VAN 211: Veterinary Histology and Embryology (2+2)

OESOPHAGUS

• The wall of oesophagus consists of a mucous membrane lined by stratified squamous epithelium and a muscular coat, which in the cervical region is covered by a loose fibrous adventitia. In the thoracic region, the latter is replaced by a serous membrane.

Mucosa

• It is lined by stratified squamous epithelium and is thrown into longitudinal folds.
• The lamina propria is made up of closely woven collagenous fibres with some elastic fibres interspersed in it.
• Its well-developed papillary body is overlaid by superficially cornified, stratified squamous epithelium.
• The musclaris mucosae is made up of longitudinal smooth muscle fibres, which may consist of a part of few muscle fibres, only in the initial part in some species.

Submucosa

• It is composed of loose network of coarse collagenous fibres, which permit formation of longitudinal folds.
• Mucous glands occur in the submucosa and they are made up of typical mucous alveoli with short ducts, which pass through the submucosa and muscularis mucosae and open between the two adjacent connective tissue papillae.
• The initial portions of the duct are lined by cuboidal epithelium but this change to a stratified epithelium in the lamina propria. The development of the submucosal glands varies in different parts of the oesophagus and also in different species.

Tunica muscularis

• It is made up of striated muscle with some smooth muscle at the caudal end.
• It consists of two layers, which course spirally at the beginning and become distinctly an inner and outer longitudinal layer gradually.

Tunica fibrosa

• This is composed of loose connective tissue which binds the oesophagus to the surrounding structures in the cervical region.
• In the thoracic region there is serosa, covering the muscular coat.

Bloods vessels and nerves

• Vascular trunks run longitudinally in submucosa. The branches ramify and form capillary networks in layers.
• Nerve cells occur in plexuses located in submucosa and between the main layers of tunica muscularis.

Species differences

• The muscularis mucosae is complete in man but in ruminants, solipeds and cat it consists at first only of isolated bundles.
• In the dog and pig it is entirely lacking in the initial portion in the caudal half, muscle bundles made their appearance but form a continuous layer only in the vicinity of the stomach.
• The submucosal glands are present only in the pharyangeo-oesophageal junction in the horse, ruminants and cat.
• In the dog, the glands form a continuous stratum up to the stomach and in pigs the glands extend to about middle of the oesophagus. In the pig numerous lymph nodules are present adjacent to the glands.