I understand that loss of blood pressure and oxygen to the brain can cause one to pass out, but how can the sight of something like blood cause it?
In: Biology
Vagus nerve over-stimulation: the nerve responsible for fight or flight sometimes over-does the response in people with true phobias. This causes a massive surge in blood flooding the body to ensure all your muscles and organs are ready for “go” that the brain gets left out. Loss of blood to the brain = loss of consciousness
Blood triggers a primal reflex in our brains, because seeing it means that we’ve been wounded and in our earlier history that would have been a big deal. That reflex is what triggers the transient drop in blood pressure and heart rate- because both of those would provide a short term benefit in slowing the bleeding.
Today, we don’t have much use for it. Most people experience it to a certain degree, but certain people are on the “fainting” extreme.
Answer: If someone has a phobia of blood, when they see it, most likely the body’s “fight or flight” response starts up. The persons heart rate goes up, sometimes accompanied by hyperventilation, they feel sweaty and they freeze up. Occasionally they may also pass out, which answers why someone might pass out at the sight of blood.
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