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Histology of GIT
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This notes contains about the Histology of Gastrointestinal tract (GIT) in which layers which are present in our GIT system such as mucosa,submucosa ,etc
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GENERAL HISTOLOGICAL FEATURES OF DIGESTIVE SYSTEMThe digestive system consists of a series of tubular organs and associated glands, the
main function of which is to break down the ingested food into smaller units that can be
absorbed into smaller units that can be absorbed into the circulation. It consists on an oral cavity,
esophagus, Stomach, small and large intestine and anal canal.
General Histological Features of the Oral Cavity
(a) Lips
The junction between the integument and the digestive system occurs on the lips, which are
covered on the outside of skin and on the inside by a mucosa. The mucosa of lip is covered by
stratified squamous epithelium that is keratinized in ruminants and horses, but nonkeratinized in
carnivors. Some minor salivary glands referred to as labial glands are also present
ANAT-104 Systematic Veterinary Histology & Embryology Dr. Nisar Ahmed
, (b) Tongue
The tongue is a muscular organ covered by mucosa. The epithelium covering the tongue is
stratified squamous epithelium that is keratinized and thick on the dorsum and nonkeratinized
and thin on the ventral surface. The dorsum surface contains macroscopic papillae, filliform,
conical and lenticular papillae are purely mechanical they facilitate the ingesta within the oral
cavity. The fungi form, vallate and foliate papillae are gustatory; they contain the taste buds
which are responsible for sense of taste. The filliform papillae are the most numerous types.
They are slender, thread like structures that project above the surface of tongue. Lenticular
papillae are flattened, lens shaped projections are found on the torus linguae of ruminants.
Fungiform papillae are scattered among the filliform papillae and have dome shaped on upper
surface. The vallate papillae are located on the dorsum of the tongue, just rostral to the root.
They are large flattened structures. The foliate papillae are parallel folds of the lingual mucosa
located on the margin of the tongue.
The Taste buds are ellipsoid clusters of specialized epithelial cells embedded in the stratified
squamous epithelium of different papillae.
(c) Teeth
Teeth are highly mineralized structures in the oral cavity that serve domestic mammals
during the procuring, cutting and cursing of food and as weapons of offense and defense. The
tooth consists of a highly mineralized outer part surrounding the pulp cavity which contains
dental pulp, a core of connective tissue, blood vessels and nerves.
Parts of teeth
Enamel covers the external surface of the crown and hardest substance in the body,
composed of 99% mineral (hydroxyapatite) and 1% organic matrix. Histologically enamel is
composed of long, slender rods, enamel prisms held together by interred enamel. The enamel is
produced by cells known as amelobasts.
Cementum resembles bone in all its structural features. Acellular Cementum is composed of
lamellar oriented parallel to the surface of tooth. Cellular cementum consists on cementocytes
cells, which occupy lacunae and canaliculi similar to those of bone.
Dentin is a highly mineralized tissue that constitutes the major part of tooth. Dentin also forms
the wall of the pulp cavity. It consists of a matrix of organic material, mainly randomly oriented
collagen fibrils and glycoprotein upon which is deposited minerals hydroxyapatite. It contains
70% mineral and 30 % organic material. Dentin is produced by columnar layer of cells
odontoblasts.
Dental pulp occupies the pulp cavity of the tooth. It is composed of connective tissue cells and
fibers, amorphous ground substance, numerous blood and lymph vessels.
ANAT-104 Systematic Veterinary Histology & Embryology Dr. Nisar Ahmed
, General Histological Features of the esophagus
1. MUCOSA
a) Surface Epithelium
It is lined with non-keratinized stratified squamous type. In some mammals
is keratinized, thrown into longitudinal folds reducing lumen to small star-shaped space.
b) Lamina Propria
It is rich in collagen fibers; it has papillae projecting into epithelium. Some
mucus secreting esophageal glands occur here at either extremity of the esophagus.
c) Muscularis Mucosa
It is thick, fibers longitudinally arranged. In man it is incomplete or absent
from the upper third.
2. SUB-MUCOSA
The sub mucosa is loose connective tissue containing large, longitudinally
oriented arteries, veins large lymph vessels and nerves. Some seromucous glands
containing mucous acini.
3. MUSCULARIS EXTERNA
Two layers: Outer Longitudinal and inner Circular forming a thick muscular
coat. In upper third part has skeleton muscles ; middle mixed (smooth + skeleton
muscles) and lower third has smooth fibers only.
4. SEROSA
It is composed of loosely arranged connective tissue or collagen fibers,
which known as fibrosa and binds the esophagus with the surrounding structures.
Glands of esophagus
Mucous Glands occur in Sib-Mucosa, some occur in Lamina Propria, few
glands in Man.
Diagnostic Features of esophagus
1. Folded Mucosa 2. Stratified Squamous Epithelium
3. Thick Muscularis Mucosa 4. Thick Muscularis Externa
5. Papillac Project into Epithelium
ANAT-104 Systematic Veterinary Histology & Embryology Dr. Nisar Ahmed
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