Physiologic Adaptation to Extrauterine Life Flashcards
What are the three phases of lung development?
- Canalicular phase: 17 - 27 weeks; capillary network begins; type II cells begin to differentiate
- Saccular phase: 27 weeks to 36 weeks; type I cells and endothelial cells associate
- Alveolar phase: 36 weeks to 3 years; presence of true alveoli
Prior to about _________, the alveoli are not close enough to the endothelium for gas exchange to occurs.
22 weeks
Why is it important to prevent the alveoli from completely closing?
If the alveoli close, then the force to open them is much higher than if they remain open. (Think of how hard it is to blow up a balloon that has totally deflated.)
Surfactant is secreted by _______________.
type II pneumocytes
Recall that type I pneumocytes are the long, flat, epithelial cells (like the number I).
Surfactant deficiency presents with what radiologic sign?
“Whiteout” in the lungs – that is, a diffuse opacity without enough air to create a heart shadow
Surfactant deficiency is also called ______________.
hyaline membrane disease (because proteinaceous fluid leaks into the alveolar spaces as in RDS)
What are physical signs of hyaline membrane disease?
Belly breathing that leads to pectus excavatum (because the ribcage is mostly cartilage at birth and can be sucked in by the negative pressure generated by forceful inspiration)
Why do babies grunt when they have respiratory insufficiency?
Grunting is expiration against a partially closed epiglottis. That closure generates positive end-expiratory pressure (PEEP) that prevents the bronchioles from closing.
What three treatments can be administered to babies with HMD?
- Surfactant
- Nasal CPAP
- Intubation with mechanical ventilation
During gestation, the lungs actually produce ______________.
amniotic fluid
In all babies, the first few breaths push fluid _____________. Without sufficient breathing, however, the fluid can _________________.
into the interstitial spaces; seep back into the alveoli
Differentiate primary and secondary apnea.
- Primary apnea: HR and BP maintained; stimulation elicits a cry
- Secondary apnea: HR and BP drop; ventilation required
What is the APGAR range?
0 (dead) to 10
How is APGAR scoring usually done?
- 1 min
- 5 min
- 10 min
- 15 min
- 20 min
(or until a score of 7 or more is reached)
What are the five categories in APGAR scoring?
- (Pulse) HR: absent; less than 100, or greater than 100
- (Respiration) Respiration: absent, irregular, or regular/crying
- (Activity) Motion: limp, some flexion, or actively moving
- (Grimace) Response to suction: none, grimace, or coughing/sneezing
- (Appearance)Color: pale blue, acrocyanotic, or pink
What happens to the pulmonary circulation after birth?
Two things: (1) the larger chest volume decreases pulmonary vascular resistance, leading to increased pulmonary flow, and (2) the increased arterial PO2 leads to closure of the ductus arteriosus.
The umbilical arteries arise from the _____________.
common iliac arteries (remember the vestigal umbilical artery in adults)
What are normal pulmonary responses to extrauterine life?
- Tachypnea (sometimes greater than 60/min) for the first hour
- Pauses of several seconds without hypoxia, cyanosis, or bradycardia
- No retractions and RR 40-60 after the first hour
What are normal cardiac responses to extrauterine life?
- Tachycardia up to 180 BPM during the first hour; decreasing to 110-140 BPM after the first hour
- Murmurs (50%)
- BP (60 - 90) / (30 - 60) mm Hg
Signs of neonatal hypoglycemia include __________________.
jitteriness, irritability, apnea, and seizures
In which stage of lung development does the capillary network form?
Canalicular (17 - 27 weeks)
“The canalicular phase forms canals for blood.”
The umbilical vein enters the circulation through the ______________.
ductus venosus (which itself becomes the ligamentum venosus)
Why do obstetricians often wait until the newborn is breathing strongly to clamp the umbilical cord?
The umbilical artery (away from the baby) constricts with increasing oxygenation. As such, the baby is receiving a net influx of blood during the first couple minutes of life, because the artery is constricting while the vein remains patent. Delaying the clamping can improve neonatal blood volume.
Lengthening and sprouting of the alveolar network occurs during the ____________ stage.
alveolar
Surfactant is stored as _____________ bodies in type II pneumocytes.
lamellar
How does surfactant prevent alveoli from closing?
Its hydrophobic tails repel one another when forced into close contact by contracting alveoli.
Why does C-section lead to more lung disease in infants?
Labor helps expel fluid from the lungs. Without labor, a disorder called transient tachypnea of the newborn develops.
What is Apgar scoring NOT used for?
- Diagnosis of asphyxia
- Determine need to resuscitate
- Gauge long-term outcome
How does lung transition also determine cardiac transition?
Oxygenation of the alveoli leads to pulmonary vasodilation. This directs blood through the adult circuit in the heart and increases left atrial pressure, thereby closing the foramen ovale and ductus arteriosus.
Closing of the _____________ is reversible.
DA and FO
How do prostacyclin and pO2 affect the pulmonary vascular resistance?
They decrease it.
talk about the fluid secretion and absorption in the fetal lungs
in the fetus the lungs are filled with fluid, it is secreted by lung epithelial cells driven by Cl- secretion (active)
at birth the fluid needs to be cleared through absorption dependent on Na+ absorption
talk about the specific Na channel involved in fluid clearance from the lungs
the ENaC channels increase in late gestation probably due to increased fetal production of cortisol, so this can be induced by exogenous glucocorticoids if needed for preterm babies
