14. Lung Development (and Digestive System) Flashcards
1
Q
Lung
A
- Endodermal origin
- Derived from foregut: respiratory diverticulum
- Depend on retinoic acid produced by mesoderm
- Upregulation of TBX4 (endoderm), induces bud formation
- Laryngotracheal orifice is the opening between trachea and larynx
- Cartilage, muscle, connective tissue from splanchnic/visceral mesoderm or neural crest cells (ectoderm)
- Tracheoesophageal ridge separates trachea and lung buds from esophagus
- Abnormal septation: fistulas and atresias
2
Q
Lung development stages
A
Embryonic
Pseudoglandular
Canlicular
Saccular
Alveolar
Alveolar cells
Pulmonary surfactant
3
Q
Embryonic
A
- Bronchiol buds: invagination of foregut
- Primary (26-28 days)
- Secondary (early week 5): 3 right, 2 left (form lung lobes)
- Tertiary (week 6): form bronchopulmonary segments
4
Q
Pseudoglandular
A
- Bronchiol buds expand int he pericardioperitoneal canals
- Week 10: ciliated cells
- Week 11: cartilage appears
- By week 16: terminal bronchioles
5
Q
Canlicular
A
- Until week 28: division into more respiratory bronchioles with stubby branches
- week 13-24: bronchial glands develop
- Epithelium specialization (type II → I)
- Canaliculi compose the proper respiratory part of lungs, pulmonary parenchyma
- Week 24: sufficient differntiation into type I pneumocytes and proliferation of capillaries allow breathing
- Week 25: production of amniotic fluid
6
Q
Saccular
A
- Bronchioles subdivide to produce terminal sacs
- Development of gas-exchange
- Week 25-26: alveolar-capillary membrane able to sustain extrauterine life
- Week 28-29: terminal sacs line with mature Type II cells
- Surfactant appears
- Produced by type II alveolar cells
- Week 34-36: mature alveolar structure evident
7
Q
Alveolar
A
Continues after birth
- New sacculi form and are divided by septa
- Until week 38: alveoli mature
- Terminal sacs continue to form, mostly until age 2, finished at 10
- Gas-exchange only when alveoli are thin-walled (last weeks before birth)
8
Q
Alveolar cells
A
- Type I: gas exchange
- Type II: surfactant (decreased surface tension)
- 16% present at birth, remainder develop for 10 years
- RDS: respiratory distress syndrome
- Insufficient surfactant
- Increased surface tension
- Collapse of alveoli
9
Q
Pulmonary surfectant
A
- Reduces surface tension (no collapse)
- Prevents inflammatory response
- Phospholipids and protein
- Lecithin: major surfactant
- Sphinomyelin (in amniotic fluid)
10
Q
Delayed and increased pulmonary surfectant
A
- Delayed
- Acidemia
- Hypoxia
- Circulatory shock
- Over or underinflation
- Pulmonary oedema
- Increased
- Maternal heroin adiction
- Premature rupture of membranes
- Maternal hypertension
- Maternal infection
- Placental insufficiency
- Betamethasone or thyroid hormone