ICL 1.13: Mediastinum Flashcards
what is the mediastinum?
the anatomic region located between the lungs described as a partition separating the two pleural cavities
it serves as a corridor through which structures from the head and neck region connect with lower regions of the body and vice versa
it contains all the principal tissues and organs of the chest EXCEPT the lungs
where is the manubriosternal joint?
the second rib!! it’s in-between T4 and T5
the sternal angle is at the 2nd rib!! aka Angle of Louis where the manubrium meets the body of the sternum
what are the boundaries of the mediastinum?
it extends from the sternum back to the vertebral column
it’s bound laterally by the pericardium and the mediastinal pleurae
which structures are in the mediastinum?
- heart
- thymus
- portions of the esophagus and trachea
what are the divisions of the mediastinum?
the mediastinum is split into a superior and inferior division at the sternal angle
the inferior division is split into the anterior, middle and posterior
slide 8 and 10
where is the superior mediastinal compartment located?
it is located above the manubriosternal angle
its posterior boundary is made up of the first four thoracic vertebrae
above, the superior mediastinum is continuous with the neck
below it is continuous with both anterior and posterior mediastina
laterally it is limited by parietal (mediastinal) pleura
what are the contents of the superior mediastinum?
- thymus
- aortic arch
- superior vena cava
- trachea
- esophagus
- right and left vagus nerve
- phrenic nerves
- thoracic duct
all of these pass through the superior mediastinum!! some of these go through multiple parts of the mediastinum
where is the anterior mediastinal compartment located?
anterior mediastinal compartment is bordered by
- the sternum anteriorly
- the pericardial sac posteriorly
so basically it’s the part of the inferior mediastinum in front of the heart
what are the contents of the anterior mediastinum?
- sternopericardial ligament (it’s actually just fat)
- fat
- lymph nodes
where is the middle mediastinal compartment located?
the borders are:
ventrally: the anterior mediastinal compartment
dorsally: the posterior mediastinum
what are the contents of the middle mediastinum?
- the pericardium
- heart
- phrenic nerves
- pericardiacophrenic vessels
- stems of great vessels
where is the posterior mediastinal compartment located?
the borders are:
anteriorly: pericardial sac
posteriorly: the anterior surface of the vertebral bodies
what are the contents of the posterior mediastinum?
- descending aorta
- azygous system of veins
- vagus nerve
- thoracic duct
- lymph nodes
- thoracic splanchnic nerves
- esophagus
where is the thymus located?
it’s a lymphoid organ located in the lower part of the neck and the anterior part of the superior mediastinum
it lies posterior to the manubrium and extends into the anterior mediastinum
it grows till you’re 5-6 years old then turns into fat after puberty!
what are the terminal branches of the internal thoracic artery?
it ends at the sixth costal cartilage by dividing into musculophrenic and superior epigastric arteries
what are the subdivisions of the aorta?
- aortic arch
- ascending aorta
- descending aorta
the sternal angle is the landmark for these divisions!!!
what is the ascending aorta?
from left ventricle to aortic arch mostly within pericardial sac
coronary arteries originate from the ascending aorta!
what is the aortic arch?
above plane of manubriosternal angle
courses posteriorly and laterally
what is the descending aorta?
continuation of arch on left side of vertebrae
course downward toward midline
reaches midline at T12 as it passes through diaphragm and goes to the abdomen!
what are the 3 major branches of the arch of the aorta?
- brachiocephalic (R)
- left common carotid
- left subclavian
what are the 3 major branches of the descending aorta?
- intercostal branches
- mediastinal branches
- esophageal branches
what is the ligamentum arteriosum?
used to be the ductus arteriosus; a connection between the aortic arch and pulmonary trunk that closed off during development and turned into a ligament
it comes off the left pulmonary artery and connects to the aortic arch
what are the great veins of the thorax?
- inferior vena cava
pierces diaphragm at T8 and immediately enters pericardium and the heart
- left brachiocephalic vein
formed by confluence of internal jugular and subclavian and courses obliquely to right in front of great arteries and joins right brachiocephalic v. behind intercostal space 1
- right brachiocephalic vein
courses vertically behind the manubrium
- superior vena cava
formed behind intercostal space 1 by two brachiocephalics and courses vertically to the right atrium; receives azygous vein
- pulmonary veins
what is the course of the thoracic duct?
it originates from the abdomen!
then it ascends through aortic hiatus of diaphragm then ascends between azygous vein and aorta and crosses to the left at T4-5 (sternal angle) to ascend behind the esophagus into neck joins confluence of internal jugular and subclavian veins
what is the thoracic duct?
it drains all of body below diaphragm and left side of thorax!!
the remainder of the body is drained by the right lymphatic duct`
where does the trachea bifurcate?
T4/T5 aka the sternal angle!
what is the course of the esophagus?
it courses through superior and posterior mediastinum
continuous superiorly with pharynx in neck then pierces diaphragm at T10 to join stomach
upper portion in thorax is slightly left of midline because it’s pushed toward midline by aortic arch
then at the lower end it passes through diaphragm to left of midline
what types of muscles compose the esophagus?
striated muscle in neck
smooth muscle in lower third
mixed in middle
what is the blood supply of the esophagus?
esophageal branches of thoracic aorta which anastomose with inferior thyroid aa. and left gastric aa.
which veins drain the esophagus?
submucosal plexus and surface plexus
drain to azygos system
may drain superiorly to inferior thyroid vv.
may drain inferiorly to gastric vein (portal-caval)
which nerves innervate the esophagus?
vagus nerve from the esophageal plexus
striated muscle is innervated by the vagal recurrent branch
smooth muscle is innervated by the parasympathetic vagal
esophageal plexus surrounds the lower thoracic esophagus
which nerves are located in the mediastinum?
- phrenic nerve
- vagus nerve
- left recurrent laryngeal nerve
- cardiac plexus of nerves
- thoracic sympathetic trunks
- thoracic splanchnic nerves
- esophageal nerve plexus
where are the left vs. right vagus and phrenic nerves located?
right phrenic nerve stays superficial while right vagus is deep
left phrenic and vagus nerves are both superficial!
slide 43
which veins are part of the the azygos system of veins?
- azygos vein
- hemiazygos vein
- accessory hemiazygos vein
- left superior intercostal vein
they’re the veins that drain the intercostals and then as they drain the intercostals they end in the superior vena cava! basically it drains the whole thorax!
EXCEPT the left superior intercostal vein which drains directly into the left brachiocephalic vein
slide 49
