Mediastinum & Superficial Anatomy of the Heart Flashcards
What is the mediastinum?
It is a broad central partition that separates the two laterally placed pleural cavities.
Describe the boundaries of the mediastinum
Anteriorly – Body of sternum
Posteriorly – Vertebral bodies of thoracic vertebrae
Inferiorly – Diaphragm
Superiorly – Thoracic aperture
What divides the mediastinum into superior and inferior mediastinum?
A transverse plane that passes between the sternal angle and the intervertebral disc at T4/T5
Describe the boundaries of the superior mediastinum
Superior Boundary: Oblique plane passing from jugular notch to superior border of T1.
Inferior Boundary: Transverse plane between sternal angle and intervertebral disc at T4/T5.
Lateral Boundary: Pleural cavities on either side.
Anterior boundary – Posterior surface of manubrium.
Posterior boundary – Body of first four thoracic vertebrae.
List the contents of the superior mediastinum
Thymus
Left and Right Brachiocephalic veins
Left Superior Intercostal vein
Superior vena cava
Arch of Aorta
Trachea and Oesophagus
Phrenic and Vagus nerves
Left recurrent branch of vagus nerve
Thoracic Duct
Superior
Describe the thymus in terms of it’s position in the mediastinum and it’s function
-Most anterior component of superior mediastinum.
-Immediately posterior to manubrium.
-Asymmetrical, bilobed structure.
-Involved in early development of immune system
Position of left and Right Brachiocephalic veins in the mediastinum
Immediately posterior to the thymus
Position of the left superior intercostal veins
-Passes over left side of aortic arch.
-Situated lateral to the vagus nerve and medial to the phrenic nerve.
Which structure is palpable in jugular notch as it enter the superior mediastinum?
Trachea
Position of the oesophagus in the mediastinum
Oesophagus is posterior to the trachea and immediately anterior to the vertebral bodies.
Which vessel crosses the both the trachea and oesophagus laterally on the right and the arch of the aorta on the left?
Azygos vein
Position of the thoracic duct on the superior mediastinum
This is the major lymphatic vessel in the body.
Enters superior mediastinum inferiorly.
Continues upward posterior to the arch of aorta between oesophagus and parietal pleura.
Describe the boundaries of the anterior mediastinum
Superior Boundary: Transverse plane between sternal angle and intervertebral disc at T4/T5.
Inferior Boundary: Diaphragm
Lateral Boundary: Pleural cavities on either side.
Anterior boundary – Body of sternum
Posterior boundary – Pericardial sac.
What are the contents of the anterior mediastinum?
- Inferior extension of thymus gland.
- Mediastinal branches of internal thoracic vessels.
- Sternopericardial ligaments. (This attaches the mediastinum to the posterior surface of the sternum)
What are the boundaries of the middle mediastinum?
Superior Boundary: Transverse plane between sternal angle and intervertebral disc at T4/T5.
Inferior Boundary: Diaphragm
Lateral Boundary: Pleural cavities on either side.
Anterior boundary – Anterior margin of pericardium.
Posterior boundary – Posterior margin of pericardium.
What are the contents of the middle mediastinum?
Pericardium, heart, great vessels and nerves.
What are the borders of the posterior mediastinum?
Superior Boundary: Transverse plane between sternal angle and intervertebral disc at T4/T5.
Inferior Boundary: Diaphragm
Lateral Boundary: Pleural cavities on either side.
Anterior boundary – Pericardial sac.
Posterior boundary – Bodies of T5-T12 Vertebrae.
What are the contents of the posterior mediastinum?
Oesophagus and oesophageal nerve plexus.
Descending aorta and its branches.
Azygos system of veins.
Thoracic duct and lymph nodes.
Sympathetic trunk and thoracic splanchnic nerves.
Where does the oesophagus begin and end?
Begin: Level of C6, behind the cricoid cartilage
Ends: level of T11
Describe the course of the oesophagus as it descends
Descends on anterior aspect of vertebral bodies, in midline.
Moves slightly to the left inferiorly to lie anterior to descending aorta.
Right side of the oesophagus is covered with____________, left side in contact with
aorta.
parietal pleura
What structure lies posterior to the oesophagus?
Thoracic duct
The _____________ lies anterior to the oesophagus below the bifurcation of the trachea
Right pulmonary artery
What nerves make up the oesophageal plexus?
Left and right vagus nerves
Explain how the oesophageal plexus is formed
The left and right vagus nerves pass behind the root of lung.
Both of these nerves divide into several branches
which spread over the oesophagus to create the oesophageal plexus.
What mainly makes up the anterior vagal trunk?
Anterior vagal trunk – mainly left vagus nerve fibres.
What mainly makes up the posterior vagal trunk?
Posterior vagal trunk – mainly right vagus nerve fibres.
Where does the thoracic aorta begin, and where does it end?
Begins: Lower edge of T4 vertebrae
Ends: Lower edge of T12 vertebrae
How does the descending aorta enter the abdomen?
Through the aortic hiatus of the diaphragm
List the branches of the thoracic aorta
Pericardial
Bronchial
Oesophageal
Mediastinal
Posterior intercostal
Superior phrenic
What is the azygos system of veins?
Series of longitudinal vessels on either side
of the body draining blood into the
Superior vena cava
What makes it possible for the azygos veins to drain blood directly to the heart if the SVC is blocked?
It’s due to the anastomotic pathway
How are azygos veins formed?
Arises opposite L1/L2 by union of right ascending lumbar vein and right subcostal vein.
(May arise as direct branch of IVC)
How do azygos veins enter the thorax?
Through the aortic hiatus, lies on the right of the thoracic duct
At what level does the vein arch over the root of the right lung to join the SVC before entering the pericardium?
At T4 it arches over the root of the right lung.
What are the tributaries of the azygos vein
Right superior intercostal vein, 5th-11th
posterior intercostal veins.
Where does the hemiazygos vein arise?
Arises at junction between left ascending lumbar and left subcostal vein.
How does the hemiazygos vein enter the thorax?
Enters thorax by ascending through left crus.
What are the tributaries of the hemiazygos vein?
Lower 4-5 Posterior intercostal veins,
oesophageal and mediastinal veins.
Describe the accessory hemiazygos vein
Descends from left side of posterior mediastinum till T8
Crosses vertebral column to join azygos or ends in
hemi-azygos.
Has a connection to the left superior intercostal vein.
Where does the thoracic duct begin?
Begins: Confluence of lymph trunks in abdomen – dilation
What is the name of the dilation at the beginning of the thoracic duct, and where is it found?
Cisterna Chyli - L2
What does the cisterna chyli drain?
Abdominal viscera
Pelvis and perineum
Lower limb
How does it enter the thorax?
It enters the thorax posterior to the aorta as it passes through the aortic hiatus.
Describe the course of the thoracic duct
Runs on the right side of the midline between the thoracic aorta
and the azygos vein.
At what level does the thoracic duct move to the left of the midline and enter the superior mediastinum where it continues into the neck?
T5
Where does the thoracic duct drain?
Drains into the junction between the left subclavian and left jugular veins
Describe the sympathetic trunks
Consists of 2 cords that have 11-12 ganglia each.
The ganglia are connected to adjacent thoracic spinal nerves by white and gray rami communicantes.
Thus, they are named according to these thoracic spinal nerves
What is the Ganglion impar?
It is the point where the two sympathetic trunks fuse anterior to the coccyx
Describe type 1 sympathetic trunk
Branches from upper 5 ganglia, has postganglionic sympathetic fibres.
Contain visceral afferent fibres, supply thoracic viscera.
Describe type 2 of the sympathetic trunk
Branches from lower 7 ganglia, has preganglionic sympathetic fibres.
Has visceral afferent fibres, supply abdominal and pelvic viscera.
Describe the greater planchnic nerve
T5-T9 Ganglia.
Descends across vertebral bodies medially.
Ends in coeliac ganglion.
Some fibres go straight to the medulla of the adrenal gland.
Describe lesser splanchnic nerve
T10-T11 Ganglia.
Ends in aorticorenal ganglion
Describe the least splanchnic nerve
T12 Ganglion.
Ends in renal plexus.
