Protection of the GI Tract
Attack and defence in the gut
Damaging Protective
Acid and pepsin Mucous – HCO3
Ingested drugs (e.g. alcohol and aspirin) Cell membrane
Refluxed bile Cell migration + renewal
Smoking Mucosal blood flow
Micro-organisms Prostaglandins
Ischaemia Immune system
Food allergens Acid inhibition
Programmed cell death
Physical protection in the stomach
- pH in the lumen of stomach is 2 or 3
- activated proteases (e.g. pepsin) in stomach has as
an optimum pH of 2
- 1st barrier is mucous layer – sits above epithelial
cells
- mucous is secreted by the mucous cells in crypts of
the stomach
- produces a physical barrier to the acid and pepsin
- underneath the mucous there is an apical and
basolateral layer – has a pH of 7
o cells in the two layers are polar
- apical layer is highly populated with phospholipids (are hydrophobic) – repel aqueous
solutions
o therefore, any H+ that penetrate mucus layer will be repelled by the surface of the
epithelium
- the epithelial cells are very specialised and have tight junctions between them which slows
down H+ diffusion
Chemical protection in the stomach
- epithelial cells secret bicarbonate which neutralises acid as it comes through
- very little nutritional intake by the stomach but has rich blood supply, especially the mucosa
o blood carries H+ away – helps antioxidant function
- mucous provides chemical and physical protection
Attack and defence in the gut
Damaging Protective
Acid and pepsin Mucous – HCO3
Ingested drugs (e.g. alcohol and aspirin) Cell membrane
Refluxed bile Cell migration + renewal
Smoking Mucosal blood flow
Micro-organisms Prostaglandins
Ischaemia Immune system
Food allergens Acid inhibition
Programmed cell death
Physical protection in the stomach
- pH in the lumen of stomach is 2 or 3
- activated proteases (e.g. pepsin) in stomach has as
an optimum pH of 2
- 1st barrier is mucous layer – sits above epithelial
cells
- mucous is secreted by the mucous cells in crypts of
the stomach
- produces a physical barrier to the acid and pepsin
- underneath the mucous there is an apical and
basolateral layer – has a pH of 7
o cells in the two layers are polar
- apical layer is highly populated with phospholipids (are hydrophobic) – repel aqueous
solutions
o therefore, any H+ that penetrate mucus layer will be repelled by the surface of the
epithelium
- the epithelial cells are very specialised and have tight junctions between them which slows
down H+ diffusion
Chemical protection in the stomach
- epithelial cells secret bicarbonate which neutralises acid as it comes through
- very little nutritional intake by the stomach but has rich blood supply, especially the mucosa
o blood carries H+ away – helps antioxidant function
- mucous provides chemical and physical protection
