Pulmonary Anatomy

Pulmonary Arterial Blood Supply

Lungs Have a Dual Arterial Blood Supply (Insights Imaging, 2020) [MEDLINE]

Pulmonary Arteries

  • Function
    • Pulmonary Arteries Predominantly Supply the Lung Parenchyma
  • Size/Pressure
    • Pulmonary Arteries are Larger Caliber than the Bronchial Arteries
    • Pulmonary Arteries are a Low-Pressure System
      • Consequently, Most Episodes of Hemoptysis Originate from the Pulmonary Arterial Circulation and are Not Life-Threatening
  • Anatomy
    • Pulmonary Arteries Originate from the Right Ventricle
  • Source of Hemoptysis (see Hemoptysis)
    • The Bronchial Arterial System is the Predominant Source of Hemoptysis in 90% of Cases of Massive Hemoptysis (Crit Care Med, 2000) [MEDLINE]
      • Other Sources Include
        • Pulmonary Arteries (5% of Cases)
        • Non-Bronchial Systemic Arteries (5% of Cases)

Bronchial Arteries

  • Function
    • Bronchial Arteries Predominantly Supply the Tracheobronchial Tree, Large Blood Vessels, Lymph Nodes, Esophagus, and Pleura (Radiographics, 2006) [MEDLINE]
      • The Bronchial Arterial Circulation Accounts for Only 2% of the Total Vascular Supply to the Lung
    • Bronchial Arteries are Very Plastic, Potentially Increasing Their Blood Flow from 1% to 30% of the Cardiac Output in Response to a Pulmonary Insult
      • Consequently, Bronchial Artery Hypertrophy and Dilatation of Thin-Walled Distal Bronchial-to-Pulmonary Artery Anastomoses May Occur
  • Size/Pressure
    • Bronchial Arteries Have a Smaller Caliber than the Pulmonary Arteries
      • On Contrast-Enhanced CT, They are Very Thin and Difficult to Detect
      • Normal Caliber of the Bronchial Arteries is <1.5 mm Near the Origin and <0.5 mm Distally, as They Branch in the Pulmonary Hila
      • When Bronchial Artery Hypertrophy Occurs, Their Diameter Can Exceed 2 mm, and They Tend to Have a More Tortuous Course
    • Bronchial Arteries are a High-Pressure System (Under Systemic Arterial Pressure)
  • Anatomy
    • Orthotopic Origin
      • The Bronchial Arteries Most Commonly Originate from the Descending Thoracic Aorta, Usually at the T5-T6 Vertebral Plane, 1–2 cm Above or Below the Level of the Carina
      • The Orthotopic Right Bronchial Artery Originates Preferentially from the Posteromedial Aortic Wall (Directly or or More Commonly from a Short Intercostal-Bronchial Trunk), Running Retrotracheally Towards the Hilum
      • The Orthotopic Left Bronchial Artery Originates Preferentially from the Anterior or Lateral Aortic Wall, Running Retrotracheally Towards the Hilum
      • Most Patients Have 1-2 Bronchial Arteries on Each Side and a Total of 3-4 Bronchial Arteries
    • Ectopic Origin
      • In Up to 36% of Cases, the Bronchial Arteries Ectopically Originate from Aortic Arch, Subclavian Artery, Thyrocervical Trunk, Internal Mammary Artery, or Coronary Arteries (J Thorac Imaging, 2003) [MEDLINE] (Eur Radiol, 2007) [MEDLINE]
        • Ectopic Bronchial Arteries are Recognized Due to Their Adjacent Course with the Associated Bronchi
    • Bronchial Arteries Have Distal Microvascular Anastomoses Connecting to the Pulmonary Arterial System (Chest, 1972) [MEDLINE]
  • Source of Hemoptysis
    • Despite the Bronchial Arteries Accounting for Only 2% of the Total Vascular Supply to the Lung, the Bronchial Arteries are the Predominant Source of Hemoptysis in 90% of Cases of Massive Hemoptysis (Crit Care Med, 2000) [MEDLINE]
      • Other Sources Include
        • Pulmonary Arteries (5% of Cases)
        • Non-Bronchial Systemic Arteries (5% of Cases)

Other Arteries

  • The Non-Bronchial Arterial Circulation (Aorta, Intercostal Arteries, Coronary Arteries, Thoracic Arteries, Axillary Arteries, Subclavian Arteries, Upper and Lower Inferior Phrenic Arteries) Can Supply the Lungs in <5% of Cases (Chest, 2008) [MEDLINE] (Respiration, 2010) [MEDLINE]
    • Many Chronic Inflammatory Lung Lesions are Jointly Supplied by Hypertrophied Bronchial Arteries, as Well as by Collateral Systemic Arteries

Pulmonary Venous Drainage

  • Bronchial Veins: uncommonly affected by pulmonary vasculitis
  • Pulmonary Veins: typically located in the intralobular septa

Respiratory Muscles

  • Diaphragm: innervated by C3–5
  • Inspiratory Accessory: external intercostals, scalene, and sternocleidomastoid muscles
  • Expiratory Accessory: internal intercostals and abdominal muscles


Definition of Airways

  • Conducting Airway: extends from the trachea to the terminal bronchioles
    • Functions to filter, humidify and heat air
  • Respiratory Airway: includes the respiratory bronchioles, alveolar ducts, and sacs
    • Site of gas exchange
  • Acinus: portion of lung supplied by a primary respiratory bronchiole

Cartilage Composition of Airways

  • Trachea: C-shaped cartilage with dorsal smooth muscle
  • Main Bronchi: semicircular cartilage
  • Bronchi: irregularly shaped cartilage plates
  • Bronchioles: no cartilage support, surrounded by muscular layer

Components of Alveolar-Capillary Surface

  • Surfactant
  • Alveolar Epithelium: type 1 and type 2 alveolar cells (the latter of which produces surfactant)
  • Interstitium
  • Endothelium

Influence of Particle Size on Airway Deposition

  • Particles 2–5 μm in Size: reach small airways
  • Particles 5–10 μm in Size: impact on the carina or main bronchi
  • Particles >10 μm: stopped in the upper airways

Lobar Anatomy (Frontal View of CXR)


Secondary Pulmonary Lobule

The Secondary Pulmonary Lobule is a Functional Unit of the Lung Surrounded by an Interlobular Septum (W.S. Miller [The lung. 2nd ed. Springfield, IL: Charles C Thomas, 1947]) (NEJM, 2020) [MEDLINE]

  • The Lobular Bronchiole and a Pulmonary Artery Branch Supply Multiple Acini within a Pulmonary Lobule
  • Lymphatics and Pulmonary Veins are Located within the Interlobular Septum
  • Lymphatics Also Surround the Bronchovascular Sheath

Ground-Glass Infiltrates Occur on the Chest CT Scan When Air within the Acini in the Pulmonary Lobule is Displaced by Any of the Following Four Mechanisms

  • Partial Alveolar Collapse (Atelectasis) (see Atelectasis)
    • Due to Obstruction, Compression, etc
  • Partial Alveolar Filling (Consolidation)
  • Interstitial Thickening
    • Due to Interstitial Lung Disease (ILD) (see Interstitial Lung Disease)
      • Thickened Interstitium
    • Due to Interstitial Pulmonary Edema (see Pulmonary Edema)
      • Lymphatic Engorgement by Fluid
    • Due to Lymphangitic Spread of Cancer (see Lung Cancer)
      • Lymphatic Engorgement by Tumor Cells
  • Increased Pulmonary Capillary Blood Flow


  • Miller WS. The lung. 2nd ed. Springfield, IL: Charles C Thomas, 1947
  • Evaluation of the bronchial arteries: normal findings, hypertrophy and embolization in patients with hemoptysis. Insights Imaging. 2020 May 19;11(1):70. doi: 10.1186/s13244-020-00877-4 [MEDLINE]
  • Case 25-2020: A 47-Year-Old Woman with a Lung Mass. N Engl J Med. 2020 Aug 13;383(7):665-674. doi: 10.1056/NEJMcpc2004977 [MEDLINE]