Oesophagus - Anatomy & Physiology

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Introduction

The oesophagus (or gullet) is a muscular tube which transports food from the pharynx to the stomach. A bolus of food is passed down the oesophagus by peristalsis.

The oesophagus is devided into cevical, thoracic and abdominal sections.

Functional Anatomy

• Begins dorsal to cricoid cartilage of larynx

• Follows trachea down neck, first on the left and then medially once in thorax in the mediastinum

• Passes over heart then through the oesophageal hiatus of the diaphragm

• Passes over the dorsal border of the liver then joins the stomach at the cardia

• The cervical section is accompanied by the common carotid artery, the vagosympathetic trunk and the recurrent laryngeal nerves

• The thoracic section is accompanied by the right and left vagus nerves (CN X)

• Different proportions of striated muscle across the species

  -Dog and ruminant = 100%
  -Cat              = 80% (rostral)
  -Horse            = 65% (rostral)
  -Pig              = 33% (rostral)

Histology

• Stratified squamous epithelium

• Mucosal folds for distension

• Degree of keratinisation depend on diet

• Lamina propria contains collagen and elastic fibres sparsely distributed

• Lamina muscularis is smooth muscle

• No glands in mucosa

• Mucous glands (tubulo-acinar) present in submucosa

• Inner circular layer of tunica muscularis thickens near gastric junction forming a sphincter

Innervation

• Sympathetic nerves

• Parasympathetic from the vagus nerve (CN X) and recurrent laryngeal nerves

• myenteric plexus extends the length of the oesophagus

Species Differences

• Canid has no keratinisation

• Pig and horse have some keratinisation

• Ruminant has a lot of keratinisation

• Lamina muscularis absent cranially in pigs and dogs

• Lamina muscularis present caudally in pigs (very thick) and dogs (spirally arranged)

• Mucous glands abundant cranially but absent caudally in pig

• Mucous glands throughout in dog but more abundant caudally

• Mucous glands present in horse, cats and ruminants only at pharyngeal-oesophageal junction

• Thick and strong sphincter of tunica muscularis in dogs and pigs

• Ruminants, horse and pig have stratified squamous epithelium continuing from oesophagus into stomach. carnivores have an abrupt transition to columnar epithelium.