Mediastinum Flashcards
anterior boundary of superior mediastinum
manubrium
posterior boundary of superior mediastinum
bodies of T1-T4
great vessels found in the superior mediastinum
- arch of the aorta
- ligamentum arteriosum
- brachiocephalic veins
- superior vena cava
- cardiac plexus
where is the arch of the aorta
at level of manubriosternal joint
what three arteries arise from the upper convexity of the arch of the aorta
the brachiocephalic trunk, and the left common carotid and left subclavian arteries
what does the adventitial layer of the arch contain
baroreceptors innervated by vagal nerve fibres - reflex control of heart rate
what is found under the arch
he aortic bodies (also supplied by vagal fibres) - chemoreceptors concerned with respiratory reflexes.
brachiocephalic trunk pathway
arises in midline → up across trachea → back of right sternoclavicular joint → divides into right common carotid and right subclavian arteries
branches of braciocephalic trunk
No branches apart from the thyroidea ima artery - arises from it or directly from the arch of the aorta
left common carotid artery pathway
Left common carotid artery: arises behind brachiocephalic trunk → straight up along side trachea → neck
branches of left common carotid artery
none in mediastinum
left subclvian artery pathway
arises behind left common carotid → straight up along trachea → moves away from left common carotid behind left sternoclavicular joint
left subclavian artery branches
none in the mediastinum
ligamentum arteriosum pathway
- Beginning of left pulmonary artery → concavity of the aortic arch beyond subclavian artery
- It lies almost horizontally
where are the brachiocephalic veins formed
behind the sternoclavicular joints by confluence of the internal jugular and subclavian veins.
four tributaries of the brachiocephalic vein
- vertebral
- inferior thyroid
- internal thoracic
- superior intercostal (only on left side)
where does the right brachiocephalic vein commence
behind the right sternoclavicular joint and runs downwards
what lymphatics are received by the right brachiocephalic veins
the right jugular, subclavian and bronchomediastinal lymph trunks separately or their confluent channel, the right lymphatic duct.
left brachiocephalic vein pathway
passes to the right with a downward inclination → across the superior mediastinum → above the arch of the aorta → behind the thymus and the upper half of the manubrium
what does the commencement of the left brachiocephalic vein receive
- the thoracic duct, which often divides into two or three branches that join the vein separately
- the vertebral and internal thoracic veins, most of the inferior thyroid veins, the left superior intercostal vein, and a large thymic vein
superior vena cava pathway
Lower border of first right costal cartilage → vertically downwards → behind the right border of the sternum → pierces pericardium at the level of the second costal cartilage → upper border of the right atrium at the lower border of the third right costal cartilage
does the inferior vena cava have valves
no
what does the cardiac plexux consist of
sympathetic, parasympathetic and afferent fibres and small ganglia
divisions of cardiac plexus
- The superficial part which lies anterior to the ligamentum arteriosum.
- The deep part is larger and lies to the right of the ligamentum arteriosum
what does the cardiac plexus receive
- ympathetic fibres from the three cervical and the upper four or five thoracic sympathetic ganglia of both sides
- parasympathetic fibres from both vagi in their cervical course and both recurrent laryngeal nerves.
sympathetic fibres function
cardiac plexus
accelerate the heart and dilate the coronary arteries
parasympathetic fibres function
cardiac plexus
slow the heart and constrict the coronary arteries
where does the trachea commence
in the neck below the cricoid cartilage at the level of C6 vertebra, 5 cm above the jugular notch
trachea pathway
Entering the thoracic inlet, it passes downwards and backwards behind the manubrium to bifurcate into the two principal or main bronchi level with the upper border of T5 vertebra
trachea dimensions
10 cm long and 2 cm in diameter
blood supply of trachea
- Branches from the inferior thyroid and bronchial arteries form anastomotic networks in the tracheal wall
- Veins drain to the inferior thyroid vein
lymphatic drainage of trachea
Lymphatic channels pass to pre- and paratracheal nodes and to inferior deep cervical nodes
nerve supply of trachea
- The mucous membrane is supplied by afferent fibres from the vagi and recurrent laryngeal nerves.
- Sympathetic fibres from upper ganglia of the sympathetic trunks supply the smooth muscle and blood vessels.
functions of the parts of the trachea
- The cartilaginous rings keep the airway open
- Mucus traps particles
- Cilia beat upwards to clear debris
- Glandular secretion helps to humidify the passing air
- During swallowing the trachea is stretched as the larynx moves
upwards and elasticity restores the normal position. - The trachealis muscle controls the diameter of the tube.
functions of the parts of the trachea
- The cartilaginous rings keep the airway open
- Mucus traps particles
- Cilia beat upwards to clear debris
- Glandular secretion helps to humidify the passing air
- During swallowing the trachea is stretched as the larynx moves
upwards and elasticity restores the normal position. - The trachealis muscle controls the diameter of the tube.
phrenic nerve pathway
Arises from C4 → passes down anterior scalene muscle → across dome of pleura behind subclavian vein → crosses anterior to vagus → through mediastinum in front of lung root
what type of structures is the right phrenic vein related to
venous
what structures lie medially to the right phrenic nerve
The right brachiocephalic vein, the superior vena cava, the pericardium over the right atrium, and the inferior vena cava
how does the right phrenic nerve reach the underside of the diaphragm
y passing through the central tendon alongside the inferior vena cava, piercing the tendon
fibres that fuse with the caval wall.
what type of structures is the left phrenic nerve related to medially
arterial
what lies medially to the left phrenic nerve
common carotid and left subclavian arteries
how does the left phrenic nerve reach the underside of the diaphragm
by piercing the muscular part just to the left of the pericardium.
how much of the phrenic nerve fibres are motor and where do they supply
2/3 and the diaphrahm
where do the sensory fibres of the phrenic nerve supply
the diaphragm, the mediastinal pleura, the fibrous pericardium, the parietal layer of serous pericardium, and the central parts of the diaphragmatic pleura and peritoneum
vagus nerves associations to the trachea
- The right vagus is in contact with the trachea
- The left vagus is seperated from the trachea by arteries that spring from the arch of the aorta.
vagus nerve pathway
Each vagus passes down behind the lung root, dividing into branches which contribute to the pulmonary plexuses and pass onwards to form a plexus around the oesophagus.
recurrent laryngeal nerve origins and pathway
Left vagus flattens on arch of aorta → gives of recurrent laryngeal nerve → hooks around ligamentum arteriosum → passes on right side of aortic arch → ascends in groove between trachea and oesophagus
what do the recurrent laryngeal nerves supply
the whole trachea, the adjacent oesophagus and the larynx
where is the anterior mediastinum
between the pericardium and sternum
what does the anterior mediastinum contain
the thymus, sternopericardial ligaments, a few lymph
nodes and branches of the internal thoracic vessels.
what lies anterior to the thymus
the sternohyoid and sternothyroid muscles, the manubrium and upper part of the body of the sternum and their adjacent costal cartilages
what lies posteriorly to the thymus
he pericardium, the arch of the aorta with its three large branches, the left brachiocephalic vein and the trachea.
blood supply to the thymus
Small branches enter the thymus from the inferior thyroid and internal thoracic arteries, and their corresponding veins.
lymphatic drainage of the thymus
- Efferent channels drain into parasternal, tracheobronchial and brachiocephalic nodes.
- The thymus does not receive any afferent lymphatics.
what does the middle mediastinum contain
Contains the pericardium and heart, the adjoining parts of the great vessels, the lung roots, the phrenic nerves, and the deep part of the cardiac plexus.
