Diseases of the small intestine

image of Diseases of the small intestine
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Diseases of the small intestine (SI) are common in dogs and cats, and cause a range of signs including diarrhoea, vomiting and weight loss (or failure to thrive). The initial aim of diagnostic investigations is to exclude diseases of other organs or body systems; more specific diagnostic tests can then be used to obtain a definitive diagnosis. However, given the current limitations in testing, such a definitive diagnosis is sometimes difficult to achieve. In these circumstances treatment trials may provide more diagnostic information. This chapter explains Structure and function; Pathophysiology disease; Diagnosis; Treatment; and Disorders of the small intestine.

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20.1 Schematic diagram of the villus structure of the small intestine and an enterocyte.
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20.2 Diagrammatic summary of digestion and absorption. Note that galactose is carried on the glucose carriers. ○ = carrier; = enzyme; * = pancreatic enzyme.
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20.3 Assimilation of folate and cobalamin. (a) Dietary folate is present in the diet as a conjugated form (with glutamate residues). This conjugate is digested by folate deconjugase, an enzyme on the microvillar membrane that removes all but one residue, before uptake via specific carriers situated in the mid-small intestine. (b) Following ingestion, cobalamin is released from dietary protein in the stomach. It then binds to non-specific binding proteins (e.g. ‘R-proteins’). This complex is degraded by pancreatic proteases in the small intestine and cobalamin transfers on to intrinsic factor (IF), which is synthesized by the pancreas. Cobalamin-IF complexes pass along the intestine until the distal small intestine, where cobalamin is transported across the mucosa and into the portal circulation.
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20.7 Radiographic studies on a 10-month-old male Akita with severe vomiting and diarrhoea. (a) Abnormal intestinal loop can readily be identified on close examination of the plain radiograph (arrowed). (b) Contrast radiography highlighted a dilated loop of small intestine and possible obstruction. (c) The intestinal obstruction was confirmed and found to be caused by a triangular wooden object. (Courtesy of AE Kerins and A Stell, Department of Veterinary Clinical Sciences, University of Liverpool.)
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20.8 Examples of abdominal ultrasonography in cases of GI disease. (a) Ultrasonograph from a 3-year-old male German Shepherd Dog with chronic diarrhoea, demonstrating the normal appearance of the intestinal wall. (b) Ultrasonograph from a 14-year-old neutered male Domestic Shorthair cat with alimentary lymphoma. There is increased thickness of the bowel wall and loss of normal layering. (c) Ultrasonograph from a 10-year-old neutered male crossbred dog with an intestinal haemangiosarcoma (see Figure 20.17 ); the normal intestinal wall is grossly disrupted by a variably echoic mass. (d) Ultrasonograph from the cat in (c) demonstrating a mesenteric lymphadenopathy. (Courtesy of AE Kerins, Department of Veterinary Clinical Sciences, University of Liverpool.)
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20.10 Appearance of a duodenal biopsy sample acquired via brush collection for cytological assessment. Rapid Romanowsky stain (Rapi-Diff II).
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20.11 Photomicrograph of small intestinal lymphoid tissue from a dog with confirmed canine parvovirus infection. There is severe disruption of the structure of the overlying mucosa. Although the architecture of the Peyer’s patch remains, the number of lymphoid cells is severely depleted. H&E stain. (Courtesy of R Fox, Department of Veterinary Pathology, University of Liverpool.)
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20.14 Photomicrograph from the duodenum of an 8-year-old neutered male crossbred dog with diarrhoea, ascites and severe panhypoproteinaemia (albumin 10 g/l, reference interval: 25–31 g/l; globulins 20 g/l, reference interval: 27–40 g/l). There is evidence of villous atrophy, epithelial erosions and mild lacteal dilatation. There is a variable, mixed inflammatory cell infiltrate within the mucosa. These findings would be consistent with a mixed inflammatory bowel disease. H&E stain. (Courtesy of R Fox, Department of Veterinary Pathology, University of Liverpool.)
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20.15 Endoscopic appearance of linear mucosal ulceration, observed in a case of eosinophilic enteritis. (Courtesy of Edward Hall)
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20.16 Endoscopic appearance of grossly distended lacteals associated with lymphangiectasia. (Courtesy of Edward Hall)
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20.17 Pathological, histopathological and immunohistochemical findings from a 10-year-old male crossbred with weight loss and melaena. (a,b) Gross findings from mass resected at surgery. (c,d) Microscopic findings of the resected mass confirmed it as a haemangiosarcoma. H&E stain; original magnification x100. (c) and x200 (d). (e) Immunohistochemical stain demonstrating that some of the neoplastic cells are positive for vimentin; immunoperoxidase method, original magnification x200. (f) Immunohistochemical staining of biopsy material demonstrating positivity for factor VIII; immunoperoxidase method, original magnification x200. (Courtesy of R. Fox, Department of Veterinary Pathology, University of Liverpool.)
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