The structure of the lower respiratory tract David Fishwick Consultant Respiratory Physician Honorary Professor of Respiratory Medicine University of Sheffield d.fishwick@sheffield.ac.uk

Main functions Gas exchange 20m2 gas exchange area per lung Minute ventilation approx 5 litres Cardiac output approx 5 litres per minute Regional differences in ventilation and perfusion (blood supply)

Thoracic cage

Lower respiratory structure Main Airways Trachea Main Bronchi Lobar Bronchi Segmental branches Respiratory Bronchiole Terminal Bronchiole Alveolar Ducts and Alveoli Pleura

Lower respiratory structure Main Airways Trachea Main Bronchi Lobar Bronchi Segmental branches Respiratory Bronchiole Terminal Bronchiole Alveolar Ducts and Alveoli Pleura

Trachea Larynx to carina (5th thoracic vertebra, T5) Oval in cross section Pseudo stratified, ciliated, columnar epithelium Goblet cells Semicircular cartilages Mobile (3 cm and 1cm, superior and inferior)

Lower respiratory structure Main Airways Trachea Main Bronchi Lobar Bronchi Segmental branches Respiratory Bronchiole Terminal Bronchiole Alveolar Ducts and Alveoli Pleura

Main bronchi Left and Right main bronchi Sharp division between these The carina R main bronchus more vertically disposed 1-2.5cm long, related to the R pulmonary artery L main bronchus 5cm long, related to the aortic arch

Lower respiratory structure Main Airways Trachea Main Bronchi Lobar Bronchi Segmental branches Respiratory Bronchiole Terminal Bronchiole Alveolar Ducts and Alveoli Pleura

Lobar bronchi Lobar Bronchi (normal) Right Left Upper lobe Middle lobe Lower lobe Left Upper lobe and lingular

Lower respiratory structure Main Airways Trachea Main Bronchi Lobar Bronchi Segmental branches Respiratory Bronchiole Terminal Bronchiole Alveolar Ducts and Alveoli Pleura

Segmental branches Segmental Bronchi Right Upper lobe Apical, Anterior, Posterior Middle lobe Medial and Lateral Lower lobe Apical, Ant, Post, Med, Lat

Segmental branches Segmental Bronchi Left Upper lobe Apico-posterior, Anterior Lingular Superior and Inferior Lower lobe Apical, Ant, Post, Lat

Segmental branches Segmental Bronchi Right Upper lobe Apical, Anterior, Posterior Middle lobe Medial and Lateral Lower lobe Apical, Ant, Post, Med, Lat

Segmental branches Segmental Bronchi Right Upper lobe Apical, Anterior, Posterior Middle lobe Medial and Lateral Lower lobe Apical, Ant, Post, Med, Lat

Segmental branches Segmental Bronchi Right Upper lobe Apical, Anterior, Posterior Middle lobe Medial and Lateral Lower lobe Apical, Ant, Post, Med, Lat

Lower respiratory structure Main Airways Trachea Main Bronchi Lobar Bronchi Segmental branches Respiratory Bronchiole Terminal Bronchiole Alveolar Ducts and Alveoli Pleura

Bronchioles

Acinus Distal to the terminal bronchiole Alveoli more profuse with increasing generation of subdivision Ducts are short tubes with multiple alveoli Interconnection between alveoli exist (pores of Kohn)

Alveoli Type I pneumocytes Pavement Type II pneumocytes Surfactant producers Alveolar macrophage Basement membrane Interstitial tissue Capillary endothelial cells

Lung Innervation Controls many aspects of function Smooth muscle tone, mucus gland secretion, vascular permeability, blood flow Sympathetic BRONCHODILATION Parasympathetic BRONCHOCONSTRICTION NANC

The Lung Structure Main Airways Pleura Trachea Main Bronci Lobar Bronchi Segmental branches Respiratory Bronchiole Terminal Bronchiole Alveolar Ducts and Alveoli Pleura

Pleura 2 main layers, of mesodermal origin Visceral Applied to the lung surface Parietal Applied to the internal chest wall Each a single cell layer Small amount of fluid between Continuous with each other at lung root Parietal pleura has pain sensation Visceral pleura has only autonomic innervation

Blood supply Bronchial and pulmonary circulations L and R pulmonary arteries run from R ventricle 17 orders of branching Elastic (>1mm ) and non elastic Muscular (<1mm ) Arterioles (<0.1mm ) Capillaries