30.0 GI: AVIAN DIGESTIVE SYSTEM, COMPOUND STOMACH
a) Define and use properly the following words: Avian tongue, Esophagus, Mucus glands,
Crop, Diverticulum, Stratified nonkeratinized squamous epithelium, Crop milk,
Proventriculus avian, Rugae, Submucosal glands, Adenomere cells, HCl and
pepsinogen, Ventriculus, gizzard, Koilin, Gastric pits, Papillae, Cloaca, Bursa of
Fabricius, Cecal tonsils, Rumen, Papillae, Keratinized stratified squamous epithelium,
Reticulum, Omasum, Abomasum.
b) Describe and associate basic structure/function for the following: 1) all structures listed
above; 2) histological differences between the glandular and nonglandular regions of the
stomach; 3) species that have prominent nonglandular regions; 4) location of the
papillae in the compound stomach.
c) Identify by microscopy: Avian Esophagus, Mucus glands, Crop, Stratified nonkeratinized
squamous epithelium, Proventriculus avian, Rugae, Submucosal glands, Adenomere
cells, Ventriculus, gizzard, Koilin, Gastric pits, Papillae, Cecal tonsils, Rumen, Papillae,
Keratinized stratified squamous epithelium, Reticulum, Omasum, Abomasum.
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AVIAN DIGESTIVE SYSTEM
I.
BUCCAL CAVITY AVIAN
1. Avian tongue has hyaline cartilage.
2. Tooth buds
a. Don't go to completion
b. Have primordial teeth during early development.
3. Mucous glands are responsible for crushing and mixing
II.
ESOPHAGUS AVIAN
1. Stratified squamous epithelium.
2. Mucous secreting glands in the lamina propria
3. Very similar to mammals.
III.
CROP AVIAN
1.
2.
3.
4.
5.
6.
IV.
Diverticulum of the esophagus.
Nearly identical to the esophagus; cannot differentiate the crop from the esophagus.
Stratified nonkeratinized squamous epithelium
Has mucous glands
Smooth muscle in the muscularis externa
Crop milk
a. sloughed layers of the epithelium.
b. fed to the young birds by both the male and female.
c. Top layers of epithelium filled with fat
d. Prolactin stimulates the crop to produce crop milk.
PROVENTRICULUS (GLANDULAR STOMACH) AVIAN
1. Rugae are the folds in the proventriculus (like the mammalian stomach).
a. Mucosal (rugosal glands)
i. viscous secretion (mucous)
ii. line the surface of proventriculus
b. Submucosal glands
i. Complicated gland with opening into the lumen.
ii. Made up of the adenomere cells.
1. form a serrated appearance.
2. produce HCl and pepsinogen
3. comparable to both the chief and parietal cells in the mammalian
fundic stomach.
c. Function
i. digestion
ii. mixing the food particles
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V.
VENTRICULUS (GIZZARD) AVIAN
1. Muscular stomach
2. Very thick walled structure.
a. muscle aides in mixing the food.
3. Mucosal portion is very thin.
4. Mucosal lining
a. Mucus glands go into the submucosal
i. Similar to gastric pits.
ii. Columnar and cuboidal cells.
b. produce Koilin.
i. Cornified material similar to keratin.
ii. Protects the gizzard from abrasion.
iii. Forms a thick acellular layer
VI.
LOWER DIGESTIVE TRACT AVIAN
1. Lymphatic nodules in the cloaca (Bursa of Fabricius)
a. B lymphocytes develop and mature here
2. Cecae
a. Cecal tonsils are lymphatic aggregates.
b. Function to aid in storage of food.
3. Rectum
VII.
CLOACA
1. unique to birds
2. common passageway for the digestive, urinary, and reproductive tracts
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COMPOUND STOMACH
I.
ANATOMY AND SPECIES DISTRIBUTION
1. Made up of four components
a. Rumen
i. Largest of the four stomachs
ii. Bacterial fermentation occurs here.
b. Reticulum
c. Omasum
d. Abomasum
2. Found in ruminants,
a. includes cows, sheep, goats, deer, elk
II.
RUMEN
1. Papillae
a. Epithelium is keratinized.
i. Keratinized stratified squamous epithelium,
ii. variable thickness depending on the animal's diet.
b. Has CT core (lamina propria).
i. Contains blood vessels, nerves, fibroblasts
c. Does not contain the muscularis mucosa or externa.
2. Lamina propria and submucosa blend insensibly.
IV.
RETICULUM
1. Mucosa contains permanent anastomosing folds
a. Conical shaped papilla.
i. Lined by stratified squamous keratinized epithelium
ii. Contains lamina propria and muscularis mucosa in the tip.
V.
OMASUM
1. Large laminae
a. Page-like or leaf-like folds.
b. Long projections into the lumen.
c. Studded with conical or other papilla.
d. In the center one finds lamina propria, muscularis mucosa on each side with the
muscularis externa in between.
i. Thus, there are three muscle layers all together
VI.
ABOMASUM
1. Functions exactly like the monogastric stomach
2. has a fundic (with chief and parietal cells) and pyloric stomach.
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VII.
FUNCTIONS OF THE FORESTOMACH.
1. Bacteria and protozoa help to convert the digested material into Volatile fatty acids
(VFA), which get absorbed in the rumen and reticulum.
VIII.
EQUINE STOMACH.
1. Has a non-glandular and glandular component.
2. These are separated by the margo plicatus.
3. Histologically the margo plicatus shows the transition from stratified squamous
epithelium to columnar epithelium
4. Thus, in the horse the transition occurs within the stomach.
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