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.(EGUC)  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(Sanchez).  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

====Intrinsic protective factors====  

====Intrinsic protective factors====  

=====Glandular mucosal defence mechanisms=====

=====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>=====

*'''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.(EGUC)

*'''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.(EGUC)

*'''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.

*'''Epidermal growth factors:''' found in salivary gland secretions, promote DNA synthesis and proliferation of gastric mucosal cells. Also play a role in prostaglandin synthesis and inhibit HCl secretion by the parietal glands.(EGUC)

*'''Epidermal growth factors:''' found in salivary gland secretions, promote DNA synthesis and proliferation of gastric mucosal cells. Also play a role in prostaglandin synthesis and inhibit HCl secretion by the parietal glands.

*'''Epithelial restitution mechanisms:''' important in the maintenance of gastric mucosal integrity (maintain tight junctions). Epithelial injury induces migration of adjacent cells to replace damaged cells within minutes without the need of new cell proliferation.  Shear forces, induced by mixing of ingested material, are counteracted by epithlial restoration.(EGUC)

*'''Epithelial restitution mechanisms:''' important in the maintenance of gastric mucosal integrity (maintain tight junctions). Epithelial injury induces migration of adjacent cells to replace damaged cells within minutes without the need of new cell proliferation.  Shear forces, induced by mixing of ingested material, are counteracted by epithlial restoration.

*'''Adequate mucosal blood supply:''' required to provide the mucosa with oxygen and nutrients to produce the mucus-bicarbonate layer and to support rapid turnover of epithelial cells.  Also required to remove acid that has diffused through the mucous layer to the mucosa.(EGUC) Mucosal perfusion may be important in the stress-related ulceration of neonates(Sanchez)

*'''Adequate mucosal blood supply:''' required to provide the mucosa with oxygen and nutrients to produce the mucus-bicarbonate layer and to support rapid turnover of epithelial cells.  Also required to remove acid that has diffused through the mucous layer to the mucosa.  Mucosal perfusion may be important in the stress-related ulceration of neonates(Sanchez)

*'''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.(EGUC)

*'''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=====

=====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.=====

The squamous mucosa has comparatively few defence mechansims:(EGUC)

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

*'''Epidermal growth factor''' has also been found to contribute to the healthy maintenance and repair of gastric squamous epithelium (Jeffrey et al. 200 in(Martineau 2009)

*'''Epidermal growth factor''' has also been found to contribute to the healthy maintenance and repair of gastric squamous epithelium (Jeffrey et al. 200 in(Martineau 2009)