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by emilyw on June 4th, 2005
Syncope [pronounced sin-co-pee]: a sudden brief loss of consciousness
In the case of fainting at the sight of blood, syncope results from non-cardiovascular causes, particularly due to problems with the autonomic nervous system, which is responsible for many of our bodily functions, including regulating blood pressure, heart rate, and our responses to anxiety, fear and emotional stress. Vasovagal syncope, typically precipitated by unpleasant physical or emotional stimuli (eg, pain, fright, sight of blood), usually occurs when a person is standing upright. The feeling of fear or anxiety at the sight of blood is the cause of the onset of fainting:
* As the heart beats faster and stronger [a response of the autonomic nervous system to person seeing blood], it sends a wrong message that tells receptors in the heart's chambers that the ventricle is filled with blood.
* The receptors send a message telling the nervous system that blood pressure is too high. In fact, the ventricle is not full and the blood pressure is too low.
* When the brain receives the faulty message, it slows the heart rate and further dilates the blood vessels.
* The blood pressure drops even lower, less blood is pumped to the brain and the risk of fainting increases.
(Retrieved from http://hrspatients.org/patients/signs_symptoms/fainting/non-cardiovascular_syncope.asp and http://www.merck.com/mrkshared/mmanual/section16/chapter200/200b.jsp)
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Comments
Thanks, I fainted twice when I was in school watching human biology videos, never understood why! :-)
by Daydreamer on June 4th, 2005