2. Development of Respiratory Control:
- Human fetal breathing is detectable as early as the 11th
week of gestation, and is consistent by the 13th week (this
corresponds to the peak of the Pseudoglandular phase of lung
development, during which……………..develop).
- Breathing is associated with REM-like activity (brainstem mediated).
- By the 30th week breathing occurs for a total of ~8 hours
in a day (correlates with maternal blood glucose levels, circadian rhythm).
Frequency: 40's to 50's.
- Fetal breathing decreases with onset of labor, and becomes almost absent
with active phase of labor.
- Fetal breathing responses to Pco2 and pH are similar to
those seen in postnatal life, ??timing of development of responses. Hypoxia
has inhibitory effects (profound hypoxia induces gasping). Hyperglycemia
estimulates fetal breathing, hypoglycemia inhibits it.
- Hering-Breuer inflation reflex (apnea following increase in lung volume),
laryngeal reflex, somatic stimulation reflex (temperature, touch) are present
if fetal life, ??timing of development.
- Central neuronal groups develop early and are active during fetal life,
timing of events not determined yet. At birth neurons are small and have
low numbers of dendritic arborizations. During first month of life extensive
development of synapses and increase in neuronal size, as well as in concentrations
of neurotransmitters, occur. Dendritic elaboration extends beyond first
month and continues into postnatal years.
- Transition of intermittent fetal breathing to continuous post-natal
breathing mechanism ?????. Not dependent on chemical stimuli (Pco2,
Po2, pH), not dependent on external stimuli (reflexes). Once
established, Po2 level important in maintaining it.
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Index Normal
Physiology Development of Respiratory Control Definitions
Specific Disorders Readings
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