The Mediastinum Flashcards
what is the mediastinum?
the central area of the thorax that lies between the 2 pleural cavities
what are the superior, inferior, anterior, and posterior boundaries of the mediastinum?
- superior = superior thoracic aperture
- inferior = diaphragm
- anterior = sternum
- posterior = thoracic vertebrae
what is the mediastinum divided into?
- superior and inferior mediastinum
- superior
- inferior: anterior, middle, posterior compartment
is the superior or inferior mediastinum larger?
inferior
what divides the superior and inferior mediastinum?
the transverse thoracic plane
where does the transverse thoracic plane pass?
passes through the sternal angle anteriorly and the intervertebral disc between T4 + T5 posteriorly
anteriorly to posteriorly, what are the contents of the superior mediastinum?
- thymus
- brachiocephalic veins + SVC, arch of aorta + branches (brachiocephalic trunk, common carotids + subclavian), vagus and phrenic nerves, cardiac plexus
- trachea
- oesophagus
- vagus and phrenic nerves
- sympathetic trunk
- thoracic duct + lymphatic trunks
= essentially anything that need to pass from the neck to the thorax/abdomen and any vascualr structures involved in head/neck/upper limbs
where does the oesophagus pass through the diaphragm and at what level?
oesophageal hiatus, T10
identify A, B, C, D, E
A = brachiocephalic vein B = arch of aorta C = trachea D = oesophagus E = azygos vein
identify A, B, C, D, E, F, G
A = right brachiocephalic vein B = left brachiocephalic vein C = SVC D = brachiocephalic trunk E = left common carotid artery F = left subclavian vein G = right phrenic nerve
identify H, I, J
H = left phrenic nerve I = left vagus nerve J = aortic arch
what unites to form the SVC?
right and left brachiocephalic veins
where does the thoracic aorta pass through the diaphragm and at what level?
aortic hiatus, T12
what innervates the diaphragm?
phrenic nerve
identify A, B, C
A = arch of aorta (cut) B = trachea C = right vagus nerve
identify D, E, F, G
D = left vagus nerve E = left recurrent laryngeal nerve F = oesophagus G = azygos vein
what are the superior and inferior boundaries of the inferior mediastinum?
superior = transverse thoracic plane inferior = diaphragm
what separates the middle compartment of the inferior mediastinum from other compartments?
fibrous pericardium
what are the anterior and posterior boundaries of the anterior mediastinum?
anterior = sternum posterior = fibrous pericardium
what are the contents of the anterior mediastinum?
sternopericardial ligament, fat, remnants of the thymus, lymph nodes
what are the contents of the middle mediastinum?
- pericardium
- heart
- roots of great vessels (SVC, ascending aorta pulmonary trunk, pulmonary veins)
- lung roots
- phrenic nerves
- cardiac plexus
identify A, B, C, D, E, F
A = ascending aorta B = SVC C = heart D = left lung root E = left phrenic nerve F = right lung root
what are the anterior and posterior boundaries of the posterior mediastinum?
anterior = fibrous pericardium and upper surface of diaphragm
posterior = T5-T12
what are the contents of the posterior mediastinum?
- oesophagus
- thoracic aorta
- azygos system of veins
- sympathetic chains
- vagus nerves
- thoracic duct
IN GENERAL: structures that need to transverse the whole thorax (from inlet to outlet) will need to go through the superior and posterior mediastinum
identify A, B, C, D
A = oesophagus B = thoracic aorta C = left vagus nerve D = thoracic duct
what does the thoracic duct contain?
lymph
where does the thoracic duct begin? level?
cisterns chyli, level L1 + L2
what does the thoracic duct empty into and where?
venous system at the left venous angle
identify A and B
A = azygos vein B = right sympathetic chain
where does the azygos vein pass through the diaphragm and at what level?
aortic opening, T12
what drains into the azygos vein?
- lower 8 RHS posterior intercostal veins
- superior intercostal vein
- hemiazygos and accessory hemiazygos veins
what does the azygos vein drain into?
SVC
what are drained by the azygos system of veins?
- posterior thoracic wall
- bronchi
- pericardium
- oesophagus
identify structures A-F of this transverse section at level of C5
a - ascending aorta b - descending aorta c - bifurcation of pulmonary trunk d - azygos vein e - oesophagus f - SVC
identify A, B, C, D, E — transverse section at level of C6
A = fibrous pericardium B = heart C = sternopericardial ligament D = oesophagus E = descending aorta
what are the 3 branches of the aortic arch and what do they supply?
- brachiocephalic trunk — largest branch, supplies the right side of the head and neck and right upper limb
- left common carotid artery — supplies the left side of the head and neck
- left subclavian artery — supplies the left upper limb
what is the thoracic duct located between?
the oesophagus anteriorly and the thoracic vertebrae posteriorly
what side of the thorax is the thoracic duct typically on?
the left
what is the oesophageal nerve plexus formed from and what does it surround?
- surround the inferior aspect o the oesophagus
- formed by the vagus nerve and visceral branches of the sympathetic trunk
widened mediastinum is a mediastinum with a width great er than what on a PA CXR?
> 8cm
describe pulmonary circulation + what vessels are involved
= carries oxygen depleted blood away from the heart, to the lungs, and returns oxygenated blood back to the heart
- involves pulmonary arteries and veins, lobar and segmental arteries and veins
what factors promote gas exchange?
- large SA in the lungs
- thin respiratory membrane for a short diffusion distance
- large diffusion gradient
- moist exchange surface — alveoli release a surfactant which reduces surface tension - increases compliance and decreases risk of alveolar collapse
- close proximity of blood vessels to alveoli
what factors inhibit gas exchange?
- surface tension caused by water molecules on the alveoli — alveolar collapse/difficult to expand alveoli during inhalation
- smoking - COPD - airflow obstruction, destruction of alveoli
describe systemic circulation
= the part of the CV system which carries oxygenated blood away from the heart to the body, and returns deoxygenated blood back to the heart
- blood leaves via LV and enters back into RA
what artery is used to draw blood from?
radial artery
what artery is used to take BP?
brachial artery
bronchial vs. vesicular breathing
BRONCHIAL:
- loudest over sternum
- from larger airways
- higher frequency
- loud on expiration
- expiration > inspiration
VESICULAR:
- most areas over chest
- from smaller airways
- lower frequency
- soft on expiration
- inspiration > expiration
differences between phrenic and vagus nerves
- phrenic: straight from neck to diaphragm with no branches
- vagus: has branches
- vagus innervates lots of things
- phrenic innervates diaphragm
what side of the vertebral column does the azygos vein travel on?
right
describe the accessory hemiazygos and hemiazygos veins
- on LHS
- accessory hemiazygos vein at top
- hemiazygos vein at bottom
- both cross to RHS to join the azygos vein
