Lung Development Flashcards
What are the 4 main phases of lung development
Embryonic phase
Pseudoglandular phase
Canalicular phase
Saccular/alveolar phase
When can gas exchange take place in lung development
From the canicular phase onwards
Describe the embryonic phase
0-7 weeks
Lungs buds
Formation of the main bronchi
Branching morphogenesis
Describe the pseudo glandular phase
5-17 weeks
Conducting airways formation
Bronchi and bronchioli
Pre-acinar airways (17 weeks)
Cartilage, glands and smooth muscle tissue development
Branching morphogenesis of airways -> mesenchyme
Describe the canalicular phase
15-27 weeks
Respiratory airways
Blood gas barrier development - thinning of the epithelium around capillaries
Differentiation into type I and II pneumocytes
Surfactant production (24 weeks)
Describe the saccular/alveolar phase
28-40 weeks
Alveogenesis and angiogenesis
What are the landmarks in lung development at the following times: 6 weeks, 16 weeks, 30 weeks, newborn, 3 year old
6 weeks - lobar airways
16 weeks - pre-acinar airways
30 weeks - respiratory airways present. alveoli seen
newborn - 1/3-1/2 alveolar number present
3 year old - most alveoli present
Describe vasculogenesis
Asymmetric
Occurs in the embryonic and pseudo glandular phase
What drives branching morphogenesis
Lung buds
Epithelial cells at the tips of the buds are highly proliferative
Cells behind the tip divide and differentiate
Communication between epithelial cells in distal branching lung buds and mesenchyme
What are the inductive growth factors
FGF - branching morphogenesis. subtypes found in the epithelium and mesenchyme
EGF - epithelial proliferation and differentiation
What are the inhibitory growth factors
TGFbeta - matrix synthesis, surfactant production, epithelium and blood vessel proliferation inhibition
retinoic aid - inhibits branching
Explain the process of vasculogenesis
Lung buds produce VEGF at the tip
Mesenchyme forms a matrix around the developing airway
They coalesce to form capillaries
Explain the process of alveolar wall formation
- Saccule wall formation. The epithelium on both sides with a double capillary network. Myofibroblast and elastin fibres at intervals along the wall
- Secondary septa. Elastin produced by myofibroblast leads development as the capillary lines both sides with matrix between
- Capillaries coalesce to form one sheet of alveolar wall, thinner and longer with less matrix. Muscle and elastin remain at the tip
What factor determines how prematurely a baby cam be born
Surfactant production
Describe the lungs at birth
Volume is small (Related to body weight) All airways are present and differentiated Less developed blood gas barrier less alveoli Most arteries and veins
What are the changes in the blood vessels at birth
Decrease in pulmonary vascular resistance -> increases blood flow 10x
Arterial lumen increases, wall thins -> growth
No loss of cells
Low pressure, Low resistance
What are the changes to the lungs in childhood and adolescence
Airways increase in length Alveoli increase in number (adults 300-600million) Alveoli become more complex Arteries and veins also increase
Describe primary ciliary dyskinesia
Autosomal recessive Cilia are completely stationary Dynein arms are absent (ATPase that helps motility move relative) Impedes on lung development No primary immune response Lower levels of nasal NO
Describe cartilage defects
Normally incomplete cartilage with irregular plates
They calcify with age
Can be malalic (floppy)
Describe malalic cartilage
Generalised - slowly with age e.g. laryngotracheomalcia
Localised - often occur due to other issues such as problems with the heart, Malacic segment which may occur due to external compression
What is laryngomalacia
epiglottis are omega shaped and the folds collapse into the airway and block it
What is agenesis
Complete absence of lung and vessel
Rare
Abnormal flow in the 4th week
Commonly associated with other pathology
Mediastinal shift towards an opaque hemithorax
What is aplasia
Blind ending bronchus, no lung or vessel
Describe hypoplasia
Everything is present, all elements are reduced in size and number
Common and usually secondary
Lack of space (intra/extrathoracic)
Lack of growth (congenital thoracic malformation)
Small lung volumes in post natal children - oligohydramnios (lack of fluid)
Describe congenital pulmonary airway malformation
Mostly antenatal
Defect in the mesenchyme
Abnormal differentiation
Normal blood supply
Describe type 2 congenital pulmonary airway malformation
Multiple small cysts
May be associated with renal agenesis, cardio defects, diaphragmatic hernia and syrgomyelia
What is congenital lobar emphysema
progressive lobar over expansion
Caused by weak cartilage, extrinsic compression, one way valve effect and alveolar expansion
males>females
What is intralobar sequestration
Abnormal segments share visceral pleura
No communication to the tracheobronchial tree
Due to chronic bronchial obstruction and chronic post obstructive pneumonia
What is scimitar syndrome
Dextrocardia - heart switches to the opposite direction
Anomalous pulmonary venous drainage of the right lung to the IVC
associated with hypoplasia of the right vein and lung
