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
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2
Q

Lung development stages

A

Embryonic
Pseudoglandular
Canlicular
Saccular
Alveolar
Alveolar cells
Pulmonary surfactant

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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
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4
Q

Pseudoglandular

A
  • Bronchiol buds expand int he pericardioperitoneal canals
    • Week 10: ciliated cells
    • Week 11: cartilage appears
    • By week 16: terminal bronchioles
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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
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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
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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)

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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
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9
Q

Pulmonary surfectant

A
  • Reduces surface tension (no collapse)
  • Prevents inflammatory response
  • Phospholipids and protein
  • Lecithin: major surfactant
  • Sphinomyelin (in amniotic fluid)
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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
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