Anatomy Lecture 3 -- The Mediastinum Flashcards
Subdivisions of the mediastinum
Anterior Superior Posterior Middle
Anterior boundary of the mediastinum
Sternum
Posterior boundary of the mediastinum
Thoracic vertebrae
Lateral boundaries of the mediastinum
Ribs
Define the mediastinum
Organs contained in the middle of the thoracic cavity that are not the lungs
Ribs in the superior subdivision of the mediastinum
Ribs 1 and 2
Boundary of superior mediastinum
T1 to T4
Contents of the superior mediastinum
Vessels, namely the aortic arch Trachea
Contents of the posterior mediastinum (from most posterior to most anterior)
Descending aorta Thoracic duct Eosophagus
What happens to the contents of the mediastinum when you lie down to sleep at night?
Heart moves upwards and backwards in the curvature (a difference of 1 - 2 vertebrae), thus pulling the other structures with it
4 reasons why T4 is a clinical landmark
Trachea bifurcates Thoracic duct crosses to dump load into the brachiocephalic vein on the left Upper border of the heart Manubriosternal angle
Location of the phrenic nerve in the mediastinum
Infrton of the hilum, glued to the left ventricular pericardium, descending from C 3, 4, and 5.
Phrenic nerve function
Feed diaphragm efferent information Secondarily transmit sensation to the pericardium and pleura
Describe the pathway of the vagus nerve in the mediastinum
Wanderer/ hobo nerve. Behind the hilum and encircles esophagus at a lower point. Hooks around the ligament between the pulmonary trunk and aortic arch to become the recurrent laryngeal nerve
Recurrent laryngeal nerve function
Innervate the larynx (cut = no speech)
Where does the intercostal space 1 vein empty to?
Vertebral vein
Which veins join to become the left superior intercostal vein?
Intercostal space veins 2 and 3
Which veins join to form the superior hemiazygous vein?
Intercostal space veins 4, 5, 6
Which veins join to form the inferior hemiazygous vein?
Intercostal space veins 7 - 12
Where do all of the intercostal arteries come from? What is the exception?
All come from aorta except 1 and 2, which come from subclavian artery
Inferior boundary of the mediastinum
Diaphragm
Where does the esophagus exit the mediastinum?
At the level of T10 through the diaphragm
Where does the aorta exit the mediastinum?
At the level of T12 through the diaphragm
What is the significance of the hole formed by the esophagus in the diaphragm?
Potential diaphragmatic herniation at the T10 hole, causing regurgitation and spontaneous vomiting (a reflux condition) If the hole is big enough, the whole stomach can move through into the mediastinum
What is a potential cause of diaphragmatic herniation at T10?
Woman with several pregnancies can eventually stress the esophageal hole to the point where it widens too much
Define the boundaries of the sympathetic trunk
T1 to L2
Describe the relationship of the intercostal nerves to the sympathetic system
Pick up post ganglionic fibres from the sympathetic trunk
What are the beads at each intercostal nerve?
Synapses between pre-ganglionic and post-ganglionic fibres
What happens to the pre-ganglionic fibres that do not synapse in the mediastinum?
Form the splachnic nerve series that travels to the abdomen
Describe the sources of sensation in the diaphragm
Middle = phrenic nerve Edges (and pleura) = intercostals
What is the superior vena cava actually comprised of?
The two brachiocephalic veins
Where does the parasympathetic nervous system come from?
Vagus
6 effects of sympathetic system activation
1) Rate and strength of contraction of heart increases 2) Coronary artery dilation 3) Dilation of bronchi = max air input (main secondary and tertiary) 4) Redirect blood from G.I. to arm/leg muscles 5) Liver: glycogen -> glucose 6) Adrenal gland = adrenaline
