F1iii: Outline the anatomy of pulmonary and bronchial circulations

Pulmonary Circulation

  • Pulmonary trunk from RV
  • Branches into L & R Pas
  • Pass posteriorly to main bronchi
  • Further bronchi to lungs
  • Each bronchopulmonary segment has their own artery
  • Media of PAs only half as thick as Systemic A.

  • Transition to pulmonary arterioles when <100µm
  • No muscular tissue (cf. systemic arterioles)
  • Thin media of elastic tissue separated from blood by endothelium

  • Pulmonary capillaries form dense network around alveoli
  • Caps have very thin walls which fuse with BM of alveolar epithelium

  • @ rest, 75% capillary bed is filled with blood but % of congregation is higher in dependent parts of lung
  • One capillary network is not confined to one alveolus, but passes from one alveolus to another, crossing many for efficient gas exchange before reaching a venule
  • Pulmonary blood is collected by venules
  • Eventually draining into 4 pulmonary veins, one from each lung, into LA

Bronchial Circulation

  • Bronchial arteries arise from systemic circulation
  • Come off Thoracic Aorta
  • They follow bronchi and form a capillary plexus, supplying its muscle coat & mucosa
  • Importantly provides heat for warming & humidifying inspired air
  • It only runs up until the Resp Bronchioles, wherein there it anastomoses with pulm vessels
  • The bronchial veins drain bronchi of lung & join pulmonary veins (50%), the remaining 50% drain into IVC → constituting PHYSIOLOGICAL SHUNT