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

Alimentary Tract
1. Normal Histology (Alimentary Tract)
  1. Stratified Squamous epithelium
    1. Mouth
      1. Oesophagus
        Non-glandular part of stomach: Pigs, Horses
        Forestomachs: Ruminants
        Anus:
        Keratinized: Ruminants, Horses, Pigs
        Non- Keratinized: Dogs & Cats
  2. Simple columnar glandular epithelium
    1. Stomach; Abomasum
      1. Surface epithelium
        Simple tubular glands
        Chief (peptic, zymogen) cells: Pepsinogen
        Parietal (oxyntic) cells: HCl
        Neuroendocrine cells
        Stem cells: Neck of gland
    2. Small intestine
      1. Progenitor cells: Crypts
        Enterocytes: Villi
        Mucous (goblet) cells
        Neuroendocrine cells
    3. Large Intestine
      1. Enterocytes: Crypts, surface epithelium
        Mucous(goblet) cells
2. Defense Mechanisms (Alimentary Tract)
  1. GI tract sterile at birth -> becomes colonized w/ bacteria
  2. Routes of Entry:
    1. Oral ingestion
      1. Secretions swallowed from the respiratory tract
        Haematogenous dissemination
        Parasite migration
  3. Secretions
    1. Saliva
      1. 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
      2. Flushing effect & antibacterial components (Ex. lysozyme, secretory IgA)
  4. Epithelium
    1. Mucosal barrier
      1. Stomach, Intestine
      2. Tight junctions (b/w epithelial cells)
        Prevent entry of macromolecules & pathogens (but allows ions & H2O to diffuse through)
      3. Very high cell turnover
      4. Stratified Squamous epithelium
        Oral cavity
        Multilayered
        Relatively high cell turnover
        Keratinized surface layer at some sites
  5. Commensal Flora
    1. Act as barrier to pathogens
      1. Secrete VFAs & compete w/ pathogens for nutrients
        Essential for digestion in herbivores
        Any disequilibrium of microflora can lead to disease
  6. Movement
    1. Continuous movement/peristalsis discourages persistence of insult/agent
  7. Cell-mediated & Humoral Defenses
    1. Lamina propria:
      1. Macrophages, B & T Lymphocytes, Plasma cells, mast cells
      2. Epithelium:
        Intraepithelial lymphocytes (T lymphocytes)
        Lymphoid Aggregates:
        Peyer's Patches (esp. ileum), GALT
        Ab production (esp. secretory IgA)
        Regional Lymph Nodes
        Omental macrophages
3. Inflammation in the Alimentary Tract
  1. Vascular changes
    1. Hyperaemia (Congestion)
      1. Reddening, Oedema
        Haemorrhage: Petechiae, Ecchymoses
  2. Exudates
    1. Serous/Mucous/Seromucous: Catarrhal
      1. Suppurative (Purulent)
        Mucopurulent
        Diptheritic: Fibrin & Necrotic material, secondary bactrerial invasion
Oral Cavity
1. Defense Mechanisms (Oral Cavity):
  1. Taste buds
    1. Normal bacterial flora
      1. Saliva (flushing, coating, lysozyme & Igs)
2. Developmental Anomalies (Oral Cavity)
  1. Brachygnathia superior/inferior
    1. Short maxilla/mandible
  2. Prognathia
    1. Abnormal prolongation of maxilla/mandible
  3. Cleft palate/palatoschisis
    1. Inadequate growth of palatine shelves leaves a central defect
    2. Communication of nasal & oral cavities may result in aspiration pneumonia & problems w/ suckling
    3. Affects hard &/or soft palate
  4. Hare lip/cheiloschisis
    1. Absence of part of lip rostral to nasal septum
3. Inflammatory Lesions (Oral Cavity)
  1. Inflammation predominates in Chronic lesions of bacterial or fungal origin
  2. Granulomatous inflammation
    1. Actinobacillosis ("Wooden togue")
      1. Actinobacillus lignieresii
    2. Actinomycosis ("Lumpy jaw")
      1. Actinomyces bovis
      2. Mandible becomes enlarged due to chronic osteomyelitis
  3. Eosinophilic Inflammation
    1. Oral eosinophilic granuloma (Cats)
  4. Necrotizing Inflammation
    1. Calf diptheria
      1. Fusobacterium necrophorum
      2. Coagulative necrosis & surrounding granulation tissue affecting the gingival & oral mucosa
  5. Vesicular Inflammation
    1. Often viral
    2. Vesicular, ulcerative or proliferative patterns may also co-exist or progress (e.g. vesicles -> ulcers)
    3. Foot & mouth disease
    4. Feline calcivirus
  6. Erosive Inflammation
    1. Ulcers may progress from vesicles, but can also be caused by: some bacterial & immune-mediated diseases, trauma
    2. Feline calcivirus & Feline herpesvirus
      1. Causes mouth ulceration
    3. Mucosal Disease
      1. Bovine viral diarrhoea virus (BVDV)
      2. Causes ulceration of oral cavity, muzzle & more distal alimentary ytact
    4. Immune - mediated diseases
      1. Autoantibodies directed against epithelial cell surface Ags
      2. Ex. Pemphigus vulgaris, bullous pemphigold (Dogs, Cats & Horses)
  7. Papular Inflammation
    1. Proliferative (papular) lesions
    2. Contagious pustular dermatitis ("orf")
      1. Firm, raised papules & pustules on lips & oral mucosa
      2. Sheep & Goats
      3. Hydrophobic degeneration, mixed inflammatory cell infiltration & secondary bacterial invasion
4. Neoplasia (Oral Cavity)
  1. Epithelial Tumors
    1. Papillomas
      1. Benign
      2. Raised, sometimes cauliflower-like lesions (Lips & Oral Mucosa)
      3. Thick squamous epithelium over a branching pedunculated fibrous stroma
    2. Squamous cell carcinoma
      1. Malignant
      2. Most common oral malignancy (Cats)
      3. 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
  2. Melanoma
    1. Tumor of pigment producing melanocytes
    2. Most common oral neoplasm (Dog)
    3. Nearly always Malignant (in oral cavity)
    4. Grow rapidly & are not always pigmented
    5. Oval or spindle-shaped melanocytes w/ variable melanin content
  3. Epulis
    1. Group of benign neoplasms of peridontal origin affecting gingivae
    2. Particularly in brachycephalic Dog breeds (boxer)
    3. Firm lesions on gums, surrounding teeth, esp. carnassial/canine region
    4. Dense collagenous & sometimes ossified tissue covered with stratified squamous epithelium (descends into dermis in cords)
Oesophagus
1. Congenital Anomalies
  1. Segmental aplasia
    1. Rare failure of fusion
      1. Band of fibrous tissue where distal oesophagus should be
  2. Achalasia
    1. Failure of cardiac sphincter to open
2. Functional (Neuromuscular) Disorders
  1. Megaesophagus
    1. Dilated oesophagus lacks peristalsis
      1. Accumulates ingesta due to underlying neuromuscular disorder (or obstruction), but lower oesophageal sphincter is usually normal
        Aspiration pneumonia may be a sequel
    2. Idiopathic
      1. Developmental disorder of vagus nerve/motor nucleus (esp. Great Dane, German shepherd, Siamese cat)
    3. Acquired
      1. Neurological
        Dysautonomias (ex. Equine grass sickness, feline dysautonomia), Myaesthenia gravis
      2. Muscular
        Myodegeneration (ex. nutritional myopathy (Vit. E/ selenium deficiency in cattle)
3. Obstruction
  1. Intraluminal
    1. Foreign bodies ("Choke")
      1. Ex. Root vegetable, sugar beet pulp, bone
    2. Most likely sites are narrow areas: Thoracic inlet, base of heart & cardiac sphincter
    3. May cause inflammation, pressure necrosis, ulceration & perforation
    4. Obstruction of Ruminant oesophagus may cause bloat
    5. Healing may cause narrowing (Stricture)
  2. Intramural (w/in wall of oesophagus)
    1. Inflammatory lesion (abscess, granulation tissue), fibrosis or neoplasm => Narrowing
  3. Extrinsic ( outside the oesophagus)
    1. Vascular ring anomaly (persistent RT. aortic arch constricts oesophagus & leads to megaoesophagus cranially)
    2. Also pressure from abscess, haematoma, neoplasm
4. Inflammation (Oesophagitis)
  1. Reflux Oesophagitis
    1. Damage from gastric acid due to gastric-oesophageal reflux or vomiting
      1. => Erosion of epithelium (may progress to ulcers)
  2. Infectious Agents
    1. Ex. Actinobacillosis, feline calcivirus
5. Neoplasia
  1. Papillomatosis
    1. Cattle: Bovine papillomavirus type 4 (transforms squamous cell carcinoma w/ bracken fern toxins)
  2. Squamous cell carcinoma
    1. Cats
  3. Leiomyoma
    1. Benign tumor of smooth muscle

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

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	Created by melian.yates over 10 years ago