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| | ==Developmental Pathology== | | ==Developmental Pathology== |
| − | ===Congenital Achalasia - Megaoesophagus===
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| − | [[Image:Megaoes.gif|left|thumb|125px|<small><center>Megaoesophagus (Courtesy of Alun Williams (RVC))</center></small>]]
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| − | *This condition has been termed achalasia but this implies (in man) a cardiac sphincter defect, which is not found in the dog.
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| − | *A functional rather than a [[#Traumatic Pathology|physical blockage]]
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| − |
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| − | *Inherited disorder in several breeds:
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| − | **Autosomal recessive in Fox Terrier.
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| − | **Also in Miniature Schnauzer, Great Dane, German Shepherds and others.
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| − | **Also in Siamese cats.
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| − | ====Clinical====
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| − | *See at approx. 6-7 months of age when growing quickly.
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| − | *Eats food, [[Control of Feeding - Anatomy & Physiology#The Vomit Reflex|vomits]], eats again and [[Control of Feeding - Anatomy & Physiology#The Vomit Reflex|vomits]] again because [[Oesophagus - Anatomy & Physiology|oesophagus]] has no tone to it.
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| − | *[[Oesophagus - Anatomy & Physiology|Oesophagus]] may become extremely dilated producing a megaoesophagus.
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| − | *Can affect the whole length of [[Oesophagus - Anatomy & Physiology|oesophagus]].
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| − | ====Pathogenesis====
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| − | *Appears to be due to due to delay in maturation of [[Oesophagus - Anatomy & Physiology|oesophageal]] innervation, either:
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| − | **in upper motor neurones of central swallowing centre or
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| − | **in the afferent sensory arm of the reflex involved with [http://en.wikipedia.org/wiki/Peristalsis| peristalsis].
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| − | *If dog eats from raised bowel may be satisfactory as food goes down by gravity.
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| − | *Once in [[Forestomach - Anatomy & Physiology|stomach]] it is passed on normally.
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| − | ===Megoesophagus Secondary to Dextra-Aorta===
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| − | [[Image:Praa.gif|right|thumb|125px|<small><center>Dextra-aorta (Courtesy of Alun Williams (RVC))</center></small>]]
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| − | *Vascular rings are congenital abnormalities of the aortic arch system which interfere with [[Oesophagus - Anatomy & Physiology|oesophageal]] function. Normally, the aortic arch, pulmonary artery and ductus arteriosus (ligamentum arteriosum) all lie on the left side of the [[Oesophagus - Anatomy & Physiology|oesophagus]].
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| − | *However, when there is anomalous development of the aortic arch, for example in the [[right-sided arch]], the [[Oesophagus - Anatomy & Physiology|oesophagus]] becomes enclosed within a ring formed by the '''heart base''', '''aorta''', '''ductus arteriosus''' and '''pulmonary artery'''.
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| − | *The compression and stricture produced by the “ring” prevents passage of solid food beyond the heart base and food accumulates rostral (cranial) to the obstruction, resulting in dilatation or megaoesophagus.
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| − | *In most cases food is eventually regurgitated undigested.
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| − | *The condition is seen in pups just after weaning and if these are presented for treatment before severe dilatation occurs, then surgical correction of the ring (if possible) offers a good prognosis.
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| | ==Erosive & Ulcerative Pathology== | | ==Erosive & Ulcerative Pathology== |