02: Lung History & Embryology Flashcards
Describe the components of the conducting zone.
- Trachea
- Bronchi: ciliated & goblet cells, elastic tissue, smooth muscle, glands, cartilage
- Bronchioles (1 mm): no cartilage or bronchial glands, ciliated lining, no goblet cells, smooth muscle
Basal cell
Reserve cell; undifferentiated epithelial cell; divides when injury
Kulchitsky cell
Neuroendocrine cells; contain serotonin (5-HT)
Lactoferrin
Antioxidant in airway epithelium; bacterio/fungicide
Describe the components of the respiratory zone.
- Terminal bronchiole to respiratory bronchiole
- Lined by ciliated and clara cells (transitional zone to respiratory bronchiole: all clara cells)
- Alveolar ducts/sacs
- Type I & II cells
Clara cells
Produce component of surfactant; bronchiolar reserve cell.
Increase in number distally in conducting bronchiole.
P450 (CYP4, CYP1A1): chemical detoxification.
Secrete **CCSP **(antioxidant effect) and surfactant protein B.
Encodes SLPI, a neutrophil protease inhibitor.
Progenitor cell for ciliated bronchiolar cells and other Clara cells.
Type I cells
Thin lining cell for gas exchange.
90% of alveolar surface.
Terminally diferentiated.
Type II cells
Releases surfactant proteins and lipid.
Regeneration of alveolar epithelial cells (type I & II).
Sodium transport.
Recycle surfactant.
Source of PDGF, TGF B, TGF A, ET-1.
Describe laryngeal development.
- Occurs during week 4
- Respiratory primordium arises from distal/caudal pharynx: laryngo-tracheal groove.
- Endodermal derivative of epithelium of larynx, trachea and bronchi.
- Connective tissue, smooth muscle and cartilage from splanchnic mesenchyme surrounding the foregut.
- Formation of proximal larynx: cranial tube.
- Arytenoid swellings grow towards tongue.
- Airway gets closed off, eventually recanalizes.
- LT groove evaginates to form LT diverticulum.
- Becomes invested with splanchnic mesoderm to form lung bud.
- Maintains a laryngeal inlet.
- Septum that forms by folds and fusion keeps a septate inlet that becomes the trachea and esophagus.
Laryngeal webs
Incomplete recanalization of larynx
Laryngeal atresia
Complete upper airway obstruction.
Ascites (hydrops)
Improper lung formation (hypoplasia)
Polyhydramnios
Excess intrauterine amniotic fluid 2/2 tracheoesophageal fistula.
Describe early budding/branching.
- By 4 weeks: endodermal buds grow along with splanchnic mesenchyme.
- By 5 weeks: second degree bronchi, upper middle and lower on right, upper and lower on left.
- By 6 weeks: tertiary bronchopulmonary segments, 10 on right and 8-9 on left
Describe the stages of lung maturation.
- **Pseudoglandular **(5-17 wks)
- No gas exchange zones
- Lung resembles exocrine gland
- **Canalicular **(17-25 wks)
- Terminal bronchioles enlarge and branch
- 2-3 respiratory bronchioles then 3-6 alveolar ducts
- Terminal sacs begin to form
- Vascularized (caudal slower than cranial)
- **Terminal sac/saccular **(25-34 wks)
- Epithelium thins to become type I like
- Capillaries grow in
- Blood air barrier forms: Type I & II cells
- Surfactant
- **Alveolar period **(late fetal - childhood)
- Surfactant & gas exchange present
- Pulmonary vs. systemic circulation
- Alveoli continue maturing from ages 3-8; increase in number from 50 million (birth) to 300 million (age 8; adult number)
Describe the three major congenital malformations of the lungs.
- Cystic adenomatoid malformations: maturation arrest in lung segments
- Azygos lobe: superior apical bronchus grows medially instead of laterally; vein at bottom of superior lobe fissure
- Sequestration: accessory piece of lung that becomes disconnected from tracheobronchial tree and parasitizes systemic circulation from diaphragm
