EXAM #1: FETAL AND NEWBORN PULMONARY PHYSIOLOGY Flashcards
When do the alveoli begin to develop?
Week 28
When does the majority of lung development occur?
Post-natal
What are the phases of lung development?
1) Embryonic
2) Pseudoglandular
3) Canalicular
4) Saccular
5) Alveolar
In what stage of lung development does surfactant get produced?
Saccular
What week does surfactant development start?
~25-26
What is the embryonic phase of lung development?
0-8 weeks
- 1st segments of the 5 lobes appear
- Pulmonary vessels form
How are the breathing movements described in the embryonic phase?
Paradoxical
What is paradoxical breathing?
Diaphragm contract and the chest wall moves INWARD (not the normal outward)
What is the pseudogranular phase of lung development?
8-17 weeks
- Lungs resemble a gland
- Type II pneumocytes precursors form (surfactant producing)
What is the canalicular phase of lung development?
16-26 weeks
- Type I pneumocytes differentiate from Type II
- Respiratory epithelium produces amniotic fluid
*Note that the maturity of the lung is dependent on the Type II pneumocytes
What is the saccular phase of lung development?
24-38 weeks
- Sacs form on terminal bronchioli
- Primary septa contain 2x networks of capillaries
What marks the onset of functional lung maturity?
Apperance of LAMELLAR BODIES in Type II pneumocytes
*These contain the lipids that compose surfactant
What are the two phospholipids that contribute to surfactant?
Lecithin and sphingomyelin
What is the clinical utility of the Lecithin/Sphingomyelin ratio?
- This is a marker of fetal lung maturity (Greater than 2.0)
- Lecithin is produced in high quantities as the lung matures
What are the surfactant specific proteins?
SP-A, B, C, and D
What surfactant proteins play a role in immune defense?
SP-A*
SP-D
*Note that this is water soluble and it NOT a part of the synthetic surfactant given to premature babies.
What surfactant proteins are critical for relieving surface tension?
SP-B
SP-C
*Both are present synthetically
What stimulates surfactant synthesis?
1) Glucocorticoids
2) Thyroid hormone
3) cAMP
4) Epidermal growth factor
5) B-adrenergic agonist
6) Purinoceptor agonist
What is the clinical significance of the surfactant stimulators?
IF baby has low Lecithin/Sphingomyelin ratio, THEN prescribe a stimulator
What can inhibit surfactant synthesis?
Maternal DM
What is the alveolar phase of lung maturation?
36 weeks to 2 week post-partum
- Alveoli increase in diameter
- Connective tissue septa decreases
- Increased number and size of alveoli
Describe the full-term lung while it is “intrauterine.”
1) Filled with fluid
2) 30% shallow breathing
3) Vessels constricted
4) Low lung compliance
5) High chest compliance
What are the stimuli for the first breath?
1) Chemical
- Increased pCO2 and decreased pO2
2) Environmental
*The pressure of the birthing process in the vaginal canal, temperature change, and light/ sound stimulate the first breath
Physiologically, what happens with the first breath? What pivotal events occur at this point?
Forced inspiration and active expiration generates the pressure gradient needed to open the air passages
*The FRC is established at this point and the new air interface opens pulmonary capillaries b/c the hypoxic vasoconstriction is counteracted.
What stimuli promote the absorption of fetal lung fluid?
1) Perinatal epi surge
- Beta receptors activated
- Na+/K+ ATPase is activated
- Na+ excreted and water follows
2) Thyroid and steroid hormones promote absorption
3) Alveolar-capillary pressure gradient
How is the neonatal breathing apparatus described?
“Low efficiency”
*Note that there is also an “inhomogenous” air distribution that alters the V/Q relationship
What happens to the pulmonary circulation with birth?
- Decreased pulmonary arteries
- Increased alveoli
*Thus, there is a decrease in pulmonary vascular resistance
Periodic episodic breathing is normal in the neonate. What can you do to facilitate the transition to normal breathing pattern?
Arousal
What is the biphasic response to oxygen in the neonate?
N/A
