Lecture One; GI function overview

Question 1

What is the function of the GI tract?

Answer 1

• Ingestion
• Secretion
• Digestion
• Absorption
• Integration with metabolism
• Elimination

Question 2

Whats the typical volume of fluid movement through the GI tract?

Answer 2

8.5L

Question 3

What is the embryological origin of the GI tract?

Answer 3

Derived from endoderm (part of yolk sac, except oral cavity and anal canal).

Lined by epithelium derived from endoderm

Question 4

What can the endoderm be divided into?

Answer 4

• Foregut
• Midgut
• Hindgut

Implications of this for pain referral. i.e pain in gut can be referred to the back.

Question 5

Describe the gut microbiology;

Answer 5

• 100 trillion microbes.
• Contribute to barrier function of epithelium to prevent peritonitis and sepsis.
• Incredibly diverse.

Question 6

What is the gut microbiology like at birth?

Answer 6

• No microbes at birth.

- Receive microbes during birth and this has implications on long term outcomes.

Question 7

What are the implications of the normal bacterial flora?

Answer 7

• Undigested CHO enter colon and are fermented; Gas, H2 and CH4
• Short chain FA broken down by bacteria and feed colonic cells.
• Vit K production.

Question 8

Why does the infant immune system not react to commensual flora?

Answer 8

Tolerance is learnt in the early years of life.

• Loss of tolerance can lead to autoimmune diseases i.e ulcerative collitis or Crohns.

Question 9

What does an imbalance of gut bacteria lead to?

Answer 9

Post-antibiotics can potentially lead to;

• Diarrhoea
• IBS
• C. difficile infections

Question 10

Describe in general terms the gut barrier;

Answer 10

Epithelial barrier
Physical
- Tight junctions
- Mucins
Immune system
- IGA
- Intra-epithelial lymphocytes
- Macrophages
- Dendritic cells
- Paneth cells release defensins (antimicrobial peptides)
- M cells transports antigens from intestinal lumen to peyeres patches
- Lymph nodes
- Innate immune receptors

Question 11

What is the role of gastric acid?

Answer 11

• Sterilse food
• Initial digestion

H. pylori only know bacteria to survive stomach acid.

Question 12

What is the nervous supply of the GI tract?

Answer 12

Enteric nervous system

Question 13

What are some examples of sensory neurons in the ENS?

Answer 13

Eosophagus - Chemoreceptors
Stomach - release 5HT
Duodenum - Cholecystokinin (CCK)
Jejenum - Mechano stretch receptors

Question 14

Describe the gut brain axis;

Answer 14

Brain influences;

• Motility
• Secretion
• Nutrient delivery
• Microbial balance

Gut influences;

• Neurotransmitter
• Stress/anxiety
• Mood
• Behaviour

Question 15

What conditions can the gut lead to on the brain?

Answer 15

Visceral hypersensitivity
Hypervigilance
Emotional state

Question 16

Describe some of the hormones involved in eating homeostasis;

Answer 16

Ghrelin - Hunger
Leptin - Energy expenditure and inhibits hunger
CCK - Satiety

i.e Appetite vs satiety

Question 17

How else is food intake regulated?

Answer 17

Enteroenteric reflexes i.e mechanical stretch inhibits hunger

Vagal reflexes

GI hormones

Paracrine signalling (Enteroendocrine cells)