alleryStart learning →Why is survival low for a baby born before 26 weeks?
AThe trachea has not yet separated from the gut
BSurfactant and gas exchange surfaces are lacking
CThe medulla cannot yet set a breathing rhythm
DThe diaphragm has not yet formed completely
Answer & Solution
Correct answer: B. Surfactant and gas exchange surfaces are lacking
1. Two separate requirements must be met before a newborn lung can work.
2. It needs enough surfactant to reduce alveolar surface tension so the lungs inflate.
3. It also needs adequately formed surfaces across which gas can be exchanged.
4. Before 26 weeks neither condition is met.
5. Survival is therefore low, and preterm birth around 26 weeks frequently results in severe respiratory distress even when the baby survives.
6. Tracheal separation from the foregut happens in the first trimester, so the first option describes a step long since completed.
_Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 22 "The Respiratory System", section 22.7 Embryonic Development of the Respiratory System_
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