Wedge shaped between manubrium and T1-T4 (concave)
Oesophagus at back, lying on T1 vertebral body
Trachea next, may
touch jugular notch.
-
these two wholly occupy the thoracic inlet, with lung
apices laterally
Vessels and nerves pass between lung apices and tubes
Below the inlet, trachea slopes back and manubrium slopes forward
- space created: makes room for brachiocephalic trunk, left brachiocephalic vein and thymus
Concavity of the arch: lies in the plane of the sternal angle (wholly in superior mediastinum)
- arches over beginning of left bronchus and bifurcation of pulmonary trunk to posterior.
- brachiocephalic trunk begins in midline and diverges right as it ascends in front of trachea, only branch is the rare thyroid ima. Divides behind L SC jt.
- left common carotid (no branches) and left subclavian (deeply grooves lung) pass up on L; keep L vagus and apex of left lung away from the trachea (they lie against it on the R)
- R brachiocephalic passes downwards, L runs across the superior mediastinum
- Confluent at superior vena cava, runs to R of aortic
- R phrenic descends in contact with the lateral aspect of the R brachiocephalic and SVC
See written notes
Arch begins at manubrium level.
Crossed on L by phrenic & vagus nerves (anterior & posterior to lung root respectively).
L superior intercostal vein passes anterior to arch, between L phrenic & vagus nerves, to enter L brachiocephalic vein.
L RLN passes beneath ligamentum arteriosum & up R side of aorta to run up tracheo-oesophageal groove.
Main pulmonary trunk bifurcates below the arch. Trachea & oesophagus lie to R.
Remnant of ductus arteriosus, from commencement of L pulmonary artery.
- L recurrent laryngeal hooks behind it
- Superficial part of cardiac plexus lies anterior, deep part to its right b/n arch and carina.
Operation: Pleura over aortic arch (186) is incised behind vagus (195) up to left subclavian origin
ˆ the pleural flap is reflected forwards with the vagus and its left recurrent nerve
Formed behind SC joints; lateral to common carotids in front & just medial to anterior scalenes.
- each receives tributaries corresponding to branches of 1st part of subclavian artery: vertebral, inferior thyroid, internal thoracic, and superior intercostal (L side only)
R brachiocephalic receives right lymphatic duct or separately the right jugular, subclavian and bronchomediastinal lymph trunks at is commencement
L brachiocephalic descends above/anterior to aortic arch, behind thymus, above notch in infants / adults with distended veins (beware in suprasternal incisions)
- receives the thoracic duct at its commencement
Pretracheal fascia passes behind the vein, directing retrosternal goitre between it and brachiocephalic trunk.
Commences at lower border 1st CC, pierces pericardium at 2nd CC, enters RA at 3rd CC.
- receives azygos vein behind the sternal angle. No valves in it or brachiocephalics.
Sympathetics, parasympathetics and some small ganglia. Deep and Superficial parts are really one.
¨ cardiac arteries (vasomotor); SA & AV nodes (inhibitory & accelerator)
Superficial part lies in front of ligamentum arteriosum
Deep is larger, lies to right of ligamentum, in front of tracheal bifurcation, behind aortic arch.
Sympathetic from three
cervical and upper 4-5 thoracics (also carry pain afferents)
- pain follows usual path ¨ sympathetic ganglia ¨ spinal nerves via white comitantes \ referred.
Parasympathetic from both vagi and both recurrent laryngeals (also carry sensory afferents)
10cm, 2cm diameter. Continuation of larynx, commencing at cricoid (C6 level), 5cm above sternal notch. Thus cricoid and sternal angle are surface markings of start and bifurcation of trachea.
- in infants is only 3mm in diameter; during inspiration length may stretch to 15cm
Anterior to trachea in thorax:
(1) R brachiocephalic trunk
(2) L brachiocephalic vein
(3) Long straps
Pulmonary trunk bifurcates anterior to, below & to L of the tracheal bifurcation. Arch of azygos vein hooks over the R main bronchus. (226)
- the R vagus is separated from trachea by pleura and arch of azygos
- the L vagus is separated by the carotid & subclavian; L recurrent laryngeal does ascend in the groove between trachea and oesophagus.
Branches of inferior thyroid + bronchial arteries; veins drain into inferior thyroid plexus.
Nerves: sympathetics ¨ from upper ganglia of sympathetic trunks (smooth muscle and vessels)
- afferent in vagi / recurrent laryngeals carry pain.
(1) Elasticity allows lengthening during swallow and elastic recoil during breathing
(2) Hyaline cartilage rings (15-20 horse-shoe shaped) prevent collapse during inspiration
(3) Trachealis posteriorly controls diameter (where gaps in rings are)
(4) Mucous membrane (pseudostratified columnar, ciliated) traps debris; cilia propel mucus to larynx ¨ expulsion by cough; also secretes mucous Ð keeps air humidified.
From C4 ¨ passes down over scalenus anterior, over dome of pleura and anterior to subclavian vein ¨ runs as far lateral as possible through mediastinum, anterior to lung root, in contact with mediastinal pleura throughout.
In contact with venous structures throughout (R brachiocephalic ¨ SVC ¨ R atrium ¨ IVC) ¨ passes with IVC through central tendon.
In contact with arterial structures throughout (L Subclavian and CCA, then aortic arch medially. Crosses arch anterior to vagus nerve ¨ runs down pericardium over L ventricle towards apex of heart. Pierces muscle of diaphragm lateral to pericardium cf R nerve pierces tendon.
Each nerve is sole motor supply to ipsilateral diaphragm, splitting into radiating anterior, lateral & posterior branches. 2/3 of phrenic fibres motor, rest are sensory (to diaphragm, fibrous pericardium, parietal serous pericardium, mediastinal pleura). Referred to C4.
Attempt to reach midline at all levels.
R contacts trachea; L separated from it by great vessels.
R vagus lies on trachea medial to arch of azygos; L crosses aortic arch deep to superior intercostal vein.
Each nerve runs behind lung, contributes to ipsilateral lung rootÕs pulmonary plexus ¨ enters oesophageal plexus on posterior surface of oesophagus ¨ mixing of fibres.
RLNÕs hook around (R) R subclavian and (L) ligamentum arteriosum ¨ ascend up tracheo-oesophageal grooves. Supply trachea, oesophagus above lung roots, and muscles of larynx.