Superior Mediastinum

Question 1

Boundaries

Answer 1

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

Question 2

Thymus Gland

Answer 2

immediately behind sternum
T cells mature here
Lymph drains through from parasternal, brachiocephalic and tracheobronchial nodes
After puberty, it atrophies and is replaced by fat
Supplied by internal thoracic arteries

Question 3

Branches of Aorta

Answer 3

Ascending: left and right coronary arteries
Arch: brachiocephalic, left carotid, subclavian
Descending: posterior intercostal, bronchial lumbar arteries

Question 4

Veins

Answer 4

Superior vena cava formed by union of right and left brachiocephalic vein
Each brachiocephalic vein is formed by the union of an internal jugular vein and subclavian vein

Question 5

Ligamentum Arteriosum

Answer 5

Embryological remnant of ductus arteriosus (open duct connecting pulmonary trunk and arch of aorta)
Important in foetal circulation - blood bypasses lungs
Closes at birth and remains as a ligamentous structure

Question 6

Trachea and Oesophagus

Answer 6

Trachea: tube C-shaped cartilage structure, trachealis muscle runs posteriorly, runs from larynx –> bronchi
Oesophagus: muscular tube, runs from pharynx to stomach

Question 7

Phrenic Nerves

Answer 7

originates form anterior rami of C3, C4 and C5
enters SM between brachiocephalic veins and subclavian arteries
pass anterior to main bronchi
motor supply to diaphragm and parietal pleura

Question 8

Vagus nerves

Answer 8

cranial nerves (originate from brainstem).
each enters the SM just medial to phrenic nerve.
each gives rise to a recurrent larygeal branch to supply the larynx.
continues into posterior mediastinum, behind the main bronchi.
provide parasympathetic supply via pulmonary, cardiac and oesophageal plexi

Question 9

Anterior Mediastinum

Answer 9

narrow cavity containing thymus gland, lymph nodes and vessels, pericardial-sternal ligaments, internal thoracic artery.
boundaries: sternum, pericardial sac, diaphragm, level T4/5.

Question 10

Embryology of the heart

Answer 10

angiogenic clusters form in the mesoderm and cannalise to form early blood vessels.
2 large blood vessels form in cardiogenic area.
these heart tubes grow and fuse at day 21.
heart tube can be divided into sinus venosus, promordial atria, primordial, ventricle, truncus arteriosus.
after day 23, heart tube folds, and septa grow dividing into 4 heart chambers

Question 11

Foetal heart

Answer 11

foramen ovale (hole in heart) and ductus arteriosus allow blood to bypass lungs
fossa ovalis: remnant of foramen ovale which closes after birth
ligamentum arteriosum: remnant of ductus arteriosus