Posterior mediastinum Flashcards
At what level does the descending aorta start?
T4/5
In what direction does the aorta descend?
It descends, first to the left of the vertebral column, and then in the midline in front of the vertebral bodies
At what level does the aorta pass the diaphragm?
Does it pass in front or behind the diaphragm?
T12
Behind
What are the main branches of the descending thoracic aorta?
Bronchial, oesophageal, posterior intercostal, and subcostal arteries
Where does the oesophagus begin?
In the neck opposite C6 just below the cricoid cartilage
At what point does the oesophagus pass through the diaphragm?
T10
Where does the oesophagus lie?
Initially, it lies in the midline, following the curve of the vertebral column. In the posterior mediastinum, it passes to the left, anterior to the aorta, so that it pierces the diaphragm to the left of the midline with the anterior and posterior vagal trunks
How does the right crus of the diaphragm interact with the oesophagus?
The right crus of the diaphragm forms a sling round the oesophagus and provides some sphincteric action at the lower end
What lines the oesophagus?
Stratified squamous (“wear and tear”) epithelium with mucous glands for lubrication
How is blood supplied to the oesophagus?
The upper part is supplied by branches of the inferior thyroid artery, the middle part directly by aortic branches, and the lower part by a branch of the left gastric artery ascending through the diaphragm
How is blood returned to the veins from the oesophagus?
Veins from the upper part drain to the systemic circulation via the azygos vein, but the lower third drains via the left gastric vein to the portal vein.
These veins anastomose freely in the submucous layer and constitute a site of portosystemic anastomosis
How is the oesophagus innervated?
Nerve supply in the upper third is from recurrent laryngeal and sympathetic nerves from the middle cervical ganglion via the inferior thyroid artery. The lower part is supplied by the vagi and sympathetic nerves in the oesophageal plexus
Where does the azygous vein start?
In the abdomen to the right of the first or second lumbar vertebra as the union of the right subcostal vein and ascending lumbar veins inferior to the diaphragm
What is the path taken by the azygous vein as it leaves the abdomen?
It ascends to pass through the aortic opening in the diaphragm to the right of the aorta and thoracic duct. It arches over the right lung hilum to enter the superior vena cava
Where are the hemiazygous veins?
To the left of the thorax
both cross the midline and join the azygos vein
How many hemiazygous veins are there?
2
How is blood returned to the venous system from the thoracic walls, oesophageal and bronchial veins?
The posterior intercostal veins on the left drain to the hemiazygos veins, and into the azygos on the right
What region does the superior intercostal vein drain?
The second and third intercostal spaces
What is the asymmetry in the azygous system?
The superior intercostal vein drains into the azygous vein on the right
On the left it drains anteriorly, across the ascending aorta, in between the vagus and phrenic nerves, to empty into the left brachiocephalic vein
How is blood from the first intercostal space returned to the venous system?
The supreme intercostal veins which drain into their respective brachiocephalic veins
What is the main lymph trunk of the body?
The thoracic duct
Where does the thoracic duct start?
In the abdomen as a continuation of the cisterna chyli which receives the lumbar and intestinal lymph trunks
What path does the thoracic duct take as it leaves the abdomen?
It passes up on the right, behind the median arcuate ligament, ascending on the vertebral column behind the oesophagus, between the aorta and the azygos vein
At what level does the thoracic duct pass the oesophagus?
In what direction does it pass?
T4/5
Behind the oesophagus and to the left
