Prematurity and pre-natal medicine Flashcards
How much of the respiratory system has developed by weeks 5-6 of gestation?
- Mainstem bronchi
- Secondary bronchi
- Development of caudal growth
- Tertiary bronchi
When is the pseudoglandular period?
6 - 16 weeks
What occurs during the pseudoglandular period?
14 generations of branching terminal bronchioles formed
NO respiratory bronchioles
Co-branching of pulmonary arteries
When is the canilicular period?
16 - 26 weeks
What occurs during the canilicular period?
- Terminal bronchioles divide into respiratory bronchioles
2. Alveolar ducts
When is the saccular period?
28 - 36 weeks
What occurs during the saccular period?
- Terminal sacs form
2. Capillaries in close contact with primitive alveoli
What do the terminal sacs give rise to?
Alveoli
When is the alveolar period?
8 months to childhood
What occurs during the alveolar period?
Maturation of alveoli
How many terminal sacs are there at birth?
20-70 million
How long does terminal sac formation continue for?
Until about 8 years old
How many terminal sacs are there in the mature lung?
300-400 million
How does the blood-air barrier change at 8-9 months?
Sac lining cells (type I pneumocytes) are thinner
Capillaries protrude into alveolar sacs
Increasing contact points for gas exchange
When does surfactant start being produced?
End of 6th month when type II pneumocytes appaer
What is surfactant?
Saturated and unsaturated phospholipids, proteins and carbohydrates
Reduces surface tension
Continuous synthesis, secretion and re-uptake cycle
What causes the fall in pulmonary vascular resistance at term birth?
- Lung distension
- Alveolar oxygen tension
- Nitric oxides
- Prostacyclins
- Endothelins
What are the effects of prematurity on lung function?
- Small lungs
- Reduced number of alveoli, which are immature
- Reduced epithelial-endothelial contact
- Deficient surfactant
- Retained lung fluid
What signs might you see in an infant with respiratory distress syndrome?
- Tachypnoea
- Dyspnoea
- Grunting
- Nasal flaring
- Subcostal recession
- Cyanosis
- Tachycardia
- Inability to feed
How is RDS diagnosed?
- History
- Examination
- Chest x-ray
- Blood gas analysis
How is RDS treated?
- Prenatal steroids to stimulate lung maturation in women at risk of having preterm birth
- Postnatal surfactant
When can primitive gas exchange start?
22 - 24 weeks
What developmental problems may develop in the embryonic period?
- Agenesis/aplasia
- Tracheal stenosis
- Congenital cysts
What developmental problems may develop in the pseudoglandular period?
- Diaphragmatic hernia
2. Hypoplasia following amniocentesis
What developmental problems may develop in the canilicular period?
- Hypoplasia
2. Potter’s
What is the liquid in the lungs?
NOT aspirated amniotic fluid or plasma
Actively secreted by the lungs
What promotes clearance of liquid in the lungs at birth?
- Active sodium reabsorption
- Lymphatic drainage
- Pulmonary blood vessels
- Squeezed out during birth
When does lung liquid start to clear?
2-3 days before term delivery
