Changes

====Anatomy====

====Anatomy====

[[File:Margo Plicatus.jpg|400px|thumb|right|]]

[[File:Margo Plicatus.jpg|400px|thumb|right|]]

In the horse, the '''squamous (non-glandular) mucosa''' covers the lining of the oesophagus and about one third of the gastric wall.  It provides a protective barrier comprising a tightly bound superifcial layer of cornified cells.<ref name="EGUC">The Equine Gastric Ulcer Council (1999) Tutorial Article: Recommendations for the diagnosis and treatment of equine gastric ulcer syndrome (EGUS).  ''Equine Vet Educ'', 11(5):262-272.</ref>  This squamous epithelium has no absorptive or secretory function.  The '''glandular''' region of the stomach contains mucus-secreting cells and gastric glands.  The '''''margo plicatus''''' is analagous to the gastro-oesophageal junction in man, however it lacks the lower oesophageal sphincter that helps to prevent acidic injury of the squamous mucosa(Sanchez).  Equine gastric ulcers largely occur in the squamous region of the stomach.  The predilection sites in various groups are:

In the horse, the '''squamous (non-glandular) mucosa''' covers the lining of the oesophagus and about one third of the gastric wall.  It provides a protective barrier comprising a tightly bound superifcial layer of cornified cells.<ref name="EGUC">The Equine Gastric Ulcer Council (1999) Tutorial Article: Recommendations for the diagnosis and treatment of equine gastric ulcer syndrome (EGUS).  ''Equine Vet Educ'', 11(5):262-272.</ref>  This squamous epithelium has no absorptive or secretory function.  The '''glandular''' region of the stomach contains mucus-secreting cells and gastric glands.  The '''''margo plicatus''''' is analagous to the gastro-oesophageal junction in man, however it lacks the lower oesophageal sphincter that helps to prevent acidic injury of the squamous mucosa.<ref name="Sanchez">Sanchez, L.C (2010) 'Diseases Of The Stomach' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), Saunders, Chapter 15.</ref>   Equine gastric ulcers largely occur in the squamous region of the stomach.  The predilection sites in various groups are:

*'''Neonatal foals''': glandular mucosa

*'''Neonatal foals''': glandular mucosa

*'''Healthy suckling foals younger than 50 days''': squamous mucosa adjacent to ''margo plicatus'' along the greater curvature, squamous epithelial desquamation

*'''Healthy suckling foals younger than 50 days''': squamous mucosa adjacent to ''margo plicatus'' along the greater curvature, squamous epithelial desquamation

*'''Suckling foals with older than 50 days with clinical signs''': squamous mucosa along lesser curvature, squamous mucosa of fundus and adjacent to ''margo plicatus''.

*'''Suckling foals older than 50 days with clinical signs''': squamous mucosa along lesser curvature, squamous mucosa of fundus and adjacent to ''margo plicatus''.

*'''Sucklings and early weanlings''': gastroduodenal ulcer disease (GDUD) – lesions in proximal duodenum, also severe lesions in squamous or glandular region

*'''Sucklings and early weanlings''': gastroduodenal ulcer disease (GDUD) – lesions in proximal duodenum, also severe lesions in squamous or glandular region

*'''Yearlings and adults''': squamous epithelium, particularly adjacent to ''margo plicatus'', glandular and antral involvement becoming more common (9, 23 in Sanchez), severe cases of ulceration can extend dorsally into squamous fundus (Sanchez)

*'''Yearlings and adults''': squamous epithelium, particularly adjacent to ''margo plicatus'', glandular and antral involvement becoming more common (9, 23 in Sanchez), severe cases of ulceration can extend dorsally into squamous fundus.<ref name="Sanchez">Sanchez, L.C (2010) 'Diseases Of The Stomach' in Reed, S.M, Bayly, W.M. and Sellon, D.C (2010) '''Equine Internal Medicine''' (Third Edition), Saunders, Chapter 15.</ref>

====Intrinsic protective factors====  

====Intrinsic protective factors====  

=====Glandular mucosal defence mechanisms<ref>The Equine Gastric Ulcer Council (1999) Tutorial Article: Recommendations for the diagnosis and treatment of equine gastric ulcer syndrome (EGUS).  ''Equine Vet Educ'', 11(5):262-272.</ref>=====

=====Glandular mucosal defence mechanisms<ref name="EGUC">The Equine Gastric Ulcer Council (1999) Tutorial Article: Recommendations for the diagnosis and treatment of equine gastric ulcer syndrome (EGUS).  ''Equine Vet Educ'', 11(5):262-272.</ref>=====

*'''Mucus:''' secreted by specialised mucous neck cells.  A viscous, hydrophobic glycoproteinaceous gel that adheres to the mucosa and resists acid and pepsin contact. Also acts as a lubricant to minimise mechanical damage.

*'''Mucus:''' secreted by specialised mucous neck cells.  A viscous, hydrophobic glycoproteinaceous gel that adheres to the mucosa and resists acid and pepsin contact. Also acts as a lubricant to minimise mechanical damage.

*'''Bicarbonate:''' secreted by gastric mucosal cells.  Secretion triggered by luminal acid concentrations, mechanical irritation, and release of endogenous prostaglandins. Bicarbonate trapped in the mucous layer forms a pH gradient allowing a physiological pH at the mucosal surface and a gastric acid pH at the luminal surface.

*'''Bicarbonate:''' secreted by gastric mucosal cells.  Secretion triggered by luminal acid concentrations, mechanical irritation, and release of endogenous prostaglandins. Bicarbonate trapped in the mucous layer forms a pH gradient allowing a physiological pH at the mucosal surface and a gastric acid pH at the luminal surface.

*'''Prostaglandins:''' inhibit acid secretion, promote mucosal blood flow (through vasodilation), increase mucus and bicarbonate secretions and support mucosal cell repair.  PGE2 is especially important in these functions.

*'''Prostaglandins:''' inhibit acid secretion, promote mucosal blood flow (through vasodilation), increase mucus and bicarbonate secretions and support mucosal cell repair.  PGE2 is especially important in these functions.

=====Squamous mucosal defence mechanisms<ref>The Equine Gastric Ulcer Council (1999) Tutorial Article: Recommendations for the diagnosis and treatment of equine gastric ulcer syndrome (EGUS).  ''Equine Vet Educ'', 11(5):262-272.=====

=====Squamous mucosal defence mechanisms<ref name="EGUC">The Equine Gastric Ulcer Council (1999) Tutorial Article: Recommendations for the diagnosis and treatment of equine gastric ulcer syndrome (EGUS).  ''Equine Vet Educ'', 11(5):262-272.</ref>=====

The squamous mucosa has comparatively few defence mechansims:

The squamous mucosa has comparatively few defence mechansims:

*'''Intercellular tight junctions''' and '''intracellular buffering systems''' act as barriers

*'''Intercellular tight junctions''' and '''intracellular buffering systems''' act as barriers