How the Dive Reflex Protects the Brain and Heart

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What is the mammalian dive reflex?

The mammalian diving response, or "dive reflex," is the way our body automatically prioritizes blood delivery to the brain and heart when we hold our breath underwater. When your head is underwater, you are using up the oxygen in your blood and not replacing it by breathing, a condition known as hypoxia. The brain and the heart are exceptionally sensitive to hypoxia, whereas other parts of our body, such as our arms and our legs, can tolerate hypoxia much more easily.