Superior Vena Cava, Aorta, Pulmonary Trunk, Thoracic Duct, Azygos and Hemiazygos Veins, and Thoracic Sympathetic Trunks

Question 1

[27-minute video]: the Aorta

Answer 1

😎

Question 2

Outline the relational anatomy of the aortic arch.

Answer 2

[Study relational anatomy with an atlas!]
Posterior and to the right:
1. Trachea
2. Esophagus
3. Left recurrent laryngeal nerve
4. Thoracic duct
5. Vertebral column

Anterior and to the left:
1. Left lung and pleura
2. Left phrenic nerve
3. Left vagus nerve
4. Left cardiac nerves (i.e., superior cervical cardiac branch of left sympathetic chain and inferior cardiac branch of left vagus nerve)
5. Left superior intercostal vein

Inferior:
1. Left bronchus
2. Bifurcation of pulmonary trunk
3. Ligamentum arteriosum
4. Left recurrent laryngeal nerve
5. Superficial cardiac plexus

Superior:
1. Brachiocephalic trunk
2. Left common carotid artery
3. Left subclavian artery
4. Left brachiocephalic vein
5. Thymus

Question 3

a) The ascending aorta arises from the upper end of the left ventricle (i.e. aortic vestibule) and continues as arch of aorta at the _______________________.
b) State the branches of the ascending aorta. These branches are given off at the root of aorta which have aortic sinuses of Valsalva.

Answer 3

a) sternal angle
b) right coronary artery from right aortic or anterior aortic sinus
left coronary artery from left aortic or left posterior aortic sinus

Note: The ascending aorta develops from the truncus arteriosus after its partition by the spiral septum.

Question 4

State the branches of the arch of aorta.

Answer 4

1. Brachiocephalic (innominate) artery.
2. Left common carotid artery.
3. Left subclavian artery.

Notes:
㊨ Occasionally a fourth branch called thyroidea ima artery may arise from the arch of aorta.
㊨ The arch of aorta arches over the root of left lung.
㊨ The arch of aorta develops from the following sources:
1. Aortic sac.
2. Left horn of aortic sac.
3. Left fourth aortic arch artery.
4. Left dorsal aorta (between the attachment of the fourth aortic arch (artery) and 7th cervical intersegmental artery.

Question 5

The descending aorta is the continuation of the arch of the aorta in the posterior mediastinum. It is divided into descending thoracic aorta and abdominal aorta.
Describe the course of the descending thoracic aorta.

Answer 5

It begins on the left side of the lower border of the fourth thoracic (T4) vertebra and descends in the posterior mediastinum with an inclination towards the right. As a result it terminates in front of the lower border of the body of 12th thoracic (T12) vertebra.
At its lower end it passes through the aortic opening of the diaphragm to continue as the abdominal aorta.

㊨ Note that the descending thoracic aorta produces a deep vertical groove on the mediastinal surface of the lung posterior to the hilum of the lung.

Question 6

State the branches of the descending thoracic aorta.

Answer 6

Parietal branches:
㊨ 3rd to 11th posterior intercostal arteries on each side.
㊨ subcostal artery on each side
㊨ superior phrenic artery on each side

Visceral branches:
㊨ pericardial branches to posterior surface of the pericardium
㊨ mediastinal branches to the lymph nodes and areolar tissue of the posterior mediastinum
㊨ two left bronchial arteries (upper and lower)
㊨ esophageal branches, supplying middle one-third of the esophagus

Question 7

Discuss the formation, course and termination of the superior vena cava.

Answer 7

☛ formed at the lower border of the right 1st costal cartilage by the union of right and left brachiocephalic (innominate) veins
☛ It passes vertically downwards behind the right border of the sternum and pierces the pericardium at the level of the 2nd costal cartilage and terminates into the upper part of the right atrium at the lower border of the right 3rd costal cartilage

Note:
㊨ The SVC has no valves in its lumen because gravity facilitates the blood flow in it.

Question 8

State the subdivisions of the superior vena cava.

Answer 8

㊨ Extrapericardial part (in superior mediastinum).
㊨ Intrapericardial part (in middle mediastinum).

Question 9

State the tributaries of the superior vena cava.

Answer 9

㊨ Right and left brachiocephalic veins.
㊨ Azygos vein, which arches over the root of the right lung and opens into SVC just before it pierces fibrous pericardium.
㊨ Mediastinal and pericardial veins.

Question 10

There are two brachiocephalic veins: right and left. What forms these veins?

Answer 10

Internal jugular and subclavian veins.

㊨ Note that these brachiocephalic veins are devoid of valves.

Question 11

State the differences between the right and left brachiocephalic veins in terms of length and course.

Answer 11

㊨ The right brachiocephalic vein is shorter than the left brachiocephalic vein.
㊨ The course of the right brachiocephalic vein is vertical while that of the left brachiocephalic vein is oblique.

Question 12

State the tributaries of the right brachiocephalic vein.

Answer 12

㊨ Right vertebral vein
㊨ Right internal thoracic vein
㊨ Right inferior thyroid vein
㊨ First right posterior intercostal vein

Question 13

State the tributaries of the left brachiocephalic vein.

Answer 13

㊨ Left vertebral vein
㊨ Left internal thoracic vein
㊨ Left inferior thyroid vein
㊨ First left posterior intercostal vein
㊨ Left superior intercostal vein

Question 14

The SVC may be obstructed (compressed) at two sites: (a) above the opening of azygos vein (i.e., in superior mediastinum), and (b) below the opening of azygos vein (i.e., in the middle mediastinum). In such cases, collateral pathways may develop. Check out the following images to show this.

Answer 14

[1]

Question 15

State the origin and course of the pulmonary trunk.

Answer 15

Origin
The pulmonary trunk is about 5 cm long and arises from the upper part (infundibulum/conus arteriosus) of the right ventricle at the level of the sternal end of left 3rd costal cartilage.
Course
After arising from infundibulum in the middle mediastinum, it passes backwards and to the left and terminates below the arch of aorta and in front of left principal bronchus by dividing into right and left pulmonary arteries.

Note:
㊨ The right pulmonary artery is larger than the left and lies slightly at a lower level.

Question 16

Why does;
a) the lymph in the thoracic duct appear milky-white in appearance?
b) the thoracic duct appear beaded?

Answer 16

a) because it contains a product of fat digestion (chyle) from the intestine.
b) due to the presence of numerous valves in its lumen.

Question 17

State the area of drainage of the thoracic duct.

Answer 17

The thoracic duct drains the lymph from all the parts of the body except the (a) right side of the head and neck, (b) right side of the chest wall, (c) right lung, (d) right side of the heart, and (e) right surface of the liver.

N.B. Thoracic duct drains lymph from whole of the body except the right upper quadrant of the body which is drained by the right lymphatic duct.

Question 18

State the extents of the thoracic duct.

Answer 18

The thoracic duct extends from the upper end of cisterna chyli on the posterior abdominal wall at the lower border of T12 vertebra to the junction of left internal jugular and left subclavian veins at the root of the neck.

Note:
㊨ During the course of the thoracic duct, as it reaches the T5 vertebra, it crosses the midline from right to left side and enters the superior mediastinum to run along the left border of the esophagus and reaches the root of the neck.
㊨ At the root of neck it arches laterally at the level of C7 vertebra—in front of vertebral system (e.g., vertebral artery and vertebral vein) and left cervical sympathetic trunk and behind the carotid system (e.g., left common carotid artery, left internal jugular vein, and left vagus nerve). The summit of arch lies 3–4 cm above the clavicle.

Question 19

State the tributaries of the thoracic duct:
a) in the abdomen
b) in the thorax
c) in the neck

Answer 19

a) in the abdomen
Efferent from lower six intercostal lymph nodes of both sides.
b) in the thorax
㊨ A pair of the ascending lymph trunks which drains lymph from the upper lumbar lymph nodes (para-aortic lymph nodes).
㊨ A pair of the descending lymph trunks which drain lymph from the posterior intercostal lymph nodes of upper six spaces.
㊨ Lymph vessels from the posterior mediastinal lymph nodes.
c) in the neck
㊨ Left jugular lymph trunk, draining lymph from the neck.
㊨ Left subclavian lymph trunk, draining lymph from the left upper limb.
㊨ Left bronchomediastinal trunk.

Question 20

Azygos venous system consists of?

Answer 20

azygos vein
hemiazygos vein
accessory hemiazygos vein

Notes:
㊨ azygos means single ie. without a companion
㊨ these veins lie in front of thoracic part of vertebral column and play an important role in the venous drainage of the thorax.

Question 21

The azygos vein is present only on the right side in the upper part of the posterior abdominal wall and the posterior mediastinum. It connects the ___________________________ with the _______________________. It is provided with valves and may appear tortuous.

Answer 21

It connects the inferior vena cava with the superior vena cava.

Question 22

State the functions of the azygos vein.

Answer 22

㊨ It drains venous blood from the thoracic wall and upper lumbar region.
㊨ It forms an important collateral channel connecting the superior vena cava and inferior vena cava.

Question 23

The formation of azygos vein is variable. State the various ways in which the azygos vein is formed.

Answer 23

1. Formed by the union of right subcostal and right ascending lumbar vein at the level of T12 vertebra (common).
2. Arises from the posterior aspect of the inferior vena cava (IVC) near the renal veins.
3. As a continuation of right subcostal vein.
4. Occasionally, it may arise from right renal or right first lumbar vein.

Question 24

State the course and termination of the azygos vein.

Answer 24

The azygos vein after formation ascends up and leaves the abdomen by passing through the aortic opening of the diaphragm and enters the posterior mediastinum. There it ascends vertically lying in front of vertebral column up to the level of T4 vertebra, where it arches forwards above the hilum of the right lung to terminate in the superior vena cava at the level of the 2nd costal cartilage.

Question 25

List the tributaries of the azygos vein.

Answer 25

1. Lower 7th right posterior intercostal veins except first.
2. Right superior intercostal vein (formed by union of 2nd, 3rd, and 4th right posterior intercostal veins).
3. Hemiazygos vein (at the level of T8 or T9 vertebra).
4. Accessory hemiazygos vein (at the level of T7 or T8 vertebra).
5. Right subcostal vein.
6. Right bronchial vein.
7. Right ascending lumbar vein.
8. Esophageal veins with the exception of those at its lower end.
9. Mediastinal veins.
10. Pericardial veins.

Notes:
㊨ In case of obstruction of SVC, it serves as the main collateral channel to shunt the blood from the upper half of the body to IVC.
㊨ The arch of azygos vein is related below to the root of right lung, on right side to the right lung and pleura, and left side to the right border of esophagus, trachea, and right vagus nerve.

Question 26

The hemiazygos vein (syn. inferior hemiazygos vein) lies on the left side only and corresponds to the lower part of the azygos vein (i.e., mirror image of the lower part of the azygos vein). State its formation.

Answer 26

Formed on the left by the union of left ascending lumbar vein and left subcostal vein. It may arise from the posterior surface of the left renal vein.

Question 27

List the tributaries of the hemiazygos vein.

Answer 27

1. Lower three (9th–11th) left posterior intercostal veins.
2. Left subcostal vein.
3. Left ascending lumbar vein.
4. Small esophageal and mediastinal veins.

Question 28

The accessory hemiazygos vein (syn. superior hemiazygos vein) lies on the left side only and corresponds to the upper part of the azygos vein (i.e., mirror image of the upper part of the azygos vein). List its tributaries.

Answer 28

1. Fifth to eighth (5th–8th) left posterior intercostal veins.
2. Left bronchial veins (sometimes).

Question 29

The thoracic sympathetic trunk is a ganglionated chain situated on either side of the vertebral column. What is it continuous with superiorly and inferiorly?

Answer 29

Superiorly, continuous with the cervical sympathetic chain at the thoracic inlet.
Inferiorly, continuous with the lumbar sympathetic chain after passing behind the medial arcuate ligament of the diaphragm.

[Video 1 - 4:14 minutes]; thoracic sympathetic trunk (animation)
[Video 2 - 12:15 minutes]; thoracic sympathetic trunk and splanchnic nerves (has cadavers in the illustration)