer 19

1) Cell bodies are within GIT wall
2) Project to pre-vertebral sympathetic ganglia (coelial, superior, inferior mesenteric ganglia).
3) Produce reflex inhibition of proximal regions when distal regions are distended.

Question 20

Hormone released when fat is detected

Answer 20

Cholecystikinin.

Released from GIT wall, effects local GIT wall, gets into portal system, goes to liver.

Question 21

Basic function of vagal and sympathetic activity on enteric nervous system

Answer 21

Usually modulate enteric neural circuits (increase or decrease activity)

Question 22

Effect of neural activity on intestinal smooth muscle

Answer 22

Interstitial cells of Cajal act as pacemakers.
Neural activity can change level of excitation or inhibition that can alter whether smooth muscle will contract on stimulation

Question 23

Which nerve mediates cephalic phase?

Answer 23

Vagus

Question 24

Amount of gastric acid secretion attributable to cephalic phase

Answer 24

~30%

Question 25

Effects of cephalic phase 
1
2
3
4

Answer 25

1) Causes salivation
2) Gastric acid secretion
3) Pepsin secretion
4) Relaxation of gastric corpus and fundus

Question 26

General control of gastric acid, pepsin secretion in stomach
1
2
3
4
5

Answer 26

1) Brain directly innervates parietal cells
2) Brain innervates, via enteric nervous system, enterochromaffin-like cells, D cells.
3) ECL cells release histamine, which stimulates gastric acid release.
4) D cells release somatostatin, which counteracts release of acid.
5) This results in a balance between gastric acid secretion and inhibition thereof.

Question 27

General control of gastric acid, pepsin secretion 
1)
2)
3) a, b
4) a

Answer 27

–Acetylcholine from enteric neurons excited by vagal efferent neurons
–Gastrin from G cells in antrum and duodenum
–Histamine from ECL cells
•Excited by ACh from enteric neurons
•Inhibited by somatostatin from local D cells and duodenal D cells
–Somatostatin inhibits parietal cells and G cells
• D cells stimulated by acid in duodenum and by gastrin

Question 28

Control of oesophageal peristalsis

Answer 28

Entirely neural, via vagus

Question 29

GORD

Answer 29

Gastro-oesophageal reflux disease

Question 30

What happens when food enters stomach?
1
2
3
4

Answer 30

1) Food enters corpus
2) Distension of corpus activates enteric and vaso-vagal reflexes.
3) This results in more acid and pepsin secretion.
4) Pacemaker activity propagates from corpus to antrum, causing ripples of constriction to propagate to pylorus (grinds food even more)

Question 31

Effect of food and acid entering antrum

Answer 31

Triggers reflex inhibition of acid secretion in the corpus.
To maintain an even pH

Question 32

What does fat do in the stomach?

Answer 32

Floats to the top of chyme, where it forms a separate layer

Question 33

Consequence of fat floating to top of stomach

Answer 33

Fat empties from stomach after everything else

Question 34

What stimulates opening of pylorus?

Answer 34

Enteric neuronal activity

Question 35

Components of chyme from stomach

Answer 35

Food, acid, pepsin (initially low in fat, later high in fat)

Question 36

Aspect of stomach filling that suppresses hunger

Answer 36

Stomach distension