14- Lung Development

Question 1

“To understand the continuum of lung growth and development from conception to adulthood and the factors that interfere with normal development.

Answer 1

4-5 weeks gestation: tracheal bud emerges from foregut
16 weeks gestation: bronchial branching finishes, leading to pulmonary artery branching
8-10 years of age: alveolar development finishes

malformation is influenced more by the timing of an insult than its nature
- prematurity, birth weight, and smoking determine lung function the most through life

Question 2

“To understand how congenital lung defects arise.

Answer 2

an example of a congenital lung defect is cystic adenomatoid malformation, which leads to - disorganised and non-functional lung tissue

Question 3

“To be able to summarize the morphological and/or cellular events associated with the phases of intrauterine lung development.

Answer 3

0-7 weeks lung buds+ main bronchi (branching morphogenesis)
5-17 conducting airways (pseudoglandular)
18- 27 respiratory airways (canalicular)
28-40 alveoli appear (alveolar)

Question 4

“To understand the early life origins of susceptibility to lung disease.

Answer 4

the baby’s mother smokes while pregnant, it causes noticeably reduced lung function from birth. The airways’ radius is reduced, there are fewer alveolar attachments, and increased lymphocyte proliferation causing more inflammation in response to even the commonest allergens like house dust mites. This puts the baby at a higher risk of asthma and COPD later in life, as well as a 4x higher risk of wheezing as an infant.

Question 5

“To summarize the main aspects of lung growth and the evolution of lung function in the postnatal period.

Answer 5

X

Question 6

“To be able to give a brief account of the changes in the lungs and circulation that occur at birth to permit air breathing

Answer 6

Immediately:

• massive CNS stimulation
• low pressure placental circulation cut; causes a rise in systemic pressure
• lung aeration causes vasodilation: pulm. artery pressure falls, pO2 rises, pCO2 falls

Question 7

“To briefly describe the changes that occur at birth that facilitate the transition to air breathing. Comment particularly on the role and fate of lung liquid and the importance of pulmonary surfactant in stabilizing breathing.

Answer 7

first day: - blood flow to the lungs increases 5x

• chemoreceptors and respiratory centres ‘reset’
• lung volume rises to optimum and airway resistance falls (first 2 hours) - lung compliance rises (but takes at least 24 hours)

Hormonal stimulation is required for surfactant release from lamellar bodies in the epithelium.

Question 8

What can influence lung development

Answer 8

homeobox (HOX) genes

• transcription factors e.g. TGF-β stimulates fibroblasts to lay collagen
• peptide growth factors
• thoracic cage volume
• lung liquid pressure causing a trophic effect for growth down and outward into branches - amniotic fluid volume
• autonomic stimulation of smooth muscle contraction and relaxation around airways to
• direct development by changing pressures
• maternal nutrition e.g. vitamin A
• and maternal smoking…

Question 9

Describe IRDS

Answer 9

Infant Respiratory Distress Syndrome (IRDS):
- alveolar collapse
- alveolar hypoventilation
- hypoxia and acidosis
- pulmonary vasoconstriction (HPV) - shunting
- even less surfactant stimulation…
The baby is treated with oxygen, continuous positive airway pressure (CPAP) to help reinflate the alveoli, intravenous fluids for stability, and surfactant via the breathing tube

Question 10

What is primary ciliary dyskinesia

Answer 10

primary ciliary diskinesia (Kartagener’s syndrome), the ciliary motor protein dynein is missing so they can’t beat, no mucous clearance