Mediastinum

Question 1

What is the mediastinum?

Answer 1

Thick midline partition spearating the 2 pleural cavities

Question 2

How far does the mediastinum extend?

Answer 2

From superior thoracic aperture to inferior thoracic aperture and between sternum ant and thoracic vertebrae post

Question 3

What is the mediastinum for?

Answer 3

Acts as a conduit for structures that pass from one body region to the other and for tructures that connect thoracic organs to other body regions

Question 4

What are the main contents of the mediastinum?

Answer 4

Trachea (larynx to bifurcation into principal bronchi), oesophagus (pharynx thru diaphragm at T10), heart, pericardium, thoracic duct, nerves, great vessels

Question 5

How is the mediastinum divided?

Answer 5

Superior (above sternal angle), Inferior (below sternal angle), Anterior (to heart), Middle (heart), Posterior (to heart and diaphragm)

Question 6

What are the contents of the superior mediastinum from anterior to posterior?

Answer 6

Thymus, Phrenic Nerves, Braciocephalic veins, thoracic duct, Vagus nerves, great arteries, Trachea and main bronchi, Upper oesophagus, left recurrent laryngeal nerve

Question 7

At what level does the trachea end?

Answer 7

T4-5 where the 2nd costal cartilage attaches - Sternal angle

Question 8

What are the great arteries present in the mediastinum?

Answer 8

Left common carotid, left subclavian and right brachiocephalic trunk (splits into right subclavian and common carotid)

Question 9

What are the great veins?

Answer 9

SVC (enters right atrium from above) and IVC (enters right atrium from below through central tendon of the diaphragm)

Question 10

Where is the phrenic nerve embedded?

Answer 10

In the pericardial sac

Question 11

At what level is the aortic arch?

Answer 11

The top is at the sternal angle

Question 12

What does each brachiocephalic vein branch off into?

Answer 12

Internal jugular (from head) and subclavian( from upper limbs) vein

Question 13

How do the brachiocephalic veins (BCV) join to become the svc?

Answer 13

Left BCV crosses from left to right, posterior to the manubrium, joining the R BCV

Question 14

Where does each brachiocephalic vein branch sit?

Answer 14

Underneath each sternoclavicular joint

Question 15

In which part of the mediastinum are the arch, ascending and descending aorta?

Answer 15

Arch: superior, Ascending: middle and descending: posterior

Asc and Desc are both in the inferior mediastinum

Question 16

What are the first branches of the ascending aorta?

Answer 16

Right and left coronary arteries

Question 17

What branches from the aortic arch?

Answer 17

Brachiocephalic trunk, left common carotid and left subclavian

Question 18

How does the aorta relate to the airways?

Answer 18

Arch rises anterior to trachea and over the left main bronchus at the lung root

Question 19

How does the trachea relate to the great arteries?

Answer 19

It lies behind and between the brachiocephalic and the common carotid/subclavian

Question 20

How are the common carotid arteries distributed?

Answer 20

They divide into external and internal carotids in the neck, vertebral arteries come from subclavian

Question 21

How does the blood flow to the lungs work?

Answer 21

Comes out from right ventricle, carrying deO2 blood via pulmonary arteries to lungs

Question 22

How does the foetus bypass the lungs?

Answer 22

Ductus arteriosus which is a structure that connects the pulmonary trunk to the aortic arch - after foetal life called ligamentum arteriosum

Question 23

What are the contents of the posterior mediastinum?

Answer 23

Oesophagus, descending aorta, thoracic duct, azygos venous system, posterior mediastinal lymph nodes, thoracic sympathetic trunks, splanchnic nerves (ignore)

Question 24

What is the structure of each level of the oesophagus?

Answer 24

Begins at C7, ends at T11, bends anteriorally at T7 deviating to the left, passes through diaphragm at T10 and is constricted at 4 places

Question 25

Where is the oesophagus constricted?

Answer 25

Junction of oesophagus with pharynx, Where oesophagus crossed by aortic arch, where oesophagus is compressed by left main bronchus and at oesophageal hiatus

Question 26

Why is the oesophageal hiatus important?

Answer 26

It prevents stomach acid from coming back up and destroying the mucous layer present in the oesophagus

Question 27

How is the oesophagus delivered blood?

Answer 27

Via the oesophageal branches from the descending aorta

Question 28

What is the azygos venous system?

Answer 28

It drains the posterior wall of chest, upper abdomen and posterior mediastinal organs

Question 29

How does the azygos venous system work?

Answer 29

Major azygos vein on RHS, with hemiazygos (lower) and accessory hemiazygos (upper) draining into it from the LHS, crossing over thoracic vertebral bodies

Question 30

Where is the azygos vein positioned?

Answer 30

Arches over right lung root to enter SVC, above the right atrium

Question 31

What nerves are present in the mediastinum?

Answer 31

Phrenic nerves - C3-5, Vagus nerves (CNX) and sympathetic trunks

Question 32

Where are the phrenics located?

Answer 32

Anterior to lung roots and cross pericardium to diaphragm

Question 33

Where are the vagus nerves located?

Answer 33

Posterior to lung roots, forming plexus following oesophagus to abdomen, branching out to lungs and heart on the way

Question 34

Where do the sympathetic trunks lie?

Answer 34

Each side of the posterior meiastinum

Question 35

What do the phrenic nerves do?

Answer 35

Motor to diaphragm and sensory to central tendon of diaphragm, parietal pleura, pericardium, peritoneum of central diaphragm

Question 36

How does the phrenic nerve reach the diaphragm?

Answer 36

It lies on the surface of the right brachiocephalic vein, SVC and RHS of heart and pericardium - in front of lung root

Question 37

How are the great arteries related to the main nerves?

Answer 37

Vagus are lateral to common carotids, left vagus passes anterior to aortic arch, left phrenic crosses vagus to cross aortic arch more anteriorly

Question 38

How does the left phrenic nerve move down into thorax?

Answer 38

Descends in front of lung root

Question 39

How does the left vagus descend into thorax?

Answer 39

Left vagus crosses behind lung root and gives off left recurrent laryngeal nerve which recurs around ligamentum arteriosum an aortic arch, then breaks into many branches around the oesophagus

Question 40

How does the right vagus nerve descend into thorax?

Answer 40

It lies on trachea, crosses behind lung root, recurrent laryngeal recurs around subclavian artery and breaks up into branches on oesophagus

Question 41

Where do the vagus nerves branch out to?

Answer 41

Branches to chest and abdomen (parasympathetic) and large sensory capacity from gut and lungs
Recurrent laryngeal not parasympathetic, runs back up to neck to supply skeletal muscles of larynx

Question 42

What do the sympathetic trunks do?

Answer 42

Receive branches from spinal nerves T1-L2, distribute sympathetic nerves to smooth muscle glands throughout the body, bring pain fibres back to CNS from viscera (referred pain)

Question 43

From which fibres of the sympathetic trunk do the splanchic nerves form?

Answer 43

T5-T12

Question 44

What is the thoracic duct?

Answer 44

Lymph duct returning lymph from lower limbs, pelvis, abdomen and left thoracic wall to blood

Question 45

Where is the thoracic duct located?

Answer 45

Begins below diaphragm at cisterna chyli, between oesophagus and aorta on RHS, crosses behing oesophagus to LHS between T7 and T4

Question 46

Where does the thoracic duct drain into?

Answer 46

Left brachiocephalic vein