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Intestinal obstruction can be the sequel to either mechanical or functional causes.  Mechanical obstruction occurs due to physical blockage of the intestinal lumen whereas functional obstruction results from a decrease or inhibition of intestinal motility due to loss of smooth muscle contraction (Brown et. al, 2007).
 
Intestinal obstruction can be the sequel to either mechanical or functional causes.  Mechanical obstruction occurs due to physical blockage of the intestinal lumen whereas functional obstruction results from a decrease or inhibition of intestinal motility due to loss of smooth muscle contraction (Brown et. al, 2007).
===Mechanical Obstruction=== 
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* Acute of chronic mechanical obstruction of the intestine can occur in all species.
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** Acute obstruction usually involves the upper or middle [[Small Intestine - Anatomy & Physiology|small intestine]]
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** Chronic obstruction typically occurs in the distal [[Small Intestine - Anatomy & Physiology|small intestine]] or [[Large Intestine - Anatomy & Physiology|large intestine]]. 
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* Three main categories of causes of obstruciton:
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** Intraluminal
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*** E.g. foreign bodies, food impaction.
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** Intramural
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*** E.g. neoplasia
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** Extrinsic
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*** E.g.  adhesions, neoplasia and prostate enlargement.
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====Intraluminal Obstruction====
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===[[:Category:Intestine - Mechanical Obstruction]]===
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=====Foreign Bodies=====
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* Foreign bodies of all types can be found in the intestines. 
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* While some may pass through posing no problems, others can cause acute obstruction,
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* Quite common in dogs
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** Rare in other species - tend to lodge in the oesophagus or in one of the ruminant [[Stomach and Abomasum - Anatomy & Physiology|stomachs]].)
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** Enteroliths can be seen in  horses greater than 4 years of age.
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*** Are stones consisting of magnesium ammonium phosphate around a central nidus (often a metallic foreign body)
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***  Typically lodge at the pelvic flexure or the transverse [[Colon - Anatomy & Physiology|colon]].
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* '''Clinical'''
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** Obstruction at pylorus produces repeated [[Control of Feeding - Anatomy & Physiology#The Vomit Reflex|vomiting]].
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** Obstrustion lower down gives less dramatic effect.
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*** Is still a problem if in the middle of the [[Small Intestine - Anatomy & Physiology|small intestine]]s.
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*** May be vague signs; some [[Control of Feeding - Anatomy & Physiology#The Vomit Reflex|vomiting]] and off food.
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* '''Diagnosis'''
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** May not show up well radiographically  (unless radio-opaque) for several days.
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*** May also be objects that are semi solid or soft,  e.g.
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**** String
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**** Plastic bags
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**** Stringy things, like pieces of material- particularly in puppies.
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** Make all of intestines have knotted appearance. 
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** May be seen in horses with baler twine.
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* '''Pathogenesis'''
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** Smooth, round objects, such as golf balls, lodge especially near the pylorus or lower down.
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** Occasionally in cattle (piece of rope or piece of tarpaulin) produces a tangled mass in [[The Rumen - Anatomy & Physiology|rumen]].
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** Cause pressure necrosis and eventually perforation. 
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** Foreign bodies can also be chronic, remaining for long periods of time without causing disturbance.
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=====Impaction=====
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* Impaction of the [[Colon - Anatomy & Physiology|colon]] can occur in all species. 
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** Dog and cat - main cause is dehydrated faecal material.
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** Horse -  faeces, digesta, sand, or fibrous material can all contribute.
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*** There are certain predisposing factors:
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**** Poor dentition
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**** Water deprivation
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**** A high roughage diet
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**** General debility.
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*Antihelminthic administration or large parasite burdens can also lead to impaction.
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====Extrinsic Obstruction====
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* Obstruction of the intestine due to external factors such as tumours, abscesses, and fibrous adhesions is a common occurrence. 
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=====Inflammatory Adhesions=====
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[[Image:colon_adhesions_horse.jpg|thumb|right|150px|colonic adhesions in the horse (Courtesy of Elspeth Milne)]]
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* Arise following gut perforation, peritonitis or surgery.
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* Consist of fibrous tissue bands that may:
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** Restrict intestinal motility
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** Cause kinks in the mesentery.
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=====Prostatic Enlargement=====
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* In the dog
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* Can lead to compression of the [[Rectum - Anatomy & Physiology|rectum]]
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=====Neoplasia=====
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* Neoplasi in structures adjacent to the intestines can spread and cause external compression.
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* Pancreatic tumours in particular can extend and impinge on the [[Duodenum - Anatomy & Physiology|duodenum]].
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* Pedicles of tumours such as lipomas in horses can become wound in loops of intestine leading to obstruction and possible strangulation. 
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[[Image:Pedunc_lipoma_closeup.jpg|thumb|right|150px|Closeup of a pedunculated lipoma (Courtesy of Elspeth Milne)]]
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* '''Clinical'''
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** Occasional [[Control of Feeding - Anatomy & Physiology#The Vomit Reflex|vomiting]] and ntermittent [[Intestine Diarrhoea - Pathology|diarrhoea]] over several weeks. 
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* '''Pathogenesis'''
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** Seen occasionally in cat (rarer in dog)
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** Usually towards end of intestines
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*** E.g. at the ileocaecocolic valve.
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** Gut proximal to tumour  becomes thickened due to hypertrophy of smooth muscle as a result of trying  to force ingesta past progessively narrowing lumen.
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** Produces "hose pipe intestine".
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** Seen with carcinoma, lymphoma, leiomyoma and other tumours.
      
===Functional Obstruction===
 
===Functional Obstruction===
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