Mediastinum Flashcards
What is the mediastinum?
Thick midline partition spearating the 2 pleural cavities
How far does the mediastinum extend?
From superior thoracic aperture to inferior thoracic aperture and between sternum ant and thoracic vertebrae post
What is the mediastinum for?
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
What are the main contents of the mediastinum?
Trachea (larynx to bifurcation into principal bronchi), oesophagus (pharynx thru diaphragm at T10), heart, pericardium, thoracic duct, nerves, great vessels
How is the mediastinum divided?
Superior (above sternal angle), Inferior (below sternal angle), Anterior (to heart), Middle (heart), Posterior (to heart and diaphragm)
What are the contents of the superior mediastinum from anterior to posterior?
Thymus, Phrenic Nerves, Braciocephalic veins, thoracic duct, Vagus nerves, great arteries, Trachea and main bronchi, Upper oesophagus, left recurrent laryngeal nerve
At what level does the trachea end?
T4-5 where the 2nd costal cartilage attaches - Sternal angle
What are the great arteries present in the mediastinum?
(off the aortic arch)
brachiocephalic trunk (splits into right subclavian and common carotid), Left common carotid, left subclavian and right
What are the great veins?
SVC (enters right atrium from above) and IVC (enters right atrium from below through central tendon of the diaphragm)
Where is the phrenic nerve embedded?
In the pericardial sac
At what level is the aortic arch?
The top is at the sternal angle
What does each brachiocephalic vein branch off into?
Internal jugular (from head) and subclavian( from upper limbs) vein
How do the brachiocephalic veins (BCV) join to become the svc?
Left BCV crosses from left to right, posterior to the manubrium, joining the R BCV
Where does each brachiocephalic vein branch sit?
Underneath each sternoclavicular joint
In which part of the mediastinum are the arch, ascending and descending aorta?
Arch: superior, Ascending: middle and descending: posterior Asc and Desc are both in the inferior mediastinum
What are the first branches of the ascending aorta?
Right and left coronary arteries
What branches from the aortic arch?
Brachiocephalic trunk, left common carotid and left subclavian
How does the aorta relate to the airways?
Arch rises anterior to trachea and over the left main bronchus at the lung root
How does the trachea relate to the great arteries?
It lies behind and between the brachiocephalic and the common carotid/subclavian
How are the common carotid arteries distributed?
They divide into external and internal carotids in the neck, vertebral arteries come from subclavian
How does the blood flow to the lungs work?
Comes out from right ventricle, carrying deO2 blood via pulmonary arteries to lungs
How does the foetus bypass the lungs?
Ductus arteriosus which is a structure that connects the pulmonary trunk to the aortic arch - after foetal life called ligamentum arteriosum
What are the contents of the posterior mediastinum?
Oesophagus, descending aorta, thoracic duct, azygos venous system, posterior mediastinal lymph nodes, thoracic sympathetic trunks, splanchnic nerves (ignore)
What is the structure of each level of the oesophagus?
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
Where is the oesophagus constricted?
Junction of oesophagus with pharynx, Where oesophagus crossed by aortic arch, where oesophagus is compressed by left main bronchus and at oesophageal hiatus
Why is the oesophageal hiatus important?
It prevents stomach acid from coming back up and destroying the mucous layer present in the oesophagus
How is the oesophagus delivered blood?
Via the oesophageal branches from the descending aorta
What is the azygos venous system?
It drains the posterior wall of chest, upper abdomen and posterior mediastinal organs
How does the azygos venous system work?
Major azygos vein on RHS, with hemiazygos (lower) and accessory hemiazygos (upper) draining into it from the LHS, crossing over thoracic vertebral bodies
Where is the azygos vein positioned?
Arches over right lung root to enter SVC, above the right atrium
What nerves are present in the mediastinum?
Phrenic nerves - C3-5, Vagus nerves (CNX) and sympathetic trunks
Where are the phrenics located?
Anterior to lung roots and cross pericardium to diaphragm
Where are the vagus nerves located?
Posterior to lung roots, forming plexus following oesophagus to abdomen, branching out to lungs and heart on the way
Where do the sympathetic trunks lie?
Each side of the posterior meiastinum
What do the phrenic nerves do?
Motor to diaphragm and sensory to central tendon of diaphragm, parietal pleura, pericardium, peritoneum of central diaphragm
How does the phrenic nerve reach the diaphragm?
It lies on the surface of the right brachiocephalic vein, SVC and RHS of heart and pericardium - in front of lung root
How are the great arteries related to the main nerves?
Vagus are lateral to common carotids, left vagus passes anterior to aortic arch, left phrenic crosses vagus to cross aortic arch more anteriorly
How does the left phrenic nerve move down into thorax?
Descends in front of lung root
How does the left vagus descend into thorax?
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
How does the right vagus nerve descend into thorax?
It lies on trachea, crosses behind lung root, recurrent laryngeal recurs around subclavian artery and breaks up into branches on oesophagus
Where do the vagus nerves branch out to?
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
What do the sympathetic trunks do?
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)
From which fibres of the sympathetic trunk do the splanchic nerves form?
T5-T12
What is the thoracic duct?
Lymph duct returning lymph from lower limbs, pelvis, abdomen and left thoracic wall to blood
Where is the thoracic duct located?
Begins below diaphragm at cisterna chyli, between oesophagus and aorta on RHS, crosses behing oesophagus to LHS between T7 and T4
Where does the thoracic duct drain into?
Left brachiocephalic vein
