Thorax

• Diaphragm

  • Dome-shaped muscle that forms partition btw thoracic and abdominal cavities
  • Chief muscle in respiration

  
• Anatomical part of diaphragm

  Muscular part: muscle fiber may be grouped into 3 parts:

  1. Sternal fibers: originates from back of xiphoid process
  2. Costal fibers: originates from inner surface of lower 6ribs + their cartilages
  3. Lumbar fibers: originates from upper lumbar vertebra via medial and lateral arcuate ligaments and right + left crura

  The muscle fiber after taking origin they arch upwards and inwards to form right + left dome which fiber them taking insertion into the central tendon

  
• Crura and arcuate ligaments

  1. Medial arcuate ligament: tendinous arch in fascia covering upper part of psoas major fascia
  2. Lateral arcuate ligament: tendinous arch in fascia covering upper part of quadratus lumborum (ant layer of thoracolumbar fascia)
  3. Right crus: longer, stronger than left. Arises from anterior surface of bodies of L1,2,3
  4. Left crus: arises from body of L1,2

  The median margin of the 2 crura forms tendinous arc in front of aorta called median arcuate ligament (forms aortic hiatus)

  
• Openings in diaphragm

  Large openings:

  • Aortic opening: at lower border of T12. Contents (aorta, thoracic duct, azygous vein)
  • Esophageal opening: T10. Contents (esophagus, right + left vagus, esophageal branches of left gastric artery
  • Vena cava opening: T8. Lies in central tendon. Comtents (IVC, right phrenic nerve)

  
• Opening of diaphragm

  Small openings:

  • Each crus: pierced by greater + lesser splanchnic nerves. Left crus is pierced by hemiazygous vein
  • Medial arcuate lig: sympathetic chain enter abdomen behind it
  • Lateral arcuate lig: subcostar nerves and vessels passes behind it
  • Foramen of morgani: gap btw sternal and subcostal origin of diaphragm . Superior epigastric vessels + lymphatics passes here
  • Musculophrenic vessels: pierces diaphragm at level of 9 costal cartilage

  
• Relations of diaphragm 


  Superior: pleura + lungs + pericardium

  Inferior: peritoneum, liver, fundus of stomacj, spleen, kidney, suprarenal glands.
• Functions of diagram

  Primary Function: Facilitates breathing by contracting and flattening during inspiration, increasing the thoracic cavity volume and decreasing intra-thoracic pressure.

  Secondary Functions:

  • Assists in the expulsion of vomit, feces, and urine by increasing intra-abdominal pressure.
  • Helps prevent gastroesophageal reflux by maintaining pressure on the esophagus where it passes through the diaphragm.
• Nerve supply of diaphragm

  Phrenic nerve: ventral rami C3,4,5

  Provides motor innervation to the diaphragm and sensory innervation to the central part.

  • T6-12: provide sensory innervation to peripheral part.
• Diaphragm 


  Here

  
• Blood supply of diaphragm

  Superior Surface:

  • Pericardiacophrenic and Musculophrenic Arteries: Branches of the internal thoracic artery.
  • Superior Phrenic Arteries: Branches of the thoracic aorta.

  Inferior Surface:

  • Inferior Phrenic Arteries: Arise from the abdominal aorta or celiac trunk.
• Mediastinum

  • Central compartment within thoracic cavity located between lungs bounded by mediastinal pleura on either side.
  • Divided into superior and inferior mediastinum by trnasverse line extending from sternal angle till body of T4
  • Inferior mediastinum is later subdivided into Anterior, medial and posterior by pericardium

  
• Boundaries of mediastinum

  • Anterior: sternum
  • Posterior: thoracic vertebra
  • Superior: thoracic inlet
  • Inferior: diaphragm
  • On each side: mediastinal pleura

  
• Superior mediastinum Contents

  • Sternal angle to T4

  Subdivided into: Retrosternal area, intermediate and prevertebral area

  Contents: 4 arteries, 4 nerves, 3 veins, 2 tubes, 1 gland, 1 duct.
• Contents on retrosternal area of superior mediastinum

  1. Sternohyoid
  2. Sternothyroid
  3. Thymus
  4. Right + left brachiocephalic vein
  5. Upper part of sup vena cava

  
• Contents of intermediate part of superior mediastinum

  1. Right + left brachiocephalic vein
  2. Left common carotid
  3. Left subclavian
  4. Phrenic, vagus and cardiac nerves

  
• Contents on prevertebral area of superior mediastinum

  • Trachea
  • Esiphagus
  • Thoracic duct
  • Left recurrent laryngeal nerve
  • Fibers of longus coli muscle
• Anterior mediastinum

  • Space in front of pericardium overlap by anterior border of lungs
  • Contents:
  • Sternopericardial ligament
  • Lymph nodes + lymphatics
  • Lower part of thymus
  • Small mediastinal branches of internal thoracic
  • Areolar tissue
• Middle mediastinum

  • Central portion, occupied by pericardium

  Contents:

  1. Heart + pericardium
  2. Ascending aorta, pulmonary trunk, 2 pulmonary arteries
  3. Lower half of superior vena cava, terminal part of azygous vein, left pulmonary vein
  4. Right + left Phrenic nerve, deep cardiac plexus
  5. Bifurcation of trachea, right + left principal bronchi

  
• Posterior mediastinum

  • Lies btw pericardium and lower 8 thoracic vertebral

  Contents:

  • esophagus
  • Descending aorta + branches
  • Azygous sytem of veins
  • Right + left thoracic sympathetic trunk
  • Thoracic duct
  • Vagus nerve
• Mediastinum scheme