VIRTUAL_L23_Histology-Digestive System (PART I)-2023
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Dr. Fabio Rosa, DVM, MSc, PhD, Dipl. ACVP Assistant Professor, Veterinary Anatomic Pathology
Contact information: Fabio.BrumRosa@liu.edu, Roth Hall, 116
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Histology helps understand diseases' pathogenesis
Canine parvovirus causes necrotizing enteritis
Parvovirus targets crypt epithelial cells in the small intestine
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Histology studies cell types (epithelial, nerve, muscle, connective tissue cells)
Histology studies cell functions (physiology)
Histology studies microanatomy/tissue architecture
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Digestive System includes:
Oral cavity/tongue
Salivary glands
Esophagus
Stomach
Intestines (Small Intestine, Large Intestine)
Liver
Gall Bladder
Pancreas
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Digestive System functions:
Prehension
Mastication
Digestion
Storage (forestomachs [ruminants] and cecum [horses])
Absorption
Expulsion (unabsorbed food, substances added by accessory glands)
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Learning objectives for the Digestive System:
Identify the structures of the oral cavity/tongue and alimentary canal
Know the function of each structure
Identify and correlate the variations in the tunica mucosa with their functions along the GI tract
Identify the types of epithelial cells in the stomach, small and large intestines, and their functions
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Oral cavity:
Mouth/cheek lining, hard & soft palate, and gingiva
Mucosa: Non-keratinized and keratinized stratified squamous epithelium
Lamina propria-submucosa: Connective tissue, minor salivary glands, labial, buccal, palatine, and lingual glands
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Tongue:
Muscular organ (skeletal muscle in multiple directions)
Mucosa covered by keratinized and non-keratinized stratified squamous epithelium
Papillae (projections of tissue from tongue surface, with or without taste buds)
Lingual salivary glands, skeletal striated muscle
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Lingual (minor) salivary glands:
Serous (cells with granular eosinophilic cytoplasm)
Mucous (cells with pale, "frothy" cytoplasm)
Stain lighter than serous glands
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Salivary Glands:
Major (separated from oral cavity, long ducts): Parotid, mandibular, sublingual, zygomatic
Minor (within oral cavity)
Exocrine glands: secretory product transported to oral cavity by a duct
Merocrine glands: do not lose cytoplasm during secretion
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Salivary Glands classified by type of secretion produced:
Serous (watery, low viscosity, high protein content)
Mucous (high viscosity for lubrication, high sugar content)
Mixed (serous & mucous secretory components)
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Salivary Glands structure:
Grossly: Multilobular, secretory units (acini or tubules), ducts surrounded by myoepithelial cells
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Salivary Glands functions:
Moisten oral cavity
Lubrication of food
Initiate digestion of carbohydrates and lipids
Antibacterial activity
Stimulate wound healing
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Tubular organ: Esophagus
General organization of the wall of a tubular organ:
Mucosa (epithelium, lamina propria, muscularis mucosae)
Submucosa
Tunica muscularis (inner circular layer, outer longitudinal layer)
Adventitia or Serosa
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Esophagus: Function is to transport food bolus and liquid from oral cavity to stomach
Structure includes longitudinal folds (rugae) for expansion
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Esophagus
Muscularis externa
2 layers of muscle: inner circular + outer longitudinal
Auerbach’s myenteric plexus (between inner circular and outer longitudinal layers)
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Esophagus
Adventitia: Cervical portion (connective tissue only)
Serosa: Variable present on thoracic & abdominal portions, lined by simple squamous epithelium (mesothelium)
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Esophagus
L
M
MM
S
ME
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Esophagus
Lamina propria
Muscularis mucosae
Submucosa
Submucosal glands
Duct
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Esophagus
Muscularis externa (tunica muscularis)
Inner circular
Outer longitudinal
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Esophagus
Auerbach's (myenteric) plexus
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Stomach
Non-Glandular x Glandular
Non-Glandular
Non-Glandular stomach of horses
Rumen, Reticulum and Omasum of ruminants
Storage and digestion
Lined by keratinized stratified squamous epithelium
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Horse
Ruminant
R
Re
A
O
Non-Glandular
Glandular
Non-glandular stomach separated from glandular stomach by margo plicatus
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Ruminant Non-Glandular Stomach
Divided into 3 compartments
Rumen
Reticulum
Omasum
Divisions have distinctly different morphologic features although their functions are similar
Omasum
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Ruminant Non-Glandular Stomach
Rumen
Ruminal “leaf-like” papillae (to increase absorptive surface area and movement)
Mucosa lined by str. sq. epithelium
No muscularis mucosae
Has a lamina propria-submucosa
Muscularis externa
Serosa
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LP-S
ME
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Rumen function
“Fermentation vat”
Conversion of cellulose to volatile fatty acids (butyric, propionic, acetic acids)
Absorption of volatile acids provides 70% of daily energy requirement
Absorption of urea, ammonia, minerals, vitamins and amino acids produced by bacteria
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Ruminant Non-Glandular Stomach
Reticulum
“Honeycomb”
Muscularis mucosae present only in apex of crests (folds, cristae)
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Ruminant Non-Glandular Stomach
Reticulum
Muscularis mucosae present only in apex of crests
Mechanical breakdown (grinding) of ingested material into fine particles
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Ruminant Non-Glandular Stomach
Omasum (aka “bible”)
Numerous longitudinal laminae (mucosal folds) projected from wall to lumen.
Assist with grinding of food into finer particles and movement from omasum to abomasum.
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Ruminant Non-Glandular Stomach
Omasum
Complete (continuous) muscularis mucosae in laminae
Muscularis mucosae presents a trilaminar appearance
Primary laminae
Secondary papillae
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Ruminant Non-Glandular Stomach
Omasum
Primary laminae
Secondary papillae
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Muscularis mucosae has a trilaminar appearance
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The