The stimulus to breathe results primarily from the increasing amounts of oxygen in the blood after the umbilical cord is cut after delivery.

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The stimulus to breathe after birth results primarily from the increasing levels of carbon dioxide in the blood, not oxygen. Prior to birth, the fetus receives oxygen from the mother's placenta, and as a result, the fetal lungs are not used for oxygen exchange. After birth, the lungs must quickly exchange oxygen and remove carbon dioxide, leading to an increase in carbon dioxide levels in the bloodstream that triggers the newborn to breathe.

The Stimulus to Breathe Results Primarily from the Increasing Amounts