W10 Gut-Brain axis

Question 1

The GI tract wall has what 4 layers?

Answer 1

Mucosa
Submucosa
Muscularis externa
Serosa or adventitia

Question 2

Adventitia or Serosa?

Question 3

What is the gut-brain axis?

Answer 3

The gut-brain axis (GBA) consists of
bidirectional communication between the central and the enteric nervous system, linking emotional and cognitive centre’s of the brain with peripheral intestinal functions

Question 4

What is extrinsic and intrinsic innervation?

Answer 4

EXTRINSIC INNERVATION - Sympathetic (dec digestion)
- Parasympathetic (inc digestion)

INTRINSIC INNERVATION
- Enteric Nervous System (2nd Brain)!

Question 5

Enteric nervous system:
What does the myenteric plexus regulate?
What does the submucosal plexus regulate?

Answer 5

• As soon as food enters the mouth, it is detected by receptors that send impulses along the sensory neurons of cranial nerves.
• 100 million motor, sensory, and interneurons
• The myenteric plexus (plexus of Auerbach) – regulates motility e.g. peristalsis.
• The submucosal plexus (plexus of Meissner) – regulates digestive secretions and reacting to the presence of food

Question 6

Short reflex – mediated by entirely by enteric nervous system in response to local stimuli within GI tract

Answer 6

1. Food
2. Distends walls of GI
3. Mechanoreceptors in the muscularis externa and the mucosa & chemoreceptors in mucosa detect ↑ protein, fat, sugar concentrations
4. send afferent information through axons that synapse with ganglia in the submucosal plexus
5. Stimulate glands and enteroendocrine cells in mucosa that helps with digestion and absorption

Question 7

Disassembly line…

Answer 7

• Includes Peristalsis and Segmentation
  Largely automatic, involving pacemaker cells and reflex arcs between enteric neutrons in the same or different organs.

Question 8

What are pacemaker cells? (for info)

Answer 8

Pacemaker cells: Interstitial cells of Cajal in the myenteric plexus
* Generate rhythmic
depolarization and repolarization (slow wave potentials)
* Different number per location
* Weak depolarisation
* Thus tonic not peristaltic
* Long reflex needed to open
alternative calcium channels for full muscle contraction

Question 9

Nerve supply of GI tract

Question 10

Long reflex

Answer 10

1. Parasympathetic Innervation: Rest and digest
   * Cholinergic – Ach
   * Peptidergic – substance P / vasoactive intestinal peptide
   (vagus nerve, pelvic nerves, spinal cord)
2. Sympathetic Innervation: Fight or Flight
   * Adrenergic – Adrenaline
   * ↓ secretion and motility
   (celiac ganglion, superior+interior mesenteric ganglion, hypogastric ganglion)

Question 11

Which GI tract layers contain muscles?

Answer 11

Muscularis externa (circular + longitudinal layer)- Motility and contractions
Submucosa- Controls glands and secretions

Question 12

Control of gastric emptying

Question 13

What are the GI hormones? (4)

Answer 13

1. Secretin: stimulates bicarbonate secretion and inhibits gastric emptying and secretions
2. Cholecystokinin: stimulates gallbladder contraction, and pancreatic enzyme secretions and inhibits gastric emptying and secretions
3. Gastric inhibitory peptide- inhibits gastric emptying and secretion
4. Glucagon-like peptide-1-inhibits gastric emptying and secretion (satiety)

Question 14

Gastrointestinal regulatory peptides

Answer 14

• Hormones: gastrin, cholecystokinin, secretin and glucose-dependent insulinotropic peptide
• Paracrines: peptidic – somatostatin – and a nonpeptidic – histamine
• Neurocrines: acetylcholine, norepinephrine, vasoactive intestinal peptide, nitric oxide, gastrin-releasing peptide, enkephalins, neuropeptide Y and substance P.

They modulate the activity of the gastrointestinal tract, regulate its motility, and coordinate the digestion and absorption process.

Question 15

What are the hormones that control our hunger?

Answer 15

Pancreas- insulin
Upper small bowl- CCK
Fat cells- Leptin
Lower small bowel- Peptide YY, Glucagon-Like Peptide 1 (GLP-1)
(all inhibit hunger)

Stomach- Ghrelin
(stimulates hunger)