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- gut tube that extends between the pharynx and the stomach descending from the superior mediastinum into the posterior mediastinum.
- innervated by a visceral or autonomic plexus called the esophageal plexus.
- contains both parasympathetic fibers (VE- para/pre fibers from the vagus nerves) and sympathetic fibers (VE-symp/post fibers from the sympathetic trunks).
- found on the surface of the esophagus within the fascia surrounding it.
- The parasympathetic contribution to the plexus is formed by the right and left vagus nerves.
- After passing posterior to the root of the lung, the left vagus nerve will rotate to form most of the plexus on the anterior surface of the esophagus.
- After passing posterior to the root of the lung, the right vagus will rotate to form most of the plexus on the posterior surface of the esophagus.
- As the esophagus and plexus reach the diaphragm, the vagal contributions will re-constitute into an anterior vagal trunk (on the anterior surface of the esophagus) and posterior vagal trunk (on the posterior surface of the esophagus) near the esophageal hiatus in the diaphragm where the esophagus and vagal trunks pass through the diaphragm into the abdomen (at the T10 level).
Post Mediastinum Veins
- posterior intercostal veins drain into the azygous vein on the right side.
- On the left side, they drain either into the accessory hemiazygous or hemiazygous veins which then drain into the azygous vein (the arrangement of these veins can be variable).
- The azygous vein then arches over the root of the right lung and drains into the superior vena cava.
- These veins form the azygous venous system which drains blood from the posterior walls of the thorax and abdomen.
the concept of "branches and tributaries."
- Only arteries are said to have "branches."
- Veins do not have "branches� they are said to have "tributaries."
- This has to do with the direction of blood flow.
- For arteries, blood flows from larger "trunks" into smaller "branches."
- For veins, blood flows from smaller "tributaries" into larger veins.
- So, arteries have branches, and veins have tributaries.
- Arteries do not have tributaries, and veins do not have branches.
- main lymphatic duct which lies on the bodies of the inferior seven thoracic vertebrae.
- conveys most lymph of the body (i.e., from the lower limbs, pelvic cavity, abdominal cavity, left side of thorax, left side of head, neck, and left upper limb) into the venous system.
- The thoracic duct may be located between the azygous vein and descending aorta on the bodies of the thoracic vertebrae.
- As it ascends in the posterior mediastinum, it crosses to the left, posterior to the esophagus to reach the superior mediastinum.
- There, it terminates in the junction between the left internal jugular vein and left subclavian vein.
descending or thoracic aorta
- descends posteriorly and to the left of the esophagus.
- gives rise to the posterior intercostal arteries.
- Because it descends to the left of the esophagus, it is related more to the left pleural cavity and the mediastinal surface of the left lung.
- It descends in the thorax and passes through the diaphragm at the aortic hiatus (at vertebral level T12).
greater, lesser, and least thorarcic splanchnic nerves
- special nerves in that they are comprised of sympathetic preganglionic fibers (VE-symp/pre), originating from cells in the (lateral gray horn of the) spinal cord, that pass through the sympathetic chain ganglia but do not synapse.
- Instead, these nerves will pass into the abdomen where they will synapse in special sympathetic �pre-aortic� ganglia.
- Postganglionic fibers from these cell bodies in these pre-aortic ganglia in the abdomen will then follow the course of the blood vessels to their target organs.
The Diaphragm Openings
- There are passages through the diaphragm for the IVC, esophagus, and aorta.
- IVC (caval) hiatius is at the T8 vertebral level
- esophageal hiatusg as at the T10 level.
- aortic hiatus is at the T12 level.
Contents of the Superior Mediastinum
- brachiocephalic veins
- superior vena cava
- aortic arch
- brachiocephalic artery
- left common carotid a.
- left subclavian a.
- ligamentum arteriosum
- left recurrent laryngeal nerve
- vagus and phrenic nerves
- trachea and primary bronchi
- The esophagus also travels through the superior mediastinum.
right and left brachiocephalic veins
- bring blood into (and form) the superior vena cava which drains into the right atrium of the heart.
- Each brachiocephalic vein is formed by its two tributaries: the internal jugular vein and subclavian vein.
- Blood from the left ventricle of the heart goes into the aortic arch and into its branches:
- brachiocephalic artery (which then divides into the right common carotid and right subclavian arteries),
- left common carotid artery
- left subclavian artery.
- Joins the pulmonary trunk and the aortic arch
- remnant of a duct (the ductus arteriosus) in the fetus that shunted blood away from the pulmonary system into the systemic system.
- left vagus nerve sends a branch posterior to the ligamentum arteriosum which wraps around the aortic arch and ascends towards the larynx in the groove between the trachea and esophagus. The branch is called "the left recurrent laryngeal nerve." On the right side, the right recurrent laryngeal nerve wraps around the subclavian artery as it branches from the vagus nerve.
- also seen in the superior mediastinum.
- They pass from the superior into the middle mediastinum as they descend inferiorly to innervate the diaphragm.
- derived from cervical spinal cord segments C3, 4, 5.
- C3,4, and 5 keep the diaphragm alive
- diaphragm is a skeletal muscle under voluntary control so its motor innervation is somatic and not autonomic.
- Remember, the phrenic nerves pass anterior to the root of the lung and the vagus nerves pass posterior to the root of the lung.
- deep to the brachiocephalic veins, ascending aortic, and pulmonary arteries.
- The tracheobronchial lymph nodes lie on the surface of the tracheal bifurcation.
- These can become enlarged when bronchogenic cancer develops.
- The tracheal bifurcation is anterior to the esophagus.
- The relationships of structures in and around the bifurcation should be known.
(an abnormal �ballooning out�) of the arch could impinge the left recurrent laryngeal nerve (which supplies nearly all the laryngeal muscles) and cause vocal cord paralysis on one side resulting in �hoarseness� of voice
Phrenic nerve paralysis (impingement)
- -A lesion of the phrenic nerve could result in a corresponding paralysis of the diaphragm on that side.
- This would disrupt normal respiratory function since the diaphragm is the major muscle of respiration.
Other Clinical Mediastinum
- Aortic coarctation
- Tracheitis and bronchitis
- Lymph node enlargement
Thoracic duct injury
Clinical Note: Injury of the thoracic duct (e.g., as a complication of surgery, trauma, or disease) may cause lymph to build up in the posterior mediastinum.Mediastinitis
Patent ductus arteriosus-
- Clinical Note: If the ligamentum arteriosum does not shut down and become ligamentous at birth, then it is a patent (open) ductus arteriosus which will result in an abnormally low amount of blood reaching the pulmonary circulation.
Vocal fold paralysis
Because the recurrent laryngeal nerves supply nearly all of the muscles of the larynx, any investigative procedure or disease process in the superior mediastinum may damage these nerves and affect the voice (and/or paralyze the vocal folds/cords).
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