Pathology of the Alimentary Tract 1 (Oral Cavity & Oesophagus)

Pathology of the Alimentary Tract 1 (Oral Cavity & Oesophagus)

1. Alimentary Tract

   • Normal Histology (Alimentary Tract)
     • Stratified Squamous epithelium
       • Mouth
         • Oesophagus
           • Non-glandular part of stomach: Pigs, Horses
             • Forestomachs: Ruminants
               • Anus:
                 • Keratinized: Ruminants, Horses, Pigs
                 • Non- Keratinized: Dogs & Cats
     • Simple columnar glandular epithelium
       • Stomach; Abomasum
         • Surface epithelium
           • Simple tubular glands
             • Chief (peptic, zymogen) cells: Pepsinogen
               • Parietal (oxyntic) cells: HCl
                 • Neuroendocrine cells
                   • Stem cells: Neck of gland
       • Small intestine
         • Progenitor cells: Crypts
           • Enterocytes: Villi
             • Mucous (goblet) cells
               • Neuroendocrine cells
       • Large Intestine
         • Enterocytes: Crypts, surface epithelium
           • Mucous(goblet) cells
   • Defense Mechanisms (Alimentary Tract)
     • GI tract sterile at birth -> becomes colonized w/ bacteria
     • Routes of Entry:
       • Oral ingestion
         • Secretions swallowed from the respiratory tract
           • Haematogenous dissemination
             • Parasite migration
     • Secretions
       • Saliva
         • Mucous
           • Inhibits contact w/ mucosa, protects surface
           • Acid
             • Parietal cells in stomach
             • Digestive enzymes
               • Salivary amylase, Pepsin from gastric chief cells, pancreatic & SI enzymes
               • Bile secretions
                 • Kill some pathogens
         • Flushing effect & antibacterial components (Ex. lysozyme, secretory IgA)
     • Epithelium
       • Mucosal barrier
         • Stomach, Intestine
         • Tight junctions (b/w epithelial cells)
           • Prevent entry of macromolecules & pathogens (but allows ions & H2O to diffuse through)
         • Very high cell turnover
         • Stratified Squamous epithelium
           • Oral cavity
           • Multilayered
           • Relatively high cell turnover
           • Keratinized surface layer at some sites
     • Commensal Flora
       • Act as barrier to pathogens
         • Secrete VFAs & compete w/ pathogens for nutrients
           • Essential for digestion in herbivores
             • Any disequilibrium of microflora can lead to disease
     • Movement
       • Continuous movement/peristalsis discourages persistence of insult/agent
     • Cell-mediated & Humoral Defenses
       • Lamina propria:
         • Macrophages, B & T Lymphocytes, Plasma cells, mast cells
         • Epithelium:
           • Intraepithelial lymphocytes (T lymphocytes)
           • Lymphoid Aggregates:
             • Peyer's Patches (esp. ileum), GALT
             • Ab production (esp. secretory IgA)
               • Regional Lymph Nodes
                 • Omental macrophages
   • Inflammation in the Alimentary Tract
     • Vascular changes
       • Hyperaemia (Congestion)
         • Reddening, Oedema
           • Haemorrhage: Petechiae, Ecchymoses
     • Exudates
       • Serous/Mucous/Seromucous: Catarrhal
         • Suppurative (Purulent)
           • Mucopurulent
             • Diptheritic: Fibrin & Necrotic material, secondary bactrerial invasion

2. Oral Cavity

   • Defense Mechanisms (Oral Cavity):
     • Taste buds
       • Normal bacterial flora
         • Saliva (flushing, coating, lysozyme & Igs)
   • Developmental Anomalies (Oral Cavity)
     • Brachygnathia superior/inferior
       • Short maxilla/mandible
     • Prognathia
       • Abnormal prolongation of maxilla/mandible
     • Cleft palate/palatoschisis
       • Inadequate growth of palatine shelves leaves a central defect
       • Communication of nasal & oral cavities may result in aspiration pneumonia & problems w/ suckling
       • Affects hard &/or soft palate
     • Hare lip/cheiloschisis
       • Absence of part of lip rostral to nasal septum
   • Inflammatory Lesions (Oral Cavity)
     • Inflammation predominates in Chronic lesions of bacterial or fungal origin
     • Granulomatous inflammation
       • Actinobacillosis ("Wooden togue")
         • Actinobacillus lignieresii
       • Actinomycosis ("Lumpy jaw")
         • Actinomyces bovis
         • Mandible becomes enlarged due to chronic osteomyelitis
     • Eosinophilic Inflammation
       • Oral eosinophilic granuloma (Cats)
     • Necrotizing Inflammation
       • Calf diptheria
         • Fusobacterium necrophorum
         • Coagulative necrosis & surrounding granulation tissue affecting the gingival & oral mucosa
     • Vesicular Inflammation
       • Often viral
       • Vesicular, ulcerative or proliferative patterns may also co-exist or progress (e.g. vesicles -> ulcers)
       • Foot & mouth disease
       • Feline calcivirus
     • Erosive Inflammation
       • Ulcers may progress from vesicles, but can also be caused by: some bacterial & immune-mediated diseases, trauma
       • Feline calcivirus & Feline herpesvirus
         • Causes mouth ulceration
       • Mucosal Disease
         • Bovine viral diarrhoea virus (BVDV)
         • Causes ulceration of oral cavity, muzzle & more distal alimentary ytact
       • Immune - mediated diseases
         • Autoantibodies directed against epithelial cell surface Ags
         • Ex. Pemphigus vulgaris, bullous pemphigold (Dogs, Cats & Horses)
     • Papular Inflammation
       • Proliferative (papular) lesions
       • Contagious pustular dermatitis ("orf")
         • Firm, raised papules & pustules on lips & oral mucosa
         • Sheep & Goats
         • Hydrophobic degeneration, mixed inflammatory cell infiltration & secondary bacterial invasion
   • Neoplasia (Oral Cavity)
     • Epithelial Tumors
       • Papillomas
         • Benign
         • Raised, sometimes cauliflower-like lesions (Lips & Oral Mucosa)
         • Thick squamous epithelium over a branching pedunculated fibrous stroma
       • Squamous cell carcinoma
         • Malignant
         • Most common oral malignancy (Cats)
         • Ventrolateral tongue
           • Locally invasive +/- metastases
             • Composed of elevated firm, white plaques or nodules that may ulcerate
               • Irregular masses & cords of squamous epithelium invading the lamina propria
                 • May be circular pearls of keratin
     • Melanoma
       • Tumor of pigment producing melanocytes
       • Most common oral neoplasm (Dog)
       • Nearly always Malignant (in oral cavity)
       • Grow rapidly & are not always pigmented
       • Oval or spindle-shaped melanocytes w/ variable melanin content
     • Epulis
       • Group of benign neoplasms of peridontal origin affecting gingivae
       • Particularly in brachycephalic Dog breeds (boxer)
       • Firm lesions on gums, surrounding teeth, esp. carnassial/canine region
       • Dense collagenous & sometimes ossified tissue covered with stratified squamous epithelium (descends into dermis in cords)

3. Oesophagus

   • Congenital Anomalies
     • Segmental aplasia
       • Rare failure of fusion
         • Band of fibrous tissue where distal oesophagus should be
     • Achalasia
       • Failure of cardiac sphincter to open
   • Functional (Neuromuscular) Disorders
     • Megaesophagus
       • Dilated oesophagus lacks peristalsis
         • Accumulates ingesta due to underlying neuromuscular disorder (or obstruction), but lower oesophageal sphincter is usually normal
           • Aspiration pneumonia may be a sequel
       • Idiopathic
         • Developmental disorder of vagus nerve/motor nucleus (esp. Great Dane, German shepherd, Siamese cat)
       • Acquired
         • Neurological
           • Dysautonomias (ex. Equine grass sickness, feline dysautonomia), Myaesthenia gravis
         • Muscular
           • Myodegeneration (ex. nutritional myopathy (Vit. E/ selenium deficiency in cattle)
   • Obstruction
     • Intraluminal
       • Foreign bodies ("Choke")
         • Ex. Root vegetable, sugar beet pulp, bone
       • Most likely sites are narrow areas: Thoracic inlet, base of heart & cardiac sphincter
       • May cause inflammation, pressure necrosis, ulceration & perforation
       • Obstruction of Ruminant oesophagus may cause bloat
       • Healing may cause narrowing (Stricture)
     • Intramural (w/in wall of oesophagus)
       • Inflammatory lesion (abscess, granulation tissue), fibrosis or neoplasm => Narrowing
     • Extrinsic ( outside the oesophagus)
       • Vascular ring anomaly (persistent RT. aortic arch constricts oesophagus & leads to megaoesophagus cranially)
       • Also pressure from abscess, haematoma, neoplasm
   • Inflammation (Oesophagitis)
     • Reflux Oesophagitis
       • Damage from gastric acid due to gastric-oesophageal reflux or vomiting
         • => Erosion of epithelium (may progress to ulcers)
     • Infectious Agents
       • Ex. Actinobacillosis, feline calcivirus
   • Neoplasia
     • Papillomatosis
       • Cattle: Bovine papillomavirus type 4 (transforms squamous cell carcinoma w/ bracken fern toxins)
     • Squamous cell carcinoma
       • Cats
     • Leiomyoma
       • Benign tumor of smooth muscle

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