1. The mediastinum Flashcards
Describe the mediastinum
Contains the heart and the great vessels
Split into the superior (great vessels) and inferior (heart)
These are split between T4 and T5 at sternal angle - this is the transthoracic plane
Describe the superior mediastinum and what it consists of
Area above the sternal angle Consists of: • The thymus • Veins matching the great vessels • Arch of the aorta and the great vessels • Vagus nerve (CN X) • Laryngeal nerves • Trachea • Oesophagus • Thoracic duct • Lymphatic trunks
Name the veins of the superior mediastinum
Brachiocephalic veins
Subclavian veins
Azygous vein
Describe the brachiocephalic veins of the superior mediastinum
There are two that join up to one another to form into the superior vena cava
One on the right goes straight down on the right side of the manubrium and the one on the left goes diagonally behind the manubrium to then join the SVC
Describe the subclavian veins of the superior mediastinum
There are two of these
Only one subclavian artery
Describe the azygous vein
This vein is at the back
Drains up through the right side of the thorax
Enters the posterior portion of the SVC just before it enters the right atrium
Describe the nerves of the superior mediastinum
The phrenic nerves are just posterior to the veins
C3, 4, 5 (helps keep a man alive) are somatic nerves from spinal segment
These run over the anterior scalene muscle and descend down onto the first rib and into the thorax, between the parietal pleura and fibrous pericardium
Describe the arteries of the superior mediastinum
Ascending aorta and aortic arch - also is the ‘aortic sinus’ where the beginning of the aorta is slightly larger than the rest
Descending aorta - covered by the parietal pleura
Brachiocephalic trunk - consists of right subclavian artery
• Right vertebral artery: extends up
• Thyrocervical trunk: goes to the thyroid gland and the neck
• Costocervical trunk
Left common carotid artery
Left subclavian artery - branches of these match those on the right by they do not come off of the brachiocephalic like on the right SO they are most likely longer
• Left vertebral artery
• Left internal thoracic artery
• Thyrocervical trunk
• Costocervical trunk
Give the positioning of the contents of the superior mediastinum from anterior to posterior
Veins Nerves Arteries Vagus Nerve X Trachea Oesophagus Thoracic duct
Describe the vagus nerve (CNX) in the superior mediastinum
Large sympathetic nerve going to viscera of the body
Goes to all of the thoracic viscera and most of the abdominal viscera
Emerges through the skull from the jugular foramen and is accompanied by cranial nerves 9 and 11
Encapsulated in a carotid sheath with common carotid artery and internal artery
Nerve is motor to the pallet, pharynx and larynx
Briefly describe the trachea extending from the superior mediastinum
Posterior to the vagus nerve C6-T4 U shaped cartilaginous rings Descends down into the thorax Bifurcates at carina
What is the ‘carina’?
Bifurcation of the trachea to the two primary bronchi
Occurs between T4 and T5
At the level of the sternal angle
Describe the oesophagus extending from the superior mediastinum
Immediately posterior to the trachea
C6-T10
Mixture of skeletal and smooth muscle fibres
Describe the thoracic duct
Main vessel of the lymphatic system
Starts in the abdomen and ascends through the diaphragm through the opening for the aorta on the right of the midline
Crosses midline at T4/5 and runs on the left of the oesophagus up into the root of the neck
Briefly describe the inferior mediastinum
Below the level of T4 and T5 and is split into anterior, middle and posterior
Describe the anterior inferior mediastinum
Contains the thymus - lymphoid organ in the lower part of the neck
Describe the middle inferior mediastinum
Contains the pericardium and the heart
Serous pericardium:
The heart is surrounded by the visceral pericardium followed by the pericardial space which is filled with pericardial fluid and then the parietal pericardium follows
Phrenic nerves are either side of the pericardial sac
Fibrous pericardium:
The heart is then encapsulated by another pericardium layer which is continuous with the great vessels
This is a protective layer attached to the diaphragm
This anchors the heart in place
Describe the posterior inferior mediastinum
Located between T5-T12
Is posterior to the pericardium and the diaphragm
In-between the parietal pleura of the two lungs
Contains: Primary bronchi Oesophagus (and oesophagul plexus) - passes posteriorly to the heart right next to the left atrium and desends down at C6, also passes through diaphragm at T10 Descending aorta Thoracic duct Azygous and hemizygous veins
Briefly describe the layers of the heart wall
(In middle inferior) Three layers to the heart wall Epicardium -Visceral layer of the serous pericardium Myocardium -Cardiac muscle fibres -Arranged in bundles -Squeezes the blood out of the heart Endocardium -Continuous with the endothelium
Briefly describe the diaphragm
In the middle inferior
Positioned in the 4th intercostal space down to the 5th rib
Left side of the heat i.e. apex goes down the midclavicular line
Describe the thoracic arterial supply i.e. arterial supply to the chest
Arterial supply to the chest is supplied by intercostal arteries
These run in the upper part of each intercostal space (between ribs) with their corresponding nerve and veins in a ‘neurovascular bundle’ - these are in each costal groove
There is an anterior intercostal artery (AI) and posterior intercostal artery (PI) in each space
These all arise from the internal thoracic artery (deep to the costal cartilage)
The PI are branches of the descending aorta
Anteriorly, there are two arteries called the internal thoracic arteries - sometimes called ‘internal mammary arteries’ and these descend either side of the sternum
These give off the AI branches of the intercostal arteries
Describe the thoracic venous drainage
The intercostal arteries drain into the intercostal veins
The AI intercostal veins drain into the internal thoracic vein
The PI intercostal veins from the right side drain into the azygous vein
PI intercostal veins from the left side drain into the hemi-azygous vein
Briefly describe the azygous veins
Azygous vein and inferior hemi azygous veins originate in the abdomen
They drain blood from the PI veins SO from posterior intercostal spaces, posterior abdominal wall, pericardium, diaphragm and bronchii
Hemi-azygous veins usually cross anterior of T7 and T8
The azygous vein drains up through the right side of the thorax and enters the posterior portion of the SVC before it enters the right atrium
“Distinguish between the pulmonary and systemic blood supply to the lungs”
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