27.0 GI: ORAL CAVITY, ESOPHAGUS AND SALIVARY
GLANDS
Upon completion of this lecture, students will be able to:
a) Define and use properly the following words: Brachydont Teeth, Hypsodont, Crown,
Neck, Dental lamina, Enamel organ, Dental mesenchyme, Dental papilla, Ameloblasts,
Odontoblasts, Dental sac, Alveolar bone, Cementum, Periodontal ligament,
Hydroxyapatite, Acellular cementum, Cellular cementum, Cementocytes (blasts), Dentin,
Dental pulp, Tongue, Ventral surface, Stratified squamous epithelium, Dorsal surface,
Papillae, Filiform, Fungiform, Vallate (Circumvallate), Foliate, Taste buds, Striated
muscle, Glands of the tongue, Esophagus, Layers of tubular organ, Mucosa, Epithelium,
Lamina propria (interstitium), Muscularis mucosa, Submucosa, Muscularis externa,
Adventitia or fibrosa or serosa, Stratified squamous epithelium, Keratinization, Salivary
glands, Parotid gland, Acinar cells, Myoepithelial cells (basket cells), Submandibular
gland, Serous glands, Mucous glands, Mixed glands, Serous demilunes, Sublingual
gland, Zygomatic gland, Molar gland, Compound tubuloacinar, Minor salivary glands,
Duct system, Intercalated duct, Striated ducts.
b) Describe and associate basic structure/function for the following: all structures listed
above.
c) Identify by microscopy: Brachydont Teeth, Hypsodont, Crown, Neck, Enamel organ,
Dental mesenchyme, Dental papilla, Ameloblasts, Odontoblasts, Dental sac, Alveolar
bone, Cementum, Periodontal ligament, Acellular cementum, Cellular cementum,
Cementocytes (blasts), Dentin, Dental pulp, Tongue, Ventral surface, Stratified
squamous epithelium, Dorsal surface, Papillae, Filiform, Fungiform, Vallate
(Circumvallate), Foliate, Taste buds, Striated muscle, Glands of the tongue, Esophagus,
Layers of tubular organ, Mucosa, Epithelium, Lamina propria (interstitium), Muscularis
mucosa, Submucosa, Muscularis externa, Adventitia or fibrosa or serosa, Stratified
squamous epithelium, Keratinization, Salivary glands, Parotid gland, Acinar cells,
Myoepithelial cells (basket cells), Submandibular gland, Serous glands, Mucous glands,
Mixed glands, Serous demilunes, Compound tubuloacinar, Duct system, Intercalated
duct, Striated ducts.
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I.
TEETH
1. All teeth have the same components:
a. Enamel
b. Dentin
c. Cementum
d. Pulp
2. Brachydont Teeth
a. Simple teeth
b. short and cease to grow
c. contain: crown, neck, roots
d. Carnivores, man, incisors of ruminants, pig (except canine of the boar)
3. Hypsodont
a. Ruminants, rodents, horses, canine or boar
b. Constant eruption
c. No crown and neck
d. elongated body with roots
II.
DEVELOPMENT
1. A thickening of oral epithelium forms the dental lamina
2. Enamel organ forms by the growth of the epithelium with dental mesenchyme
3. Dental papilla is delimited by ameloblasts, which differentiate from the inner enamel
epithelium.
a. Odontoblasts form a differentiated layer in the mesenchyme and the rest
becomes the pulp (blood vessels, nerves and loose CT).
4. Dental sac is a dense connective tissue that surrounds the enamel organ and dental
papilla. The dental sac forms the alveolar bone, layer of cementum, and periodontal
ligament.
III.
HISTOLOGY OF THE DEVELOPING AND MATURE TOOTH
1. Enamel organ
a. Brachydont teeth
i. External surface of crown
b. Hypsodont teeth
i. Beneath layer of cementum
c. Hardest substance in body
i. 99% mineral hydroxyapatite
ii. 1% organic
iii. long slender rods
d. ameloblasts
i. synthesize enamel
ii. disappear from the mature bachydont tooth
iii. some remain in the hypsodont (for grinding throughout life)
2. Cementum
a. Similar to bone
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b. Acellular cementum
i. Lamellae
c. Cellular cementum
i. Cementocytes (blasts)
1. Found in lacunae and canaliculi
2. Secrete fibrous matrix, which mineralizes
d. Collagen fibers extend from alveolar bone into cementum
i. Forms periodontal ligament to hold tooth
e. Hypsodont teeth
i. Cementum covers outside of tooth
1. Above and below gingival
ii. Equine
1. Cementum is vascular and innervated
3. Dentin
a.
b.
c.
d.
e.
f.
Major part of internal area of tooth
Under the enamel crown and cementum of root
Mineralized
Forms wall of pulp cavity
Produced by odontoblasts
Species differences
i. Hypsodont teeth
1. Cementum and enamel invaginate into the dentin
2. Horse and ruminants
3. Dentin is less resistant than enamel, so will wear in grinding teeth
4. Dental pulp and odontoblasts
a. Cavity of tooth
b. Blood and lymph vessels and nerve
c. Loose connective tissue
d. Odontoblasts
i. Peripheral region
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IV.
TONGUE
1. Anatomy of the tongue
a. Musculature covered by a mucus membrane.
i. Muscles run in different planes including longitudinal, oblique, and
transverse.
1. The different patterns of muscles aid in the function of the tongue
including.
a. Mastication
b. Swallowing
c. Vocalization
b. Papilla vary in structure between species
i. Papilla can also vary within different areas of the tongue.
2. Histology of the tongue
a. Epithelium
i. Ventral surface
1. Stratified squamous epithelium that is relatively thin and not
keratinized.
ii. Dorsal surface
1. Thicker than the ventral surface.
2. Stratified squamous epithelium that is keratinized.
3. Has surface modifications called papillae
b. Papillae
i. Role and location.
1. Mechanical or sensory function depending on the type.
2. Located on the dorsal surface of the tongue.
ii. Types of papillae.
1. Filiform
a. protrude above the lingual surface
b. sharp, barbed, and pointed conical appearance.
c. most numerous especially in the dog and cat.
d. devoid of taste buds, so no sensory function
e. mechanical function only, which helps to push food back
into the oropharynx.
f. Papilla is keratinized stratified squamous epithelium
protects cells from abrasion.
g. Connective tissue core
h. Species differences
i. Abrasive in cat and dog tongues
2. Fungiform
a. mushroom shaped.
b. protrudes above the lingual surface.
c. stratified squamous epithelium; non-keratinized.
d. Connective tissue core.
e. occurs singly or at the most may have 2-3 in a row
f. usually found between filiform papilla.
g. sensory role because of the taste buds.
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3. Vallate (Circumvallate)
a. largest papilla (2-3 x the size of others)
b. No aggregates
c. deep side trenches
d. very rare (except in human)
e. doesn't extend above the lingual surface.
f. non-keratinized stratified squamous epithelium
g. taste buds, so sensory
4. Foliate
a. folds of the lingual surface found in aggregates.
b. rectangular or box shape.
c. stratified squamous epithelium.
d. connective tissue core.
e. taste buds; so sensory
f. more numerous in certain species, such as the rabbit.
g. when present, they are more numerous than the fungiform
or vallate papillae
c. Taste buds
i. Ovoid in structure
1. Contains a trench that allows for the contact with food (taste pore
communicates with the surface)
ii. Dark and light cells
iii. Seen on fungiform, vallate, and foliate papillae
d. Striated muscle
i. longitudinal, transverse, and oblique planes
ii. provides for accurate movement
e. Glands of the tongue
i. Mucous and serous salivary glands.
ii. Especially prominent in the rabbit tongue
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V.
ESOPHAGUS
1. GENERAL ASPECTS OF THE DIGESTIVE SYSTEM
PRINCIPAL LAYERS (Tunics) OF A HOLLOW TUBULAR ORGAN
a. One long hollow tube.
b. Consist of four parts.
i. Mucosa
1. Epithelial lining
a. Lines the lumen of the cavity.
b. All types of epithelia found in tubular organs
2. Lamina propria (interstitium)
a. connective tissue sheath underneath the epithelium
b. also blood vessels and nerves
3. Muscularis mucosa
a. thin band of smooth muscle
b. below the epithelium
c. May not be present in certain regions
ii. Submucosa
1. Thick layer of connective tissue underneath the mucosa.
2. Some places may have glands present in this region
iii. Muscularis externa
1. Thick muscle layer
2. Can be smooth muscle, skeletal muscle, or combo of both
3. Inner circular
4. Outer longitudinal
5. Some places have cartilage
iv. Adventitia or fibrosa or serosa
1. connective tissue, fat , blood vessels, and nerves.
2. ESOPHAGUS
a. General information
i. No digestive function
ii. Serves as a conduit to transport food from the oral cavity to the stomach.
b. Stratified squamous epithelium
i. Species differences
ii. Keratinization varies with species and diet, eg. ruminants usually
keratinized because of their diet.
Dog
Cat
Horse
Pig
Cow
Goat
Sheep
Epithelium
Non-K
Non-K
Keratin
Keratin
Keratin
Keratin
Keratin
Submucosal +
+
+
glands
throughout PGEJ
PGEJ
PGEJ = pharyngoesophageal junction
+
cranial
+
PGEJ
+
PGEJ
+
PGEJ
c. Lamina propria
i. Collagen and elastin
ii. Contains histiocytes, lymphocytes, and fibroblasts.
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d. Muscularis Mucosae
i. Species variability; different areas of the esophagus.
1. Pig:
a. Cranial esophagus; no muscularis mucosae
b. Middle esophagus discrete bands of muscularis mucosae.
c. Caudal esophagus very thick and prominent muscularis
mucosae.
e. Submucosa
i. May have glands in certain regions
1. Serous and mucous.
2. Pig
a. most prominent in the cranial region.
ii. Blood vessels, nerves, and lymphatics.
f.
Muscularis Externa.
i. Tremendous variability between and within species.
ii. Varies also with location in certain species.
iii. Always present.
iv. Can be smooth muscle, skeletal muscle, or combo of both.
g. Esophagus / Gastric junction
i. Transition of stratified squamous epithelium (esophagus) to simple
columnar (stomach)
ii. Abrupt change
iii. Glands in submucosa of the esophagus will extend into the stomach.
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SALIVARY GLANDS
I.
ANATOMY AND MORPHOLOGY SALIVARY GLANDS
1. Group of organs in the head region.
2. Major and minor salivary glands.
II.
HISTOLOGICAL STRUCTURE OF SALIVARY GLANDS
1. Parotid gland
a. Largest of the salivary glands.
b. CT capsule with septae that go into the gland (like the pancreas).
c. acini like the pancreas.
d. Predominantly serous but in some species this can vary.
i. Mucous in dog and cat.
e. Cells have broad base and narrow apex (pyramidal).
f. Cells not as basophilic as the acinar cells of the pancreas.
g. Outside of the acinar cells are myoepithelial cells (basket cells).
i. Present in other salivary glands
ii. Help to move secretions into the duct.
2. Submandibular gland
a. Species differences
i. Rodents
1. Serous glands
ii. Dogs and cats
1. Mucous glands
iii. primates, horses, and ruminants
1. Mixed glands
b. Acinar structure.
i. Serous demilunes
1. Represent serous secretions “at the end of acinus”
2. Will see serous gland around mucous gland
3. Sublingual gland
a. Species differences
i. primates, horses, and carnivores
1. Mixed glands
ii. Pigs and rodents
1. Mucous glands
4. Zygomatic gland
a. Mucous (few serous cells).
b. Species differences
i. carnivores (dogs and cats)
1. Small glands
ii. In dogs may see serous demilunes
5. Molar gland
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a.
b.
c.
d.
Only in the cat
Similar to zygomatic gland
Compound tubuloacinar
Mucous (may see some serous demilunes)
6. Minor salivary glands
a. Lingual
b. Gustatory
c. Labial
d. Buccal,
e. Palatine
f. Pharyngeal
g. Zygomatic
h. Molar
IV.
DUCT SYSTEM OF SALIVARY GLANDS
1. Intercalated ducts are the first portion
a. unlike the pancreas they don't extend into the salivary gland
2. Striated ducts
a. Next portion of the ducts
b. In basal portion of these cells will see lines or striations
i. due to the unique mitochondria arrangement
c. Columnar epithelium
V.
SALIVARY GLAND FUNCTION
1. Acinar secretions will have some role in digestion
2. Will aid in moving the fluid down the GI tract
3. Duct cells are involved in reabsorbing some of the electrolytes
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