Posterior Mediastinum Flashcards

thoracic aorta
Terms Definitions
Superior boundary
Transverse plane passing from the sternal angle to the intervertebral disc between vertebrae T4/T5.
Inferior boundary
Diaphragm.
Laterally
Mediastinal part of parietal pleura on either side.
Superiorly, it is continuous with
the superior mediastinum.
Esophagus is a
muscular tube passing between the pharynx in the neck and the stomach in the abdomen.
It begins at the
inferior border of the cricoid cartilage, opposite vertebra C6, and ends at the cardiac opening of the stomach, opposite T11
Esophagus has a slight anterior-to-posterior
curvature that parallels the thoracic portion of the vertebral column.
It is secured superiorly by
its attachment to the pharynx
Inferiorly by
its attachment to the diaphragm.
Four areas where the esophagus may be compressed:
- Junction of the esophagus with the pharynx in the neck. - Superior mediastinum where the esophagus is crossed by the arch of aorta. - Pos mediastinum where the esophagus is compressed by the left main bronchus. - Pos mediastinum at the esophageal hiatus in the diaphragm.
An ingested corrosive substance would move more slowly
through a narrowed region, causing more damage at this site.
Esophageal arteries arise from
The thoracic aorta, bronchial arteries, and ascending branches of the left gastric artery in the abdomen.
Venous drainage involves small vessels returning to the
azygos vein, hemiazygos vein, and esophageal branches to the left gastric vein in the abdomen.
Lymphatic drainage of the esophagus in the posterior mediastinum returns to
posterior mediastinal and left gastric nodes.
Esophageal branches arise from
Vagus NErves and sympathetic trunks
Striated muscle fibers in the superior portion of the esophagus originate from the
brachial arches and are innervated by brachial efferents from the vagus nerves.
Smooth muscle fibers are innervated by
parasympathetic part of the Autonomic division of the PNS, visceral efferents from vagus nerves.
What are they?
Preganglionic fibers that synapse in the myenteric and submucosal plexuses of the enteric nervous system in the esophageal wall.
Sensory innervation of the esophagus
Involves the visceral afferent fibers originating in the vagus nerves, sympathetic trunks, and splanchnic nerves.
Visceral afferents from the vagus nerves are not involved in
pain recognition. they are responsible for normal body relfexes and physiological processes to CNS.
Visceral afferents that pass through the sympathetic trunks and the splanchnic nerves are the
primary participants in esophageal pain, and transmission of this info to the CNS.
After passing posteriorly to the root of the lungs, the right and left vagus nerves
approach the esophagus.
AS they reach the esophagus, each nerve
divides into several branches that spread over this structure, forming the esophageal plexus.
Anterior vagal trunk
On the anterior surface of the esophagus. Mainly from fibers originally in the left vagus nerve.
Posterior vagal trunk
Posterior surface of the esophagus, mainly from fibers originally in the right vagus nerve.
Thoracic portion of the descending aorta (thoracic aorta) begins
at the lower edge of the vertebra T4, where it is continuous with the arch of aorta.
It ends
anterior to the lower edge of vertebrae T12, where it passes through the aortic hiatus posterior to the diaphragm.
Branches of the Thoracic Aorta
Pericardial, Bronchial, Esophageal, Mediastinal, Posterior Intercostal Arteries, Superior Phrenic Arteries, Subcostal Artery
Pericardial branches - origin and course
A few small vessels to the posterior surface of the pericardial sac
Bronchial branches
Vary in number, size, and origin - usually two left bronchial arteries form the thoracic aorta and one right bronchial artery from the third posterior intercostal artery or the superior left bronchial artery.
Esophageal branches
Four or five vessels from the anterior aspect of the thoracic aorta, which forms a continuous anastomotic chain - anastomotic connections include esophageal branches of the inferior thyroid artery superiorly, and esophageal branches of the left inferior phrenic and left gastric arteries inferiorly.
Mediastinal branches
Several small branches supplying lymph nodes, vessels, nerves, and areolar tissue in the posterior mediastinum.
Posterior intercostal arteries
Usually nine pairs of vessels branching from the posterior surface of the thoracic aorta - usually supply lower nine intercostal spaces.
Superior phrenic arteries
Small vessels from the lower part of the thoracic aorta supplying the posterior part of the superior surface of the diaphgragm - they anastomose with the musculophrenic and pericardiophrenic arteries.
Subcostal artery
The lowest pair of branches from the thoracic aorta located inferior to rib 12.
The azygos system of veins consists of
A series of longitudinal vessels on each side of the body that drain blood from the body wall and move it superiorly to empty into the superior vena cava.
The azygos system of veins serves as
an important anastomotic pathway capable of returing venous blood from the lower part of the body to the heart if the inferior vena cava is blocked.
Major veins in the system are:
Azygos Vein on the right. Hemiazygos Vein and the accesory hemiazygos vein, on the left.
Azygos vein arises opposite vertebra
L1 or L2 at the junction between the right ascending lumbar vein and right subcostal vein.
It may also arise as
a direct branch of the inf vena cava, which is joined by a common trunk from the junction of the right ascending lumbar vein and the right subcostal vein.
Azygos vein enters the thorax through what?
The aortic hiatus of diaphragm, or it enters through or posterior to the right crus of the diaphragm.
At approx. vertebral level
T4, it arches anteriorly, over the root of the right lung, to join the superior vena cava before the superior vena cava enters the pericardial sac.
Tributaries
Right superior intercostal Vein. 5 to 11 right posterior intercostal veins. Hemiazygos Vein. Accessory Hemiazygos Vein. Esophageal Veins. Mediastinal Veins. Pericardial Veins. Right Bronchial Veins.
Hemiazygos vein arises
At the junction between the left ascending lumbar vein and the left subcostal vein.
Usually enters the thorax through
the left crus of the diaphragm, but may enter through the aortic hiatus.
Ascends through the
posterior mediastinum on the left side, to approx. T9.
At that point, it will
cross the vertebral column, posterior to the thoracic aorta, esophagus, and thoracic duct to enter the azygos vein.
Tributaries to the hemiazygos vein
The lowest four or five left posterior intercostal veins. Esophageal Veins. Mediastinal veins.
Accessory hemiazygos vein descends on the
left side from the superior portion of the posterior mediastinum to T8.
At that point, it will
cross the vertebral column to join the azygos vein, or ends in the hemiazygos vein.
Usually, it alsohas a connection
superiorly to the left superior intercostal vein.
Vessels that drain into the accessory hemiazygos vein:
Fourth to eighth left posterior intercostal veins and sometimes the left bronchial veins.
Thoracic duct
Principle channel through which lymph from most of the body is returned to the venous system.
Thoracic duct begins as
Confluence of lymph trunks in the abdomen, sometimes forming a saccular dilation - cisterna chyli, which drains the abdominal viscera and walls, pelvis, perineum, and lower limbs.
The thoracic duct extends from
Vertebra L2 to the root of the neck.
The thoracic duct ascends through
the posterior mediastinum to the right of midline between the thoracic aorta on the left and the azygos vein on the right.
It lies posterior to the
diaphragm and the esophagus.
Anterior to the
bodies of the vertebra.
At about T5, thoracic duct moves to the
left of the midline and enters the superior mediastinum. It continues into the neck.
After being joined by the left jugular trunk, which drains the upper left side of the head and neck and left subclavian trunk which drains left upper limb,
thoracic duct empties into the junction of the left subclavian and left internal jugular veins.
Thoracic duct receives the contents from:
Confluence of lymph trunks in the abs. Descending thoracic lymph trunks draining the lower 6 or 7 spaces on both sides. Upper intercostal lymph trunks draining the upper left five or six intercostal spaces. Ducts from posterior mediastinal nodes. Ducts from posterior diaphragmatic nodes.
Sympathetic trunks are an important component of
the sympathetic part of the autonomic division of the PNS and are usually considered a component fo the posterior mediastinum as they pass through the thorax.
They consist of two parallel cords punctuated by
11 or 12 ganglia, connected to adjacent thoracic spinal nerves by white and gray rami communicantes.
In the superior portion of the posterior mediastinum,
trunks are anterior to the neck of the ribs.
Inferiorly, they become
more medial in position until they lie on the lateral aspect of the vertebral bodies.
Throughout their course, the trunks are covered by
Parietal pleura.
Branches from the ganglia
First type includes branches from the upper five ganglia. Second type includes branches from the lower seven ganglia.
First type consists mainly of
postganglionic sympathetic fibers, which supply the various thoracic viscera. These branches are relatively small and also contain visceral afferent fibers.
Second type consists mainly of
Preganglionic sympathetic fibers which supply the various abdominal and pelvic viscera. Branches are large and carry visceral afferent fibers. Form 3 thoracic splanchnic nerves.
Greater splanchnic nerve
5 to 9 thoracic ganglia. Moving in a medial direction, passes into the abdomen through the crus of diaphragm, and ends in the celiac ganglion.
Lesser splanchnic nerve
9 to 10 thoracic ganglia. Descends across the vertebral bodies moving in a medial direction. Passes into the abdomen through the crus of diaphragm to end in the aorticorenal ganglion.
Least splanchnic nerve
Usually arises from 12 thoracic ganglion. It descends and passes into the abdomen through the crus of the diaphragm to end in the renal plexus.
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