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-portion of the thoracic cavity found between the two pleural cavities on either side
Borders of Mediastinum
1. Anterior = sternum and costal cartilages
2. Posteriorly = thoracic vertebral bodies and intervertebral discs T1-T12
3. Left and Right = mediastinal pleura
Inferior mediastinum
-divided into 3 parts, mainly by relationship of pericardium
Anterior mediastinum
-bordered anteriorly by sternum and transversus thoracis muscles
-bordered posteriorly by anterior border of pericardial sac
Superior mediastinum
-separated from posterior mediastinum by imaginary line drawn from sternal angle directly posteriorly to intervertebral disc between T4 and T5
-located in superior mediastinum
-gradually becomes involuted as we become older
-usually bilobed
-a primary lymphoid organ of the body
-receives blood from anterior mediastinal branches of internal thoracic artery as well as from anterior intercostals
-venous drainage through inferior thyroid vein which drains into internal thoracic vein
-cancer of thyroid
-can be deadly
Right brachiocephalic vein
-formed by right subclavian v. and right internal jugular vein
Left brachiocephalic vein
-formed by junction of left subclavian vein and left internal jugular
-much longer than right brachiocephalic vein
-passes anterior to vessels coming off arch of aorta
Arch of the aorta
-crosses over left main bronchus as it ascends at the bifurcation of the trachea
-at this point it is anterior to the esophagus
3 Branches of arch of aorta
1. brachiocephalic trunk
2. left common carotid
3. left subclavian
Phrenic nerve
-descends down on lateral aspect of pericardial sac
-runs with pericardiacophrenic artery (branch of internal thoracic artery)
Left Vagus nerve
-descends between trachea and esophagus
-gives off recurrent left laryngeal branch that hooks under ligamentum arteriosum
Ligamentum arteriosum
-remant of ductus arteriosus from embryological development
-connects pulmonary trunk to aorta
Recurrent laryngeal nerve
-closely associated w/ left main bronchus
-innervates larynx
-gives off motor branches that innervate esophagus for voluntary movements
Superior part of esophagus
-voluntary skeletal muscle
Middle 1/3 of esophagus
-mixture of skeletal and smooth muscle
Distal 1/3 of esophagus
-made up of involuntary smooth muscle
Are phrenic nerves posterior or anterior to the vagus nerves?
Posterior mediastinum
-area below the superior mediastinum
-border w/ superior mediastinum is intervertebral disc between T4 and T5
When the esophagus passes through the diaphragm is it anterior or posterior to the aorta?
Hiatal hernia
-when stomach or other organs push back up through diaphragm
-common in obese people
Branches of descending thoracic aorta
-right bronchial artery
-2 small left bronchial arteries
-intercostal arteries (posterior)
-superior phrenic branch
-subcostal branch
Thoracic duct
-ascends from inferiorly
-drains into the junction of the internal jugular and subclavian vein
-usually lies on left side of esophagus deep to aortic arch
Cisterna chyli
-large structure below diaphragm that receives lymphatic drainage from abdominal viscera
-3 major channels pass into here
-gives rise to thoracic duct
Main thoracic duct
-drains almost entire body except right upper half of torso
Right lymphatic duct
-drains right arm, head, and neck
-terminates by draining into the junction on the right between the right subclavian and internal jugular veins
Esophageal plexus
-receives sympathetic innervation from sympathetic chain
-vagus nerve contributes
-inferior 1/3 has parasympathetic and sympathetic innervation
-inferior portion innervated by recurrent laryngeal nerve for voluntary movement
-inferior portion innervated by by sympathetic and parasympathetic for involuntary movement
Anterior vagal trunk
-continuation of left vagus nerve
Posterior vagal trunk
-made up primarily of continuation of right vagus nerve
Greater Splanchnic nerve
-preganglionic sympathetic nerve
What accompanies the aorta through the diaphragm?
-thoracic duct
-azygos vein
Lesser splanchnic nerve
-preganglionic sympathetic nerve
Least splanchnic nerve
-preganglionic sympathetic nerve
Celiac ganglion
-receives greater and lesser splanchnic nerves
Aorticorenal ganglion
-receives least splanchnic nerve
Accessory hemiazygos vein
-descends on left side of vertebral column from T5-T8
-crosses over T7-T8 vertebra posterior to thoracic aorta and thoracic duct to join azygos vein
Azygos vein
-ascends in posterior mediastinum, passing close to right sides of bodies of the inferior eight thoracic vertebrae
-arches over superior aspect of root of right lung to join SVC

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