THORACIC CAVITY

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THORACIC CAVITY

• MEDIASTINUM

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Mediastinum

• Mediastinum space between lungs.
• Superior mediastinum
• Separated from inferior by horizontal plane
  between sternal angle and IV disc T4-T5.
• Fig. 1.34, p 135.

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Mediastinum

• Inferior
• Anterior
• Middle
• Posterior

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Superior Mediastinum

• Retrosternal
• Great vessels and branches.
• Thymus.
• Prevertebral
• Trachea
• Esophagus
• Thoracic duct
• Sympathetic trunks
• Vagus nerves

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Inferior Mediastinum

• Anterior
• Thymus, fat, lymph nodes
• Middle
• Pericardium
• Phrenic nerves
• Pericardiacophrenic artery
• Heart and great vessels

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Inferior Mediastinum

• Posterior
• Esophagus
• Thoracic duct
• Aorta and branches
• Vagus nerves
• Sympathetic trunks
• Azygos system of veins

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SUPERIOR MEDIASTINUM
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Thymus

• Occupies superior mediastinum on either side of
  the midline.
• Behind manubrium.
• Covered by converging pleura of the lungs.
• Involutes with fat after puberty.

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Thymus

• Blood supply
• Anterior mediastinal arteries from internal
  thoracic artery.
• Inferior thyroid arteries from subclavian
  artery.
• Venous drainage
• Into left brachiocephalic vein.

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Thymus

• Innervation
• Vagus nerve.
• Cardiac sympathetic plexus.

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Middle Mediastinum (inferior)

• Pericardium
• Encloses heart.
• (Fig. 1.35, p 137).

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Middle Mediastinum (inferior)

• Pericardium
• Visceral (serous) (Fig 1.37, p 139)
• epicardium.
• Arterial mesocardium.
• Venous mesocardium.
• Transverse sinus
• Space between arterial and venous
  mesocardium.
• Oblique sinus
• Space between right and left pulmonary veins.

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Middle Mediastinum (inferior)

• Pericardium
• Pericardial cavity.
• Parietal (serous)
• Fused to fibrous pericardium.
• Fibrous
• Fused with central tendon of diaphragm
• Pericardiacophrenic ligament.
• Fused with sternum
• Superior and inferior sternopericardial
  ligaments.

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Middle Mediastinum (inferior)

• Pericardium
• Blood supply (Fig. 1.38, p 139)
• Pericardial arteries.
• Pericardiacophrenic arteries.
• Musculophrenic arteries.
• Nerve supply
• CN X.
• Phrenic nerve.
• Sympathetic trunk.

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POSTERIOR MEDIASTINUM
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Esophagus

• From base of neck to
• Left of midline to
• Midline to
• Left of midline.
• Passes through diaphragm at level of T10.
• Lies
• Behind trachea.
• In front of vertebral column.

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Esophagus Blood Supply

• Bronchial artery.
• Thoracic aorta.
• Left gastric artery.
• Left inferior phrenic artery.

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Esophagus Innervation

• Esophageal plexus
• Continuation of posterior pulmonary plexus.
• Formed by right and left vagus nerves
• Right vagus nerve ? posterior vagus nerve.
• Left vagus nerve ? anterior vagus nerve.

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Esophagus Innervation

• Upper third
• Voluntary muscle.
• Innervated by recurrent laryngeal nerve.
• Lower two-thirds
• Involuntary muscle.
• Innervated by vagus and sympathetic chain.

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Left Thoracic duct

• Arises from cisterna chyli
• At union of right and left lumbar trunks.
• Begins on the front of vertebral body T-12 or
  L-1.
• Runs up through the thorax along the front of the
  vertebral column.
• At first it lies to the right of midline.

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Left Thoracic duct

• It moves over to the left side when it reaches
  level T-5.
• Receives most of lymph from body below diaphragm.
  
• Drains left side of thoracic cavity and part of
  right.

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Left Thoracic duct

• Receives lymph from left internal jugular lymph
  trunk.
• Receives lymph from left subclavian lymph trunk.
• Empties into venous system at junction of
• Left internal jugular vein.
• Left subclavian vein.

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Right Thoracic duct

• Drains upper right thoracic cavity, right upper
  extremity, and right side of head and neck.
• Empties into venous system at junction of
• Right internal jugular vein.
• Right subclavian vein.

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Thoracic Sympathetic Chain

• Lies against neck of ribs and costovertebral
  junctions.
• 12 thoracic ganglia pairs
• First one often fused with inferior cervical
  ganglion
• Referred to as stellate ganglion collectively.

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Thoracic Sympathetic Chain

• Cervical ganglia
• Superior.
• Middle.
• Inferior.

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Thoracic Sympathetic Chain

• The preganglionic sympathetic supply to the
  thoracic viscera are from T15.
• The postganglionics are from
• Superior, middle, and inferior cervical
  ganglia.
• T1-T5 paravertebral ganglia.
• They exit the chain as direct fibers and travel
  downwards to enter the thorax
• As cardiopulmonary splanchnic nerves.

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Thoracic Sympathetic Chain

• The cardiopulmonary splanchnic nerves travel on
  their own and do not accompany other nerves or
  vessels.
• Function
• Coronary artery dilation.
• Increase heart rate.
• Bronchodilation.

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Splanchnic Nerves

• Composed of preganglionic fibers and visceral
  sensory fibers.
• Supply abdominal viscera.
• Synapse in prevertebral ganglia.
• Refer in text to Figure 1.41, page 63.

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Splanchnic Nerves

• Greater
• T5-T9.
• Synapses in celiac ganglion.
• Lesser
• T10-T11.
• Synapses in the superior mesenteric ganglion.

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Splanchnic Nerves

• Least
• T12.
• Synapses in the aorticorenal ganglion.

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Vagus Nerve

• Cranial nerve X
• Major parasympathetic supply to thoracic and
  abdominal viscera.

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Course of Vagus Nerve

• Parallel to esophagus
• Innervates esophagus
• Passes posterior to root of lung on each side.
• Pierces diaphragm with esophagus.
• Becomes gastric nerve.
• Supplies viscera in thoracic cavity.

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Vagus Nerve Branches

• Cardiac branches to cardiac plexus.
• Pulmonary branches to pulmonary plexus.
• Esophageal branches to esophageal plexus.

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Vagus Nerve Branches

• Left recurrent laryngeal nerve from left vagus
• Hooks around arc of aorta to left of
  ligamentum arteriosum.
• Right recurrent laryngeal nerve from right vagus
• Hooks around subclavian artery.
• Therefore arises in neck, not thorax.

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Phrenic Nerve

• Arises in neck from
• Ventral rami of C3-5 (C4 major contribution)
• Passes anterior to pulmonary root on each side
  (only nerve to do so).
• Sole motor innervation to diaphragm.
• Sensory fibers to pericardium, mediastinal
  pleura, and pleural and peritoneal coverings of
  diaphragm.

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Phrenic Nerve

• Pain via phrenic nerves usually referred to base
  of neck and tip of shoulder.
• Accompanied by pericardiacophrenic arteries.
• Branches of internal thoracic arteries

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Lymphatic Drainage

• 50 tracheobronchial lymph nodes
• Some of the largest lymph nodes in the body.
• Include
• Paratracheal
• Superior tracheobronchial
• Inferior tracheobroncial
• Bronchopulmonary
• Pulmonary
• Text p 131, Fig. 1.32

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Lymph Drainage of Thoracic Cavity

• Parasternal nodes
• Lie behind sternum along course of internal
  thoracic artery.
• Receive lymph from thoracic wall, upper
  anterior abdominal wall, and diaphragm.
• Also receive significant amount of lymph from
  mammary gland.
• Dump into parasternal lymph channel.

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Lymph Drainage of Thoracic Cavity

• Posterior intercostal nodes
• Lie in posterior intercostal space between
  heads of ribs.
• Receive lymph from thoracic wall and
  paravertebral regions.
• Drain into thoracic duct
• From left and lower right.
• Drain into right lymphatic duct
• From upper right.

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Lymph Drainage of Thoracic Cavity

• Diaphragmatic nodes
• Lie on upper surface of diaphragm.
• Receive lymph from diaphragm, pericardium,
  upper surface of liver.
• Drain to parasternal and posterior mediastinal
  nodes.

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Lymph Drainage of Thoracic Cavity

• Posterior mediastinal nodes
• Lie along esophagus and descending thoracic
  aorta.
• Brachiocephalic nodes
• Lie along brachiocephalic veins.

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Lymphatic Drainage of Thorax

• Lymph Trunks
• Bronchiomediastinal lymph trunks receive lymph
  from
• Posterior mediastinal nodes
• Brachiocephalic nodes
• Tracheobronchial nodes
• Parasternal nodes

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Lymphatic Drainage of Thorax

• Thoracic Duct
• Begins in abdomen on right side of midline.
• Receives most of lymph from body below
  diaphragm.
• Drains left side of thoracic cavity and part of
  right.
• Receives lymph from left internal jugular
  lymph trunk.

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Lymphatic Drainage of Thorax

• Thoracic Duct (cont.)
• Receives lymph from left subclavian lymph
  trunk.
• Empties into venous system at junction of
• Left internal jugular vein.
• Left subclavian vein.

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Lymphatic Drainage of Thorax

• Right Lymphatic Duct
• Drains upper right thoracic cavity, right upper
  extremity, and right side of head and neck.
• Empties into venous system at junction of
• Right internal jugular vein.
• Right subclavian vein.