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Why can the sight of blood make someone faint?

For some people, seeing blood can trigger a vasovagal response: heart rate and blood pressure fall, and blood flow to the brain briefly becomes insufficient to maintain consciousness. An emotionally charged sight can therefore lead to a physical loss of consciousness. The explanation concerns one particular mechanism; it does not establish the cause of every fainting episode.

3–7 min

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  • How does tracing the change in circulation make this response less mysterious?

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