Lung development

Question 1

1. When does the tracheal bud develop from the foregut?

Answer 1

4-5 weeks

Question 2

2. By what point is bronchial branching complete?

Answer 2

16 weeks

Question 3

3. What is a hypoplastic lung?

Answer 3

Interruption to bronchial branching leads to development of a small lung with little branching.

Question 4

4. What can insults to the dividing bronchus cause?

Answer 4

Agenesis (early malfunction)
Local lesion
Malformation of systemic supply
Malformation in the lung leading to normal blood supply to an abnormal lung

Question 5

5. State some factors that influence lung development.

Answer 5

Hox genes  
Thoracic cage volume 
Amniotic fluid volume 
Transcription factors 
Peptide growth factors 
Maternal nutrition e.g. Vitamin A

Question 6

6. What is the only complete cartilage ring around the trachea?

Answer 6

Cricoid cartilage

Question 7

7. How many generations of branching occur during pre-natal development of the airways?

Answer 7

25

Question 8

8. What are the three stages of prenatal development of the airways?

Answer 8

Glandular
Canalicular
Alveolar

Question 9

9. Describe the effects of smoking during pregnancy on airway development.

Answer 9

Reduces elasticity of alveoli and reduces airway diameter

This leads to a wheezy infant with increased risk of COPD in later life

Question 10

10. What percentage of the foetal blood reaches the lungs?

Answer 10

10%

Question 11

11. State two differences between foetal blood and adult blood.

Answer 11

Foetal pH = 7.2 (normal = 7.4)

Foetal pO2 = 3.4 kPa (normal = 10 kPa)

Question 12

12. What changes occur at birth?

Answer 12

Changes in prostaglandins causes the closing of the ductus arteriosus
Increase in left atrial pressure closes the foramen ovale
Systemic pressure increases and becomes greater than pulmonary pressure
There is massive CNS stimulation due to a change in environment
Placental circulation is cut
Lung aeration causes fall in pulmonary arterial pressure (as lungs stretch)
Increase in PO2 + decrease in PCO2

Question 13

13. What happens in the first day post birth?

Answer 13

Pulmonary vasodilation increases 5 fold thus increasing pulmonary blood flow
Aeration of the lungs and the lung volume increases to optimum
Within the first 2 hours resistance falls
Lung compliance rise takes around 24 hours - lymphatics is relied upon to remove the fluid from the lungs
PO2 increases, PCO2 decreases –> pH increases

Question 14

14. How can the foetus cope with the low PO2?

Answer 14

Foetal haemoglobin has a higher affinity for oxygen than adult haemoglobin

Question 15

15. Describe the two failures of breathing that could happen during birth?

Answer 15

Primary apnoea - attempted breathing occurs at birth. With umbilical strangulation, the gasp fails.
Terminal apnoea - second attempt at breathing (with failure of successful ventilation) results in a DECREASED BLOOD PRESSURE. Heart rate is relatively maintained.

Question 16

16. What scale is used to determine the severity of the apnoea and the need for resuscitation?

Answer 16

Apgar scale

Question 17

17. What produces surfactant in a foetus?

Answer 17

Lamellar Bodies in Type II Pneumocytes

Question 18

18. What does surfactant do?

Answer 18

Creates a force resulting in the distension and maintenance of distension of the airways at lower pressures so the airways remain open

Question 19

19. When is surfactant produced during pregnancy?

Answer 19

Late 2nd trimester, early 3rd trimester

Question 20

20. What can a lack of surfactant cause and what is this called?

Answer 20

Increased risk of alveolar collapse –> hypoventilation + hypoxic acidosis –> pulmonary vasoconstriction + right to left shunting
Idiopathic respiratory distress syndrome

Question 21

21. What is another name for primary ciliary dyskinesia?

Answer 21

Kartagener’s syndrome

Question 22

22. How does elasticity and compliance change with age?

Answer 22

Elasticity and compliance decrease