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.
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- Transition to pulmonary arterioles when <100µm
- No muscular tissue (cf. systemic arterioles)
- Thin media of elastic tissue separated from blood by endothelium
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- Pulmonary capillaries form dense network around alveoli
- Caps have very thin walls which fuse with BM of alveolar epithelium
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- @ 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