16 Lung Development Flashcards
What happens during embryonic phase of lung development
0-7 weeks
Lung buds and main bronchi form
Branching into mesenchyma
What happens during pseudoglandular phase
5-17 weeks
Conducting airway - bronchi and bronchioli growth complete by 17th week
Development of smooth muscle cells, glands and cartilage
Significant growth of epithelial tips with significant communications: FGF/EGF VS TGFb/retinoic acid
What happens during lung development at 16-27th week
Canalicular phase Respiratory airway and alveoli growth Thinning of epithelium Differentiation of Type II cells into Type I Surfactant produced
What happens during saccular/alveoli phase
Development of alveoli which continue after birth
Describe the mechanism of alveolar walls
1) Saccule wall: epithelium and capillary network on both sides + elastin and myofibroblast
2) Secondary septa: development of wall led by elastin produced by myofibroblast. Capillary lines both sides and there is increase in matrix content
3) Capillaries coalesce to form one sheet of alveolar wall, thinner and longer with less matrix. Muscle and elastin still at tip
Describe the changes of blood vessels at birth
Decrease in pulmonary vascular resistance
10 fold increase in pulmonary flow
Pulmonary arterial wall thins to increase lumen diameter
Change in shape and cytoskeletal organisation but not loss of cells
Once thinning has occurred, arteries grow and maintain a relatively thin wall
What are the possible mechanism for the reduction in pulmonary resistance at birth
- Physical effect from the expansion of alveoli
- Expansion stimulates vasodilator molecules
- Expansion stimulates inhibitor of vasoconstrictor molecules
- Direct effect of oxygen on smooth muscle cells
What effect does the duration of childhood and adolescence have on airway grown
Increase airway length and diameter
Lung volume increases by 30 fold
Structural elements of the wall increases
What effect does childhood and adolescence have on alveolar growth
Increase number of alveoli
Increase surface area and complexity of alveoli
Arteries, veins and capillaries grow alongside
Name a defect associated with bronchial cartilage
Laryngomalacia - softening and collapsible causing airway obstruction
Complete ring - decrease in airway lumen and hence cause respiratory distress
Name a defect associated with ciliary beat dysfunction
Primary ciliary dyskinesia: cilia dynein arm mutation resulting in the absence of apical hook. This causes dysfunction in mucociliary movement and the patient is prone to infection
What are different levels of lung growth anomalies
Agenesis - complete absence of lung and vessel
Apoplasia - blind ending bronchus with no lung or vessel
Hypoplasia - bronchus and rudimentary lung are present but they are overall smaller in size
What correlates with:
Defect in pulmonary mesenchyma
Abnormal differentiation 5-7th weeks
Normal blood supply
Cystic pulmonary airway malformation (CPAM)
Describe the pathogenesis of congenital lobar emphysema/congenital large hyperlucent lobe (CLHL)
Progressive lobar expansion Underlying cause: 1. Weak cartilage 2. Extrathoracic compression 3. One way valve effect 4. Alveoli expand (not disrupted) Associated with CHD and more often in males
