All you need to know about
the lungs
Dr David Lacy
A little about me…
• Consultant General Paediatrician with a respiratory
interest at Arrowe Park Hospital
• Trained in respiratory paediatrics in Birmingham and
Liverpool
• Been a consultant for 14 years
• Arrowe Park Hospital is a DGH for the Wirral
• Total population 320,000 of whom 60,000 are
children. Births per year 3200.
• Have speciallist clinics in asthma, cystic fibrosis,
chronic lung disease (of prematurity) and allergy.
Cases of diffuse lung disease
that I have seen
• Currently look after 28 children with Cystic
fibrosis
• Currently 10 patients with non CF
bronchiectasis
• Currently 5 patients with bronchiolitis
obliterans (10-12 in total)
• 3 patients with ILD (one of whom has
moved away)
• 1 patient with primary ciliary dyskinesia
Overview
• Embryology
• Lung development:
Prenatal
Postnatal
• Lung structure
• Alveolar cells and pulmonary
surfactant
• Investigations, X-rays and CT scans
• Pathogenesis
0-6 wk
Embryonic
6-16 wk
Pseudo
glandular
16-24 wk
Canalicular
24-40 wk
Saccular
36 wk – 2yr
Alveolar
Embryonic
• 4th week: lung bud oesophagus
• 6th week: lobar & segmental
airways
NB Tracheo-oesophageal fistula
can occurr at this stage
Lung and gut development closely
linked
Pseudoglandular: 6-16 weeks
• Conducting airways complete by
wk16
• 20 generations (branches) to
acinus (very simple air sac)
• Blood supply starts to form
• Cells become speciallised
Canalicular: 16-24 weeks
• Acinus appears (buds)
(respiratory zone)
•
multiplication of capillaries
• Alveolar cells become
speciallised
Saccular: 24-40 weeks
• Terminal air sacs form
• True alveoli 32wks onwards
• Complex capillary network forms
• Thinning of blood-air barrier
Postnatal lung
development
• Alveolar period
36/40 – 2 years
• At birth simple alveoli present
•
85% alveoli develop after birth
• Alveolar cell Type I
• Alveolar cell Type II
Postnatal lung
development
• Alveolar period
36/40 – 2 years
• 5 million at birth
• 300 million at 2
years
Premature birth
• Alveoli units not fully developed
• Air-blood barrier thick → inefficient gas exchange
• <32wks
no true alveoli
immature surfactant system (alveolar collapse)
underdeveloped surface area gas exchange
chest wall very soft - recession
Gross Anatomy of the Lungs
Left upper Lobe
Cardiac Notch
Left Lower
Lobe
Alveolar cells
• Type I
o 95% of alveolar surface
o Long and thin- ideal for gas exchange
• Type II
o More numerous but only 5% on surface
o Large cuboidal cells with microvilli
o Surfactant production
Pulmonary Surfactant
• Pulmonary surfactant forms a thin fatty layer
that coats the airways of the lung and is essential
for proper inflation and function of the lung.
• Pulmonary surfactant is composed of 90%
phospholipid (special fat substance) and 10%
protein
• Surfactant is produced by alveolar type II cells,
stored inside special structures called lamellar
bodies, and actively secreted in the alveoli.
• Upto 10% of children with ILD have now been
found to have a surfactant deficiency due to
mutations of surfactant B, C or ABCA3
Surfactant Proteins
Proteins constitute approx 10% of Surfactant
• A Involved in host immune response*
• B Required for spreading and stability of
surfactant film
• C Required for spreading and stability of
surfactant film
• D Involved in host immune response*
* Fighting infection
ABCA3
• Full name is ATP-binding cassette transporter A3
• It is in alveolar type II cells.
• It transports lipids (fats) to the lamellar bodies
(special unit within the cell) where the fats are used
to assemble surfactant and then the surfactant is
transported to the cell surface.
• Mutations of the gene that code for this protein can
occur.
• If a baby has two faulty copies (one from each
parent) this results in insufficient surfactant
production and ILD.
Investigations
• CXR
• CT scan
• Bronchoscopy
• Biopsy
• Genetic tests
Pathogenesis of ILD
• Damage to the alveoli
o Persistent inflammation
o Disordered repair of damage cellsleading to fibrosis*
o Disordered cell function and growth
*ILD is sometimes called Fibrosing alveolitis.
Interstitium refers to the tissues around the
alveoli.
Conclusions
• Lung disease can effect the airways, the
alveoli, or the surrounding structures (called
the interstitium)
• Lungs grow in 3 phases
o Early prenatal development
o Birth -2years increase in number of alveoli
o 2 years to adulthood- growth in size of alveoli
• Surfactant is produced in type II alveolar
cells and without surfactant the alveoli
collapse and cannot function properly