Fetal Lung Development

Question 1

5 stages of development

Answer 1

Embryonic (4-6 weeks)

Pseudoglandular (6-16 weeks)

Canalicular (17-28 weeks)

Saccular (24-36 weeks)

Alveolar (32 weeks and beyond)

Question 2

Embryonic stage of lung development

Answer 2

Development of major airways
and vessels

Question 3

Pseudoglandular stage of lung development

Answer 3

Bronchi and terminal bronchioles form

And related large blood vessels

6 - 16 weeks

Question 4

Canalicular stage of lung development

Answer 4

Respiratory bronchioles and alveolar ducts develop

Lumina of bronchi and terminal bronchioles enlarge

Lung tissue becomes highly vascularized

16 - 26 weeks

Question 5

Saccular stage of lung development

Answer 5

Alveolar ducts give rise to terminal saccules (primordial alveoli) which are initially lined with cuboidal epithelium that turns into squamous epithelium at about 26 weeks

26 weeks to birth

Baby can survive if born at 26 weeks

Question 6

Alveolar stage of lung development

Answer 6

Alveolar formation

32 weeks to 8 years old

Question 7

Embryonic stage of VASCULAR development

Answer 7

Vasculogenesis within immature mesenchyme; pulmonary arteries branch from 6th aortic arches; veins as outgrowths from left atrium

< 6 weeks

Question 8

Pseudoglandular stage of VASCULAR development

Answer 8

Parallel branching of large pulmonary arteries with central airways; lymphatics appear

< 16 weeks

Question 9

Canalicular stage of VASCULAR development

Answer 9

Increased vessel proliferation and organization into capillary network around airspaces

< 24 weeks

Question 10

Saccular stage of VASCULAR development

Answer 10

Marked vascular expansion with thinning and condensation of mesenchyme; thin air-blood barrier; double capillary network in septae

< 36 weeks

Question 11

Alveolar stage of VASCULAR development

Answer 11

Accelerated vascular growth, fusion of double capillary network with thinning of septae

< 2-3 years

Question 12

Postnatal stage of VASCULAR development

Answer 12

Marked vessel growth and remodeling, as surface area increases greater than 20 fold

Question 13

Vasculogenesis

Answer 13

Rudimentary mesenchymal cells of embryo differentiate into angioblasts (endothelial cell precursors) and hemangioblasts (RBC precursors)

Question 14

What are the prenatal, birth, and postnatal mechanics of the pulmonary transition?

Answer 14

Prenatal: increased fetal glucocorticoids cause alveolar maturation; increased adrenaline and AVP during labor cause lung liquid resorption

Birth: umbilical cord clamping causes ductus venosus and umbilical arteries to contract –> increased SVR; first breath of air replace lung fluid, increases O2 and decreases end expiratory lung vol –> decreased PVR, surfactant release, ductus arteriosus closes, foramen ovale closes

Postnatal: alveolar expansion (10 fold by age 18 months - 2 years)

Question 15

How many alveoli are you born with and how many do you eventually get?

Answer 15

Born with 10 million alveoli

Eventually get 300 million alveoli

Question 16

Bronchopulmonary dysplasia

Answer 16

Dilated terminal airways

Alveolar simplification

Infants who have RDS (surfactant deficiency) can develop BPD if they get too much inflammation

Question 17

Things that can lead to BPD

Answer 17

Prolonged supplemental O2

Prolonged mechanical ventilatioin

Postnatal infection

Nutrition

Question 18

Tracheoesophageal fistula

Answer 18

Usually associated with esophageal atresia

Esophagus connected around bifurcation of trachea (fistula), or esophagus just dead ends/is cut apart (atresia)

Faulty partitioning of foregut into esophagus and trachea during 4th and 5th week of development