Superior and middle mediastinum Flashcards
What is the mediastinum?
Is a thick midline partition that separates the 2 pleural cavities.
where is the mediastinum boundaries and how can the mediastinum be divided?
Boundaries: Superior: superior thoracic aperture (inlet) Inferior: inferior thoracic aperture Anterior: sternum Posterior: thoracic vertebrae.
Transverse plane between Sternal angle to T4/5 separates mediastinum into Superior + Inferior
Inferior mediastinum further split into anterior, middle + posterior parts
what does the mediastinum act as?
it acts as a conduit for structures that pass through the thorax from one region to another and for structures that connect thoracic organs to other body regions.
what are the principle content of the mediastinum and what is the thoracic inlet?
The thoracic inlet is a ring formed of:
1st thoracic vertebra (T1)
1st ribs – difficult to feel because of clavicle
Trachea –
From C6 (end of larynx) to bifurcation into principal (right and left main) bronchi (T4)
Oesophagus
From end of pharynx (C6/7) – pierces diaphragm at level of T10
Heart and pericardium (in middle mediastinum)
Thoracic duct - lymphatic drainage
Nerves
Great vessels heading for neck and upper limb, (Common carotid artery, jugular vein, subclavian artery and vein)
Subclavian vessels pass under clavicle
Veins sit anterior to the arteries
what are the contents of the superior mediastinum?
From anterior to posterior:
Thymus
Phrenic Nerves – motor + sensory supply to diaphragm (C3,4,5 keeps the diaphragm alive)
Great veins: SVC (enters Right atrium from above) + IVC (enters Right atrium from below. NB: IVC passes through central tendon of diaphragm at T8) Main lymphatic trunks Vagus nerves Great arteries Trachea and main bronchi Upper oesophagus
what are the great veins?
- superior vena cava (SVC) enters right atrium from above
- inferior Vena cava (IVC) enters right atrium from below, through central tendon of diaphragm.
SVC: Formed by asymmetric union of Left + Right Brachiocephalic veins
Each brachiocephalic vein – formed by Internal jugular vein + subclavian vein.
Thoracic duct drains at this junction
(“Brachio” = arm. “Cephalic” = head. Therefore brachiocephalic veins drain venous blood from head + arms)
What is the thoracic duct and its position?
Largest lymphatic vessel
Begins on level of T12 as a continuation of cisterna chyli
Enters thorax through diaphragm alongside the aorta (T12)
Ascends in the posterior mediastinum to the right of midline on the front of vertebral bodies.
At T5, it crosses the midline to left side and enters the superior mediastinum
Then runs along the left border of the esophagus
Empties into junction between IJV + Subclavian vein
What are the tributaries of the superior vena cava?
- Internal jugular veins from head and subclavian veins from upper limbs join to form left and right brachiocephalic veins
- Left brachiocephalic vein crosses posterior to manubrium to join the right brachiocephalic vein to form the SVC
what is the azygos vein and where does it arise from
Drains posterior wall of chest and upper abdomen + posterior mediastinal organs
Accessory hemiazygos (upper) + hemiazygos (lower) veins on left cross thoracic vertebral bodies to join single azygos vein on right
Azygos vein arches over right lung root to enter SVC from behind just above right atrium
Azygos = asymmetrical (asymmetrical organisation of venous system)*
Azygos vein arises L1/2 – at junction between Right ascending lumbar vein + right subcostal vein*
what are the 3 arteries of the mediastinum and where is it located?
Arch of aorta – superior
Ascending aorta – middle
Descending aorta - posterior.
Ascending aorta (origin at aortic orifice at base of Left ventricle/left 3rd costal cartilage)
Arch of aorta (called this from 2nd costal cartilage. This is when it enters the superior mediastinum – NB: ONLY ARCH OF AORTA in superior mediastinum. It arches over the right pulmonary artery. Arch is initially anterior then later lateral to trachea)
Descending aorta – starts at T4
what are branches of the ascending aorta and where does this arise from and aortic arch?
-Ascending aorta:
-right and left coronary arteries (end arteries supplying heart muscle).
Left coronary artery – from left aortic sinus
Right coronary artery – from right aortic sinus
The coronary arteries emerge at level of ascending aorta.
Sinuses are the pockets between the semilunar cusps (right, posterior, left) + wall of the ascending aorta
Aortic arch:
- brachiocephalic trunk: divides into right common carotid and right subclavian arteries
- Left common carotid artery
- Left subclavian artery
what is the relation of aorta and great arteries to the airway?
- aortic arch rises anterior to trachea
- Arches over the left main bronchus at the lung root
- trachea lies behind and between brachiocephalic and left common carotid arteries
what is the distribution of common carotid arteries?
- Divide into external and internal carotids high in neck
- main arteries of head and neck (with vertebral arteries from the subclavian arteries)§
where is the pulmonary trunk and what is its function?
- outflow of right ventricle
- carries deoxygenated blood via left and right pulmonary arteries to lungs
where does the pulmonary trunk come from?
- arises from the right ventricle
- carries deoxygenated blood to lungs
- divides into right and left pulmonary arteries
- Ligamentum arteriosum connects PT to aortic arch. Is remnant of the ductus arterioles-bypasses lungs into foetal life
