Thorax

• Superior boundaries of the thorax

  Manubrium, first rib, first thoracic vertebra
• Inferior boundaries of the thorax

  Xiphoid process, subcostal arch, 11th and 12th ribs, 12th vertebra, diaphragm
• Anterior boundaries of the thorax

  Sternum and ribs
• Lateral boundaries of the thorax

  Ribs and intercostal muscles
• Posterior boundaries of the thorax

  Thoracic vertebrae and discs
• Thorax is divided into

  2 pleura and 1 mediastinum
• Pleura


  • Provide the lungs with low friction
• Parietal pleura


  Lines the body wall, continuous with visceral pleura which lines the lung tissue, filled with pleural fluid
• Damaged pleura


  Results in pneumothorax, a collection of air in the parietal cavity leading to collapse of lung tissue
• Mediastinum

  Divided into superior and inferior by the sternal angle to T4 vertebra
• Inferior mediastinum


  Divided into anterior, middle, and posterior
• Pectoralis major


  Attaches to the clavicle, sternum, costal cartilages and humerus, innervated by the medial and lateral pectoral nerves
• Pectoralis minor


  Attaches to the coracoid process and ribs 3-5, innervated by the medial pectoral nerve
• Serratus anterior


  Attaches to ribs 1-9, intercostal fascia, and the medial border of the scapula, innervated by the long thoracic nerve
• Rectus abdominis


  Attaches to the costal cartilages of ribs 5-7, the xiphoid process and pubic bones, innervated by the anterior rami of T7-T12 spinal nerves
• Interbody joints of the vertebral column


  Cartilaginous for stability
• Costovertebral joints of the ribs and vertebrae

  Synovial for mobility
• Costotransverse joints of the ribs and vertebrae

  Synovial for mobility
• Sternochondral/sternocostal joint

  Between the sternum and cartilages, synovial joint except for between the sternum and the first rib which is a cartilaginous joint
• Costochondral joint


  Between the ribs and their cartilages, cartilaginous joint
• Interchondral joints


  Between the costal cartilages of ribs 6-9, synovial joints
• Synovial joints of the thoracic cage allow movement during respiration
• External intercostals

  Have an anterior inferior fibre direction and contract to lift the thoracic cage during inspiration
• Internal and innermost intercostals

  Have a posterior inferior fibre direction and contract to lower the thoracic cage during forced expiration
• Intercostal nerves


  Accompany blood vessels between the internal and innermost intercostal muscles, run off of the ventral ramus of the spinal nerves, supply the intercostal muscles, skin and parietal pleura
• Anterior blood flow

  Subclavian artery, internal thoracic arteries, anterior intercostal arteries
• Posterior blood flow

  Thoracic aorta, posterior intercostal arteries
• Anterior blood drainage

  Anterior intercostal veins, internal thoracic vein, brachiocephalic vein
• Posterior blood drainage


  Right posterior intercostal veins into azygos vein, 9th-11th left posterior intercostal veins into hemiazygos vein, 1st-8th left posterior intercostal veins into accessory hemiazygos vein, all into azygos vein and superior vena cava
• Endothoracic fascia


  Connective tissue layer with some adipose, lines the inner wall of the thorax and above the diaphragm
• From superficial to deep in the thoracic wall

  • Skin
  • Superficial fascia
  • Deep fascia
  • Pectoralis major
  • Serratus anterior
  • Rib/external intercostals
  • Internal intercostals
  • Nerves and vessels
  • Innermost intercostals
  • Endothoracic fascia
  • Parietal pleura
  • Pleural cavity
  • Visceral pleura
• Diaphragm


  Separates the thorax from the abdomen, has radiating muscle fibres and a central tendon, dome shaped when relaxed and flat when contracted, attaches to the sternum, ribs, and lumbar vertebrae, innervated by the phrenic nerve and supplied by the internal thoracic artery and vein, has 3 apertures for the aorta/thoracic duct/azygous vein (T12), inferior vena cava (T8), and oesophagus and vagus nerves (T10)
• Inspiration


  External intercostal muscles contract allowing rib cage to rise and expand, diaphragm flattens, increases thoracic cavity causing lungs to stretch, lung pressure to increase, intrapulmonary pressure to decrease so air flows in
• Expiration


  External intercostal muscles relax allowing rib cage to fall and depress, diaphragm returns to dome shape, decreases thoracic cavity causing lungs to recoil, lung pressure to decrease, intrapulmonary pressure to increase so air flows out
• Pleural cavity

  Filled with serous fluid, provides a friction free environment to move the lungs without pain
• Negative intrapleural pressure holds the parietal and visceral pleura together causing any movement of the thoracic pressure to stretch the lungs
• Lungs

  Cone shaped and asymmetrical, apex is superior tip just deep to the clavicle, base is concave and sits on the diaphragm, left lung has a medial impression called the cardiac notch
• Root of the lung


  Where structures enter and exit the lung, including pulmonary arteries, pulmonary veins and pulmonary bronchi, covered by the pulmonary ligament
• Hilum of the lung


  Depression on the medial surface, where the lung root is located
• Right lung

  Has a superior, middle and inferior lobe, has an oblique and horizontal fissure