Superior Mediastinum

Question 1

Where is the mediastinum

Answer 1

Central compartment of thorax, located between left and right pleural cavities

Question 2

how is the mediastinum divided

Answer 2

superior and inferior at t4/5 (aka sternal angle or transverse thoracic plane)

Question 3

how is the inferior mediastinum divided

Answer 3

Anterior
Middle
Posterior

Question 4

Boundaries of superior mediastinum

Answer 4

Superior: superior thoracic aperture (manubrium, 1st rib and costal cartilage, T1 vertebrae)
Inferior: transverse thoracic plane (sternal angle to vertebral level T4/5)
Anterior: manubrium
Posterior: T1-T4/5 vertebral bodies
Lateral: mediastinal pleura

Question 5

Contents of superior mediastinum

Answer 5

Arteries (arch of aorta and branches)
Veins (brachiocephalic veins and superior vena cava)
Phrenic and Vagus Nerves
Oesophagus 
Trachea 
Thoracic duct
Thymus gland (part)

Question 6

where is the thymus gland located

Answer 6

Located immediately deep to the sternum in superior and anterior mediastinum
Supplied by internal thoracic artery

Question 7

what is the thymus gland

Answer 7

Lymphoid organ

Question 8

what does the thymus gland do

Answer 8

T and B lymphocytes produced in bone marrow, T’s mature in thymus
Lymph drains through from parasternal, brachiocephalic and tracheobronchial nodes
After puberty it atrophies and replaced by fat

Question 9

what arteries are in the superior mediastinum

Answer 9

Arch of aortas and 3 branches
1 brachiocephalic trunk (branches into right common carotid and subclavian arteries)
2 left common carotid artery
3 left subclavian artery
Order is alphabetical L to R facing patient

Question 10

what makes up the branches of the aorta

Answer 10

Ascending Aorta (LCA and RCA)
Arch of aorta (1,2,3 in mediastinum)
Descending aorta (posterior intercostal, bronchial arteries (branches from intercostal), lumbar arteries)

Question 11

Veins in the superior mediastinum

Answer 11

Superior vena cava (form by union of two (L and R) brachiocephalic veins)
Each brachiocephalic vein is formed by the union of an internal jugular vein and a subclavian vein
middle, from L brachiocephalic is inferior thyroid vein

Question 12

what is the ligament arteriosum

Answer 12

Embryological remnant of the ductus arteriosus: an open duct connecting the pulmonary trunk and arch of aorta
Important in fetal circulation allowing blood the bypass the immature lungs
Closes at birth and remains in the adult as ligamentous structure

Question 13

what is the trachea

Answer 13

tube with C shaped cartilage rings, trachealis muscle runs posteriorly, runs from larynx to bronchi

Question 14

what is the oesophagus

Answer 14

muscular tube, runs from pharynx to stomach

Question 15

what does the thoracic duct do

Answer 15

Transports lymph to venous system
Receives multiple branches throughout thorax
Numerous lymph nodes associated with thoracic (descending) aorta

Question 16

what does the phrenic nerve do

Answer 16

Motor supply to diaphragm

Sensory supply to diaphragm (central region) and parietal pleura (diaphragmatic and mediastinal)

Question 17

where is the phrenic nerve found

Answer 17

Originates from anterior rami of spinal nerves (C3, C4, C5) (keep the diaphragm alive)
Enters superior mediastinum between brachiocephalic veins and subclavian arteries
Pass anterior to main bronchi

Question 18

what is the vagus nerve

Answer 18

Cranial Nerve (CNX) originates from brainstem

Question 19

where is the vagus nerve found

Answer 19

Each (L and R) enters the superior mediastinum just medial to phrenic nerve
Each gives rise to recurrent laryngeal branch to supply larynx (branch under aorta)
Continues into posterior mediastinum coursing posterior to main bronchi

Question 20

what does the vagus nerve do

Answer 20

Provides parasympathetic supply via pulmonary, cardiac and oesophageal plexi

Question 21

what is the anterior mediastinum

Answer 21

Narrow cavity containing:
Thymus gland in children 
Pericardial-sternal ligaments 
Lymph nodes (parasternal) and vessels
Internal thoracic artery

Question 22

what are the boundaries of the anterior mediastinum

Answer 22

Sternum anteriorly
Pericardial sac posteriorly
Diaphragm inferior
Level T4/5 superiorly

Question 23

where does the heart develop from

Answer 23

Angiogenic structures form in the mesoderm and these canalise for form early blood vessels

Question 24

how does the heart develop (prior to day 21)

Answer 24

Two large blood vessels known as the heart tubes form in the cardiogenic area
The paired heart tubes grow and fuse at approximately day 21

Question 25

what can the newly formed heart tube be divided into

Answer 25

divided into two regions

Sinus venosus, primordial atrium, primordial ventricle, truncus arteriosus

Question 26

what happens to the developing heart at day 23

Answer 26

too long for the pericardial cavity and starts to fold
Folding results in ventricles and outflow tracks being positioned anteriorly and atria and veins posteriorly
Septa then grow to divide heart into 4 chambers

Question 27

what does the foetal heart contain to allow blood to bypass the lungs

Answer 27

contains 2 distinct structures
Foramen ovale (hole in septum) and ductus arteriosus (blood from pulmonary trunk to arch of aorta to circulate body over lungs)

Question 28

what is the foramen ovale

Answer 28

Opening between right and left atria in the foetus and allows oxygenated blood to bypass lungs

Question 29

how does the foramen ovale develop

Answer 29

septum primum develops a hole, ostium primum (bottom) then it fuses and ostium secundum (3/4 up) forms
septum secundum forms with foramen ovale (Left of primum)

Question 30

how does blood flow through the foramen ovale

Answer 30

Driven from high to low

Only blood flowing in from pulmonary arteries

Question 31

what is the fossa ovals

Answer 31

The embryological remnant of the foramen ovale which closes after birth (slight dent in septum)

Question 32

what does the ligament arteriosum do

Answer 32

Shunts from pulmonary artery to descending aorta

Question 33

how does blood circulation differ pre and post birth

Answer 33

greater division of oxygenated and deoxygenated blood post birth