The Mediastinum Flashcards
Relations of the mediastinum
Surrounded by T1-12, sternum, costal margin, thoracic inlet, outlet, lungs
Mainly contains the heart
What are the parts of the mediastinum and how are they separated?
Superior
Inferior
Inferior made up of anterior, middle and posterior
Superior and inferior separated by sternal angle at T4/5
Describe the structure of the great veins at the superior mediastinum
L int jugular (from head and neck), L subclavian => L brachiocephalic => SVC => RA in inf mediastinum
R int jugular, R subclavian => R brachiocephalic => SVC => RA in inf mediastinum
Azygos joins SVC at sternal angle
Describe the relative positions of the SVC to the sternum
Describe the relative lengths of the R brachiocephalic to the L
How does the pulmonary trunk relate to the sternal angle
R brachiocephalic and SVC on R of sternum
R brachiocephalic, more vertical and shorter than L
Stops at sternal angle to split into the pulmonary arteries
Describe the structure of the great arteries at the superior mediastinum
Aortic arch at the level of the sternal angle
Aorta comes ant => sup => post => inf
R brachiocephalic => R subclavian and R common carotid
L common carotid (directly from the arch L subclavian (directly from the arch)
Describe the relative position of the aorta to the sternum
Describe the relative position of the arteries here to the veins
Arteries and the aorta is generally on the L
Arteries are behind the veins
Describe the location of the thymus gland
Describe the composition of the thymus gland
Describe the arterial supply of the thymus
Describe the venous drainage supply of the thymus
Small asymmetrical bilobed gland
1% glandular tissue, 99% fat, infiltrated during puberty
Found in front of the SVC and behind the sternal angle
Arteries from internal thoracic
Drains via int thoracic vein, brachiocephalic vein
Describe the thymus in adults and in children
In children, v large, covers large proportion of lungs, helps give rise to T cell population
Regress in puberty and role taken up by other glands
Describe the contents of the anterior mediastinum in the inferior mediastinum
Space infront of the heart below the sternal angle
Sternal ligament found between pericardium and sternum
Int thoracic artery also found here
Describe the relations of the oesophagus to the aorta, trachea and bronchi and pulmonary arteries
Oesophagus starts as the most posterior tube
Crossed by aortic arch, oesophagus comes post => ant
Compressed by L bronchus
Posterior to LA
Passes through the diaphragmatic hiatus in L hemidiaphragm w vagus
Describe how the position of the aorta changes in the posterior mediastinum
Aortic arch T4/5
Goes from R=> L => central as it comes up, over and behind
Describe the pathway of the L vagus
Comes between int jugular and common carotid , behind left lung root
Becomes the ant vagal trunk due to rotation of stomach
Describe the pathway of the R vagus
Parallel to trachea, post to SVC and R bronchus
Becomes the post vagal trunk due to rotation of stomach
Describe the route of the vagus around the oesophagus and the aorta
Esophageal plexus formed from R and L vagus
Both pass through diaphragm with oesophagus
L vagus => ant vagal trunk
R vagus => post vagal trunk
Both lead to the stomach
Describe the pathway of the recurrent laryngeal nerves
What does it innervate?
L vagus => L recurrent laryngeal, passes infront, under, behind aortic arch
R vagus => R recurrent laryngeal, passes infront, under, behind subclavian artery
Innervate muscles in larynx minus cricothyroid
Sensory for mucosa below vocal folds
Where is the oesophagus constricted
Cricoid cartilage (C6) -Narrowest part of the oesophagus
Skeletal muscle oesophagus, innervated by somatic vagus
Aortic arch (T4) -Where it arches around
L main bronchus (T5)
L atrium (T6-10)
Esophageal opening (T10) -Passes through muscular part of diaphragm, can act as a sphincter
Oesophagus ultimately deviates => L => stomach
What could dysphagia be due to?
May be due to compression from cancer, aneurysm
Describe the venous and lymphatic drainage in the posterior mediastinum
Azygos on the R
Accessory hemiazygos and hemiazygos (T7)
Cisterna chyli => thoracic duct runs next to R of aorta => crosses over to the L at T4 =>arches at T2-3 to join L subclavian from behind the artery and vein
SVC on the R of the L thoracic duct
R lymphatic duct drains the upper right quadrant of the body
Describe the arteries supply in the posterior mediastinum
Aortic arch wrapped around the L bronchus
Bronchial arteries supply the bronchi and areas without gas exchange
Posterior intercostal arteries, esophageal branches and mediastinal branches come off aorta
Aorta on the L of the oesophagus but goes more posterior as it descends
Describe the branches of nerves that come off the inferior vagal ganglion and what they innervate
Sup laryngeal => ext and int laryngeal
Ext laryngeal, cricothyroid muscle and sensory
Int laryngeal, sensory innervation above vocal folds
Recurrent laryngeal, sensory innervation below vocal folds, efferents for all int muscles except cricothyroid
Cervical cardiac branches off vagus, heart
Vagus innervates oesophagus via heart and lungs
Where is the vagus found entering the superior thoracic aperture
Where does it enter the lungs?
Between common carotid and int jugulars
Post to lung root and enters lung root
Describe the innervations of the phrenic and its branches
How does it relate to the lung root
C3-5
Gives off the pericardiac branches
Passes between the subclavians
Supplies diaphragmatic and mediastinal pleura
Ant to lung root but doesnt supply them
R phrenic passes down caval opening
L phrenic passes diaphragm on its own
Describe the location of the sympathetic chain
Found outside the pericardium, either side of the vertebral column behind medial arcuate ligament
Describe the autonomic supply to the lungs
Sympathetics
- Mainly T2-4, sometimes T1-5
- Afferent pain across sternum and inner arm
- T3-4 => pulmonary plexus
Parasympathetic
- Vagus, afferent to visceral stretch of pleura
- Bronchoconstriction, bonchosecretion
What are the 3 plexuses in the chest
Pulmonary
Cardiac
Oesophageal
Describe the sympathetic and parasympathetic innervation of the pulmonary plexus
Sympathetic from T1-5
Parasympathetics from vagus
innervate bronchial tree and visceral pleura
Ant, infront
Post, behind
Describe the sympathetic and parasympathetic innervation of the cardiac plexus
Sympathetics from T1-4 (pain afferents, +ve chronotropes, inotropes)
-descending tract onto T1-4 => enter symapthetic chain, some fibres extend into the sup/mid/inf cervical ganglion => onto heart as sympathetic cardiac nerves
Parasympathetics from vagus
Describe the sympathetic and parasympathetic innervation of the esophageal plexus
Sympathetics from T2-6 (pain afferents, controls vascular tone)
Parasympathetic from vagus (motor supply of the skeletal and smooth muscle)
