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How can a fetus receive oxygen without breathing air?

A fetus needs oxygen before its lungs begin taking in air. The placenta makes that possible through exchange between two circulations, with oxygen reaching fetal blood across tissue rather than through one shared open bloodstream.

3–5 min

Questions you could explore

  • Why is keeping the circulations separate compatible with exchanging substances between them?

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  • OpenStax28.2 Embryonic Development

    Shows the placental interface and the direction of transport through the umbilical vessels. It explains the normal exchange pathway, not an individual pregnancy or a perfect barrier against every substance.

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Health and the body

How does daylight set the body’s clock?

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3–5 min

How does daylight set the body’s clock?

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4–5 min

How does a vaccine give the immune system a memory?

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Health and the body

Why won’t an antibiotic treat a viral cold?

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2–3 min

Why won’t an antibiotic treat a viral cold?

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