Structure Of The Lower Respiratory Tract

Question 1

What is the main function of the lower respiratory tract?

Answer 1

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)

Question 2

What is the structure of the lower respiratory structure?

Answer 2

Main Airways
- Trachea
- Main Bronchi
- Lobar Bronchi
- Segmental branches
- Respiratory Bronchiole
- Terminal Bronchiole
- Alveolar Ducts and Alveoli

Pleura

Question 3

What is the trachea?

Answer 3

Found from the 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)

Question 4

What are the Main Bronchi?

Answer 4

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

Question 5

What is the Lobar Bronchi?

Answer 5

Lobar Bronchi (normal)
- Right
Upper lobe
Middle lobe
Lower lobe

• Left
  Upper lobe and lingula
  Lower lobe

Question 6

What is the Segmental Bronchi?

Answer 6

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

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

Question 7

What is the Acinus?

Answer 7

• 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)

Question 8

What is the Alveoli?

Answer 8

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

Question 9

What is the Pleura?

Answer 9

• 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

Question 10

Explain the blood supply in the Lower Respiratory Tract?

Answer 10

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

Question 11

Explain oxygenation in the Lower Respiratory Tract

Answer 11

Alveolar epithelium
Tissue interstitium
Capillary endothelium
Plasma layer
Red cell membrane
Red cell cytoplasm
Hb binding forces