T2 L1: Pleura and the lungs

• What is the mediastinum?

  central compartment that contains oesophagus, thoracic aorta, great vessels etc.

  
• How does the embryological development of the respiratory system occur?

  begins at 4-6 weeks → gut tube → lung bud → 2 bronchial buds (endodermal origin; covered in splanchnic mesoderm) → where gut tube meets lung bud: laryngeal inlet → rapid division → form secondary and tertiary bronchi → division continues until fully formed

  
• How do the developing lungs in the embryo locate themselves in the thorax?

  the lungs push their way out into the primitive thoracic cavity

  As they do they take the lining with them (visceral pleura) to meet the lining of the body wall (parietal pleura)
• What are the embryological origins of different components of the respiratory system?

  endoderm - visceral pleura

  mesoderm - smooth muscle, connective tissue, vessels
• Visceral pleura lines the developing lungs and parietal pleura lines the body wall.
• How are the pleural relationships during lung development?

  visceral and parietal pleura do not touch → week 4 → lungs start to develop → still no touching; between them is 'primitive thoracic cavity' → week 6 → rapid growth of lungs; occupy most space → layers of pleura now closer together → between them is 'pleural cavity' → in adult, becomes 'potential space'

  
• Where do the two layers of pleura meet?

  hilum
• What does parietal pleura line?

  body wall
• What does visceral pleura line?

  lungs, enters fissures of lung

  
• What is the pulmonary ligament?

  Extension

  allows free movement of the structures passing through the hilum with the movement of the lung (superiorly and inferiorly)

  
• What are the 4 parts of the parietal pleura?

  costal: internal rib cage

  mediastinal: lateral wall of mediastinum

  diaphragmatic: superior diaphragm

  cervical: cervical region

  
• What is visceral pleura innervated by?

  autonomic innervation
• What is parietal pleura innervated by?

  somatic innervation

  sensitive to pain (hence inflammation of pleura very painful)
• What nerves are the different parts of the parietal pleura innervated by?

  Cervical: 1st intercostal nerve

  Costal: intercostal nerves

  Mediastinal: Phrenic nerve

  Diaphragmatic: lower intercostals and phrenic nerves
• What is the travelling route of Phrenic nerve?

  travel alongside mediastinal part of parietal pleura (innervating) → over pericardium → innervate diaphragm and diaphragmatic part of parietal pleura

  
• What is the pleural cavity?

  a potential space

  contains a thin layer of serous pleural fluid that creates surface tension

  also lubricates
• What is the relationship between surface tension and pneumo/haemothorax?

  surface tension between pleural layers is lost
• What are the 2 recesses in the pleural cavity?

  Costodiaphragmatic recess – behind the dome of the diaphragm

  Costomediastinal recess – beside the lung

  During passive respiration the pleural recesses aren’t occupied but these recesses can be occupied by lung during forced inspiration

  Recesses are also a site where fluid likely to collect

  
• What are the lobes and fissures of the right lung?

  lobes: superior, middle, inferior

  fissures: oblique, horizontal

  
• What are the lobes and fissures of the left lung?

  lobes: superior, inferior

  fissures: oblique

  
• What are the surfaces and the borders of the lungs?

  Surfaces: costal, mediastinal, diaphragmatic

  Borders: anterior, inferior and posterior (anterior better defined than posterior)

  
• What does the hilum of the lungs contain?

  Pulmonary arteries

  Pulmonary veins

  Bronchial arteries and veins – supply the lungs with blood and return venous blood back to venous system

  Pulmonary plexus – autonomic nerves

  Lymph nodes – can often be seen as blackened spots at hilum

  
• How is the bronchial circulation arranged?

  Bronchial arteries supply oxygen/nutrients to lung and visceral pleura

  • Left bronchial arteries branch from descending aorta.
  • Right bronchial arteries branch from intercostal arteries

  Bronchial veins terminate in the azygos system of veins

  
• How is the innervation of the lungs?

  Sympathetic – from sympathetic trunk

  Parasympathetic – from vagus

  both via pulmonary plexus

  
• How does lymphatic drainage occur?

  hilum → bronchopulmonary (hilar) nodes → tracheobronchial nodes. Either to:

  • paratracheal nodes → thoracic duct → left / right venous angle
  • bronchomediastinal trunk → venous angle
• How does the trachea run?

  from C6 to T4/5 (transverse thoracic plane)

  
• What are the parts of the respiratory tree?

  trachea → carina → primary bronchi (main) → secondary bronchi (lobar) → tertiary bronchi (segmental) → bronchioles (non-respiratory / respiratory) → alveolar sacs → alveoli

  
• What are the parts of the trachea and what are their functions?

  Anteriorly: c-shaped cartilage rings. Holds airways open

  Posteriorly: trachealis muscle. allows flexibility for movement of bolus of food

  
• What are the differences between the primary bronchi?

  Right primary bronchus is:

  • wider
  • shorter
  • runs more vertically

  both primary bronchi contain cartilage

  
• What are secondary bronchi?

  supply one lobe each

  hence:

  • right lung: 3 secondary bronchi
  • left lung: 2 secondary bronchi

  
• What are tertiary bronchi?

  Each Tertiary bronchus supplies a bronchopulmonary segment

  • right lung: 10 tertiary bronchi
  • left lung: 8-10 tertiary bronchi

  
• What are bronchopulmonary segments?

  Each bronchopulmonary segment is:

  • Supplied by a single tertiary bronchus
  • Receives a single branch of the pulmonary artery
  • Separated by connective tissue
  • Can be surgically resected

  
• What is the difference between conducting non-respiratory bronchioles and respiratory bronchioles?

  conducting bronchioles: no cartilage in walls (conducting zone)

  Respiratory bronchioles: have alveoli (respiratory zone)

  
• What is a terminal bronchiole?

  last non-respiratory bronchiole

  terminal bronchiole → respiratory bronchiole → alveolar duct and sacs