Mediastinum Flashcards
Describe borders of sup mediastinum
Neck to thorax, continuous with neck
Sup = rib 1, t1 to jugular notch
Inf = sternal angle plane ~t4
Post = t1-t4 vertebrae
Ant = manubrium
Lat = mediastinal surface of lungs
Describe content of sup mediastinum = organs
Esophagus
Trachea
Thymus (technically belongs to ant mediastinum but can extend to sup)
Describe content of sup mediastinum = vessels
Aortic arch (bends and becomes thoracic aorta) and its first 3 branches
Left and right brachiocephalic veins
Svc
Arch of azygous
Pericardiophrenics (off internal thoracic artery)
Roots of great vessels
Describe brachiocephalic veins - sup mediastinum
Receive from internal jugular and subclavian (int jug in neck)
Forms svc when left and right brachiocephalics meet
Describe branches of aorta
After coronary arteries =
1. Brachiocephalic trunk (= common trunk of right common carotid and subclavian)
2. Left carotid artery
3. Left subclavian artery (towards arm)
ALL 3 go out through thoracic inlet
Describe content of sup mediastinum = lymphatics
Thoracic duct
Drains 3/4 of lymphatics of body
Back into venous system
Attaches where subclavian ,meets int jug
Describe content of sup mediastinum = nerves
Left and right vagus, left recurrent laryngeal (right = outside sup mediastinum)
Left and right phrenics, sympathetic chain (towards back)
Cardiac and pulmonary plexuses (psns and sns branches = sympathetic chain and vagus)
Describe what happens to vagus nerves in sup mediastinum
Runs in the neck and into superior thoracic aperture
Gives rise to psns nerves contributing to cardiac and pulmonary plexuses
Gives rise to recurrent laryngeal nerves (only left one in sup mediastinum)
Describe what happens to vagus nerves in sup mediastinum = recurrent branches
Right = loops under right subclavian or sometimes brachiocephalic trunk (outside mediastinum)
Left = loops under aortic arch, posterior (just behind) ligamentum arteriosum in sup mediastinum
What can lead to hoarseness
Recurrent laryngeal nerves are motor to most laryngeal muscles (phonation)- impingement of the nerves (like under aortic arch, vessels can pinch) = leads to hoarseness = raspy scratchy voice or dysphonia
Describe borders of anterior mediastinum
In front of middle but behind sternum
Sup = sternal angle
Inf = diaphragm
Post = pericardium - mid mediastinum
Ant = sternum
Lat = mediastinal surface of lungs
What is anterior mediastinum occupied by
Thymus Gland = lymphoid organ responsible for differentiation of T cells (lymphocytes), school for T cells to be educated, only for dev
Also lymph nodes, fat and ct
Describe thymus
Involved in immune system development so relatively larger in children/youth and will degenerate
Remainder of thymus = thymus fat, extends into sup mediastinum= fibrofatty tissue
Describe borders of middle mediastinum
Sup = sternal angle
Inf = diaphragm
Post = posterior surface of fibrous pericardium
Ant = anterior surface of fibrous pericardium
Lat = mediastinal surface of lungs
Describe important parts of middle mediastinum
Heart, roots of great vessels, nv (inside pericardium and outside), primary bronchi
Right and left pulmonary arteries
Right and left pulmonary veins = 4, root with coronary arteries emerging
Svc and ivc
Describe borders of posterior mediastinum
Top of thoracic and neck to abdomen
Sup = sternal angle
Inf = diaphragm
Post = vertebrae t5-t12
Ant = fibrous pericardium
Lat = mediastinal surface of lungs
Describe posterior and superior mediastinum
Post communicates freely with superior mediastinum = several structures continuous between the 2 =
Sympathetic chain, esophagus, nerves, aorta (arch +thoracic), azygous (arch and vein, hemi azygous vein, left only behind aorta), thoracic duct
Splanchnic nerves
Esophageal plexus
Describe azygous and hemi azygous veins
drain posterior thoracic (intercostal veins) and abdominal walls but azygous also offers a collateral passage for venous blood to bypass blockages in vena Cavan = cavo-caval anastomoses (ivc to svc) = another way for venous blood to make it back to heart
Describe azygous vein specifically
Unpaired
Starts in abdomen
On right
Hooks on hilum and drains into svc
Describe hemi azygous vein specifically
Left side but jumps over vertebrae and drains into azygous first
What is thoracic duct
Main collecting duct
Drains 3/4ths of body lymph, rest= drained by right lymphatic duct
Where does thoracic duct drain
Both into brachiocephalic veins At venous angles = right and left
Where int jug and subclavian meet to form brachiocephalic
Describe thoracic aorta - descending
Thoracic portion of aorta = gives rise to posterior intercostal arteries from rib 3 to 12
(10 pairs, last = subcostal)
Anastomose with anterior counter parts from internal thoracic arteries
What can we find in posterior thoracic wall
Neurovascular bundle = posterior intercostal arteries (from aorta), posterior intercostal veins (to azygous/hemi azygous), intercostal nerves (passing into space between innermost and internal intercostal muscles)
Can we see thoracic aorta branches in post mediastinum
Nahhhhh
Since passsing behind azygous, behind esophagus
Describe esophagus generally
Muscular tube that connects pharynx to stomach
Runs through superior and posterior mediastinum
Describe esophagus in posterior mediastinum
First to right of thoracic aorta but moves anteriorly to it as it passed inferiority through diaphragm
Describe esophageal hiatus
Anterior to aortic hiatus (against vertebral Column)
Describe vagus nerve as enters post mediastinum
In sup = vagus gave psns Fibers to cardiac and pulmonary plexuses —> now as enter post= vagus nerves pass posteriorly to hilum of lungs, lateral to eso
What does larp mean
Left vagus = anterior vagal trunk
Right vagus = posterior vagal trunk (bind eso, for plexus)
Describe esophageal plexus
Vagal trunks send branches to each other and join with branches from sympathetic chain to form esophageal plexus = ans innervation to esophageal smoooth muscle - peristalsis
Where do vagal trunks go
Continue through diaphragm with esophageal to provide psns innervation to abdomen- gi tract
Describe sympathetic chain
Bilateral ganglionated chain that runs from base of skull to coccyx, on either side, transmitting sympathetic info to be distributed broadly
Describe sympathetic chain in posterior mediastinum
Located on either side of vertebral bodies, anterior to costovertebral joint, in close association with spinal nerves from same level
Describe sympathetic system = ans
Psns and ans efferent signals relayed via 2 neurons = pre and post ganglionic neuron, synapse somewhere in body
Describe sympathetic system = psns
Synapses tend to be close to target organs
Describe sympathetic system - sns
Synapses occur in ganglia further from target organs
Has broad distribution to periphery =skin, sweat glands and to viscera (no psns in skin)
Pathways and synapses of pre and post ganglionic neurons depends on target organs
Describe sympathetic innervation for thoracic and cervical viscera
Preganglionic Fibers travel in sympathetic chain to same or different spinal levels, synapse in ganglia and then post ganglionic Fibers emerge and join to form named sympathetic nerves to their organs (cardiac nerves, pulmonary nerves)
Paravertebral ganglia
Describe sympathetic in certain for abdominopelvic viscera
Preganglionic Fibers pass through sympathetic chain w/o synapse, join Fibers from other levels to form splanchnic nerves
Synapse occurs instead in ganglia situated in front of the abdominal aorta = 3 splanchnics
Prevertebral ganglia
Where are plexuses located
Psns and sns = plexuses near organs they control (cardiac, pulmonary and esophageal)
How many splanchnic nerves
3
Describe the 3 thoracic splanchnic nerves- gen
Visible running from sympathetic chain obliquely from posterior/superior to anterior/inferior
Pass through diaphragm to enter abdominal cavity = little splits, where their Preganglionic Fibers will synapse in several ganglia on the aorta (prevertebral ganglia), brining sns innervation to abdominopelvic viscera
Name and describe the thoracic splanchnic nerve s
Greater= usually only see this one, colllects from t5-9 (sympathetic Fibers from nerve)
Lesser = t11
Least = t12
What are vagal trunks
Psns = along esophagus, has vagal trunks
Through esophageal hiatus, now will form mesh work of plexuses with sympathetic nerve Fibers
