Structure Of Lower Respiratory Tract Flashcards
Main function of lungs
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)
Trachea
mobile cartilaginous and membranous tube
• larynx to carina (5th thoracic vertebra T5)
• Oval in cross section
• Pseudostratified, ciliated, columnar epithelium
• Goblet cells
• Semicircular hyaline cartilages keep tube open- posterior free ends of cartilage connected by trachealis muscle
• Mobile (3cm and 1cm, superior and inferior)
Blood supply to trachea
Upper 2/3 supplied by inferior thyroid arteries and lower 1/3 supplied by bronchial arteries
Lymphatic drainage of trachea
Lymph drains into the pretracheal and paratracheal lymph nodes and deep cervical nodes
Innervation of trachea
Sensory nerve supply from vagi and recurrent laryngeal nerves
• Sympathetic nerves supply trachealis muscle
Movement of carina
During expiration, the bifurcation rises by about one vertebral level, and during deep inspiration may be lowered as far as the 6th thoracic vertebra.
Main bronchi
left and right main bronchi
• carina- sharp division between bronchi
• Right main bronchus more vertically disposed- 1-2.5cm long, related to right pulmonary artery
• Left main bronchus- 5cm long, related to aortic arch
Lobar bronchi
right- upper, middle, lower lobe
• Left- upper (and lingular), lower lobe
Segmental bronchi
10 per lung which each supply a segment
right:
• upper lobe- apical, anterior and posterior
• Middle lobe- medial and lateral
• Lower lobe- apical, anterior, posterior, medial and lateral
Left:
• upper lobe- apico-posterior and anterior
• Lingular- superior and inferior
• Lower lobe - apical, anterior, posterior an lateral
Bronchopulmonary segment
It is a subdivision of a lung lobe.
• It is pyramid shaped, with its apex toward the lung root.
• It is surrounded by connective tissue.
• It has a segmental bronchus, a segmental artery, lymph vessels, and autonomic nerves.
• The segmental vein lies in the connective tissue between adjacent bronchopulmonary segments.
• Because it is a structural unit, a diseased segment can be removed surgically.
Order of bronchi
Main bronchi → lobar bronchi → segmental branches → respiratory bronchioles → terminal bronchioles →alveolar ducts and alveoli
Bronchioles
no cartilage in their walls and are lined with columnar ciliated epithelium.
• The submucosa possesses a complete layer of circularly arranged smooth muscle fibres
• The bronchioles then divide and give rise to terminal bronchioles- which show delicate outpouchings from their walls- Gaseous exchange between blood and air
• diameter of a respiratory bronchiole is about 0.5 mm.
• The respiratory bronchioles end by branching into alveolar ducts, which lead into tubular passages with numerous thin-walled outpouchings called alveolar sacs
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)
Pores of Kohn
Interconnection between alveoli
Alveoli
• type I pneumocytes- pavement
• type II pneumocytes- surfactant producers
• Alveolar macrophage
• Basement membrane
• Interstitial tissue
• capillary endothelial cells
Oxygenation
- Alveolar epithelium
- Tissue interstitium
- Capillary endothelium
- Plasma layer
- Red cell membrane
- Red cell cytoplasm
- Hb binding forces
How much alveolar ducts do each respiratory bronchiole divide into to
2 to 11
Pleura
2 main layers of mesodermal origin
1. Visceral- applied to the lung surface
2. 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 of lower respiratory tract
bronchial and pulmonary circulations
Pulmonary circulation
left and right pulmonary arteries run from right ventricle
• 17 orders of branching
• Elastic (>1mm) and non-elastic
• Muscular (<1mm)
• Arterioles (<0.1mm)
• Capillaries
Segments in right upper lobe
Apical, anterior and posterior
Segments in right middle lobe
Medial and lateral
Segments in right lower lobe
Apical, anterior, posterior, medial and lateral
Segments in left upper lobe
Apico-posterior and anterior
Segments in left lingular
Superior and inferior
Segments in left lower lobe
Apical, anterior, posterior and lateral
Venous drainage of lower respiratory tract
Bronchial veins
What do goblet cells secrete
Mucus
Which cells secrete surfactant
Type II pneumocytes
How many cell layers in air:blood barrier
2:
Type I pneumocytes
Vascular endothelium
Thickness of air:blood barrier
600 nm
Pores of Kohn
Holes in alveolar walls
Allow for equal inflation of the lungs
Enable macrophage movement
But allow infection to spread quickly
Acinus
composed of respiratory bronchioles, alveolar ducts, and alveolar sacs. It is roughly spherical, resembling a bunch of grapes. Each respiratory bronchiole gives rise to several alveolar ducts and alveolar sacs, giving it the characteristic grape bunch appearance
Thickness of blood:air barrier
200nm - 1um
% of cell population that are type 1 pneumocytes
40%
% of cell population that are type 2 pneumocytes
60%
% of surface area that is type 1 pneumocytes
90%
% of surface area that is type 2 pneumocytes
10%
