All you need to know All you need to know about the lungsabout the lungs

Dr David Lacy

A little about me…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 Cases of diffuse lung disease that I have seendisease 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 Overview • Embryology • Lung development:

PrenatalPostnatal

• Lung structure• Alveolar cells and pulmonary

surfactant• Investigations, X-rays and CT scans• Pathogenesis

0-6 wk 6-16 wk 16-24 wk 24-40wk 36 wk – 2yr Embryonic Pseudo Canalicular

Saccular Alveolarglandular

EmbryonicEmbryonic

• 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 Pseudoglandular: 6-16 weeksweeks

• 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 Canalicular: 16-24 weeksweeks• Acinus appears (buds)

(respiratory zone)

• multiplication of capillaries

• Alveolar cells become speciallised

Saccular: 24-40 weeksSaccular: 24-40 weeks• Terminal air sacs form

• True alveoli 32wks onwards

• Complex capillary network forms

• Thinning of blood-air barrier

Postnatal lung Postnatal lung developmentdevelopment

• Alveolar period36/40 – 2 years

• At birth simple alveoli present

• 85% alveoli develop after birth

• Alveolar cell Type I

• Alveolar cell Type II

Postnatal lung Postnatal lung

developmentdevelopment

• Alveolar period36/40 – 2 years

• 5 million at birth• 300 million at 2

years

Premature birthPremature birth• Alveoli units not fully developed• Air-blood barrier thick → inefficient gas exchange

• <32wksno true alveoliimmature surfactant system (alveolar

collapse)underdeveloped surface area gas exchangechest wall very soft - recession

Gross Anatomy of the LungsGross Anatomy of the Lungs

Cardiac Notch

Left Lower Lobe

Left upper Lobe

Alveolar cellsAlveolar cells

• Type Io 95% of alveolar surfaceo Long and thin- ideal for gas exchange

• Type IIoMore numerous but only 5% on surfaceo Large cuboidal cells with microvillio Surfactant production

Pulmonary SurfactantPulmonary 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 ProteinsSurfactant ProteinsProteins 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

ABCA3ABCA3• 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.

InvestigationsInvestigations• CXR• CT scan• Bronchoscopy• Biopsy•Genetic tests

Pathogenesis of ILDPathogenesis of ILD• Damage to the alveolioPersistent inflammationoDisordered repair of damage cells-

leading to fibrosis*oDisordered cell function and growth

*ILD is sometimes called Fibrosing alveolitis. Interstitium refers to the tissues around the

alveoli.

ConclusionsConclusions• Lung disease can effect the airways, the

alveoli, or the surrounding structures (called the interstitium)

• Lungs grow in 3 phaseso Early prenatal developmento Birth -2years increase in number of alveolio 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