GI Tract - Oesophagus Flashcards
What is the oesophagus?
It is a fibromuscular tube, approximately 25cm in length, that transports food from the pharynx to the stomach.
It originates at the inferior border of the cricoid cartilage (C6) and extends to the cardiac orifice (T11).
Anatomical course?
The oesophagus begins in the neck, at the level of C6. Here, it is continuous superiorly with the laryngeal part of the pharynx (the laryngopharynx).
It descends downward into the superior mediastinum of the thorax, positioned between trachea and the vertebral bodies of T1 and T4. It then enters the abdomen via the oesophageal hiatus (an opening in the right crus of the diaphragm) at T10.
The abdominal portion of the oesophagus is approximately 1.25cm long - it terminates by joining the cardiac orifice of the stomach at the level of T11.
Anatomical structure - layers of the oesophagus?
The oesophagus shares a similar structure with many of the organs in the alimentary tract:
1) Adventitia - outer layer of the connective tissue.
Note: the very distal and intraperitoneal portion of the oesophagus has an outer covering of serosa, instead of adventitia.
2) Muscle layer - external of longitudinal muscle and inner layer of circular muscle. The external layer is composed of different muscle types in each third:
- Superior third - voluntary striated muscle
- Middle third - voluntary striated and smooth muscle
- Inferior third - smooth muscle
3) Submucosa
4) Mucosa - non-keratinised stratified squamous epithelium (contiguous with columnar epithelium of the stomach).
Food is transported through the oesophagus by peristalsis - rhythmic contractions of the muscles which propagate down the oesophagus. Hardening of these muscular layers can interfere with peristalsis and cause difficult in swallowing (dysphagia).
Anatomical structure - oesophageal sphincters?
There are two oesophageal sphincters, known as the upper oesophageal sphincter (UES) and the lower oesophageal sphincter (LES).
UES
The upper sphincter is an anatomical, striated muscle sphincter at the junction between the pharynx and oesophagus. It is produced by the cricopharyngeus muscle. Normally, it is constricted to prevent the entrance of air into the oesophagus.
LES
This is located at the gastro-oesophageal junction (between the stomach and oesophagus). The gastro-oesophageal junction is situated to the left of the T11 vertebra, and is marked by the change form oesophageal to gastric mucosa.
The sphincter is classified as a physiological (or functional) sphincter, as it does not have any specific sphincteric muscle. Instead, the sphincter is maintained by four factors:
1) Oesophagus enters the stomach at an acute angle.
2) Walls of the intra-abdominal section of the oesophagus are compressed when there is a positive intra-abdominal pressure.
3) Prominent mucosal folds at the gastro-oesophageal junction aid in occluding the lumen.
4) Right crus of the diaphragm has a ‘pinch-cock’ effect.
During oesophageal peristalsis, the sphincter is relaxed to allow food to enter the stomach. Otherwise at rest, the function of this sphincter is to prevent reflux of acidic gastric contents into the oesophagus.
Anatomical relations?
The anatomical relations of the oesophagus give rise to four physiological constrictions of the lumen - it is these areas where food/foreign objects are most likely to become impacted. They can be remembered using the acronym ‘ABCD’:
A - arch of the aorta
B - bronchus
C - cricoid cartilage
D - diaphragmatic hiatus
Cervical and thoracic anatomical relations:
Anterior - trachea, left recurrent laryngeal nerve, pericardium
Posterior - thoracic vertebral bodies, thoracic duct, azygous vein, azygous veins and the descending aorta.
Right - Pleura, terminal part of the azygous vein
Left - Subclavian artery, aortic arch, thoracic duct and pleura
Abdominal anatomical relations:
Anterior - left vagus and posterior surface of the heart.
Posterior - right vagus nerve, left crus of the diaphragm.
Vasculature?
Thoracic
The thoracic part of the oesophagus receives its arterial supply from the branches of the thoracic aorta and the inferior thyroid artery (a branch of the thyrocervical trunk).
Venous drainage into the systemic circulation occurs via branches of the azygous veins and the inferior thyroid vein.
Abdominal
The abdominal oesophagus is supplied by the left gastric artery (a branch of the coeliac trunk) and left phrenic artery. This part of the oesophagus has a mixed venous drainage via two routes:
1) To the portal circulation via the left gastric vein
2) To the systemic circulation via the azygous vein
These two routes form a porto-systemic anastomosis, a connection between the portal and systemic venous systems.
Innervation?
The oesophagus is innervated by the oesophageal plexus, which is formed by a combination of the parasympathetic vagal trunks and sympathetic fibres from the cervical and thoracic sympathetic trunks.
Two different types of nerve fibre run in the vagal trunks. The upper oesophageal sphincter and upper striated muscle is supplied by fibres originating from the nucleus abiguus. Fibres supplying the LES and smooth muscle of the lower oesophagus artise from the dorsal motor nucleus.
Lymphatics?
Superior third - deep cervical lymph nodes
Middle third - superior and posterior mediastinal nodes
Inferior third - left gastric and coeliac nodes
Clinical relevance - disorders of the oesophagus?
Barret’s oesophagus
Refers to the metaplasia (reversible change from one differentiated cell type to another) of lower oesophageal squamous epithelium. It is usually caused by chronic acid exposure as a result of a malfunctioning LES. The acid irritates the oesophageal epithelium, leading to a metaplastic change.
The most common symptom is a long-term burning sensation of indigestion.
It can be detected via endoscopy of the oesophagus. Patients who are found to have it will be monitored for any cancerous changes.
Oesophageal carcinoma
Arouns 2% of malignancies in the UK are oesophageal carcinomas. The clinical features of this carcinoma are:
- dysphagia - difficulty swallowing. It becomes progressively worse over time as the tumour increases in size, restricting the passage of food.
- weight loss
There are two major types of oesophageal carcinomas: squamous cell carcinoma and adenocarcinoma.
1) Squamous cell carcinoma - the most common subtype of oesophagus cancer. It can occur at any level of the oesophagus.
2) Adenocarcinoma - only occurs in the inferior third of the oesophagus and is associated with Barret’s oesophagus. It usually originates in the metaplastic epithelium of Barret’s oesophagus.
Oesophageal varices
The abdominal oesophagus drains into both the systemic and portal circulation, forming an anastomosis between the two.
Oesophageal varices are abnormally dilated sub-mucosal veins (in the wall of the oesophagus) that lie within this anastomosis. They are usually produced when the pressure in the portal system increases beyond normal, a state known as portal hypertension. Portal hypertension most commonly occurs secondary to chronic liver disease, such as cirrhosis or an obstruction in the portal vein.
The varices are predisposed to bleeding, with most patients presenting with haematemesis (vomiting of blood). Alcoholics are at a high risk of developing oesophageal varices.
