Lecture 8 DA

Question 1

What seperates the superior and inferior mediastinum?

Answer 1

The plane of Louis at the sternal angle (T4-5)

Question 2

Describe the pathway taken by the arch of the aorta.

Answer 2

It arches posterior, and to the left, towards the vertebral spine.

Question 3

The inferior mediastinum can be further subdivided. What are they and where are they found?

Answer 3

Posterior mediastinum - Between the heart and the spine.
Middle mediastinum - The heart and its immediate structures.
Anterior mediastinum - Between the heart and sternum.

Question 4

What is the thymus, and where is it located?

Answer 4

It is a gland important for immunity in pre-puberescent children, but becomes redundant at teen years and onwards. It is found at the arch of the aorta.

Question 5

Which of the vessels in the mediastinum is most superficial?

Answer 5

Veins.

Question 6

Which two branches form the superior vena cava?

Answer 6

The left and right brachiocephalic veins.

Question 7

Are the left and right brachiocephalic veins symmetric? Explain why.

Answer 7

The left is longer, as the superior vena cava is on the right side of the heart.

Question 8

What two branches form the brachiocephalic veins?

Answer 8

The jugular and subclavian veins (left and right each).

Question 9

Describe the branches of the arch of the aorta.

Answer 9

The ascending aorta is found at the plane of Louis, and branches into the brachiocephalic artery, which branches into the right subclavian and right common carotid arteries. There is no left brachiocephalic artery, the left common carotid and left subclavian branch straight off the arch (carotid branches first, followed by subclavian).

Question 10

Where are the phrenic nerves in relation to the vagus nerves?

Answer 10

They are lateral to the vagus nerves.

Question 11

What is the recurrent laryngeal nerve? What is the clinical significance behind it?

Answer 11

The left vagus nerve travels over the arch of the aorta, and as it does so, it gives off a branch that hook under the arch and back up to the larynx. It is close to ligamentum arteriosum. For this reason, it can often be mistaken for a patent ductus arteriosus (an unclosed ductus arteriosus), and during an operation to close it off if it hasn’t done so, the recurrent laryngeal nerve can accidentally be sutured tight, affecting the patients voice.

Question 12

Where are the phrenic and vagus nerve in relation to the heart?

Answer 12

The phrenic nerve is found on either side of the heart, and the vagus nerve is just medial to it.

Question 13

Where does the thoracic duct drain to?

Answer 13

It enters at the origin of the left brachiocephalic vein, before the vein branches into jugular and subclavian veins.

Question 14

What do the anterior, middle and posterior mediastinum of the inferior mediastinum contain?

Answer 14

Anterior - Fat, lymph nodes, internal thoracic/mammary artery and inferior thymus (in children).
Middle - Superior vena cava, heart, phrenic nerve, pulmonary trunk, and aorta.
Posterior - Thoracic duct, vagus nerve, thoracic aorta and oesophagus.

Question 15

How do the oesophagus and thoracic aorta travel relative to each other?

Answer 15

The oesophagus travels left to reach the stomach. Thoracic aorta travels right. Eventually, the two cross over.

Question 16

Where does the thoracic duct run?

Answer 16

It runs on the right of the midline. At the plane of Louis, it veers left towards the left brachiocephalic vein.

Question 17

What does the thoracic aorta give off as it travels down?

Answer 17

It gives off segmental branches, known as the posterior intercostal arteries.

Question 18

Where does the oesophagus receive its blood supply?

Answer 18

It receives it from the aorta, which gives off oesophageal branches as it travels down with it.

Question 19

Where do bronchial arteries originate, and what do they supply?

Answer 19

They branch off of the aorta, close to the trachea bifurcation.

Question 20

Describe the muscles and shape of the oesophagus.

Answer 20

The oesophagus has 3 muscle layers. They are striated in the upper part, smooth in the lower part, and the middle is a mix of the two.
It is flattened in the anteroposterior direction -> ( _ )

Question 21

Which duct does all lymph below the diaphragm drain?

Answer 21

Thoracic duct.

Question 22

What is the cisterna chyli?

Answer 22

It is found in 20% of individuals, and if found inferior to the diaphragm, giving off the thoracic duct.

Question 23

Where does the upper right quadrant of the body drain to?

Answer 23

To the Right lymphatic duct. Everywhere else drains to the left thoracic duct.

Question 24

Describe the standard azygous system of veins.

Answer 24

The azygous vein is found on the right side of the vertebral body, and drains into the pulmonary trunk, looping around the right main bronchus first.
On the right inferiorly, is the hemiazygous vein, to which the lower posterior intercostal veins drain. The hemiazygous vein drains to the azygous vein at around T8/9.
On the right superiorly, is the accessory hemiazygous vein, to which upper posterior intercostal veins drain. It can directly drain to the azygous vein at T8/9, or drain to hemiazygous first.
In situ, it almost never follows the above as it is highly variable, but the following are always certain - azygous is on the right (or very close to the midline), and hemiazygous and accessory hemiazygous veins are on the left.