Overview
The oesophagus is a fibromuscular organ joining the pharynx and stomach,
allowing the passage of food through peristaltic contractions. It measures around
27 cm in length and is predominantly contained within the thoracic cavity.
Gross Anatomy
Development
The
oesophagus develops from embryonic gut tube from the endoderm, subsequently
developing into the foregut tube. Its innervation originates from the 4th
pharyngeal arch.
Surface anatomy
Begins at C6
and runs inferiorly to T11.
Macro-anatomy
The
oesophagus descends anterior to the vertebral bodies in the mid-line before
moving anteriorly and left as it approaches the diaphragm. Its anatomical
relations are as follows:
- Anterior: trachea at T4/5, recurrent laryngeal
nerves, left bronchus, left atrium, diaphragm
- Posterior: Vertebrae, hemiazygos vein,
descending aorta, thoracic duct
- Left: aorta, left subclavian artery and lung
- Right: Lung and azygos vein
There are
three main levels at which constriction of the oesophagus can occur:
- The level of the cricoid cartilage (at its
origin),15 cm from the mouth (as measured during endoscopy)
- Where it lies posterior to aortic arch and left
main bronchus at 27cm from the mouth
- The diaphragmatic orifice at T10 level at 40cm
from the mouth
Micro-anatomy
Predominantly
consists of non-keratinised stratified squamous epithelium, a smooth lamina
propria and a muscularis propria containing both striated and smooth muscle. The
muscularis layer is thich and contains both longitudinal and circular muscle. Adventitia
line the oesophagus externally.
Columnar
epithelium lines the last 0.5 cm, which produce mucus to counteract the acidic
environment of stomach. Mucus-producing glands are also located in the lamina
propria to aid smooth peristalsis.
Blood supply
The blood
supply to the oesophagus is split into three regions, with communication
existing between vessels of different regions:
- Upper third: inferior thyroid artery and vein
- Middle third: aortic arterial branches and
azygos venous branches
- Lower third: left gastric artery and vein
(branch of portal vein)
Nerve supply
The
innervation of the oesophagus is complex and come from the branches of the
vagus nerve and sympathetic trunks. Sensation and motor components are
generally both supplied by the left and right vagus nerves (CN X), with
sympathetic fibres also contributing. The oesophageal plexus is formed from
fibres from the left (mainly anterior vagal trunk) and right (mainly posterior
vagal trunk) vagus nerves.
Physiology
The third part of the swallow reflex involves the unconscious contraction
of oesophageal muscle in a sequential fashion producing peristalsis and moving
the food bolus towards the lower oesophageal sphincter. The two sphincters
(upper and lower oesophageal) of the oesophagus are functional as opposed to
anatomical sphincters and reduce reflux.
Clinical Anatomy
Gastro-oesophageal reflux: secondary to dysfunction
of lower oesophageal sphincter
Barrett’s oesophagus: An example of metaplasia,
where chronic gastro-oesophageal reflux causes stratified squamous epithelium
to change to columnar epithelium. It is a pre-malignant condition and requires
regular follow-up with endoscopy.
Oesophageal cancer: There are two main histological
types of oesophageal cancer - squamous (occurring in the middle third of the
oesophagus) and columnar epithelium (the lower third). Risk factors include
smoking and excess alcohol intake.
Achalasia: A condition where the lower oesophageal
smooth musculature fails to relax, together with the lower oesophageal
sphincter. Classically a ‘swan-neck’ deformity is seen on barium swallow
studies.
Quick Anatomy
Key Facts
Development |
Developmental
precursor - foregut |
Blood
vessels |
Arteries:
Inferior thyroid (originates from the thyrocervical trunk), aortic branches
and left gastric (coeliac plexus) Veins:
Inferior thyroid (drains directly into the brachiocephalic vein), azygos vein
and left gastric vein (portal vein) |
Nerves |
Vagus
nerve (CN X) and cervical/thoracic sympathetic nerves |
Lymphatics |
Drains
into the deep cervical, posterior mediastinal and left gastric lymph nodes |
Aide-Memoire
The level of the oesophageal aperture in the diaphragm can be remembered
by the fact the word oesophagus has ten letters – therefore its aperture is at
T10.
Summary
The oesophagus is a muscular tube passing from the pharynx into the
abdomen via the thoracic cavity. Particularly important are the levels at which
the oesophagus can be constricted, as these are the areas that can cause
difficulty when passing an endoscope.
References
Drake,
Richard L et al. Gray's Anatomy For Students. Philadelphia: Elsevier/Churchill
Livingstone, 2005, p192-5
Instant
Anatomy: The oesophagus. Last accessed 11th February 2016. Available
from: http://www.instantanatomy.net/thorax/areas/oesophagus.html