Fetal and Newborn Pulmonary Physiology Flashcards
what are the 5 stages of lung development
embryonic (0-8)–> pseudoglandular (8-17)–>canalicular (16-26)–>saccular (24-38)–>alveolar (after birth)
what type of tissue are the lungs developing from
endoderm
when does alveolar formation begin in humans
28 wks
when does is the most major increase in the number of alveoli
after birth
how is lung growth regulated in the fetus
lung fluid stimulates growth/external compression inhibits growth
what is developing/occurring during the embryonic phase?
- paradoxical breathing movement
- main bronchus and the 5 lobes
- aortic arches, lung buds, and pulmonary plexus
what is developing during the pseudoglandular phase
- lungs resemble a gland
- type II pneumos are making amniotic fluid
- capillaries are developing
what is developing during the canalicular phase
- type I pneumo out of type II cells
- alteration of the epithelium
- maturity of the lungs can be measured near the end
what is developing during the saccular phase
- clusters of sacs from on the terminal bronchioli
- basically everything but the alveoli are completely developed now
- 2 networks of capillaries are developing around the sacs
what is surfactant stored in?
Lamellar bodies
list 4 reasons why the fetal lungs are not very good at respiration at birth
- filled with fluid
- pulmonary vascular resistance is high
- compliance of the lung is low
- chest wall compliance is too high
what 4 changes then need to occur at birth for efficient gas exchange?
- breathing and ventilation must start
- FRC must be established
- pulmonary vasculature must dilate
- fetal pulmonary fluid must be absorbed
What are the surfactant specifc proteins?
A/D: immuno function
B/C: critical for pulmonary surface activity
Lecithin/sphingomyelin normal ratio?
1.8-2.0
What L/S ratio would indicate a high risk for infantile respiratory distress syndrome?
name some stimulators of surfactant synthesis
- glucocorticoids
- thyroid hormones
- cAMP
- epidermal growth factor
- beta-adrenergic agonists
- purinoceptor agonists
what is a major inhibitor of surfactant synthesis
maternal diabetes
at what developmental stage can you start to measure L/S for lung maturity?
cannalicular
what is developing during the alveolar phase
- 1/3 of the alveoli have developed
- then they increase in size and number
- thinning of the alveolar lining
- thinning of the CT septa between alveoli
what hormones promotes absorption of fetal lung fluid?
- epinephrine –> transepithelial Na transport
- thyroid and steroid hormones
- pressure gradient from airspaces to capillaries
describe the respiratory mechanics (lung compliance)
- low lung compliance
- highly compliant cw/poor chest recoil
- loss of energy/intrinsic mechanical properties of respiratory muscle
how does pulmonary circulation change after birth
- ratio of small pulmonary arteries to alveoli decreases 2-fold
- vascular walls gradually thin
- pulmonary vascular resistance continues to fall
describe respiratory responses to stimuli
- response to CO2 is increased
2. response to hypoxia is biphasic - initial hyperventilation followed by respiratory attenuation of even apnea
