superior mediastinum Flashcards
what is the mediastinum
midline partition that separates thee pleural cavities
where is the mediastinum
from the superior thoracic aperture to inferior thoracic aperture
between sternum anteriorly and thoracic vertebrae posteriorly
what happens at the superior thoracic cavity
airways enter and vein drains back to the heart
what is the role of the mediastinum
acts as a conduit for structures that pass through thorax and structures that connect thoracic organs to other body structures
2 way conduit - head and neck to chest cavity and in reverse
airway from superior to carina to lungs pharynx opening in nasal cavities through thorax and to abdomen, nerve control heart and lung from brain into pericardium and airways
what does a PA x ray mean
x ray go through back of body and detector is at the front
why is a PA x ray done
PA/AP give different size of organs
heart is anterior - if PA short distance to detector - little dispersion
if AP - big distance to detector= large dispersion
components of the mediastinum
trachea - C6-T4/5 from larynx to bifurcation into principle bronchi
oesophagus - from pharynx, muscular tube, pierce diaphragm T10
heart and pericardium
thoracic duct - lymphatic drainage (remove interstitial fluid and involved in metastatic disease)
nerves and great vessels
what is the larynx
air way in throat
what structures pass through the diaphragm and where
T8 - inf V C
10 - oesophagus
12 - aorta
what do 8 10 12 relate to in the chest
pleural cavity
what does 6 8 10 levels relate to in the chest
level lungs
where is the superior mediastinum
above sternal angle
from superior thoracic aperture
where is the inferior mediastinum
below sternal angle
above inferior thoracic aperture
what 3 parts make up the inferior mediastinum
middle
anterior
posterior
middle mediastinum
has pericardial sac and heart
anterior mediastinum
anterior to heart
small
posterior mediastinum
behind pericardial sac and diaphragm
has nerves of SNS and veins that drain chest from abdomen to heart
has everything that moves from superior to inferior
what are the contents of the superior mediastinum
thymus - immunologically active, replaced by fat phrenic nerves - contract diaphragm and provide sensation for pericardium and peritoneal lining (under diaphragm) great veins main lymphatic trunk vagus nerves great arteries trachea and main bronchi upper oesophagus
what are the great veins
superior vena cava (enter RA from above)
inferior vena cava (enter RA from below - through the central tendon of diaphragm T8!)
describe the superior vena cava in situ
offset to the R
formed by the union of R and L brachiocephalic veins
brachiocephalic vein forms internal jugular veins (drain head) and subclavian veins (drain arms)
what is the path of the L brachiocephalic vein
crosses at sternoclavicular joint, and manubrium and 1st rib posterior to manubrium to reach R brachiocephalic vein to form the SVC
the veins move anterior to the arteries
describe the azygous vein
asymmetric
largest on R
anterior intercostal vessels drained into internal thoracic vessels
drains posterior wall of thorax and abdomen
hemiazygos and accessory hemiazygos on L - drain chest wall
arches over the R lung root
runs behind SVC carrying deoxygenated blood
drains into the superior VC
inferior vena cava in situ
little in thorax
goes straight into the RA
most is in the abdomen
where does the L superior intercostal vein drain into
brachiocephalic vein
arteries in superior mediastinum
ascending aorta - come superior from the heart
arch of aorta - move superiorly, laterally and down
descending aorta - down back, diaphragm and to abdomen at T12
ascending aorta
R and L coronary arteries
supply heart muscle with the most oxygenated blood
terminal arteries
may need bypass (from leg vein)
aortic arch
brachiocephalic trunk - R common carotid and R subclavian arteries
L common carotid
L subclavian artery - under clavical - to axilla and upper limbs
relation of aortic arch to pulmonary branch
anterior
relation of aorta nad arteries to airways
aortic arch anterior to trachea
arches over L main bronchus at lung root
trachea is behind and between the brachiocephalic and L common carotid arteries
azygous vein runs along the back of the chest - arch over airways over lung root into back of superior vena cava
explanation of the points components pass through diaphragm
aorta almost vertical at the back - pass more posteriorly and so at a lower vertebral level than oesophagus and IVC
then oesophagus
than IVC
distribution of the common carotid arteries
divide into internal and external carotids high in the neck at laryngeal prominence
they are the main arteries of the head and neck - with vertebral arteries from subclavian arteries)
internal supply brain
pulmonary trunk
outflow of the R ventricle
deox blood via L and R pul arteries to the lungs
1st travels backwards behind the arch - emerge to L of aorta from RV
when listen to aorta you listen
to R of sternum
when listen to pulmonary artery you listen
L of sternum
pulmonary trunk
from RV
deox blood to lung
divide into L and R pul arteries
describe the remnant of fetal circulation in the pulmonary trunk
remnant of the ductus arteriosus - vessel from pul trunk to aorta to bypass lungs - blood into the systemic system
this closes off - forms ligamentum arteriosum
where are the phrenic nerves formed
in cervical p5 plexus - C3, 4 5
what do the phrenic nerves do
they are motor to the diaphragm
sensory to- central tendon of diaphragm, mediastinal pleura, pericardium, peritoneum of central diaphragm - innervate underside of the diaphragm
C3 4 5 …. (rhyme)
keeps diaphragm alive
what does the R phrenic nergve lie on top of to reach the diaphragm
R brachiocephalic vein
SVC
R side of heart and pericardium - in front of the lung root
what is the effect of damage to the laryngeal nerves
change voice
need to know about the difference in length
why is the point of the ligamentum arteriosum anatomically important
nerves emerging from neck winds round here and goes back towards the neck
from vagus nerve
2 small branches - recurrent laryngeal nerves, 1 winds round here other around R subclavian artery on the R side
discrepancy in length
describe the relations of the great arteries to main nerves
vagus nerves are lateral to the common carotid
left vagus - anterior to the aortic arch
left phrenic crosses vagus to cross the aortic arch anteriorly
vagus is behind the lung root
R phrenic is in front of the lung, runs right next to the SVC - down pericardium through diaphragm - innervates other side
describe the path of the left phrenic and vagus nerves
cross arch of aorta
left phrenic decends in front of lung root
L vagus - behind the lung root - gives off L recurrent laryngeal nerve - recurs around ligamentum arteriosum and aortic arch
break into many branches round oesophagus forms oesophageal nerve and through diaphragm at T10 with oesophagus
path of the R vagus nerve
lies on the trachea
crosses behind the root lung
recurrent laryngeal branch recurs around R subclavian artery
breaks up into branches on the oesophagus
