Mediastinum Flashcards
Divisions of mediastinum
Transverse thoracic plane divides superior and inferior
- runs from sternal angle to between vertebrae 4-5 (just above pericardium)
Inferior portion divided into anterior, middle/pericardium, posterior
Borders of mediastinum
Superior thoracic aperture Diaphragm Sternum (anterior) Vertebral bodies (posterior) Pleural cavities (lateral)
Thymus
Lies anterior to heart and great vessels (anterior portion of mediastinum)
Immune function during childhood
Usually involutes to fat in adults
Membranes surrounding heart
Fibrous pericardium - dense connective tissue, doesn’t stretch, attached to diaphragm and great vessels (at transverse thoracic plane)
Parietal serous layer - simple squamous layer, attached to internal surface of fibrous
Visceral serous layer - simple squamous layer, attached to heart
- also call epicardium as a “layer of the heart”
- serous layers are continuous (“fist in balloon”), secrete serous fluid, enclose the pericardial cavity
Great veins of thorax
Internal jugular and subclavian -> brachiocephalic
Right and left brachiocephalic -> superior vena cava -> right atrium
Inferior vena cava -> inferior right atrium (blood from lower body)
Course of aorta through thorax
Ascending aorta - leaves heart posterior to pulmonary trunk!
Aortic arch - curves superior to pulmonary vessels, posterior from ascending
Descending/thoracic - behind heart and other vessels (just left of esophagus)
Aortic arch starts and ends at transverse thoracic plane (sternal angle -> T4-5)
Branches of aortic arch
Normal:
Brachiocephalic -> right subclavian and right common carotid
Left common carotid
Left subclavian
Variations:
Left common carotid and subclavian stem from a left brachiocephalic trunk
Left common carotid branches from (right) brachiocephalic
Branches of descending/thoracic aorta
Bronchial arteries
Esophageal arteries
Posterior intercostal arteries
Course of pulmonary arteries
Pulmonary trunk arises anterior to aorta
Splits just superior to heart
Right pulmonary artery is posterior to ascending aorta and SVC
Left pulmonary artery is anterior to descending aorta
Ligatmentum arteriosum
Remnant of ductus arteriosus between pulmonary trunk and aortic arch
Runs through “aortopulmonary window”
Course of pulmonary veins
Run between lung segments
Four veins enter directly into left atrium
Course of trachea/bronchi
Bifurcates at T4 = carina
Right main bronchus is more vertical - choking more likely
Where do IVC, esophagus and aorta cross the diaphragm?
IVC - rib 8
Esophagus - rib 10
Aorta - rib 12
(Say it out loud: I 8 10 eggs at 12)
Lymphatics of mediastinum
Bronchotracheal nodes at hilum
Paratracheal nodes near carina
Thoracic duct runs from cisterna chyli (abdomen), between aorta and azygous vein -> joins with L jugular and subclavian trunks -> enters venous system at L brachiocephalic (where it branches into jugular and subclavian)
Right jugular and subclavian trunks -> right duct -> right brachiocephalic vein (where it branches)
Veins of posterior thorax
Azygous system - lots of variations
Azygous vein - right side, just anterior to vertebral column (lateral to thoracic lymphatic duct)
Hemiazygous crosses, runs inferior along left side
Accessory hemiazygous crosses, runs superior along left side
Empties into both SVC and IVC (can be collateral if they are blocked)
Vessels of posterior mediastinum
Aorta on left
Thoracic (lymph) duct midline
Azygous vein on right
Hemiazygous on left, posterior to aorta
SNS within thorax
Sympathetic chain along lateral vertebral column (anterior to ribs)
White and grey rami connect with spinal nerves
“Cardiac nerves” - run anterior from cervical and T1-4 -> all thoracic organs via cardiac plexus (aortic arch), pulmonary plexus (trachea and bronchi) and esophageal plexus
Splanchnic nerves -> anterior to abdomen: greater (T5-9), lesser (T10,11), least (T12)
Phrenic nerve
Arises from C3-C5 (somites of diaphragm)
Runs anterior to root of lungs (phrenic = “phront”), within fibrous pericardium
Motor fibers -> diaphragm
Sensory fibers from diaphragm, fibrous/parietal pericardium, pleura along mediastinum and medial diaphragm
Phrenic nerve is NOT part of ANS!
Vagus nerve
Vagus nerve = cranial nerve 10 = parasympathetic!
Runs with carotid arteries into thorax
Right - lateral to trachea, posterior to lung root -> posterior esophageal plexus
Left - anterolateral to aortic arch, posterior to lung root -> anterior esophageal plexus
Both vagus nerves innervate ANS plexuses (cardiac, pulmonary, esophageal) -> all thoracic organs -> continue as vagal trunks into abdomen
Vagus is parasympathetic -> lower heart rate, constricted bronchi, increased peristalsis and mucus
Sensory from heart, lungs, reflexes
Recurrent layrngeal nerves
Innervate laryx (voice box - ie “hoarse voice”)
Branches of vagus nerves
Right runs under subclavian near junction (not in mediastinum)
Left runs through aortopulmonary window (posterior to ligamentum arteriosum), back up along lateral trachea - susceptible to injury!
