Neonatal Lung Flashcards
Stages of lung embryology
Embryonic (0-5) Pseudogaldn 5-16 Canalicular 16-25***** Saccular 25-36***** ALveolar 36+
Preterm babies have problems because
Fewer alveoli and less SA relative to adults
Embryonic Period important hings
Day 26- primitive lung bud first appears as ventral outgrowth fro mthe foregut
PRoximal airways
Tracheal-esophageal fistual …what when, and most common
Occurs from incomplete sep of foregut into resp and digestive tracts (4th week)
Most common prox esoph atresia with distal tracheoesoph fistula
Congenital diaphrag hernia
Failure of pleuroperitoneal emmbrane to close
5-6 weeks
Herniation of intestinal contents into thorax at 10 weeks
Bochdalek defects (posterolateral) - 98%
Pseudogland stage
5-16 weeks
Conducting airways
Divisosn complete by 16 weeks
Glandular appearance on miccroscopic section
Canalicular period
16-24 weeks
Fromatiin of acini
Apposition of cap endothelial cells and alveolar lining cells (19-20)
Type 2 cells and lamellar bodies (20-22 weeks)
Type 1 flattened cells (24 weeks)
Produccing surfactant
Saccular period
24-36 weeks
Expansion of gas exchange sites
Secondary crests divide saccules into sub-saccules or primitive alveoli (27 weeks)
Major diff in survival
Alveolar stage
36 weeks to 3 years
Alveolarization
Exp of gas exchange SA
Pretemrm infants
Canalicular or saccular are before microvascular proliferation
24 - canalic
26 - saccular
Term - alcveolar
Term
Preterm
Post-term
37 0/7 to 41 6/7
Preterm less than 37
Late preterm is 34 and 0 to 36 6/7
Post is over 41 6/7
Normal fetus and pulmonary fluid
Pulmonary vascular resistance is high
Low alveolar oxygen and low pO2 tension
Vasoconstricted and most blood shunted from lungs via the ductus arteriossi
Fetal shunts
RV dominant
Pumps 90% across PDA and 10% to lungs
Low pul flow due t high pul vasc resistacne
Umbilical vein
Oxygenated from placenta…across DA to IVC…majority across the PFO, LA, LV, out
From SV, out through pulm artery and across DA
Fetal Lung
Active lung fluid secretion necessary for lung growth
Need normal neurolgic (phasic stretch)
Production of fetal lung fluid
Early on, from the placenta
Then comes from the lung**
In utero, type 2 cells produce surfactant and fetal lung fluid
Pump chloride actively into the alveolar air space and sodium and water follow
Neonatal production**
Majority of lung fluid reabsorbed
Multiple triggers…most important is the onset of active labor via adrenaline
actively pump sodium out of the alveolar space and reabsorbing into interstitial
Surfactant and composition
Type 2 pneumocytes produce
Capable at end of 2nd trimester
80% phospholipids
Composition of surfactant
Major is dipalmitoylphosphatidylcholine
Phosphatidylinositol is majjor in premature
SP-A and D
Non immune host defensive protein
Opsonin type
Immunologic
SP-B and C
Hydrophonic
Lowers surface tension
Facilitates absorption of lipids
30% of term that die have SP-B def aused by 2 base insertion resulting in frame-shift and premature termination
Def causes decreased lamellar bodies
Normal sufactant metabolism
Macrophages in the lung are important…lamellar are critical precursor from the type 2 cells
Defects result in accumulation of surfactant
Synthesis and secretion compared to adults
Preterm have similar amount of surfactant to adults, but they NEED more
PReterm needs 3-4 days to produce levels comparable to term
Majority of exogenously given given surfactant is recycled within surfactant pool
Surfactant function
P=2T/r
Amount of pressure needed to keep a bubble open
Results in collapse fo small alveoli to collapse and large to enlarge
